Genetic influence on caste determination underlying the asexual queen succession system in a termite
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The question of how reproductives and sterile workers differentiate within eusocial groups has long been a core issue in the study of social insects. Recent studies have shown that not only environmental factors but also genetic factors affect caste differentiation. In the termite Reticulitermes speratus, queens produce their replacements (neotenics) asexually but use normal sexual reproduction to produce other colony members. Here, we demonstrate a genetic influence on caste determination underlying the asexual queen succession system in this termite species. Thelytoky in termites is accomplished by automixis with terminal fusion, yielding almost completely homozygous offspring; thus, parthenogenetically and sexually produced offspring profoundly differ in heterozygosity. An analysis of the relationship between the reproductive dominance of female neotenics obtained from experimentally orphaned colonies and their genotypes at five microsatellite loci showed that homozygosity at two loci influenced the developmental priority and/or reproductive quality of neotenics. These results suggest the existence of a multi-locus system affecting the queen fecundity and explain why parthenogens have genetic priority to become neotenics in this termite species.
KeywordsGenetic caste determination Caste differentiation Parthenogenesis Queen fecundity Social insect
We thank H. Nakano and T. Yashiro for research assistance; and E.L. Vargo, C. Himuro, K. Shimizu, and T. Yokoi for helpful advice. This work was supported by the Japan Society for the Promotion of Science (no.09001407) to K.M. and the Programme for Promotion of Basic and Applied Researches for Innovations in Bio-oriented Industry to K.M.
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