Phylogeography of cryptic species of Heleocoris (Heteroptera: Naucoridae) in Southeast Asia

Species delimitation continues to be an issue affecting a broad range of biological studies, especially when considering the additional problems posed by cryptic species.  Because easily observable morphological characteristics are not available for cryptic species, they are commonly studied through use of genetic information.  This study examined the phylogeography of Heleocoris ovatus and Heleocoris malayensis (Hemiptera: Naucoridae), two cryptic species found across mainland southeast Asia, based on sequences from the mitochondrial cytochrome oxidase subunit I (COI) gene and the nuclear ribosomal internal transcribed spacer 2 (ITS2).  These species appear identical to the naked eye and are delimited primarily by a few differences in male genitalia and associated somatic structures. Phylogenetic analyses revealed significant genetic differentiation among nine populations from Thailand and one from Vietnam with two well supported groups that are consistent with morphological character states and current species determinations, but also revealed the presence of one-way mitochondrial introgression.  The combination of morphological and genetic data allows us to investigate not only patterns of speciation across a landscape, but also to speculate on the selection mechanisms involved.