Friedel Anna, Lattorf H. Michael G., Quezada-Euán J. Javier. G., Boff Samuel (2020) Shared reproduction and sex ratio adjustment to clutch size in a socially polymorphic orchid bee. Ethology 126: 88-96. https://doi.org/10.1111/eth.12963
Abstract
Nests of the primitively eusocial orchid bee Euglossa viridissima
are generally founded by a solitary female but can be reactivated by
female offspring, in the presence or absence of the mother. The
population therefore exists of solitary and social nests that co‐occur
in an area. A female can stay as a subordinate helper under a dominant
female or disperse to become a solitary foundress. Yet, the costs and
benefits of the different social phenotypes are so far little
understood. Here, we compared solitary and social nests of orchid bees.
We used offspring of solitary and social nests to calculate offspring
sex ratio, and applied molecular markers to calculate intranidal
relatedness, infer maternity and test whether sociality may have a
genetic component. We found that social nests had on average more brood
than solitary nests. The overall sex ratio in the population did not
differ from 1:1. However, social nests tended to produce a split sex
ratio with some nests producing mainly males and others mainly female
offspring. Regardless of social phenotype, the number of offspring was
correlated with the sex ratio, with smaller nests having a more
female‐biased offspring. In social nests, not all offspring resulted
from a single‐mated mother, which was also the case for some solitary
nests. This suggests shared reproduction in social nests and may be an
indication that intraspecific parasitism and nest takeover are not
uncommon. Structure analyses did not reveal different genetic background
of the two social phenotypes. Our results suggest that there is no
clear benefit that favours one of the two social phenotypes over the
other and that the population is kept at balance in terms of sex ratio.
