Reproductive strategies and breeding systems in Reticulitermes subterranean termites (Isoptera, Rhinotermitidae)

Termites are eusocial insects that live in colonies characterized by cooperative behavior, where most individuals forego their own reproduction and help to raise the offspring of a few nest members. This may impact on the colony abilities to adapt and exploit the environment. In subterranean termites of the genus Reticulitermes, a new colony is settled by a single, heterosexual pair of winged individuals (primary reproductives; kings and queens); as colony maturate and/or upon founders death, neotenics (secondary reproductive; SRs) develop and contribute to offspring production. This leads to inbreeding as SRs are genetically related. In some species, including the Italian R. lucifugus, primary queens produce secondary queens by parthenogenesis (P); then, secondary queens will mate with the primary king extending the genetic contribution of the primary queen through time (Asexual Queen Succession, AQS), eventually helping to avoid inbreeding. As a consequence of the increasing genetic contribution of the primary queen, AQS colonies show a female-biased sex ratio of winged reproducers. Here we present population genetics and sex ratio analyses of R. lucifugus, and compare results with data on two other species: R. flavipes and R. grassei. Genetic data indicated the presence of AQS in R. lucifugus and its absence in the other two species, accordingly to winged sex ratio observations. Data confirmed that P occurs through a mechanism of terminal fusion. Moreover, winged reproductives resulted all produced by amphigony, confirming that P is only used for secondary queen production. Finally, morphometric and biomass analyses performed on R. lucifugus winged reproductives suggested a larger investment in female sex in AQS colonies. The AQS system has been observed to be scattered among termites, occurring through different mechanisms and leading to different outcomes. This variability still need to be explained in the light of social behavior evolution.