The role of the environment in the evolution of reproductive strategies

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

Parental breeding age effects on descendants' longevity interact over 2 generations in matrilines and patrilines

Individuals within populations vary enormously in mortality risk and longevity, but the causes of this variation remain poorly understood. A potentially important and phylogenetically widespread source of such variation is maternal age at breeding, which typically has negative effects on offspring longevity. Here, we show that paternal age can affect offspring longevity as strongly as maternal age does and that breeding age effects can interact over 2 generations in both matrilines and patrilines. We manipulated maternal and paternal ages at breeding over 2 generations in the neriid fly Telostylinus angusticollis. To determine whether breeding age effects can be modulated by the environment, we also manipulated larval diet and male competitive environment in the first generation. We found separate and interactive effects of parental and grand-parental ages at breeding on descendants' mortality rate and life span in both matrilines and patrilines. These breeding age effects were not modulated by grand-parental larval diet quality or competitive environment. Our findings suggest that variation in maternal and paternal ages at breeding could contribute substantially to intrapopulation variation in mortality and longevity

Data from: Ontogenetic timing as a condition-dependent life history trait: high-condition males develop quickly, peak early and age fast

Within-population variation in ageing remains poorly understood. In males, condition-dependent investment in secondary sexual traits may incur costs which limit ability to invest in somatic maintenance. Moreover, males often express morphological and behavioural secondary sexual traits simultaneously, but the relative effects on ageing of investment in these traits remain unclear. We investigated the condition-dependence of male life history in the neriid fly Telostylinus angusticollis. Using a fully factorial design, we manipulated male early-life condition by varying nutrient content of the larval diet and, subsequently, manipulated opportunity for adult males to interact with rival males. We found that high-condition males developed more quickly and reached their reproductive peak earlier in life, but also experienced faster reproductive ageing and died sooner than low-condition males. By contrast, interactions with rival males reduced male lifespan but did not affect male reproductive ageing. High condition in early life is therefore associated with rapid ageing in T. angusticollis males, even in the absence of damaging male-male interactions. Our results show that abundant resources during the juvenile phase are used to expedite growth and development and enhance early-life reproductive performance at the expense of late-life performance and survival, demonstrating a clear link between male condition and ageing

Competitive assays data

Competitive assays dat

No choice assay data

No choice assay dat

Offspring size data

Offspring size dat

Focal data

Focal dat

Accompanying guide to stored data

Accompanying guide to stored dat

Reproductive output from no choice assays

Reproductive output from no choice assay