A Breeding System Derived From Asexual Queen Succession in Termite Colonies From Cold Climate Regions

In social insects, geographic variation is often accompanied not only by physiological changes but also by changes in their social system. In the subterranean termite Reticulitermes speratus that exhibits a sophisticated social system, colonies in subtropical and temperate areas are founded by a pair of primary king and queen derived from sexually produced alates. Some years after colony establishment, many neotenic queens are produced parthenogenetically, which is known as asexual queen succession (AQS). This strategy boosts reproduction without inbreeding. Here we show that subarctic populations of R. speratus, where colonies founded by alates cannot be sustained due to the cold conditions, undergo inbreeding rather than AQS, with colonies headed by numerous neotenic reproductives. Genetic analysis found that most neotenic queens were produced sexually in the subarctic populations, rather than asexually. Rearing experiments using colonies consisting only of nymphs (reproductive-destined individuals) and workers revealed that more nymphs successfully established as neotenic reproductives in the subarctic populations than in temperate populations, and that a higher number of individuals were maintained in the subarctic populations. These results suggest that sexually produced nymphs in subarctic populations are highly predisposed to develop into neotenic reproductives, whereas in temperate populations, their developmental potential is predominantly directed towards becoming alates. This study demonstrates that R. speratus has adjusted to colder climatic zones by changing its sophisticated AQS reproductive system into a secondary strategy to maintain colonies, elucidating the flexible adaptation and acclimation of reproductive systems in social insects.