> ||qh|l
’39.... “VI;
' H
>ul“""
'.‘.','f"l1.‘,l‘(q... J. l
.. .
:’I -i' luff}
rant.- u a 11‘- V
:3:ch .1.
‘Ezwn‘ ‘ '
Al 1'
6.2 ‘!‘.
“u".‘L‘J.
“.1 ~ LL
3:
9‘ H"? '1 ”1313‘“?
l" “‘1”
UL
A“? . V
1“1:31;,1‘rvufiL-
‘ I1
14Mfi‘fl‘i‘kéi Vi
' ur'v u
’ L' w * - n ‘ mx‘?‘:."'.a ""“E
‘w‘rli ‘ ‘ '3 nun-um ;:.t;mj‘ 1 .- . ~ .
”fin-r ,3: - I 3+.“ {sag} 3:11;.“ '
‘11n’IqMfin4 m A .
mm: “a: ‘4.
an
‘x’w .'
ht. {gab
V , ‘ ,
. n' ‘. V _ . 'VV , ‘i:71"-
% ~ 'LM “3:!“ "5.“13‘3‘1 a".
'79-’1'1v‘fi‘ $141.7” , ‘ M31 K! A 151.sz MW {1‘
a2“. Wag—7n!)- . V ,~ gal wk‘dsag H'm-JQ‘N 31‘:er 1‘
V d , V 1 ' ’ ”r: 1:7th
' 23.5““
aw"
J: 5-
.E’JJRI.
‘ J. .p‘.
'o
‘ ~ .1 ‘ x x
@3333;
‘ 1" ‘6 3.3; V‘ ‘ A
CMfigL 2: KER-m :31: 9:150
n l ‘ l L "11' ‘:=~'~
. "nigh A. 3‘31 '1}... a”:- ‘1’ka fix? ”if. 1;
:15. 4&1”). 1: ‘ ' m ' I ~ 3%”, dig?» 1.445.
p s‘,,- m,‘ V .17, 7,.V Hid."
figmégg‘fiéfifidfi “:3. “i‘n " 1.. ~ ' “3)! 7 ‘0‘ "hi-i .. £3.33...
1 ~ ‘ ,
41:. v
‘1
P
3?}; a . .
k n '3 ‘3 '1’ .- 7.1' ‘Vm’w‘rrflii‘a"?
g '1 ‘ w. .1. A:
1‘23” AL ‘3‘ .
3‘"
3.‘ my L455
,t
r
. . 1-.
23"}. V
.. "*1. 'z
M41411»!
M2“ A.
l
«s.-
L .
Y It:
r211
.
ii“, . -.'~
0-! 1E7: m: “ L11: 73“»..0191":
I' “1.15%..” ‘- LEE? :1. i‘gfiw V
W fi::: «WI-A! ‘ MK Aft?“
N‘-
“ «a "-
mt; .3:
ru- ‘v‘fi " ~ -.- . - .~-- 0-:-.-n- —.-—. -.--r ‘owa
.. . ls. 1,
‘
-
_I
E 40‘
Z
O
2 30'
20‘
l0-
Figure 2.
Rainfall recorded at Farm—8, Changuinola, Bocas
del Toro, Panama during the years 1970-1971.
Dotted line indicates 45 year average.
2a’C«
27°c‘
T EMPERATURE
25° C4
MONTHLY
24°c«
AVERAGE
17
Figure 3.
Ch
24
t!
c.
.m
3
>1
3'
>
a:
(D
Z
Average monthly temperature at Balboa Heights
(solid line), Changuinola (dashed line), and
Capira (circles). This statistic was obtained
by averaging daily maxima and minima.
18
associations recognized by Holdridge and Budowski (1956)
dependent on the height of the land above the water table
and the salinity of the water. The mangrove association
is found in the lowest areas where the water is more sa—
line and consists of the red mangrove (Rhizophora mangle),
the black mangrove (Avicennia marina), and the white man-
grove (Langucularis racemosa). Nearly pure stands of orey
(Campnospermia panamensis) which is tolerant of brackish
water occurs extensively over the area just above sea lev—
el in the orey association. On slightly higher ground
where alluvial fresh water stands much of the time, there
are large forests of the silica palm (Raphia taedegera)
which form the silica palm association. Still farther
inland is another swamp association, the cerillo—sangrillo
association where cerillo (Symphonia globulifera) and san-
grillo (Pterocarpus officinalis) are common in the upper
story and the coquillo palm (Manicaria saccifera) is com—
mon in the lower canopy.
Mile—2 Station consists of a small wooden house used
occasionally by Gorgas Memorial Laboratory as a field sta—
tion and located on the west side of the railroad tracks.
North and south of the station there are numerous fresh-
water marshes which become more and more brackish as one
approaches Almirante. The freshwater marshes are sur—
rounded by dense impenetrable stands of Calathea, Helico-
nia, Cecropia, and Piper among others. A portion of the
silica palm association can be seen immediately across
19
the railroad tracks east of the station. This association
then dominates the region between the railroad and the
coast to the east. Behind the station to the west the
ground slopes gradually upward and is covered with cerillo
and sangrillo in the upperstory and the coquillo palm
(Manicaria saccifera) in the understory. The upperstory
trees are thinly distributed here allowing a dense under—
growth including the coquillo palm and numerous vines and
shrubs. Most trapping was done along the railroad tracks,
and along the edges of the clearings and marshes in stands
of bamboo and Heliconia. Unlike Santa Rita the vegetation
in Almirante is lush and green the year around.
Fauna of the Almirante study area
Mammals trapped on the Almirante site and returned
to Panama City are shown in Table 1. This fauna was limi—
ted by both trap choice and trap size.
Santa Rita study area
Santa Rita is a small rural community located on the
Pacific slope. This region lies between 50 and 200 meters
above sea level and is characterized by low rolling hills
cut by frequent seasonal streams emptying into the Rio
Caimito which has water the year around.
Table 1.
20
Mammals trapped on the Almirante and Santa Rita
study areas. Numbers of individuals brought
back to the laboratory for study are indicated
in parenthesis.
Almirante study area
Marsupials
Philander opossum (l)
Didelphis marsupialis (10)
Rodents
Oryzomys caliginosus (30)
Nectomys alfari (27
Sigmodon Eispidus (80)
Rattus rattus (5)
Proechimys semispinosus (176)
Santa Rita study area
Marsupials
Caluromys derbianus (36)
Marmosa robinsoni (10)
Philander opossum (85)
MetaChirus nudicaudatus (3)
Didelphis marsupialis (175)
Chironectes minimus (l)
Rodents
Sciurus granatensis (l)
Sciurus variegatoides (1)
Liomys adspersus (0)
Nectomys alfari (2)
Zygodontomys microtinus (24)
Sigmodon Hispidus (127)
Rattus rattus (6)
Proechimys semispinosus (963)
Diplomys labilis (377
* Scores were trapped but released immediately without be—
ing tallied.
21
Climate of the Santa Rita study area
No climatic data were available for Santa Rita; how—
ever, there was good data for Balboa Heights, Canal Zone,
35 kilometers east and 5 kilometers north of Santa Rita
and enough data from Arraijan 24 kilometers east and 5
kilometers north of Santa Rita and from Capira l6 kilome-
ters south of Santa Rita to establish that the region sur—
rounding Santa Rita has a similar rainfall pattern to
Balboa Heights (Figure 4). Comparison of Figures 2 and
4 shows that the verano dry season (mid—December through
mid-April) in the Santa Rita area is more severe than it
is in the Almirante area. At the end of 1971 the ten year
average rainfall for Balboa Heights was 181.6 centimeters
per year compared to a 45 year average of 248.7 centime-
ters per year for Farm—8, Changuinola.
Temperatures for the Santa Rita area are shown in
Figure 3 and varied from a low of 200 Celsius to a high
of 340 Celsius while the monthly averages of the daily
low temperature varied only 10 Celsius (22—23O Celsius)
and the high only 20 Celsius (32—34O Celsius). Available
data for Capira indicate a temperature regime almost iden-
tical to Balboa Heights. The temperature varied from a
low of 200 Celsius to a high of 330 Celsius during 1971
while the monthly averages of the daily low temperature
varied 2O Celsius (20—22O Celsius) and the high 10 Celsius
(31—33O Celsius).
22
100‘
90*
80‘
’E
:5 70+
3
E 60
Z
< 1
“1 .50
>.
i‘
h, 40*
Z
C)
2 130<
2(L
IOT
Figure 4.
Rainfall recorded in the area of Santa Rita de
la Chorrera during 1970—1971 (solid line) and
10 year means for Balboa Heights (dotted line).
Squares and circles represent data from Capira
and Arraijan, respectively.
23
Other climatic data from Balboa Heights show that
during the dry season there is more sunshine, the relative
humidity drOps, and wind velocities increase. The reduced
rainfall coupled with increased winds and sunshine inten—
sifies the dry season in Santa Rita and causes the soil
there to harden and crack.
Vegetation of the Santa Rita study area
Santa Rita is included in the Tropical Moist Forest
of Holdridge and Budowski (1956:94) as is Almirante.
In Santa Rita most of the forest has been removed and
only small patches of the original forest remain on some
hilltops and along a few streams and rivers. The area
is covered instead, by numerous small farms where citrus,
avocados, mangos, bananas, pineapples, rice, corn, yucca,
name, and sugercane are cultivated. Some of the more
prosperous farms have a few dairy or beef cattle. The
most conspicuous trees on the farms are citrus trees,
the corozo palm, maintained for thatch, and the mango
tree. Along the streams, the conspicuous vegetation
includes espavé (Anacardium excelsum) and several species
each of Ficus, Inga, Cecropia, Heliconia, Bursera, Piper,
Luehea, Capparis, Chrysophyllum, Terminalia, B353, Amaran—
3223’ Carica, and Bambusa. Grass is common about pastures
around dwellings, along fence rows, and surrounding
cultivated fields. Although the annual rainfall in the
study area is sufficient to maintain some of the species
24
of plants indicative of the Tropical Moist Forest, the
months of January, February, and March are generally very
dry. Much of the herbaceous vegetation dies including
grasses and many of the trees drop their leaves. The
area remains dry until the rains return in April.
