My dissertation focuses on how maternal and ecological factors influence growth rate variation, the life history consequences of growth variation, and on the evolution and development of 'reversed' sexual size dimorphism (SSD) in spotted hyenas. My dissertation consists of four chapters following the introductory chapter. The first of these research chapters, Chapter 2, describes the ontogeny of morphological sexual dimorphism in spotted hyenas, and documents sex differences in rates of growth of overall both body size as well as growth rates of individual morphological traits. Chapter 3 documents the importance of litter size, intra-litter rank, maternal parity, prey availability, and maternal social rank on variation in growth rates and adult size, and the resulting life history and fitness consequences of variation in growth rates. Chapter 4 focuses on whether selection on overall body size or on specific components of body size is present among female hyenas using lifetime measures of fitness to identify putative evolutionary mechanisms maintaining the observed dimorphism. Finally, in Chapter 5 I address hypotheses for the role of selection in males and females as drivers of degree of sexual dimorphism. The hypotheses I test include that selection on size in males does not contribute to female-biased SSD, that smaller males have better reproductive success, and finally that both males and females have increased reproductive success with increasing size, but the fitness benefit of increasing size is greater for females. I also address the quantitative genetics of morphological traits by estimating heritability; non-zero heritability is necessary for an evolutionary response to the observed selection. In its entirety, my dissertation results are consistent with the hypothesis that the difference in selection estimates between males and females contributes to the maintenance of sexual size dimorphism in the spotted hyena. On the whole, the results of the analyses in my dissertation represents an important addition to our knowledge of morphology and life history in the spotted hyena, especially with respect to SSD. My dissertation also provides the first measures of selection using lifetime fitness in a large mammalian carnivore. Finally, my dissertation presents estimates of quantitative genetic parameters, which are rarely available for mammalian carnivores, or for large mammals in general.
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