Molecular divergence between Gryllus rubens and Gryllus texensis, sister species of field crickets (Orthoptera: Gryllidae)

We assess the degree of sequence divergence in the maternally inherited mitochondrial cytochrome c oxidase I (COI) and cytochrome b (CytB) genes between two sister species of field crickets, Gryllus rubens Scudder, 1902 and Gryllus texensis Cade and Otte, 2000. We analyzed 1460 base pairs from 10 individuals of each species; individuals were sampled from areas of both allopatry and sympatry. Overall average pairwise mitochondrial sequence divergence between species was 1.4% ± 0.1% (mean ± SD); however, there was almost an order of magnitude more divergence in COI (2.59% ± 2.25%) than in CytB (0.35% ± 0.24%). Gryllus texensis appears to harbor a much greater level of genetic variation than does G. rubens. Phylogenetic trees constructed from these sequences show reasonable separation of species; however, sequences are not reciprocally monophyletic. Gene tree polyphyly may reflect recent species-level divergence and (or) interspecific gene flow. The pattern of sequence divergence and genetic variation in these taxa is consistent with allopatric or peripatric speciation in Pleistocene glacial refugia in the southeastern (G. rubens ancestral lineage) and southcentral United States (G. texensis ancestral lineage).