Although Holdridge and Budowski (1956) placed both
the Almirante and Santa Rita areas in their Tropical Moist
Forest, they recognized that the dry season is more marked
on the Pacific side than on the Caribbean side. The se—
verity of the dry season can be observed by examining
the total rainfall for the months of February and March.
The average for Cristobal (on the Caribbean coast of the
Canal Zone) is 76mm, the average for Barro Colorado (in
the Canal) is 90mm, Capira registered 76mm, but Arraijan
registered 18mm and Balboa Heights averages 32mm of rain-
fall. Moist forests are found in Cristobal, Barro Colora—
do, and Capira, and dry forests are found in Arrijan and
Balboa Heights. During the same period Almirante averages
394 mm of rainfall. Although the area between Capira
and Arraijan appears much different than the Almirante
area in the dry season, they do have several tree species
in common including Anacardium excelsum, Cecropia obtusi-
folia, and Luehea seemannii. These are found along streams
in the Santa Rita area. The dry season is shorter and
less severe between Capira and Arraijan because here the
elevated ”backbone" of the Isthmus of Panama is low allow—
ing for some Caribbean rains to reach this part of the
25
Pacific coast of Panama. To the west of Capira and to
the east of Arraijan, however, the dry season is much
longer and more severe, and many trees typical of the
Moist Tropical Forest such as Anacardium excelsum cannot
survive there.
Fauna of the Santa Rita study area
Mammals trapped on the Santa Rita study site and
returned to Panama City are shown in Table 1. Like the
Almirante site this reported fauna was limited by both
trap size and trap bait choice.
26
METHODS AND MATERIALS
Initial effort was made to find a site on the wet
Caribbean side of the Isthmus of Panama and one on the
dry Pacific side where Proechimys occurred in large num—
bers.
Wet site
Almirante (Figure 1) was chosen as the wet site be—
cause of the abundance of Proechimys and because this was
the home of a reliable collector that had worked part time
for Gorgas Memorial Laboratory. Small mammals were col-
lected intermittently from late 1970 to early 1972 and
sent via railroad to Changuinola and then by air to Panama
City.
Dry site
Attempts to find large populations of Proechimys near
Panama City failed. In trapping near Tocumen, 20 kilome—
ters northeast of Panama City during August and September
of 1970 and near Juan Diaz 11 kilometers northeast of Pana—
ma City during October 1970, I found only small popula-
tions of Proechimys. Similarly, trapping at Juan Mina
36 kilometers north and 16 kilometers west of Panama City
during September and October of 1970 revealed only a small
27
population of Proechimys.
During September 1970 a part—time animal collector
for some of the staff members at Gorgas Memorial Labora-
tory reported large numbers of Proechimys near Santa Rita
(Figure 1). Santa Rita is 55 kilometers from Panama City
by automobile and can be reached the year around since
40 kilometers of the way is an all—weather highway and
the last 15 kilometers is accessible by a gravel road
which proved to be passable even in the wet season. An
animal collector who lived on a small finca one kilometer
west of Santa Rita was hired to obtain small mammals in
the area. Animals were trapped from late 1970 to early
1972 in 15x15x18 and 23x23x70 centimeter folding live
traps baited with banana. Traps were set within walking
distance of the finca and transported using a home-made
cart. After being carted to the finca, mammals were placed
in l4xl8x26 centimeter cages hand-made out of one—half
inch hardware cloth and sheet metal. These were kept in
a spacious thatched shelter open on four sides and made
specially for this purpose. Rice hulls were used as bed—
ding and animals were given Wayne Lab—Blox(:)and water
Ed libitum. Their diet was supplemented with oranges,
yucca, name, and bananas. These animals were picked up
and transported to Panama City once each week.
28
Field data
After arriving in Panama City animals were taken to
the Gorgas Memorial Laboratory annex located behind the
United States Embassy on Calle 37.
Females were palpated for pregnancy and held until
parturition if pregnant. The remaining females were anes—
thetized with ether to relax their abdominal muscles and
palpated again. Nonpregnant females were euthanized by
chloroform and autopsied. Some females and males were
selected for breeding in the laboratory. Later in the
course of the study as laboratory space declined, even
obviously pregnant females were euthanized and autopsied.
The length of one inguinal nipple, one lateral nip—
ple, and the length and width of the clitoris were record-
ed to the nearest millimeter. The mammary tissue was ex-
amined and recorded as not developed or well-developed.
The vaginal opening was recorded as closed, partly Open,
or open. If the vaginal area was swollen and dry or if
swollen and wet, this was recorded. Among several fe-
males, vaginal smears were made by sampling the vaginal
cells using a physiological saline-soaked cotton swab.
These smears were examined under a microscope and the
cells present were recorded. Since vaginal smears made
with saline often form fern patterns when dry and since
it has been suggested that these ferns may indicate estro-
gen levels in the female, these were photographed for la-
ter study.
29
The reproductive tracts of females were fixed in AFA
and cleared using the technique of Orsini (1962). After
being cleared, embryos and recent scars were counted and
their distribution in the horns of the uterus was record—
ed.
Males were routinely euthanized and autopsied unless
held for breeding. They were identified as testis scro—
tal, cauda epididymus scrotal, or nonscrotal (see discus—
sion on the scrotum in Reproduction in field captured
males). The testes were removed, the length of the left
testis was measured to the nearest millimeter, and the
testes were preserved by fixing them in 10 per cent forma-
lin and later placed in 70 per cent alcohol.
Testes were analyzed among field—caught males by
first grouping the material into Almirante and Santa Rita
data. These two groups were each divided into material
collected October through January and material collected
February through September. Within each of the resulting
four groups the testes lengths and body lengths were trans—
formed using natural logarithms. The length of the left
testis was then regressed by simple linear regression on
body length. Within each site—season group the testes
measurements were adjusted to the mean body length by the
expression ya =yi—bl(xi—x) where bl is the slope of the
regression equition. The adjusted testes lengths are sum-
marized for each of the four groups by means and 95% con—
fidence intervals.
30
Dead animals were weighed to the nearest tenth of
a gram on a triple—beam balance, and measured to the near-
est millimeter. All measurements were made by the inves-
tigator and taken on relaxed animals just after death.
Measurements included total length, tail length, length
of hindfoot, and height of ear from the notch. These are
standard measurements used by mammal preparators and are
described in Hall (1981).
The age of field animals was estimated by comparing
their body length (total length minus tail length) with
the mean body length of known-age laboratory-reared ani-
mals of the same sex and of stock originating from the
same site. See Growth rate for equations relating age
and body length among laboratory born spiny rats. The
month of conception for each field-captured spiny rat was
estimated by noting its date of capture, estimating its
age using laboratory growth-data, and then summing its
estimated age and 64 days gestation and subtracting this
from its date of capture.
Both males and females were examined for lesions on
the extremities and if lesions were present, these animals
were referred to investigators at Gorgas Memorial Labora-
tory studying leishmaniasis.
Laboratory data
Animals held in the laboratory were placed in
14x18x26 centimeter stainless steel cages and placed in
31
a spacious room open and covered by a wire screen on the
north and west (but shaded from the sun by a porch roof).
Here animals were exposed to ambient temperature and natu—
ral photoperiod. Chopped wood, rice hulls, or Absorb—Dry
®was used as bedding. Animals were fed Wayne Lab—Blox®
and given water ad libitum. Their diet was supplemented
with spinach greens, oranges, and bananas. Cages were
cleaned by washing them with soap and water and replacing
the litter once each week or earlier if soiled. In the
laboratory Proechimys were generally kept l or 2 animals
to a cage. Other mammals collected at Santa Rita or Almi—
rante were also transported to Panama City and kept in
the same room as Proechimys.
All animals were exposed to similar temperatures dur—
ing their confinement in the laboratory. The temperature
extremes in Panama City are generally 10 Celsius lower
and 10 Celsius higher in the dry season then they are in
the wet seasons. The monthly mean percent relative humi—
dity (based on the mean of the daily averages of the maxi—
mum and minimum values) averages 11 percent lower in the
dry season. All animals were handled as uniformly as pos—
sible to keep variation at a minimum.
Pregnant females held in the laboratory were checked
for young three times daily, and new born were counted,
sexed, and toe—clipped for identification. Young were
weighed to the nearest tenth of a gram and measured to
the nearest millimeter on days 0, 5, 10, every ten days
32
until 100 days of age and then every 20 days until 200
days of age. Length measurements included total length,
body length, hindfoot length, and ear length as described
previously. The progress of the post—juvenile molt was
fully described on the days of measurement. Observations
were made to determine when the testes of males descended
and when the vaginal closure membrane of females was first
perforate. This membrane is perforate only at estrus and
parturition (Weir, 1973).
The length of gestation was determined by selecting
females with perforate vaginas and pairing them with adult
males and placing them in 25x25x35 centimeter cages. Va-
ginas were checked each day of the pairing for the pre-
sence of spermatozoa by microscopic examination of vaginal
smears made by swabbing vaginas with cotton swabs soaked
in physiological saline. When spermatozoa were observed
in the vaginal smears, males were separated from the fe-
males. Corroborative evidence of length of gestation was
obtained by noting the length of the time interval between
successive litters when males were separated from the fe-
male on the day of birth.
Body length growth data from spiny rats reared in
the laboratory were used to estimate the age, month of
birth, and month of the conception (using 64 days as the
length of gestation) of every field captured male and fe-
male.
