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Harbor porpoises seen from above

Coevolution of Asymmetric and Spiraled Genitalia with Unique Mating Behavior

Asymmetric and Spiraled Genitalia Coevolve with Unique Lateralized Mating Behavior
  • Behavior

Abstract

Asymmetric genitalia and lateralized mating behaviors occur in several taxa, yet whether asymmetric morphology in one sex correlates or coevolves with lateralized mating behavior in the other sex remains largely unexplored. While lateralized mating behaviors are taxonomically widespread, among mammals they are only known in the harbor porpoise (Phocoena phocoena). Males attempt copulation by approaching a female exclusively on her left side. To understand if this unusual lateralized behavior may have coevolved with genital morphology, we quantified the shape of female and male harbor porpoise reproductive tracts using 2D geometric morphometrics and 3D models of the vaginal lumen and inflated distal penis. We found that the vaginas varied individually in shape and that the vaginas demonstrated both significant directional and fluctuating asymmetry. This asymmetry resulted from complex 3D spirals and vaginal folds with deep recesses, which may curtail the depth or direction of penile penetration and/or semen movement. The asymmetric shapes of the vaginal lumen and penis tip were both left-canted with similar angular bends that mirrored one another and correspond with the left lateral mating approach. We suggest that the reproductive anatomy of both sexes and their lateral mating behavior coevolved. 

*This paper was recognized for being in the top 100 Scientific Reports downloads of 2020, out of more than 20,000 articles published.


Orbach, D.N., Brennan, P.L.R., Hedrick, B.P., Keener, B., Webber, M.A., Mesnick, S.L., 2020. Asymmetric and Spiraled Genitalia Coevolve with Unique Lateralized Mating Behavior. Scientific Reports, 10:3257.

behavior
Bill Keener
Marc Webber

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