Meeting Abstract
Sexually selected traits are the most extreme structures in the animal world. Ornaments and weapons, as vital components of reproductive success, have a long history of intense selection that has led to the bizarre forms we know today. Weapons are especially massive and, in some species, comprise over half the animal’s body mass. Based on first principles, these traits look like they should be expensive. Yet, we know surprisingly little about the strain these traits place their bearers. Only a handful of studies have explicitly measured the costs associated with sexually selected traits and those studies remain inconsistent. Some weapons appear to carry high costs while others do not. Here, we work to reconcile this inconsistency by exploring one hypothesized cost to sexually selected traits – metabolic strain. Using flow through respirometry, we measure resting metabolic rate across four insect systems to better understand how this metric of cost changes with increasingly large weapon sizes both within and among species. Our results suggest that metabolic costs within weapon systems are highly variable. In fact, seemingly similar weapons show extreme differences in resting metabolic rate, and show little correlation between weapon size per se and metabolic rate. Instead, metabolic costs in these systems appear to result from the large degree of muscle mass associated with some weapons. Indeed, when the metabolic costs of these weapons systems are analyzed in the context of muscle mass, they fall onto a linear spectrum where those animals with the largest amount of muscle directly associated with their weapons bear the most extreme metabolic costs.
