Abstract
In typical sexual conflict scenarios, males best equipped to exploit females are favored locally over more prudent males, despite reducing female fitness. However, local advantage is not the only relevant form of selection. In multigroup populations, groups with less sexual conflict will contribute more offspring to the next generation than higher conflict groups, countering the local advantage of harmful males. Here, we varied male aggression within-and between-groups in a laboratory population of water striders and measured resulting differences in local population growth over a period of three weeks. The overall pool fitness (i.e., adults produced) of less aggressive pools exceeded that of high aggression pools by a factor of three, with the high aggression pools essentially experiencing no population growth over the course of the study. When comparing the fitness of individuals across groups, aggression appeared to be under stabilizing selection in the multigroup population. The use of contextual analysis revealed that overall stabilizing selection was a product of selection favoring aggression within groups, but selected against it at the group-level. Therefore, this report provides further evidence to show that what evolves in the total population is not merely an extension of within-group dynamics.
Highlights
Many features of the environment influence population growth of organisms
In the case of social behaviors, differences in local population growth attributed to the differential distribution of behavioral types amongst groups can influence the overall frequency of behavioral types in subsequent generations
We have recently explored this scenario in the water strider, A. remigis, which is well known to engage in sexual conflict and occupy multigroup populations of moderately flowing streams
Summary
Many features of the environment influence population growth of organisms. For instance, fluctuations in local population growth are often attributed to differences in predation, disease, interspecific competition, abundance of resources and local climate [1]. Consider the classic example of the ‘tragedy of the commons’ (TOC) whereby individuals who exploit a shared resource are favored over their more prudent rivals within groups, despite the consequence that over-exploitation can lead to local extinction [3,4]. In these scenarios, groups containing fewer exploitative types (or more prudent types) contribute more offspring to subsequent generations, countering the local advantage of exploitation and maintaining prudent types in the population [2]. The evolutionary consequences of differential group productivity have been well appreciated with regards to the evolution of social behaviors such as resource consumption and altruism [4], yet only recently have they been attributed to scenarios involving sexual conflict [5,6,7,8]
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