Contributions to Zoology, 84 (3) – 2015Camille Meslin; Michel Laurin; Isabelle Callebaut; Xavier Druart; Philippe Monget: Evolution of species-specific major seminal fluid proteins in placental mammals by gene death and positive selection
Results

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Relationship between abundance in seminal fluid and positive selection

Only three genes (CRISP3, KLK1, and MFGE8) exhibit variation in both abundance of their product protein in the seminal fluid and in the presence of positive selection. Thus, when contrasting pairs of characters for which both vary within pairs (which is only possible on binarised data, in the Mesquite implementation), only one positive and two negative pairs were found, which is consistent with a random association (p = 0.5). When using the ‘most pairs’ selector in Mesquite (which draws the highest number of pairs, irrespective of character state), only one positive and two neutral pairs were found, which is also not significant (p = 1). Pagel’s test yielded lower probabilities (Pagel, 1994), with the lowest being for KLK1, but this is not significant (p. = 0.14; S 1, sheets ‘Pagel 1994 test’ and ‘Abundance, selection correl.’). The lack of correlation is also confirmed by a visual inspection of the evolutionary changes implied by the data, as this can best be done from mirror trees. For instance, for KLK 1 (Fig. 5), positive selection is found (in increasing number of amino acids) in the mouse, cow, and horse, but of these three taxa, only the horse has increased abundance of the gene product in its semen (in all other taxa in our sample, it is absent or in low abundance). In MFGE8 (Fig. 6), the dog (one amino acid) and humans (22 amino acids) exhibit positive selection, but only the cow has an abundance of the gene product in its semen.

FIG2

Fig. 5. Lack of correlation between abundance (left) and number of amino acids under positive selection in KLK1. Parsimony optimizations performed in Mesquite (Maddison and Maddison, 2015).

FIG2

Fig. 6. Lack of correlation between abundance (left) and number of amino acids under positive selection in MFGE8. Parsimony optimizations performed in Mesquite (Maddison and Maddison, 2015).