Occasionally rats were bled to search for blood
33
parasites. Rats were supplied at various time for feeding
mosquitos or provided to MARU (Middle American Research
Unit) in the Canal Zone for virus studies and to the Virus
Department at Gorgas Memorial Laboratory for similar work.
Others were occasionally provided for the pathology de-
partment at Gorgas to be sent to the United States.
Because of the small dispersion of many of the mea—
surements of length and weight, the standard errors are
expressed to more decimal places than the number of signi—
ficant figures in the means; this does not imply that
these estimates are more precise than the original meas—
urements. Many of the measurements considered in this
study are discrete integers and can only be approximately
normally distributed. Two—tailed tests are used through—
out for all statistical analyses. All calculations were
performed on a hand—held TI—59 calculator. Statistical
tables provided in Steel and Torre (1960) were used to
determine significance levels.
LABORATORY RESULTS
Gestation Period
A total of 50 female Proechimys were paired with
males and checked daily for sperm for a total of 1100 rat—
days. Sperm was observed in the vaginas of 6 Almirante
females and 5 Santa Rita females that produced litters
of young in the laboratory. Santa Rita spiny rats were
born an average of 64.2 days (63, 64, 64, 64, and 66) af—
ter sperm was observed and Almirante young were born after
64.7 days (63, 64, 65, 65, and 66) of gestation.
When males were left with females through the gesta—
tion period and removed the day after parturition, peri—
partum mating occurred and a second litter was produced
after an average interval of 63.5 days (63 and 64) for
Santa Rita females and 64.0 days (64, 64, 64, and 64) for
Almirante females.
Eighteen Santa Rita females and 11 Almirante females
bred in the laboratory without being observed and gesta-
tion could not be determined.
Litter size
Among pregnant spiny rats trapped near Santa Rita
and brought to the laboratory the mean litter size was
34
35
3.0(SE=0.12; R=l—6; N=68) for those giving birth and the
mean embryo count was 3.0(SE=0.09; R=l—7; N=126) for those
autopsied. There was no significant difference among
these means (£=0.01; p>0.05; d.f.=l,l92). Among pregnant
spiny rats trapped near Almirante and brought to the la—
boratory the mean litter size was 2.0(SE=0.21; R=l—5; N:
24) for those giving birth and the mean embryo count was
2.1(SE=0.15; R=l—4; N222) for those autopsied. There was
no significant difference among these two means F=0.27;
p>0.05; d.f.=l,44). Among pregnant spiny rats trapped
in Santa Rita and Almirante, litter size and the number
of embryos were larger for Santa Rita (F=l9.34; p<0.005;
d.f.=l,90; and F=l3.37; p<0.005; d.f.=l,l46 for litter
size and embryo count, respectively). However, litter
size in both populations is significantly related to ma-
ternal weight after parturition (F=8.32; p<0.01; d.f.=l,26
and F=7.69; p<0.025; d.f.=l,l8 for Santa Rita and Almiran-
te respectively), and embryo count is significantly rela—
ted to maternal body length at autopsy for Santa Rita (E:
10.26; p<0.005; d.f.=l,123) but not Almirante (Fz4.05;
p>0.05; d.f.=l,23). Furthermore Santa Rita mothers were
heavier than Almirante mothers at parturition (F=24.88;
p<0.005; d.f.=l,46), and Santa Rita mothers were larger
than Almirante mothers in body length at autopsy £28.00;
p<0.005; d.f.=l,l48). Covariance analysis indicated that
the litter size differences between Almirante and Santa
Rita merely reflected the differences in maternal body
36
weight (5:0.14; p>0.05; d.f.=l,45). The same analysis
of the number of embryos found at autopsy, however, showed
a significant difference in embryo count independent of
maternal body length (§=l3.97; p<0.005; d.f.=l,l47).
Growth and development
Ninety-three female spiny rats were pregnant when
captured and gave birth to litters in the laboratory.
Another 37 females conceived in the laboratory and gave
birth to live litters.
Size at birth
There were no significant sexual differences in the
average individual body weights of newborn from Santa Rita
F=0.54; p>0.05; d.f.=l,86 litters) or Almirante (§=l.43;
p>0.05; d.f.=l,27 litters). Average individual body
weights of Santa Rita newborn were significantly negative—
ly correlated with litter size (£23.4z—0.46; E=-2.53;
p<0.02; n—k=28 litters) but not significantly correlated
with maternal weight (£24.3=—0.006; £=—0.03; p>0.05; n-k=
28 litters). Average individual body weights of Almirante
newborn were significantly negatively correlated with lit-
ter size (£23.4=—0.53; 5:2.76; p<0.02; n—k=20 litters)
but not significantly correlated with maternal weight
( —0.07; £=—0.32; p>0.05; n-k=20 litters). Covari—
524.3:
ance analysis of mean individual body weight of newborn
versus litter size showed that newborn from Santa Rita
37
were significantly lighter in weight than those from Almi—
rante (5:4.93; p<0.03; d.f.=l,94 litters) independent of
litter size.
Growth rate
Growth in body weight between birth and twenty days
of age was not significantly correlated with weight at
birth, litter size, or maternal weight (Table 2). There
were no significant sexual differences in body weight
growth between ages 0 and 20 days for either Santa Rita
(F=2.32; p>0.05; d.f.=l,86 litters) or Almirante (F=0.ll;
p>0.05; d.f.=l,27 litters). There were no site differ—
ences in body weight between ages 0 and 20 days for either
males (£21.64; p>0.05; d.f.=l,55 litters) or females
(F=0.55; p>0.05; d.f.=l,59 litters). Analysis of growth
by linear regression of 1n(body length) on 1n(age) resulted
in the following equations:
Santa Rita
0.94
0.97
Males y=4.408(0.008)+0.204(0.002)x r
Females y=4.407(0.019)+0.195(0.002)x r
Almirante
Males y=4.47l(0.013)+0.197(0.003)x r2=0.95
Females y=4.469(0.011)+0.l84(0.003)x r2=0.95
Growth rates, estimated by the slopes of the above
regression equations, were significantly greater for males
for both Santa Rita (5:3.51; 240.001; d.f.=l49l) and Almi—
rante (£=2.82; p<0.01; d.f.=422). Males were sugufianmly
38
m No.HI mq.0| eq.01 oH.OI NH wN.o oH.o NH 0N.o oN.o
m NN.H wq.o Nq.o mH.o NH HH.HI Om.o| NH qH.O qo.o
m mo.o Ho.o mm.o MH.o NH mq.H mm.o NH oo.H oN.o
XIC u H u 9 xi: u H xi: u u
monEom monz monEom monz
oucmHHEH< wuHm mucmm
.uLwHoB Hocuoume Adv
one .oNHm HmuuHH Amv “LuHHn um uanoB zoos ANV .mhmp ON pan 0 mowm
Cmozuon uanoB xoon CH SDBOHw AHV How muCoHonwooo conmonoh HmHuwmm
MN.aHu
sm.maa
sm.NHa
.N mHnme
39
larger than females by day 30 in Santa Rita (F=8.83;
B<0.005; d.f.=l,96 litters) and significantly larger by
day 80 in Almirante(§=12.04; p<0.005; d.f.=l,25 litters).
Growth rates, estimated by the slopes of the above regres-
sion equations, showed that females from Santa Rita grew
significantly faster than Almirante females (£=3.29; p<
0.01; d.f. 966), but no significant differences in body
length were found between Almirante and Santa Rita females
for any age. There was a significant difference in
growth rate between Santa Rita and Almirante males (3:2.01;
p<0.05; d.f.=875), and Almirante males were significantly
larger (e.g., F=5.86; p<0.025; d.f.=l,60 litters on day
5 and §=9.01; p<0.005; d.f.=l,50 litters on day 100).
Molt
Molt comparisons between males and females from Santa
Rita and Almirante are shown in Table 3. The molt began
earlier among females than among males, but there was no
discernible difference between sites.
Sexual maturity
The earliest vaginal perforations observed among Al—
mirante and Santa Rita females born and reared in the la—
boratory were 60 days and 70 days of age, respectively.
The percentages of females found perforate for the first
time on each day of observation are shown in Table 4.
A significantly greater proportion of Almirante females
40
.owma uxoc Go UoDcHucoo
$m No .Louma Hmmuoo oz
Rm Nd .mummadw umsm Loumd Hmmhoa
NmN Nos qu .souaa Hamaoe .50 «can on m>aa
Noe NAN Ham Hem .mmenm co soc mmema unse<
Nmm New xw fiqH .mxcmHm mH
Honoumom use HHm co omeod uH3o<
No NN .mmema oase< co
Hmw HooH Hwa New .nouma mehoe HHQEm
m mH oposu use mumo ou BHoz ow
Nan Hwa NMN Hm .mmam on no: use:
Nwm NAN Nmm .mmNm m>onm uaoz
NNN Hon Nam .masm awesome uHoz ON
New fiHN Noe .mumo ocm moxo
osu panopm mozoumd mum mumzu
one EDuumou mo aHu co umdm uHoz
Nmm Ham Nos .mmsm and on so Nashua:
EDpumou a: commonOHa mm: uHoz co
Nam HooH .csmmn was SHoz cm
fim fimn .cswon mm: uHoz oq
monE monEom monE monEom
muemuHeHa mocmuHeH< munm macaw «one macaw
owmucmouom uHoe mo owmum ow<
.mhmp CH oohsmmoe mH ow< .oucmuHEH< pom wuHm modem 50pm monk
xcHam onEow paw onE How UHOE oHHco>Dqum0d wo mums osu mo mCOmHHmQEoo .m oHan
41
NH wH mm Nw po>pomno mHmEHcm No Honesz
ma mm mON qu mcoHum>pomno wo Honesz
$0 NN .moon udooxo owwHod UHDU<
NNH NON NMN $9 .moon mo
uoHpoumoa udooxo omeoQ UHDU<
wa New Nmo Nmo .mmema SHse< QNH
NNN Nmm NHN NmH .souma Hmmuoe Eu made On m>aa
emu New Now Has .mwmn
no moUHm udooxo omeod uH3o<
NNH NMN fie .moon wo
ponoumOQ udooxo omeod uHDo<
fie $NH .mon xomn odoUXo omeod uH3p<
xNH $N XoH .omeod uH3U< ooH
monE monEow monE monEom
oucmeEH< oucmuHEH< muHm mucmm
muam modem
owmucoopom
OHOE mo oumum ow<
.ie.ucooc m magma.
