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The Biology of Reproductive Delays in Mammals: Reproductive Decisions, Energetics, and Evolutionary Ecology


My dissertation investigates the unique ways organisms put effort (energy and nutrients) towards reproduction. My research asks how, delays might allow mammals to allocate limited resources to reproduction (i.e., are delays adaptive? ) and consisted of several components aimed at understanding the causes and consequences of reproductive delays in mammals. First, using the comparative method I examined ecological predictors and evolutionary origins of delays in the Order Carnivora in over 200 species using data published data of ecological variables. In this group I evaluated what attributes of an animal's ecology (i.e. where it lives, what it eats, how seasonal its habitat is etc.) are predictors of a species exhibiting delays. My results suggest that not only are animals that live in seasonal environments, and eat seasonality abundant foods most likely to evolve delays but also species that are larger. Second, I dissected museum specimens of male bats (N = 47 species) to assess if reproductive delays facilitate sperm competition. By reviewing the literature and inspecting museum specimens of bats with different types of delays and some without delays I was able to determine that delays might facilitate postcopulatory sexual selection (competition between the sperm from different males). Using these data I addressed the hypothesis that, once delays occur, they provide an avenue for postcopulatory sexual selection. I tested the prediction that males in species with delays between mating and egg-fertilization have larger testes than males of species that do not have delays before fertilization. Third, I empirically evaluated the costs and benefits of delays in a species that has pregnancies both with and without delays, Artibeus jamaicensis. Using this system I compared energy use, milk quality and food availability between the 2 pregnancies to evaluate the hypothesis that delays allow females to time the most expensive stage of reproduction, lactation, with periods of food abundance. My dissertation contributes previously lacking data on individual and seasonal differences of how energy is divided among the different functions; body maintenance, growth or reproduction.

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