Coevolution between a cockroach and its bacterial endosymbiont: a biogeographical perspective

Cryptocercus are subsocial, xylophagous cockroaches that live in temperate forests. Like other cockroaches, Cryptocercus harbour endosymbiotic bacteri a in their fat bodies. Two species of Cryptocercus occur in the palacarctic , one each in eastern Russia and south-central China. In the USA, there are five species: one in the north-west and four in the south-east. Little is known about the relationship between the Eurasian and North American Crypto cercus or the causes of the disjunct distribution. Here, a molecular phylog eny for six out of the seven Cryptocercus species and their endosymbionts i s inferred in an attempt to understand the evolution and biogeography of th e genus. Our analysis showed that the North American Cryptocercus are monop hyletic, suggesting that a single colonization event was followed by vicari ance. There was complete concordance between the host and endosymbiont phyl ogenetic trees. Divergence estimates based on endosymbiont DNA sequences su ggested that the palaearctic and nearctic Cryptocercus diverged 70-115 mill ion years (Myr) ago and the eastern- and western-USA species diverged 53-88 Myr ago. These divergence estimates were correlated with biogeographical e vents, and a hypothesis is presented to explain the current distribution of Cryptocercus. Our findings suggest that Cryptocercus has had a long evolut ionary history dating back to the Jurassic.