| The study of life history evolution involves the traits of organisms relating to their survivorship and reproduction. Among these traits are growth, age and size at maturity, fecundity (clutch and egg size), size at birth, and sex determination mechanisms. Reptiles are a vertebrate group where genotypic and temperature-dependent sex determination (TSD) co-occur. Multiple paternity decreases the estimated genetic correlation among clutch mates thus affecting heritability estimates of any trait. Population dynamics and genetic population structure are also influenced by the mating system. Multiple paternity can have important consequences as it increases effective population sizes relative to single paternity.;In this dissertation I present research on the Amazonian giant river turtle, Podocnemis expansa (Pleurodira:Pelomedusidae), about TSD, reproductive ecology, and population ecological genetics. The first Chapter includes a general overview of TSD, population genetics, and Podocnemis expansa biology. Chapter 2 includes a study of life history parameters of P. expansa, namely, evidence of a positive effect of female size on (1) clutch size, (2) egg mass, and (3) nest depth, found through the study of trailways left by females on nesting beaches. Chapter 3 includes evidence of multiple paternity detected using 8 microsatellite DNA loci. Chapter 4 includes evidence of genetic differentiation among four nesting beaches detected with microsatellites. Chapter 5 includes an ecological study of TSD in P. expansa. I introduce a model developed to account for heterogeneous daily fluctuations of temperature experienced in the field, by using laboratory and field data on developmental stages, Cumulative Temperature Units, and the time spent at temperatures below the survival threshold (28°C). The model explained variation in laboratory sex ratios from constant and shift-temperature experiments as well as the combined field and lab data, but was insufficient to explain field sex ratios by themselves. Small sample sizes, within-nest temperature variation, or additional factors in the field may account for this result. Chapter 6 summarizes the results from each study, and includes a critical appraisal of conservation programs based the data from Chapters 2--5, plus a discussion of current hypothesis about the maintenance of TSD and how they apply to P. expansa . |
