Evolution of Reproductive Traits Under Pre-and Post-Mating Sexual Selection

Sexual selection has shaped the evolution of a variety of reproductive traits in males and females of numerous species. Because females of most animal species mate with multiple males, sexual selection can extend beyond mate choice and inter-sexual competition for mates to post-mating events such as sperm competition and cryptic female mate choice. In this thesis I addresses the evolution of reproductive traits under selection before and after mating. In Chapter 2, I address the evolution of female choosiness and male mating displays that function as indicators of male genetic quality. I address the influence on the evolution of these reproductive traits of female ability to evaluate male genetic quality without recourse to male displays. Counter to intuition, I find that direct detection of male quality by females, instead of impeding, can facilitate the evolution of male displays at intermediate levels of detectability. I present a new continuum framework for different mechanisms of indicator displays that heretofore have been modeled as discrete types. I find that the continuum framework reveals interesting patterns in how direct detectability of male quality influences the evolution of different types of indicators. In Chapter 3 I investigate age-dependent plasticity in male mating investment using Drosophila pseudoobscura. I find that male mating investment generally increases with male age, and intermediate-aged males are most discriminatory with respect to female age, making smaller investments when mating with older females. Male mating investment was correlated with fitness payoffs from matings, but matings with young females were more profitable for males than matings with old females. In Chapter 4 addresses the evolution of male seminal fluid composition. I investigate how males evolve to allocate resources towards different seminal fluid proteins that increase male sperm-competitive fitness in different ways. I find that the relative efficiencies of proteins play a large role in determining the evolutionarily stable ejaculate composition. Also, plasticity in ejaculate composition can contribute to the maintenance of genetic variation in ejaculate composition across populations. Together these chapters form important stepping stones for designing models that address the interactions and coevolution of reproductive traits that function before and after mating.Doctor of Philosoph

Age-Dependent Male Mating Investment in Drosophila pseudoobscura

Male mating investment can strongly influence fitness gained from a mating. Yet, male mating investment often changes with age. Life history theory predicts that mating investment should increase with age, and males should become less discriminatory about their mate as they age. Understanding age-dependent changes in male behavior and their effects on fitness is important for understanding how selection acts in age-structured populations. Although the independent effects of male or female age have been studied in many species, how these interact to influence male mating investment and fitness is less well understood. We mated Drosophila pseudoobscura males of five different age classes (4-, 8-, 11-, 15-, 19-day old) to either young (4-day) or old (11-day) females, and measured copulation duration and early post-mating fecundity. Along with their independent effects, we found a strong interaction between the effects of male and female ages on male mating investment and fitness from individual matings. Male mating investment increased with male age, but this increase was more prominent in matings with young females. Male D. pseudoobscura made smaller investments when mating with old females. The level of such discrimination based on female age, however, also changed with male age. Intermediate aged males were most discriminatory, while the youngest and the oldest males did not discriminate between females of different ages. We also found that larger male mating investments resulted in higher fitness payoffs. Our results show that male and female ages interact to form a complex pattern of age-specific male mating investment and fitness

Not Just a Theory--The Utility of Mathematical Models in Evolutionary Biology

Progress in science often begins with verbal hypotheses meant to explain why certain biological phenomena exist. An important purpose of mathematical models in evolutionary research, as in many other fields, is to act as “proof-of-concept” tests of the logic in verbal explanations, paralleling the way in which empirical data are used to test hypotheses. Because not all subfields of biology use mathematics for this purpose, misunderstandings of the function of proof-of-concept modeling are common. In the hope of facilitating communication, we discuss the role of proof-of-concept modeling in evolutionary biology

Figure 2 code

This file includes the code used to create Figure 2. It includes the life cycle loop iterated over multiple generations

Figure 7 code

This file includes the code used to create one of the panels in Figure 7. It includes the life cycle loop iterated over multiple generations, for different parameter values

Figure 6 code

This file includes the code used to create Figure 6. It includes data (in form of matrices) that was generated using separate files. One such data generating file is provided separately here. See "Note" at the top of the code in this file

Figure 5 code

This file includes the code used to create Figure 5. It includes the life cycle loop iterated over multiple generations

Figure 3 data generation file Sc=0.05

This file includes the code used to create one of the panels in Figure 3. It includes the life cycle loop iterated over multiple generations across a large number of combinations of parameter values

Figure 4 code

This file includes the code used to create Figure 4. It includes data (in form of matrices) that was generated using separate files. One such data generating file is provided separately here. See "Note" at the top of the code in this file