All features great and small – an exploration of male genital evolution in mammals

Meeting Abstract

S5-10  Tuesday, Jan. 5 14:30  All features great and small – an exploration of male genital evolution in mammals ORR, T.J.*; BRENNAN, P.L.R.; Department of Biology, University of Massachusetts; Department of Biological Sciences, Mount Holyoke College

Mammalian penises are morphologically diverse, but most studies of mammalian intromittent organs have focused on the highly variable and taxonomically informative baculum (os penis) possessed by many – but not all – species. Meanwhile, soft tissue morphology of the glans penis has remained largely under-studied. This has led to two biases. First- certain clades with baculum bearing species (e.g. Carnivora, Rodentia, and Chiroptera) have been better studied relative to those that lack a baculum (e.g. Cetartiodactyla, Didelphidae, and Lagomorpha). Second- the diversity evident in soft tissue elaborations of the glans remains poorly described and un-quantified. To understand the evolution of genital morphologies as well as key structures that directly interact with female reproductive track, we undertook a comparative study of male glans elaborations across all mammalian orders. Here we describe their astounding diversity including the grooves, domes, hooks, spines and notches seen in the glans of mammals great and small. We discuss this diversity with a focus on elaborations in the context of form and function. We will present the criteria that we used to classify these diverse structures, and then ask what factors can explain the presence or absence of glans elaborations. We discuss the potential role of mating system, risk of sperm competition as well as female reproductive physiologies and phylogenetic histories. We also investigate whether the presence or absence of the baculum influences the presence and type of glans elaborations present in mammals. Our findings highlight the importance of considering the functional structure of the penis as a whole, rather than focusing only on the baculum, and make it clear that glans elaborations have been under selection in mammals.

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