42
Table 4. Percentage of laboratory reared female spiny rats
with perforate vaginas seen each observation
day.
. . 1
Age Alm1rante Santa Rita gadj. p
60 33% (1/3) 0% (0/23) 0.96 >0.05
70 27% (3/11) 6% (1/18) 1.14 >0.05
80 67% (4/6) 0% (0/9) 5.38 ((0.025
90 40% (2/5) 7% (3/44) 1.76 >0.05
100 70% (7/10) 13% (6/45) 10.04 ‘<0.005
110 100% (1/1) 33% (3/9) 0.04 >0.05
120 78% (7/9) 34% (15/44) 4.18 (0.05
l. The 2x2 test of independence using the G—statistic
with Yate's correction (Sokal and Rohlf, 1969:591).
43
were perforate on three of these observation days. By
the age of 120 days, a significantly greater prOportion
of Almirante females (ll/l8) than Santa Rita females
(10/35) had been observed perforate on some previous ob—
servation day (Eadj.=3'96; p<0.05; d.f.=1). The mean day
of perforation could not be determined because observa-
tions were not made after 120 days and many Santa Rita
females were still imperforate at that age (Table 4).
Field data (Table 5) indicated that females from both
populations became reproductively active (perforate, preg-
nant, or with placental scars) at approximately the same
size.
In the laboratory, 7 pairs of laboratory reared spiny
rats from Almirante and 11 pairs of laboratory reared ani-
mals from Santa Rita bred successfully. The earliest
mating among Santa Rita rats was 120 days of age when two
siblings bred successfully. One Almirante female bred
at 120 days of age and one male bred at 130 days after
the two were paired at 100 days of age.
Testes descended earlier among Santa Rita males
(Table 6).
Growth and development
New born Proechimys are covered by a thick pelage.
The head is dark but the back is gray because of white
hairs (about 4 millimeters long mixed in with the short
44
Table 5. Fraction of field captured females reproductively
active (perforate, pregnant, or with placental
scars) on arrival at the laboratory.
Body length Almirante Santa Rita gadj.l p
180—189 mm 0/3 0/13
190—199 mm 1/2 2/11 0.005 >0.05
200—209 mm 3/4 5/16 1.04 >0.05
210—219 mm 3/3 13/23 0.76 >0.05
220-229 mm 5/5 9/16 1.87 >0.05
230+ mm 22/27 171/202 0.02 >0.05
l. The 2x2 test of independence using the G—statistic with
correction (Sokal and Rohlf, 1969:591).
45
Table 6. Percentage of laboratory born males with
descended testes at four ages.
. . 1
Age Santa Rita Alm1rante gadj. p
70 4% (2/45) 0% (0/14) —0.02 >0.05
80 20% (8/39) 7% (1/14) 0.58 >0.05
90 56% (26/46) 12% (1/8) 3.91 (0.05
100 75% (33/44) 89% (8/9) 0.23 >0.05
l. The 2x2 test of independence using _
with Yates' correction (Sokal and Rohlf, 1969:591).
the G—statistic
46
dark hairs (about 1 millimeter in length). The ventral
surface is pink and covered with short white hairs
with a few longer ones (about 4 millimeters long).
Vibrissae (25 to 30 millimeters long) are conspicuous
on the rostrum and above the eyes (15 to 22 millimeters
long).
Within minutes of birth the ear pinnae unfold
revealing the already perforate auditory meatus. The
eyes open soon after birth, but occasionally one or
both eyes will remain closed for a few hours. The
tips of the toenails are always white at birth and
this marking persists for a day and was used occasionally
to time births not observed directly. The incisors
have usually erupted before birth but in two instances
were still covered by a thin membrane at birth. Although
no cheek teeth are visible at birth spiny rats will
nibble at solid food within hours of birth.
Molt
Juvenile Proechimys semispinosus have a brown pelage
of thin aristiforms (guard hairs) and setiforms (underfur).
The post-juvenile molt begins as agouti—colored hairs ap-
pear on the anterior rostrum, below the eyes and ears.
The agouti coloration moves up the rostrum as the patches
expand. The back is still covered with juvenile pelage
with soft aristiforms raised above the surface, but if
47
the skin of the back is examined by parting the fur, short
black hairs can be seen just erupting. The agouti colora-
tion continues to expand on the head as agouti hairs ap—
pear above the eyes and in front of the ears. At this
stage of the molt the adult pelage has advanced up the ros-
trum until it is almost to the eyes. The agouti-colored
pelage continues moving up the rostrum until it is between
or even above the eyes to the ears. Next, the agouti—col-
ored setiforms and flattened dark-colored aristiforms ap—
pear on the back forming a conspicuously dark shiny oval
patch. The agouti—colored adult pelage continues up the
head until it is between the ears. The dorsal patch ex—
pands, moving to the head and down over the shoulders to
the front legs and down and back over the sides until fin-
nally the rump, hips, and hind legs are covered by the
agouti-colored adult pelage.
Sex ratio
Laboratory born spiny rats from Almirante and Santa
Rita exhibited a 50:50 sex ratio (Table 7).
Lactation
All females observed but one had three pairs of nip—
ples, one inguinal pair cephalad from the prominent clito-
ris, and two lateral pairs just above the midline, one
immediately in front of the femur and one at mid—thorax.
48
Table 7. The number of male and female spiny rats captured
in the field and born in the laboratory (includ—
ing both field and laboratory conceptions).
Males Females X p
Spiny rats
trapped near
Almirante 92 82 0.58 >0.05
Spiny rats
trapped near
Santa Rita 471 474 0.01 >0.05
Almirante
births in the
laboratory 37 35 0.06 70.05
Santa Rita
births in the
laboratory 109 113 0.07 70.05
Total 713 718 0.02 70.05
49
One laboratory—born female had the 6 nipples described
above plus a pair on the abdomen 4.5 centimeters cephalad
of the inguinal pair.
During the period of lactation the nipples are swol—
len and elongated and the mammary tissue is thick and con—
spicuous. It is especially conspicuous around the ingui—
nal nipples where the hair is thin and where it forms a
thick l.4x4.5 centimeter patch extending from the clitoris
forward and laterally under the nipples. The mammary tis—
sue around the lateral nipples is well—developed but less
conspicuous because of the thick hair on the thorax. The
areas immediately surrounding the lateral nipples are de—
void of hair during the period of lactation when the nip-
ples are erect and prominent.
Young Proechimys were observed eating soft fruit on
the day of birth and one youngster gained 1% of its weight
on day 9 when removed from its mother for a day. When
left with the mother for longer periods young will spend
a great deal of time suckling for the first three weeks.
If the young are left with the mother longer, the inguinal
mammary tissue recedes but the young will continue suck-
ling on the lateral nipples. Well—developed lateral mam-
mary tissue was observed as late as 46 days after birth
and young were observed suckling as late as day 51. Most
young have quit suckling by day 50 and the nipples have
receded in size. Some young, if left confined with their
50
mother, continue suckling even though the mammary tissue
is no longer conspicuous. In such situations the nipple
is still enlarged and was observed as late as day 66.
Young spiny rats were observed suckling longer in
this study than has been reported elsewhere. Enders
(1935) reported lactation lasting 46 days in one case and
Maliniak and Eisenberg (1971) noted that young are nursed
until 40 days of age in captivity.
It is not known if lactation lasts as long in the
field, but Enders (1935) estimated by the size of trapped
young that they stay with their mother until 2 to 2%
months of age. Young spiny rats may be able to find food
long before this age since in this study young did eat
solid food at an early age. Other investigators have re-
ported similar observations. Enders (1935) reported young
eating solid food by the age of 11 days and Maliniak and
Eisenberg (1971) remarked that young begin to eat solid
food almost from the first day.
Since most male spiny rats were measured on arrival,
estimates can be made of their ages (Table 8). These es—
timates suggest than some young are moving about at an
early age.
51
Table 8. Frequency distribution of age estimates of male
spiny rats trapped in Almirante and Santa Rita.
Estimated Frequency of Frequency of
age(days) Almirante males Santa Rita males
10—20 1 2
20—30 4 3
30-40 1 6
40—50 3 6
50—60 5 5
60-70 0 2
70-80 4 12
80—90 2 6
90—100 2 9
100-120 8 21
120—140 6 26
140-160 2 11
160-180 6 4
180—200 6 14
N
0‘
200+ 173
FIELD RESULTS
Reproduction in field captured males
Proechimys like other caviomorphs do not have a true
scrotum (Weir, 1974; Pocock, 1922), but the testes will
descend from the inguinal canal until the caudae epididymi
or even the testes themselves are just beneath the skin.
The position of the testes was labile in field—captured
males and was not used for determining the fertility of
field-trapped males. When handled, most field captured
males pulled the testes into the inguinal canals with only
portions of the caudae epididymi exposed. Males that were
held in the labortory longer were more likely to have
external testes when handled. The testes of laboratory
born males with descended testes remained external when
examined.
The testes of most male spiny rats trapped in Santa
Rita were significantly smaller during the months of Octo—
ber, November, December and January (Figure 5). In Santa
Rita this period of four months juxtaposes the two wettest
months with the first two months of the dry season.
There was insufficient evidence to Show any seasonal
change in the testis size of Almirante males (Table 9).
