How does individual condition affect lifetime reproductive success? Patterns of male reproductive ageing in Neriid flies (#67)
Age specific reproductive performance (reproductive ageing) is a highly variable and ubiquitous trait, yet, in males in particular, the evolution of such patterns remains poorly understood. Previous studies have shown that reproductive ageing patterns are highly condition dependent. High condition individuals usually enjoy higher reproductive success early in life, yet experience faster declines with age. However, this is not always the case and patterns vary between species. Understanding these patterns is likely to reveal important insights into life history theory, but the specific factors involved in such trade-offs remain to be determined. In Neriid flies, condition (body size) in males is a highly variable trait that is an important determinant of male reproductive success. As adults, males engage in physical combat for access to females, and larger males are therefore expected to have a reproductive advantage. However, it remains unclear whether large males are able to maintain this costly strategy over their life, and in all aspects of their reproductive biology. To test whether life history trade-offs were affected by male behavioural strategy, males were housed in one of two social treatments, where males were either able or unable to engage in physical combat with another standard male. We then measured multiple aspects of male reproductive performance over their life in a fully factorial design of social treatment and high and low condition. Initial data analysis has yielded surprising results, suggesting that poor condition males have a reproductive advantage at old age, despite smaller males engaging in less aggressive behavioural strategies than larger, high condition males.