Deciphering the link between doubly uniparental inheritance of mtDNA and sex determination in bivalves: clues from comparative transcriptomics. Unionoidae (Freshwater mussels)

Comparative studies on species-specific sex determining gene networks in non-model organisms are essential in order to better understand the evolutionary forces responsible for the amazing array of sex-determining systems usually observed within and among animal taxa. One animal group that presents an astonishing diversity in sexual systems is the Bivalvia. Bivalve species can be simultaneous or sequential hermaphrodites, androgenetic, or gonochoric, with both genetic and environmental factors known to determine sex. One possible example of a sex-determiningsystem involving the mitochondrial genome has also been hypothesized in bivalves with doubly uniparental inheritance (DUI) of mtDNA. However, the genetic and environmental factors that control sexual diversification in these animals are still poorly known, and the link between DUI and sex determination also remains obscure. In this study, we performed comparative gonad transcriptome analysis for two DUI-possessing freshwater mussel species to better understand the mechanisms underlying sex determination and DUI in bivalves. Our results are compared with published sex-specific transcriptomics data from other bivalve species to identify conserved genes involved in sex determination and also from distantly-related DUI species to identify conserved genes that could be involved in the regulation of sex-specific aspects of DUI systems. Our results suggest that sets of genes associated with sex determination and DUI are similar in distantly-related DUI species.