The role of the environment in the evolution of reproductive strategies

Abstract

Understanding variation is a central theme in evolutionary biology. This thesis examines factors that contribute to variation in anatomy, reproductive development, lifespan and behaviour using the neriid fly, Telostylinus angusticollis (Diptera, Neriidae). It has been known for a long time that older mothers produce offspring with reduced life expectancy. My first empirical chapter provides the first direct comparison of maternal and paternal age effects, and the first investigation of the potential for both maternal and paternal age effects to accumulate over multiple generations. My second and third empirical chapters focus on the interaction between larval nutrition and the social environment at adulthood. Ejaculate (sperm and semen) traits can be under sexual selection and often exhibit a heightened sensitivity to diet. It is also well known that males transfer more sperm when facing a risk of sperm competition from other competing males. In Chapter 3, I manipulated the nutritional quality of male larval diet and perceived sperm competition and tracked competing ejaculates within the female reproductive tract using a new fluorescent sperm-labelling technique that I developed. I was able to show for the first time that increased sperm transfer in response to sperm competition risk is modulated by the larval resources. Chapter 4 examines the neriid genitalia which are highly complex, and whose function and evolution are poorly understood. This study is the first to explore how genitalic trait integration and the evolvability of these traits in both sexes compares with integration of somatic traits, and how integration is affected by juvenile nutrition. My last chapter was amongst the first studies to experimentally manipulate self-perception of social status. I found that social dominance treatment affected both males’ and females’ social status and chemical profiles, suggesting that both sexes can perceive their own status within a group and dynamically change their chemical signal. This thesis shows that factors such as age, social environment and resource availability have important effects that range from early ontogeny to post-copulatory processes during adulthood, and even ageing. This work is important in that it illustrates that selection for context- and state-dependent reproductive tactics drives the evolution of complex individual plasticity in allocation to reproduction, in both males and females