52
53
.mNHm oHaEmm Ucm newsmu n.H.o Nmm mowsHocH .pomeH
Mo LuwcoH mpon CH EEONN monE wUHm wucmm mo mHumou umoH mo HEEV LawCoH cam: .m opstm
J . H
ova >02huoo amm m3< Haw cSh aw: Mm< he: Lou CMW
.fi mm EEOHI
«H z .3 EEONL
MH
4 m i
54
.ponEoumomlxpw3Hnom wcsto memE oucmeEH<
mo omocu Cmnu nowme >HucmoHMchHm ohm monE muHm mucmm Mo mnuwcoH moumweke
.%MMDthIHonouoo onto wonEoudom
prmdhnom wcHHDU HomeH %HquoHMchHm ohm monE muHm mucmm mo wLOMCoH woumoH «
AHVNM AchN iwvom.oaww.am iwvow.muma.fim +oom
Amcmm.muoo.om AHva ANNVom.HHom.am AaVNN.Naow.Hm omN-owN
AmVNN.oHoo.wN Amvmq.HHmm.Hm iANNqu.HHmm.sm AvaNm.Hflmq.oN aNN-oNN
«aiocmH.Naom.NN AHVMN «Amqvmo.Hamo.Nm ASNVNH.HHom.wN sowuooN
aaflocoo.NHom.mN Amvom.NHow.mN iimquH.Hwa.Om AmHvaw.Haow.oN amNIOAN
Aavwm.NHqH.©N Accao.m+om.mm «AQNVOH.HHH©.0N Amqum.HHow.qN asmloqm
«aiovmw.mhmw.mw Amvmo.qfloo.qN aANHVmS.HHMN.NN Amwcmm.Huow.HN ammlOMN
ANVOm.wH Amado.oHHmm.0H AOHVSH.NHNS.HN AOHVNH.mHoH.wH ONN-ONN
Amvso.NHoN.OH AHVaH Aquou.quwN.om lovem.aamm.oH oHNIOHN
Amva.onm.HH AHVm ANVNm.meN.MH Amvom.NHow.NH oomloom
dominom thluoo dominom cmhluoo LOMCoH
xoom
oucmuHEH< mUHm mucmm
.mHmosu
Icowmd CH oNHm deEmm LuHB whouoEHHHHE EH Go>Hw ohm mucoEopsmon .mumu
xcHam onE Ummamhu UHon wo moumou ummH mLu wo .H.o Nmo H sowCoH cmoz .o oHan
55
Testis size increases with body length. The natural
logarithm of testis size was significantly correlated with
the natural logarithm of body length for Almirante and
Santa Rita males for the period of October through January
(5:10.93, p<0.05, d.f.=49; £=18.26, p<0.05, d.f.=210) and
February through September (5:6.04, p<0.05, d.f.=25;
5:16.14, p<0.05, d.f.=l43) respectively.
When testes lengths were adjusted to the mean body
length for each of the four site—season combinations (see
Methods), the mean testes lengths, measured in millimeters,
for the periods of October through January and February
through September were 24.97:0.63 (n=56) and 29.56:0.65
(n=64) respectively for Santa Rita and 23.66i1.64 (n=20)
and 23.98il.00 (n=29) respectively for Almirante. There—
fore even after testes lengths were adjusted to remove
the effects of body size this analysis supported the argu-
ment that the testes of Santa Rita males captured during
February through September were significantly larger than
those of males captured during October through January.
No seasonal change in testis size was observed in Almiran—
te males after testis size was adjusted to body size.
This analysis also revealed that the testes of Santa Rita
males captured during February through September were
larger than those of Almirante males regardless of season
of capture even though Almirante males were larger than
Santa Rita males.
56
Analysis of a small sample of testes taken from known
age laboratory born males supported the argument that the
testes of Santa Rita males were larger than those of Almi—
rante males (Figure 6).
Maximum testis length and the body length when testis
growth rate stops increasing and begins decreasing can
be estimated by fitting the data of Table 10 to the logis—
tic equation y=a/l+eb+cx.
The mean testis lengths were
fitted by nonlinear least squares to the midpoint of the
body length interval using Marquardt's algorithm as de-
scribed by Conway gg g1. (1970). The three partial deri—
vatives of the above logistic equation described by Conway
gg g1. (1970) are incorrect, however, and should read:
Y/a=l/l+eb+CX
Y/b=—aeb+CX/(l+eb+cx)2
Y/c=—axeb+CX/(l+eb+cx)2
Calculations were performed on a TI—59 hand—held calcula—
tor using a program written by the author. The three re—
sulting logistics have the asymptopes (maximum testes
sizes) 40.1 millimeters, 34.5 millimeters, and 33.8 milli—
meters respectively for males captured in Santa Rita dur—
ing February through September, during October through
January, and in Almirante in both seasons. This reflects
the previous conclusion that testes are larger for males
captured in Santa Rita during February through September
but that the testes of males captured in Santa Rita
57
30 _ D Almirante
0 Santa Rita
25 - 0
(225mm)
E
E
.5
go 20 ’ 0 (234mm) [:1
o (240mm)
v-l
(I)
'3 0 (214mm)
8 D (238mm)
H
15 .
0 (175mm)
40 70 100 130
Age (days)
Figure 6. Testis length of young known age spiny rats
from Santa Rita and Almirante. Body lengths
are in parenthesis.
q Hoo.HVo.Nm N Hovo.0m «ONImmN
mH HNo.ovN.mm o HwH.va.Hm o Awo.HVN.om qulmwN
MN ANq.oVN.qM «H HNo.oVH.om m Aom.va.NN qulmNN
om Hom.oVH.qm Nm Hoo.ovm.oN w ANm.HVo.wN qNNImoN
Hq Amq.ovo.Hm wH HHN.ovN.NN HH HqN.ovN.oN qulmmN
am Hom.ovo.0m NH HNm.HVN.mN oH Hmo.ovo.mN «lequ
oH Ado.ovH.wN @H ANm.ovm.NN N HNo.va.MN quImMN
oH Adm.ovq.mN qH ANN.HVN.ON MH Amw.ovq.HN QmNImNN
8 «H HNo.HVo.mH OH AOH.va.wH m Haw.ovo.oH qNNImHN
5 HH Hem.qu.oH o HHN.ovm.qH N ANVMH qHNImON
N HHH.qu.HH m Awm.ovo.MH q AoH.va.oH quImoH
m Hoq.ovo.m N AHVo o qulme
m AHm.ovo.w q AmN.oVN.¢ quImNH
m Hmm.ovm.N H o N Hom.va N «NHImoH
m Hovo.N H m «OHImmH
m Hovo.N N AHVN quIqu
c Ammvm c Hmmvm : Ammvm Hm>pmucH
Illllllllllllll IIIIIIIIIlIIIIII LuwcoH
HonEouaomINHmsunom NpmscwhlpoQOuoo MonEmooQINpmscmw Npom
SE Scam anemia:
.oquHHEH< one wuHm wucmm CH
powdudmo msmocHdeEom mNEHLooopm wo moumou umoH mo LuwCoH new: .oH oHan
59
during October through January are similar to those of
males trapped in Almirante in both seasons.
The body lengths at which inflection (body length
when the rate of testes growth begins decreasing) occurs
was determined by fitting the parameters obtained by solv—
ing the logistic for the second derivative:
2 b+cx(l+eb+cx_2eb+cx)
y”=-ac e
——F—7___
(1+e +cx)
This analysis revealed that the points of inflection were
remarkably similar, 219 millimeters, 217 millimeters, and
217 millimeters for Santa Rita during February through
September, Santa Rita during October through January, and
Almirante during the whole year.
In order to better understand the meaning of changes
in testis size with season, histological sections of the
testes from animals captured both in the dry season and
the wet season will have to be studied. Some information
is provided by the availability of testis sections of ten
adults caught in Santa Rita during October and November.
Among these, one with an adjusted testis length of 30
millimeters had enlarged seminiferous tubules with many
cell layers, few interstitial spaces, and many spermatozoa.
The remaining nine testes 25 millimeters in length or less
when adjusted to mean body length had small seminiferous
tubules with few cell layers, large interstitial spaces,
60
and few to no spermatozoa.
If the fluctuations in testis size do reflect fertil—
ity among males, then one would expect to find more preg-
nant females during the months of February through Septem-
ber in Santa Rita than in the months of October through
January but no seasonal difference in Almirante. We will
see in the next section that the reproductive activity
of female spiny rats in Santa Rita and Almirante sup-
ported this proposition.
Reproduction in field captured females
During the months of October, November, December,
and January only 26% (34/131) of females (estimated by
body length to be 120 days of age or older) trapped near
Santa Rita were pregnant on arrival to the laboratory
(Table 11). During the remainder of the year 89% (188/
211) were pregnant. This difference is very highly signi-
ficant [p(§ l47.9)<0.005, n=l). Juveniles (estimated
by body length to be less than 120 days of age) and young
adults (estimated by body length to be between 120 and
200 days of age) were more commonly trapped in the months
of October through January. This suggested that the sea—
sonality in the proportion of pregnant females found in
the field was merely a result of a seasonal change in the
age structure of the population. Although age estimates
for females that gave birth to live or still born young
61
NaN wN HH m d N ponemooo
NmH mm o m H N HonEo>oz
NNm oH m m N N MoDOOoO
Nam N NH o N CH nonEoudom
.NNo a w o H N umswsa.
NOS o S H w mm 33.
