The fecundity–longevity trade-off in a clonal eusocial insect: in isolation, subordinate workers match dominants in reproduction

Reproductive division of labor (DOL) is key to the ecological success of
eusocial insects such as ants, termites, and honeybees, in which queens
reproduce while workers perform non-reproductive tasks. DOL is often
associated with a shift in the fecundity-longevity trade-off, with queens
outliving non-reproductive workers. In most species, reproductive and
non-reproductive individuals differ significantly (e.g., in ontogeny or
morphology), which may contribute to this phenomenon. In contrast, in the
ant Platythyrea punctata, females are clonally identical, and socially
dominant workers produce female offspring from unfertilized eggs by
thelytokous parthenogenesis. We investigated whether all workers, i.e.,
dominants and subordinates, reproduce when given the opportunity. We
formed dyads of workers of the same age and allowed them to establish rank
orders. We then investigated their reproductive performance in isolation.
We found that nearly 88% of workers, regardless of social rank, activated
their ovaries in isolation. However, of the 12% that never laid eggs, a
higher proportion were previously classified as subordinates than as
dominants. This suggests that reproductive ability may differ among
workers. Isolated subordinates that were reproductively active matched
isolated dominants in their egg-laying rate, with no apparent trade-off
between fecundity and longevity. Reproductive costs, likely related to the
use of physiological or energetic resources, were evident for both workers
in isolation, as egg-laying rates declined over time in the absence of
supportive workers. These results highlight the complex interplay between
reproduction, longevity, and social status in eusocial insects and provide
insights into how eusociality has shaped aging and life history evolution.