Is the bat os penis sexually selected?

The mammalian os penis or baculum is an extremely diverse bone but our unde rstanding of the selective forces behind this diversity remains poor. While genital morphology is generally assumed to be sexually selected, there hav e been relatively few attempts to test this hypothesis. Here we investigate associations between baculum length and two measures of sexual selection i ntensity (mating system and testis mass) across bats. Analyses were conduct ed using both species-level data and phylogenetic comparative techniques. C ontrolling for the effect of male body mass, baculum length was positively associated with relative testis mass in all cross-species analyses. Additio nally, in an analysis that also included mating system, there was an intera ction between testis mass, body mass and mating system that significantly i nfluenced baculum length. However, after using independent contrasts to con trol for phylogenetic inertia in these data, baculum length was not signifi cantly associated with mating system, testis mass or body mass. Thus, incre ased length of the baculum in bats appears not to be associated with increa sed sperm competition risk or sexual selection intensity.