NNa N «N H N 0H ocsm
Nam a 3 q o S .32
New N mm H E 3 ENE
NOOH o mN m a HH Lopez
NNw q wH m o @ hhmsunom
.Nmm 2 m N m m GEES
ow>wwmno
LupHn o: uzn
Hm>HHHm Hm>HHhm Hm>HHHm woumaHma wcsoz wcsox kmmounm
co co Co No CMonHHHum o>HH ou um
ucwcmopm ucmcwoua pamcwoha ou LuHHn o>mw Luth ucmcwopd
unoohom uoz HmDOH umcu HonEDz o>mo HoQEDZ Lucoz
.MoUHo Ho mxww ONH o uwCo
%Uon % UoDMEHumo one wuHm mqum New: popsuamo mzmocH mHEom
m EHnomopm onEow mo COHqucoo o>Huospowdop mHnucoe mo Nuweesm .HH mHan
62
were not available, they were available for all other fe—
males including pregnant and nonpregnant. Analysis of
these data revealed the same seasonality in the proportion
of pregnant females for all age classes (Table 12).
Females from Almirante appear to be reproductively
active the year around (Table 13). From October through
January 93% (13/14) were pregnant on arrival and during
the remainder of the year 92% (33/36) were pregnant.
Among 16 juvenile sized individuals captured near Almi—
rante, 4 were pregnant when captured in January, February,
May and June.
Estimates of the month of conception (see Methods and
materials) for each field trapped spiny rat are summa-
rized in Figures 7 and 8. The large sample of spiny rats
from Santa Rita provided the opportunity to analyze males
and females separately. This allowed two independent esti—
mates of the months of conception for field caught spiny
rats from Santa Rita. The monthly pattern for 420 Santa
Rita males was very similar to that for 378 Santa Rita fe-
males (Figure 7). Most conceptions were estimated to have
occurred in May, June, and July and the fewest occurred in
the months of October, November, December, and January.
The observation that males and females analyzed sepa-
rately show a similar pattern increases confidence in
these estimates and further supports the argument that
breeding among Santa Rita Proechimys is concentrated into
63
Table 12. The proportion of pregnant to nonpregnant
females revealed by autopsy of spiny rats trap—
ped in the months October through January and
February through September in Santa Rita.
Age estimates Pregnant/nonpregnant
Oct—Jan Feb—Sep
Between 90 and 120 days 1/5(20%) 6/12(50%)
Between 120 and 200 days 2/40(5%) l3/l6(8l%)
Greater than 200 days 6/6l(10%) 106/115(92%)
.5-‘-: mxj‘i LE.-
64
NOOH o o o o m HonEoooo
I o o o o o HmnEo>oz
NNo H N o N o Honouoo
NooH o N o N o HonEoudom
I o o o o o umzws<
.83 o H o H o Nst
NHN N m o H q wand
.33 o q o H m .32
.83 o H o o H HHS...
NooH o m H o q Loam:
.N.Ha H 0H m m N 3838
.33 o N o o H 3.268
Uo>Homno
LHHHQ oc ujn
Hm>HMHm Hm>HHHm Hm>HHHw poundea wcso% wcnox deoqu
co co :0 Ho CHOLHHHum o>HH ou um
ucmcwopa namcmohd ucmcwoha ou LHHHD m>mw LOHHQ ucmcwopd
ucoopom uoz kuOH umfiu Honesz o>mo HonEDz Ludo:
.Hmeo Ho mxm ou
suwco N 0 NH woumEHumo can oucmHHEH< who: Umpsudmo msmocH mHEom
m EHcooOHm onEow Mo CoHqucoo o>Huodpouaop NHLHCOE mo NHmEEDm .MH oHan
65
Figure 7.
Santa Rita males
Santa Rita Females
-------- Estimate based on
pregnant females
The monthly distribution of conceptions estimat—
ed to occur throughout the year at Santa Rita.
The circle represents 8.3% or the expected
monthly proportion if breeding occurs uniformly
throughout the year.
Figure 8.
66
Almirante males
................. Almirante females
________ Males and females
combined
The monthly distribution of conceptions estimat-
ed to occur throughout the year at Almirante.
The circle represents 8.3% or the expected
monthly proportion if breeding occurs uniformly
throughout the year.
67
the months of February through September.
Obviously mortality is a confounding factor here.
If young are born during the period of October through
January and their mortality is high they will not be cap—
tured. If it is assumed that (1) the number of adult fe—
males is constant the year around, (2) the pregnancy
pattern is that shown in Table 11, and (3) the average
female‘s pregnancy was conceived one month (half the
gestation period) earlier, then the estimated pattern of
conceptions would be as shown in Figure 7. Comparison
of this estimate with the estimated month of conception
of field trapped males and females supports the argument
that the reproductive season in Santa Rita was restricted
but also suggests a higher mortality for spiny rats con—
ceived in the verano (January, February, March, and April)
since the proportion of conceptions estimated by pregnancy
patterns of captured females exceeds the proportion of
conceptions estimated by the body lengths of males and
females during these four months.
Among 84 males and 52 females from Almirante most
conceptions were estimated to have occurred in the four
months of July to October and the fewest in November,
December, and January. The sample for Almirante was small—
er and less reliable than the Santa Rita sample.
Comparison of the two Figures 7 and 8 suggests
that breeding in Almirante was shifted so that breeding
68
was reduced a month later than it was in Santa Rita. Re—
call that the heaviest rains occurred in Almirante one
month later than they did in Santa Rita and lasted into
January.
If Proechimys semispinosus in Almirante do breed
equally the year around (Table 12), then Figure 8 suggests
that mortality was highest among those spiny rats con—
ceived in November, December, and January.
Additional field results
Distribution of embryos in the uterus
Analysis of the distribution of embryos in the horns
of the uterus of Proechimys was prompted by a remark by
Fleming (1969:131) that implantation tended to occur more
frequently in one uterine horn of the spiny rats that he
examined. One caviomorph, the mountain viscacha (Lagidium
peruanum), is known to nearly always (97% in one sample)
carry embryos only in the right horn of the uterus (Pear—
son, 19492155).
The numbers of embryos found implanted in the left
and right horns of the uteri fromn pregnant spiny rats
trapped near Santa Rita and Almirante are shown in Table
14. Neither the data from Santa Rita nor that from Almi—
rante showed any significant; difference from an equal
distribution of embryos among the two horns [p(§223.43)=
0.064, d.f.=l and p(§;0.51)=0.475, d.f.=l, respectfully].
69
Table 14. The distribution of embryos in the uterine horns
of pregnant spiny rats trapped near Santa Rita
and Almirante.
Site Number of Uterine Total number
pregnant horn of embryos
females
Santa Rita 119 Right 161
Left 196
Almirante 24 Right 22
Left 27
70
When the data for both of these sites were pooled however,
the number of embryos implanted in the left horns was
significantly greater than those implanted in the right
horns [2(5223.94)=0.047, d.f.=l].
Unilateral pregnancies among females with embryo
counts of two or more were not more frequent than would
be expected if an ovule was just as likely to come from
the left as well as the right ovary at each ovulation and
there was no migration of embryos from one horn to another
(Table 15). Unilateral pregnancies among females with
embryo counts of 3 or more were less frequent than would
be expected by chance 0.005uHHDumE onE HoumH
LuBOHw Hoonm
moxhnEo Hozom
wouwcooc HomeH
wcHoooHn HMCOmmom<
wcnox
mwo>mw coHuanhumHo ow<
NqujumE mHmEom HoHHme
uHoz
mNHm HmuuHH
coHumumoo
oHo
mHo>mw coHuanHumHo ow<
NuHusumE onEow HoumH
monE UHDom HoHHmEm
NHHHDOME onE HmHHHmm
Luzopw Moummm
mowhnEo oHo:
monocooc HoHHmEm
wcHoooHn HQCOmmom
oodouomeo oz
mmHsumom
oouooHomlz
deSumom
oouooHomIH
QUCQHHEH<
muHm macaw
mCoHHMHDQom oquHHEH< oCm
.msmocHdeEom mkEHfiooonm mo
wuHm mucmm Ho mohsumow NuoumHSIoMHH mo NHmEESm
.ON oHan
88
is dependent on the taxonomic level examined. Comparisons
among higher taxonomic categories offer strong support
but support is weak for intrageneric or intraspecific com—
parisons (Stearns, 1977, 1980, 1983a, 1984a). Stearns
(1984bz264) has argued that microevolution could not have
produced the pattern because it results from differences
among higher taxa that occurred long ago and has not
changed significantly within lineages since then. I be—
lieve the present study refutes this view and shows that
this pattern involving r— and K-selection characteristics
can be explained by microevolutionary forces. In this
study intraspecific tactics were perceptible and trade—
offs among r- and K-selection attributes did occur.
Due to the logical structure of statistical infer—
ence, hypotheses can be rejected but not confirmed. The
data presented above is consistent with r— and K—selection
theory but does not confirm it. In fact, these data are
also consistent with the hypothesis that there has been
selection for larger size for Almirante rats and/or selec—
tion for smaller size for Santa Rita rats. Larger size
can help a population avoid some predation, it increases
the variety of food choices available, and increases the
efficiency of energy acquisition (Armitage, 1981:43).
Once there has been selection for size, allometric growth
will lead to life history changes consistent with r— and
K-selection (see Theory of r- and K—selection; Blueweiss,
89
gg gl., 1978; Western, 1979; Stearns, 1983a, 1984a).
Stearns (1983a) believes that many patterns attributable
to r— and K—selection among broad taxonomic groups is due
to selection on size followed by coadaptive shifts in life—
history attributes. If this is true, then not all corre—
lations between the life-history attributes are adaptive.
The life history of Proechimys semispinosus in Santa
Rita and Almirante is also consistent with the hypothesis
that density-dependent mortality applied to all age class—
es is greater in Santa Rita, or that adult mortality is
high, variable, or unpredictable in Santa Rita and Almi—
rante, and/or juvenile mortality is high, variable or un—
predictable in Almirante (Stearns, 1983bz601; Parsons,
1983:12).
