Comparative phylogeography of a marine bivalve based on male- and female-type mitochondrial DNA
Résumé
Some bivalve species show a remarkable exception of the maternal inheritance of mitochondria in metazoans: the Doubly Uniparental mode of Inheritance (DUI). In this system, females transmit “female” (F-type) mitochondria that persist in oocytes and in somatic tissues of both sexes, while males pass on “male” (M-type) mitochondria that persist in the male germ line and sperm. The M- anf F-types can be highly divergent from each other, and rate of evolution of the M-type can be higher than the F-type. Also, interspecific hybridization can lead to the disruption of the transmission mechanisms, resulting in homoplasmic hybrid males and heteroplasmic hybrid females. We evaluated the usefulness of M-type genes, compaired to F-type, for investigating the phylogeography of the marine tellinid bivalve Limecola balthica, and tested whether intraspecific hybridization may lead to disruption of DUI in this species. A total of 464 individuals were sampled at peak sexual maturity at nine sites along the French Atlantic coast, from the Gironde Estuary (southern range limit of the species) to Somme Bay, spanning some 1100 km of coastline, and crossing two known barriers to gene flow. Individuals were sexed by microscopic observation of the gonads; DNA from somatic tissues and gametes was extracted for both sexes. The M- and F-type cox1 genes were amplified for 247 males and 176 females. All males were heteroplasmic, and all females were homoplasmic, fully conforming to the expectation under DUI. Sequencing of M- and F-type cox1 genes for males is currently underway.