Evidence for sibling species in Cryptocercus punctulatus, the wood roach, from variation in mitochondrial DNA and karyotype.
The wood-feeding genus Cryptocercus is considered the basal lineage among extant cockroaches. Cryptocercus is the sole representative of the family Cryptocercidae and at present three species are recognized within the genus worldwide: Cryptocercus punctulatus in the United States, C. relictus in Eurasia and C. primarius in the Orient. The geological distribution of C. punctulatus in the USA is disjunct, with populations occurring along the Appalachian Mountains and in the Pacific North-west. In samples collected from several locations of the eastern and western USA, we investigated variation in DNA sequence of portions of the two mitochondrial rRNA genes and in chromosome number. The overall sequence divergence among 30 individuals assayed from 17 locations was 17.3 percent. A phylogenetic analysis revealed that in the east, individuals in Virginia had diverged significantly in their haplotype from those in North Carolina, Georgia and Alabama; individuals in the west (Oregon) had diverged in their haplotype from individuals in the east. The diploid chromosome number for 52 male C. punctulatus sampled from 15 locations varied from 37 (18(II) + X) to 47 (23(II) + X). In the eastern samples, the diploid chromosome number ranged from 37 to 45, whereas in Oregon all individuals had 2n = 47. No polymorphism in DNA sequence or chromosome number among individuals collected within a locality was detected. The DNA sequence and chromosome number variation data, together with preliminary studies on mating incompatibility, strongly suggest that C. punctulatus in the USA is comprised of at least two probably three sibling species, with one species occurring in western USA and one or more species in eastern USA.