Journal of Molecular Evolution

, Volume 57, Issue 2, pp 159–169

Reduced Polymorphism in the Chimpanzee Semen Coagulating Protein, Semenogelin I

Article

DOI: 10.1007/s00239-002-2463-0

Cite this article as:
Kingan, S.B., Tatar, M. & Rand, D.M. J Mol Evol (2003) 57: 159. doi:10.1007/s00239-002-2463-0

Abstract

The semen of many primate species coagulates into a mating plug believed to prevent the sperm of subsequent mating events from accessing the ova. The texture of the coagulum varies among species: from a semisoft mass in humans to a firm plug in chimpanzees. In humans, a component of the coagulum, semenogelin I, also inhibits sperm motility. We tested the hypothesis that polymorphism and divergence at semenogelin I differ among hominoid species with different mating systems. Sequence data for the semenogelin I locus were obtained from 12 humans, 10 chimpanzees, 7 gorillas, and 1 bonobo. Mitochondrial D-loop data were collected from a subset of individuals to assess levels of variation at an unlinked locus. HKA tests using D-loop sequence data revealed a significant reduction of polymorphism at semenogelin I in chimpanzees, consistent with predictions of a selective sweep at this locus. This result was supported by independent HKA tests using polymorphism data from a putatively neutral locus from the literature. Humans show a similar trend toward reduced polymorphism, although HKA tests were only marginally significant. Gorilla sequence data show evidence of functional loss at the semenogelin I locus, indicated by stop codons within the putative open reading frame as well as high levels of polymorphism. Elevated Ka/Ks ratios within the PanHomo clade suggest a history of positive selection at semenogelin I. Our results suggest that there is a positive relationship between the intensity of sperm competition in a species and the strength of positive Darwinian selection on the seminal protein semenogelin I.

Keywords

Sperm competitionMating systemPolyandryApesHumansHominoidsSemenogelinProstate-specific antigenPositive selectionSemen

Copyright information

© Springer-Verlag New York Inc. 2003

Authors and Affiliations

  1. 1.Department of Ecology and Evolutionary BiologyBrown University, Providence, RI 02912USA