Is the bat os penis sexually selected?
The mammalian os penis or baculum is an extremely diverse bone but our understanding of the selective forces behind this diversity remains poor. While genital morphology is generally assumed to be sexually selected, there have been relatively few attempts to test this hypothesis. Here we investigate associations between baculum length and two measures of sexual selection intensity (mating system and testis mass) across bats. Analyses were conducted using both species-level data and phylogenetic comparative techniques. Controlling for the effect of male body mass, baculum length was positively associated with relative testis mass in all cross-species analyses. Additionally, in an analysis that also included mating system, there was an interaction between testis mass, body mass and mating system that significantly influenced baculum length. However, after using independent contrasts to control for phylogenetic inertia in these data, baculum length was not significantly associated with mating system, testis mass or body mass. Thus, increased length of the baculum in bats appears not to be associated with increased sperm competition risk or sexual selection intensity.
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