Abstract
The link between the expression of the signals used by male animals in contests with the traits which determine success in those contests is poorly understood. This is particularly true in holometabolous insects such as horned beetles where signal expression is determined during metamorphosis and is fixed during adulthood, whereas performance is influenced by post-eclosion feeding. We used path analysis to investigate the relationships between larval and adult nutrition, horn and body size and fitness-related traits such as strength and testes mass in the horned beetle Euoniticellus intermedius. In males weight gain post-eclosion had a central role in determining both testes mass and strength. Weight gain was unaffected by adult nutrition but was strongly correlated with by horn length, itself determined by larval resource availability, indicating strong indirect effects of larval nutrition on the adult beetle’s ability to assimilate food and grow tissues. Female strength was predicted by a simple path diagram where strength was determined by eclosion weight, itself determined by larval nutrition: weight gain post-eclosion was not a predictor of strength in this sex. Based on earlier findings we discuss the insulin-like signalling pathway as a possible mechanism by which larval nutrition could affect adult weight gain and thence traits such as strength.
Highlights
Research into the role of sexual selection as a driver of evolution has led to insights into many of the most fascinating aspects of mating system and reproductive biology [1,2,3]
The chief motivation behind this work was to answer the question of whether the horn of E. intermedius, a signal which is expressed in response to larval nutrition, can reliably give information about adult resource holding potential (RHP), which is determined at least partly by adult nutrition
Using path analysis we can see a more complete picture of the effects of larval and adult nutrition on these animals than could be achieved with conventional linear models, and we find striking indirect effects of larval nutrition on adult weight gain, fat content and performance
Summary
Research into the role of sexual selection as a driver of evolution has led to insights into many of the most fascinating aspects of mating system and reproductive biology [1,2,3]. Male dung beetles engage their horns with each other and push against their opponents in tunnels, and horn length appears to be a better correlate of strength even than body size [16,17]. In these systems, it seems that at least one component of the RHP that is being signaled by the sexually selected trait is strength, which leads us to the question of how the link between signal and strength arises and is maintained
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