Baculum shape and paternity success in house mice: evidence for genital coevolution

Sexual selection is believed to be responsible for the rapid divergence of male genitalia, which is a widely observed phenomenon across different taxa. Among mammals, the stimulatory role of male genitalia and female ‘sensory perception’ has been suggested to explain these evolutionary patterns. Recent research on house mice has shown that baculum (penis bone) shape can respond to experimentally imposed sexual selection. Here, we explore the adaptive value of baculum shape by performing two experiments that examine the effects of male and female genitalia on male reproductive success. Thus, we selected house mice (Mus musculus domesticus) from families characterised by extremes in baculum shape (relative width) and examined paternity success in both non-competitive (monogamous) and competitive (polyandrous) contexts. Our analyses revealed that the relative baculum shape of competing males influenced competitive paternity success, but that this effect was dependent on the breeding value for baculum shape of the family from which females were derived. Our data provide novel insight into the potential role of sexual selected on the coevolution of the house mouse baculum and lend support to the stimulatory hypothesis for mammalian genital evolution.

Methods
Dataset 1-6: Landmarks were placed around the periphery of the baculum (36 sliding, 4 fixed) and relative warps (RWs) and centroid size were extracted. Landmark placement conducted using tpsDig 232 developed by Rohlf.

Dataset 7-8: Methodology explained in detail in the paper.