Studying communication signals from the perspective of both senders and receivers allows us to create a greater understanding of how signals are exchanged between animals. For my doctoral dissertation, I leveraged the courtship ritual of the axolotl, Ambystoma mexicanum, a fully aquatic salamander, to investigate mechanisms of signal generation and detection. I focused specifically on a courtship behavior called the “hula”, which involves a rhythmic swaying motion of the pelvic region combined with an undulating movement of the tail. Although the hula has been historically been considered a male behavior, female axolotls play a critical role in the hula behavior as the receiver, and may potentially participate in the male hula by nudging the cloaca or changing proximity to the hula-ing male. Additionally, both males and females perform the hula behavior during courtship; here, I focused on male to female communication mediated by the hula. The hydrodynamic stimuli generated by the hula behavior may serve as communication signals; female axolotls can presumably detect these stimuli via their lateral line system, which is capable of sensing both mechanical and electrical signals in aquatic environments. For my dissertation research, I characterized the motion patterns that males displayed while hula-ing and measured how females responded to a range of hydrodynamic stimuli, both through a behavioral and neurophysiological lens. Critically, I also aimed to determine if a principle known as the sender-receiver matching hypothesis occurs in the mechanosensory lateral line system; this hypothesis posits that the physical properties of signals are shaped by the sensory responses of the receiver, and vice versa. This principle has been most notably demonstrated in auditory communication; for example, the frequency and rise time of calling songs in tree crickets and songbirds (respectively) have both been shown to match the sensitivity of their receiver’s auditory system. However, it is currently unclear if sender-receiver matches occur within vibratory communication. Importantly, my research serves as a building block to ascertain whether sender-receiver matching occurs in the mechanosensory lateral line system. In Chapter 1, I characterized courtship interactions between male and female axolotls. I accomplished this by placing pairs of male and female axolotls into an aquarium together and then observing their behaviors over a 24 hr period. Chapter 2 describes the typical motion patterns that male axolotls exhibit during the hula behavior, as well as female behavioral responses to specific combinations of hula parameters. Chapter 3 describes neurophysiological responses of the anterodorsal lateral line nerve to the hydrodynamic stimuli that are generated during the hula behavior. I was able to demonstrate a moderate degree of sender-receiver matching in the female lateral line system; I found that male axolotls were most likely to display a sweep angle of 30° while hula-ing, and that the anterodorsal lateral line nerve of females had a significant excitatory response to 30°. However, given that I only tested sweep angles and speeds within the range of what male axolotls actually display during courtship, it is unknown if females exhibit significant excitatory responses to more extreme sweep angles and speeds. Thus, my findings serve to progress research on the lateral line system by providing insight into the level of matching between hydrodynamic signals generated by male axolotls as well as the behavioral and neurophysiological responses exhibited by female axolotls.
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