Reduced polymorphism in the chimpanzee semen coagulating protein, semenogelin I.
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 Pan-Homo 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.
Kingan
Sarah B
SB
Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA. Sarah_Kingan@alumni.brown.edu
Tatar
Marc
M
Rand
David M
DM
D000818:Animals; D001483:Base Sequence; D019143:Evolution, Molecular; D006071:Gorilla gorilla / Q000235:genetics; D006801:Humans; D008297:Male; D019974:Pan paniscus / Q000235:genetics; D002679:Pan troglodytes / Q000235:genetics*; D011110:Polymorphism, Genetic; D012661:Semen / Q000502:physiology*; D029607:Seminal Vesicle Secretory Proteins / Q000235:genetics*; D016415:Sequence Alignment
D029607:Seminal Vesicle Secretory Proteins; C424482:seminal vesicle-specific antigen