Eusociality and the transition from biparental to alloparental care in termites

In eusocial organisms, cooperative brood care within a colony represents a
situation where the ancestral parental care duties have shifted away from
the reproductive parent(s) towards their own offspring. The shift to
alloparental care was often instrumental in the initial emergence of
eusociality, as it ultimately contributed to the establishment of
reproductive division of labor. Remarkably, eusocial taxa such as ants and
termites, which still display an ancestral independent colony foundation
phase, must go through an obligatory parental care period, as a temporary
subsocial family unit. In termites specifically, an incipient colony
inherently remains a woodroach family unit until alloparental care is
established. Colony foundation success can then be limited by a series of
factors that may include environmental, behavioral, symbiotic, and
physiological constraints. In this study, 450 incipient termite colonies
(Coptotermes gestroi) were established to investigate the timing of
physiological changes in founders during the transition from biparental to
alloparental care. Results showed that the finite initial internal
nutritional resources that alates carry during the dispersal flight are a
primary limiting factor for successful colony establishment. The
Coptotermes queen and king must rapidly establish (< 150 d) their
first cohort of offspring to reach alloparental care or simply run out of
resources and die. Alates, therefore, carry just enough internal resources
to produce the first few alloparents (< 15 workers) to prime the
system toward colony ergonomic growth, with a definitive shift to solely
reproductive functions. Eusocial insect primary reproductive traits were
optimized for three successive functions within the life cycle of a
colony: alate dispersal (sexual reproduction), colony foundation (parental
care), and colony growth (increased egg production toward colony
maturity). However, results suggest that trade-offs involving these
functions appear to primarily favor dispersal ones (quantity vs. quality
of alates), as founder(s) carry minimal resources and have no room for
parental care inefficiency, and as they then fully rely on their
alloparents for further reproductive output. The transition toward
alloparental care during colony foundation of eusocial insects may
therefore reflect on the initial evolutionary transition from ancestral
subsociality to eusociality.