Genes Integral to the Reproductive Function of Male Reproductive Tissues Drive Heterogeneity in Evolutionary Rates in Japanese Quail

Early comparative genomics studies originally uncovered a non-intuitive pattern - genes involved in reproduction appeared to evolve more rapidly than other classes of genes.  Currently, however, the emerging consensus is that genes encoding reproductive proteins evolve under variable selective pressures, producing more heterogeneous divergence patterns than previously appreciated.  We investigate a facet of that heterogeneity and explore the factors that drive male reproductive tissue-based heterogeneity in evolutionary rates.  In Japanese quail (Coturnix japonica), genes with enriched expression in the testis evolve much more rapidly than those enriched in the foam gland, a novel gland that secretes an airy foam males transfer to females during mating.  We compared molecular evolutionary patterns among 1) genes with induced expression in breeding versus wintering conditions for both tissues and 2) genes that encode foam proteins versus those with varying degrees of expression specificity in the foam gland.  We report two major findings.  First, genes up-regulated in breeding condition testis evolve exceptionally rapidly, while those induced in breeding condition foam glands evolve slowly.  These differences hold even after correcting for horomonally-dependent gene expression and chromosomal location.  Second, genes encoding foam proteins are extremely conserved in terms of gene identity and sequence.  Together, these finding suggest that genes involved in the reproductive function of each tissue drive the marked rate heterogeneity.

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