Ecological and morphological attributes of parthenogenetic Japanese Schwiebea species (Acari: Acaridae).

We examined life history traits and spermathecal morphology of both sexual and thelytokous Schwiebea mite species to determine ecological and morphological attributes during the evolution of parthenogenesis in this lineage. We reconstructed a molecular phylogeny of eight Japanese species using the internal transcribed spacer 1 (ITS1) of the ribosomal DNA (rDNA) and compared the sex ratio, developmental period, and egg number (fecundity) of each species within a species group by rearing them in the laboratory. Habitat preference was also analyzed from both collection and literature data. The reconstructed molecular phylogeny suggested that parthenogenesis evolved independently multiple times in this lineage. There were three clusters in the tree, in each of which the idiosoma, leg, setae, and spermathecal morphology of females was similar or identical; this suggested that mites in the same cluster were sister species. There was no relationship between sexual mode and life history traits or habitat preference. These results suggest that sexual and asexual species use different microhabitats. Because S. similis (sexual), S. elongata (thelytokous), and S. estradai (thelytokous) were in the same cluster and spermathecae of the first two were similar while that of the last was distinctively reduced, we hypothesized that speciation occurred in this order and that spermathecae are reduced and eventually lost during the course of parthenogenetic evolution.