Population genetic analysis of Trichogramma kaykai using molecular markers

Population structure and genetic diversity are interrelated factors that play a significant role in the evolution and ecology of all species.  We investigated the population genetics of Trichogramma kaykai, an endoparasitoid wasp that parasitizes eggs of the butterfly Apodemia mormo in the Mojave Desert.  Trichogrammatid wasps are known to exhibit phoretic transportation.  This poses the question of whether T. kaykai breeding is limited to local geographical areas or the larger host range.  To answer this, A. mormo eggs were collected, T. kaykai were cultured and DNA extracted for population genetic analysis using the mitochondrial cytochrome oxidase subunit one (CO1) gene region.  If T. kaykai breeding is limited to a local geographical area, then a subdivided population genetic structure is expected.  Additionally, these endoparasitoid wasps may be host to the cytoplasmic bacterium Wolbachia.  Wolbachia-infection within the T. kaykai population is known to be associated with feminization of males; asexual reproduction; and co-inheritance of mitochondria and infection.  On a phylogenetic tree Wolbachia-infected individuals would be expected to occur within groups of related taxa, since mitotype and infection are vertically co-inherited.  We hypothesized that the T. kaykai population structure is not subdivided.  Additionally, we hypothesized that unique mitotypes will group by infection status.  Phylogenetic analysis supported the first hypothesis, with a panmictic population characterized by mutations divided amongst diverse geographical locations.  Unexpectedly, Wolbachia-infection did not strictly follow grouping by infection status.  Multiple Wolbachia-associated mitochondria observed were descended from uninfected lineages.   This is suggestive of Wolbachia-infection horizontal transfer, and the need for further study.