Abstract

<jats:p>
The allodapine bees are well suited for comparative studies of social
evolution because of the wide variation in social behaviour within and between
genera. There are three main clades in the endemic Australian genus
Exoneura. Two groups
(Exoneura sensu stricto and
Exoneurella) have received extensive study. In this
paper we provide the first detailed study of social behaviour in the third
group, Brevineura, based on a heathland population of
Exoneura (B.)
xanthoclypeata Rayment. This species has two seasonal
pulses of egg-laying and brood rearing occurs throughout most of the year,
including winter. This extended period of egg-laying and brood development
differs from the two other Australian Exoneura subgenera and provides
extensive opportunities for eusocial-like sib-rearing. Dissection data
indicate that reproductive differentiation among adult nestmates is well
developed and dependent on body size, with smaller females being mostly or
entirely non-reproductive. Per capita brood production
is dramatically higher in multi-female nests than in single-female nests and
relatedness between adult nestmates is moderately high
(r ≈ 0·5). These two factors suggest that
local fitness enhancement may be occurring and our limited sex allocation data
suggest female-biased ratios. Because of the opportunities for sib-rearing in
this species, local fitness enhancement has the potential to lower selective
thresholds for eusociality.</jats:p>