Meeting Abstract
One of the great mysteries of evolutionary biology is why closely related lineages, even sister lineages, diversify at different rates. Previous work has attributed this phenomenon to varying amounts of ecological opportunity. A trait-based approach would allow for large-scale patterns to be detected under a variety of habitats and ecological variables. Theory predicts that organisms undergoing sexual selection will have higher diversification rates because of the increased probability of genetic isolation. One way to test whether diversification rate heterogeneity could be linked to the presence or absence of a single trait would be to investigate a single trait which is under sexual selection in some species and nonsexual selection in others. Bioluminescence is an ideal candidate because it has evolved over 50 times and can be used for courtship display (sexual selection) or defense (nonsexual selection). We hypothesize that traits under sexual selection cause shifts in diversification rates, while traits under nonsexual selection do not. We chose two functions of bioluminescence (courtship display and defense) that have been demonstrated in recent years. Using previously published phylogenies, we compared diversity in bioluminescent clades to their non-luminescent sister lineages. When bioluminescence serves as a courtship display (under sexual selection), we find a significant pattern of higher diversification rate. We compare this finding to bioluminescence serving defensive functions (under nonsexual selection). This study demonstrates that a single trait may be under different selective regimes, and in turn, have different effects on diversification rate.
