A new species of the genus Parasesarma De Man 1895 from East African mangroves and evidence for mitochondrial introgression in sesarmid crabs

The Sesarmidae (Decapoda; Brachyura: Thoracotremata) is the most speciose family of crabs occurring in the mangroves of East Africa, accounting for 12 species belonging to seven genera. Among these, the genus Parasesarma accounts for a total of four species. Here we describe a new species, Parasesarma gazi sp. nov., based on specimens collected in mangrove forests of Kenya and Tanzania. The phylogenetic position of this new species within the family Sesarmidae was reconstructed, based on three mitochondrial and one nuclear marker. While nuclear data genetically resolve the systematic relationships, mitochondrial data reveal a surprising similarity of Parasesarma gazi sp. nov. and its sister species P. leptosoma. This result may reflect a short history of reproductive isolation or recent mitochondrial introgression between these two species. This is the first time that such an evolutionary event is reported for the family Sesarmidae and for mangrove crabs, in general.