Sexually Dimorphic Traits in the Ant Genus Cephalotes Follow Different Evolutionary Dynamics
Open Access DepositedSexual size dimorphism is the relative difference in size between the reproductive morphs of an organism. This can be related to gross size or individual traits. Drivers of dimorphism include competing forms of direct selection acting within genetic correlations and constraints. These reflect life history characteristics related to dispersal, nest founding, and mating strategy. By examining the evolutionary dynamics of sexual size dimorphism, we can determine which sex is more strongly influenced by selection for size variation. To do this we took the maximal sizes of one modular trait, and one trait of gross size, and compared phylogenetic signal and phylogenetic model across the males & females of 48 different species of the Formicidae genus Cephalotes. We used the same methods to compare the traits’ sexual dimorphism, measured as a dimorphic index. We then used a phylogenetic regression of their dimorphism to determine if selection was favoring size variability in one sex or the other. We found that the two traits followed similar patterns of evolution, but the dimorphic index followed completely different patterns. We also found that both traits showed selection for variability in different sexes, following contrasting patterns of selection bias for size. We had two main conclusions: Firstly, using either trait as a proxy for body size in comparative trait research will cause inherently biased results. Secondly, more work needs to be done to determine how this sexual size selection is being influenced by other trait interactions, or by traits relating to nest or environmental conditions.
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