In this study it was assumed that the selection of
the life—history parameters of Proechimys semispinosus
are mediated through the density of Proechimys with re-
spect to resources. Obviously any other forces impinging
on the density of Proechimys or its resources like preda-
tion or interspecific competition will require modifica—
tion of the r- and K—selection model. Many Panamanian
predators feed on fruit in season but turn to animal prey
when fruit is less abundant (Fleming, 1969:63; Smythe,
1970, 1978, 1982). Interspecific competition may also
change seasonally (Smythe, 1970). These are just a few
of the many possible dimensions of a life—history pattern
90
(Wilbur, gg gl., 1974; Parry, 1981). Until the covariance
structure of the life—history attributes can be identified
by study of other populations of Proechimys semispinosus,
one cannot identify the life history features under
strongest selective pressure.
The life history of Proechimys semispinosus in Panama
appears to be consistent with r— and K—selection theory
but before this hypothesis can be termed the cause of this
pattern with any degree of confidence, the rival hypothe—
ses must also be tested and the density of populations
measured directly.
91
LITERATURE CITED
Aldrich, J.W. and B.P. Bole, Jr. 1937. The birds and mam-
mals of the western slope of the Azuero Peninsula (Repub—
lie of Panama). Sci. Publ. Cleveland Mus. Nat. Hist. 7:1-
196.
Allen, J.A. and F.M. Chapman. 1893. On a collection of
mammals from the island of Trinidad, with descriptions
of new species. Bull. Amer. Nat. Hist. 5:203-234.
Armitage, K.B. 1981. Sociality as a life—history tactic
of ground squirrels. Oecologia 48:36-49.
Baker, R.H. 1983. Sigmodon hispidus. Pp. 490—492 in:
D.H. Janzen (ed.), Costa Rican Natural History. Univ.
Chicago Press, Chicago.
Berry, R.J. 1964. The evolution of an island population
of the house mouse. Evolution 18:468—483.
Biggers, J.D., C.A. Finn, and A. McLaren. 1962. Long—
term reproductive performance of female mice. II. Vari—
ation of litter size with parity. J. Reprod. Fertil. 3:
313—330.
Birch, L.C., Th. Dobzhansky, P.O. Elliott, and R.C. Lewon—
tin. 1963. Relative fitness of geographic races of Dro—
sophila serrata. Evolution 17:72—83.
Blueweiss, L., H. Fox, V. Kudzma, D. Nakashima, R. Peters,
and S. Sams. 1978. Relationships between body size and
some life—history parameters. Oecologia 37:257—272.
Bonaccorso, F.J., W.E. Glanz, and C.M. Sandford. 1980.
Feeding assemblages of mammals at fruiting Dipteréx ana—
mensis (Papilionaceae) trees in Panama: see pre ation,
dispersal, and parasitism. Rev. Biol. Trop., 28:61—72.
Bonner, J.T. 1965. Size and Cycle: An essay on the
structure of biology. Princeton Univ. Press, Princeton,
N.J.
Bonoff, J.B. and D.H. Janzen. 1980. Small terrestrial
rodents in eleven habitats in Santa Rosa National Park,
Costa Rica. Brenesia 17:163—174.
92
Bowdre, L.P. 1968. An examination of the ecology of sev—
eral small terrestrial mammals of three life zones in
Costa Rica. Unpublished Organization for Tropical Studies
Report.
Bowdre, L.P. 1971. Litter size in Sigmodon hispidus.
Southwestern Natur. 16:121—128.
Bunge, M. 1967. Scientific Research: The search for
system. Springer—Verlag, Berlin.
Cain, A.J. and C.A. Harrison. 1958. An analysis of the
taxonomist's judgement of affinity. Proc. Zool. Soc.
London 131:85—98.
Camin, J.H. and P.R. Ehrlich. 1958. Natural selection
in water snakes (Natrix si edon L.) on islands in Lake
Erie. Evolution 1 : —51I.
Caughley, G. 1966. Mortality patterns in mammals. Eco—
logy 47:906-918.
Christian, J.J. and C.D. Lemunyan. 1958. Adverse effects
of crowding on reproduction and lactation of mice and two
generations of their progeny. Endocrinology 63:517—529.
Cody, M.L. 1966. A general theory of clutch size. Evo-
lution 20:174-184.
Cole, L. 1954. The population consequences of life his—
tory phenomena. Quart. Rev. Biol. 29:103-137.
Conway, G.R., N.R. Glass, and J.C. Wilcox. 1970. Fitting
nonlinear models to biological data by Marquardt's algo—
rithm. Ecology 51:503—507.
Crow, J.F. and M. Kimura. 1970. An introduction to popu—
lation genetics theory. Burgess Publ. Co., Minneapolis.
Darwin, C. 1859. The origin of species by means of na-
tural selection. John Murray, London.
Deevey, E.S., Jr. 1947. Life tables for natural popula—
tions of animals. Quart. Rev. Biol. 22:283-314.
Delany, M.J. and B.R. Neal. 1969. Breeding seasons in
rodents in Uganda. J. Reprod. Fert. (Suppl.6):229-235.
Dobzhansky, Th. 1950. Evolution in the tropics. Amer.
Sci. 38:209—221.
Dunmire, W.W. 1960. An altitudinal survey of reproduc—
tion in Peromyscus maniculatus. Ecology 41:174-182.
93
Ehrlich, P.R. and J.H. Camin. 1960. Natural selection
in middle island water snakes (Natrix sipedon L.). Evolu-
tion 14:136.
Emmons, L.H. 1982. Ecology of Proechim s (Rodentia,
Echimyidae in southeastern Peru. Iropical Ecology 23:280—
290.
Enders, R.K. 1935. Mammalian life histories from Barro
Colorado Island, Panama. Bull. Mus. Comp. 201. 78:385-
502.
Endler, J.A. 1973. Gene flow and population differentia—
tion. Science 179:243—250.
Everard, C.O.R. and E.S. Tikasingh. 1973. Ecology of
the rodents, Proechimys u annensis and Oryzomys capito
5%:875—886.
on Trinidad. J. Mamm.
Fisher, R.A. 1930. The genetical theory of natural se—
lection. Clarendon Press, Oxford.
Fleming, T.H. 1969. Population ecology of three species
of neotropical rodents. Ph.D. Thesis, Univ. Mich.
Fleming, T.H. 1970. Notes on the rodent faunas of two
Panamanian forests. J. Mamm. 51:473—490.
Fleming, T.H. 1971. Reproductive patterns of 40 Pana—
manian mammals. Handbook for tropical biology in Costa
Rica. Organization for Tropical Studies, San Jose, Costa
Rica.
Fleming, T.H. 1972. Three Central American bat communi-
ties: Structure, reproductive cycles, and movement pat—
terns. Ecology 53:555-569.
Fleming, T.H. 1973. The reproductive cycles of three
species of opossums and other mammals in the Panama Canal
Zone. J. Mamm. 54:439—455.
Fleming, T.H. 1974. The population ecology of two spe-
cies of Costa Rican Heteromyid rodents. Ecology 55:493—
510.
Foster, R.B. 1982. The seasonal rhythm of fruitfall on
Barro Colorado Island. Pp. 151-172 in: E.G. Leigh, Jr.,
A. Stanley Rand, and D.M. Windsor (eds.), The ecology of
a tropical forest: Seasonal rhythms and long—term changes.
Smithsonian Inst. Press, Washington, D.C.
Frankie, G.W., H.G. Baker, and P.A. Opler. 1974. Com-
parative phenological studies of trees in tropical wet
and dry forests in the lowlands of Costa Rica. J. Ecol.
62:881—919.
94
Glantz, W.E. 1982. Adaptive zones of Neotropical mam—
mals: A comparison of some temperate and tropical pat—
terns. Pp. 95—110 in: M.S. Mares and H.H. Genoways
(eds.), Mammalian biology in South America. Special Publ.
Pymatuning Lab. Ecol. #6.
Gliwicz, J. 1984. Population dynamics of the spiny rat
Proechimys semispinosus on Orchid Island (Panama). Bio—
tropica 16:73—78.
Goertz, J.W. 1965. Reproductive variation in cotton
rats. Amer. Midl. Nat. 74:329—340.
Goldman, E.A. 1920. Mammals of Panama. Smith. Misc.
Coll. 69:1—309.
Green, P.M. 1964. Density of population as a regulating
factor in the reproductive potential of Sigmodon hispidus.
Ph.D. Diss. Abstr., Oklahoma State Univ., Stillwater.
Guillotin, M. 1982. Activity rhythms and diet of Pro-
echimys cuvieri and Oryzomys capito velutinus (Rodentia)
in french Gu1ana. Terre Vie 36:337—371.
Hairston, N.G., D.W. Tinkle, and H.M. Wilbur. 1970.
Natural selection and the parameters of population growth.
J. Wildl. Mgmt. 34:681—690.
Hall, E.R. 1981. The mammals of North America. Ronald
Press, N.Y.
Handley, C. 1966. Checklist of the mammals of Panama.
Pp. 753—795 in: R.L. Wenzel and V.J. Tipton (eds.), Ecto—
parasites of Panama. Field Mus. Nat. Hist., Chicago.
Hempel, C.G. 1966. Philosophy of natural science. Pren—
tice-Hall, Englewood Cliffs, N.J.
Hess, R., W.C. Allee and K.P. Schmidt. 1951. Ecological
animal geography. John Wiley, N.Y.
Hoffman, R.S. 1958. The role of reproduction and mortal-
ity in population fluctuations of voles (Microtus). Ecol.
Monogr. 28:79—109.
Holdridge, L.R. and G. Budowski. 1956. Report of an eco—
logical survey of the Republic of Panama. Caribbean For-
ester 17:92—110.
Hooper, E.T. 1968. Classification of Peromyscus. Pp.
27—69 in: J.A. King (ed.), Biology of Peromyscus (Roden—
tia). Amer. Soc. Mamm., Special Publ. #2.
95
Jackson, W.B. 1965. Litter size in relation to latitude
in two Murid rodents. Amer. Midl. Nat., 73:245—247.
Jewell, P.A. 1966. Breeding season and recruitment in
some British mammals confined on small islands. Symp.
Zool. Soc. London 15:89-116.
Kilgore, D.L. 1970. The effects of northward dispersal
on growth rate of young, size of young at birth, and litter
size in Sigmodon hispidus. Amer. Midl. Nat. 84:510—520.
King, J.A. 1958. Maternal behavior and behavioral devel-
opment in two subspecies of Peromyscus maniculatus. J.
Mamm. 39:177-190.
Kleiman, D.C., J.F. Eisenberg, and E. Maliniak. 1979.
Reproductive parameters and productivity of Caviomorph
rodents. 1n Vertebrate ecology in the northern Neotro-
pics, ed. J.F. Eisenberg, pp. 173-183. Washington, D.C.:
Smithsonian Institution Press.
Lack, D. 1954. The natural regulation of animal numbers.
Oxford Univ. Press, Fair Lawn, N.J.
Lack, D. 1965. Evolutionary Ecology. J. Anim. Ecol.,
34:223-231.
Leck, C.F. 1970. The seasonal ecology of fruit and nec-
tar eating birds in lower Middle America. Ph.D. Thesis,
Cornell Univ., Ithaca, N.Y.
Lewontin, R.C. 1965. Selection for colonizing ability.
Pp. 77—94 in: H.G. Baker and G.L. Stebbins (eds.), The
genetics of colonizing species. Academic Press, N.Y.
Lord, R.D. 1960. Litter size and latitude in North Amer-
ican mammals. Amer. Midl. Nat. 64:488-499.
Lusty, J.A. and B. Seaton. 1978. Oestrus and ovulation
in the casiragua Proechim s ouairae (Rodentia, Hystrico-
morpha). J. 2001. London 182:255-265.
MacArthur, R.H. 1962. Some generalized theorems of natu-
ral selection. Proc. Nat. Acad. Sci. 48:1893—1897.
MacArthur, R.H. and E.O. Wilson. 1967. Island Biogeo-
graphy. Princeton Univ. Press, Princeton, N.J.
Maliniak, E. and J.F. Eisenberg. 1971. Breeding spiny
rats, Proechimys semispinosus, in captivity. Int. Zoo
Yearb. 11:93-98.
96
Mares, M.A. and R.A. Ojeda. 1982. Patterns of diversity
and adaptation in South American hystricognath rodents.
Pp. 393-432 in: M.A. Mares and H.H. Genoways (eds.) ,
Mammalian Biology in South America. Special Publ. Pyma—
tuning Lab. Ecol. #6.
Margalef, R. 1959. Mode of evolution of species in re—
lation to their places in ecological succession. Proc.
Xv Int. Congr. 2001. 10:787-789.
McLaren, A. 1963. The distribution of eggs and embryos
between sides in the mouse. J. Endocrin. 27:157-181.
Moojen, Joao. 1948. Speciation in the Brazilian spiny
rats (Genus Proechimys, Family Echimydae). U. Kansas
Publ. Mus. Nat. Hist. 1:301—406.
Moore, J.C. 1961. Geographic variation in some reproduc-
tive characteristics of diurnal squirrels. Bull. Amer.
Mus. Nat. Hist. 12221-32.
Morrison, D.W. 1978. Foraging ecology and energetics
of the frugivorous bat Artibeus jamaicensis. Ecology 59:
716-723.
Orsini, M.W. 1962. Technique of preparation, study and
photography of benzyl-benzoate cleared material for embry-
ological studies. J. Reprod. Fertil. 3:283-287.
Parry, G.D. 1981. The meanings of r- and K-lelection.
Oecologia 48:260—264.
Pearson, O.P. 1949. Reproduction of a South American
rodent, the mountain Viscacha. J. Anat. 84:143-167.
Pengelley, E.T. 1966. Differential developmental pat-
terns and their adaptive value in various species of the
genus Citellus. Growth 30:137-142.
Petersen, M.K. 1970. Competition between the cotton
rats, Sigmodon fulfiventer and S. hispidus. Ph.D. Thesis,
Mich. State Univ., East Lansing.
Pocock, R.I. 1922. On the external characters of some
hystricomorph rodents. Proc. 2001. Soc. London 1922:365-
427.
Reig, O.A., M. Aguilera, M.A. Barros, and M. Useche.
1980. Chromosomal Speciation in a Rassenkreis of Venezue-
lan spiny rats (Genus Proechimys, Rodentia, Echimyidae).
Pp. 291-312 in: N.N. Vorontsov and J.M. Van Brink (eds.),
Animal Genetics and Evolution. Dr. W. Junk B.V. Pub—
lishers, The Hague.
97
Rensch, B. 1960. Evolution above the species level.
Columbia Univ. Press, N.Y.
Rich, P.V. and T.H. Rich. 1983. The Central American
dispersal route: Biotic history and paleogeography. Pp.
12-34 in: D.H. Janzen (ed.), Costa Rican Natural History.
Univ. Chicago Press, Chicago.
Schaffer, W.M. 1974. Optimal reproductive effort in
fluctuating environments. Am. Nat. 108:783-790.
Schmalhausen, 1.1. 1949. Factors of evolution. Blakis—
ton, Philadelphia.
Smith, F.E. 1954. Quantitative aspects of population
growth. Pp. 277-294 in: E.J. Goell (ed.), Dynamics of
population growth. Princeton Univ. Press, Princeton, N.J.
Smith, M.H. and J.T. McGinnis. 1968. Relationships of
latitude, altitude, and body size to litter size and mean
annual production of offspring in Peromyscus. Res. Pop.
Ecol. 22115-126.
Smythe, N.D.E. 1970a. Ecology and behavior of the agouti
(Dasyprocta punctata) and related species on Barro Colora-
do Island, Panama. Ph.D. Thesis. University of Maryland,
College Park, Maryland.
Smythe, N. 1970b. Relationships between fruiting seasons
and seed dispersal methods in a neotropical forest. Am.
Nat. 104225-35.
Smythe, N. 1978. The natural history of the Central
American agouti (Dasyprocta punctata). Smith. Contr.
2001. 257 1-52.
Smythe, N. 1982. Population regulation in some terres-
trial frugivores. Pp. 227—238 in: E.G. Leigh, Jr., A.
Stanley Rand, and D.M. Windsor (eds.), The ecology of a
tropical forest: Seasonal rhythms and long-term changes.
Smithsonian Inst. Press, Washington, D.C.
Sokal, R.R. and F.J. Rohlf. 1969. Biometry. W.H. Free-
man and Company, San Francisco.
Spencer, A.W. and H.W. Steinhoff. 1968. An explanation
of geographic variation in litter size. J. Mamm. 49:281-
86.
Stearns, S.C. 1977. The evolution of life history
traits: A critique of the theory and a review of the da-
ta. Ann. Rev. Ecol. Syst. 8:145—171.
98
Stearns, S.C. 1980. A new view of life-history evolu-
tion. Oikos 35:266—281.
Stearns, S.C. 1983a. The influence of size and phylogeny
on patterns of covariation among life-history traits in
the mammals. Oikos 41:173-187.
Stearns, S.C. 1983b. A natural experiment in life-
history evolution: Field data on the introduction of mos-
quitofish (Gambusia affinis to Hawaii. Evolution 37(3):
601-617.
Stearns, S.C. 1984a. The effects of size and phylogeny
on patterns of covariation in the life history traits of
lizards and snakes. Am. Nat. 123:56-72.
Stearns, S.C. 1984b. Models in evolutionary ecology.
In population biology and evolution, ed. K.W6hrmann and
V. Loeschcke, Pp. 261—265. Springer-Verlag, Berlin,
Heidelberg.
Steel, R. and J. Torrie. 1960. Principles and procedures
of statistics. McGraw—Hill, N.Y.
Tinbergen, N. 1959. Comparative studies of the behavior
of gulls (Laridae): A progress report. Behavior 15:1-
70.
Tinbergen, N. 1963. On aims and methods of ethology.
Z. Tierpsychol. 20:410—433.
Tinbergen, N. 1967. Adaptive features of the blackhead-
ed gull, Larus ridibundus L. Pp. 43-59 in: D.W. Snow
(ed.), Proc XIV Int. Orn. Congr.
Tomich, P.Q., N. Wilson, and C.H. Lamoureux. 1968. Eco—
logical factors on Manana Island, Hawaii. Pacif. Sci.
22:352-368.
Webb, S.D. and L.C. Marshall. 1982. Historical biogeo—
graphy of recent South American land mammals. Pp. 39-52
in: M.A. Mares and H.H. Genoways (eds.), Mammalian Biolo-
gy in South America. Special Publ. Pymatuning Lab. Ecol.
#6.
Weir, B.J. 1973. Another Hystricomorph rodent: Keeping
casiragua (Proechimys guairae) in captivity. Lab. Animals
7:125-134.
Weir, B.J. 1974. Reproductive characteristics of Hy-
stricomorph rodents. Symp. Zool. Soc. London. 34:265-301.
99
Western, D. 1979. Size, life history and ecology in mam—
mals. Afr. J. Ecol. 17:185-204.
Wilbur, H.M., D.W. Tinkle, J.P. Collins. 1974. Environ-
mental certainty, trophic level, and resource availability
in life history evolution. Amer. Nat. 108:805-817.
Williams, G.C. 1966. Adaptation and natural selection.
Princeton Univ. Press, Princeton, N.J.
Williams, R.H., J.L. Carmon, and F.B. Golley. 1965. Ef-
fect of sequence of pregnancy on litter size and growth
in Peromyscus polionotus. J. Reprod. Fertil. 9:257-260.
Zimmerman, K. 1950. Die Randformen der Mitteleuropai-
schen Wuhlmause. Pp. 454-471 in: A. Jordans and F. Peus
(eds.), Syllegomena Biologica Festschrift. Leipzig.
M'°ll'l1[llllfl[lllflllflljljl'lllllfllllls