Variation in sociality of two Australian allodapine bees was investigated over
a latitudinal range of 10˚, spanning subtropical to cool temperate
forests in eastern Australia. Exoneura robusta is
univoltine and singly brooded in southern populations but is able to produce
two broods per season in northern populations, leading to opportunities for
sib rearing by older brood members. In contrast, sympatric colonies of
E. angophorae show no such variation with latitude, and
all populations exhibit some colonies where opportunities for sib rearing
arise. Patterns of ovarian differentiation, relatedness and sex allocation
were examined over a one-year period for these two sympatric species in four
populations. Within each species, the timing of ovarian development and the
degree of reproductive skew were similar at all sites, but the onset of
egg-laying and brood development was earlier in
E. angophorae than in E. robusta.
Relatedness and sex allocation patterns in northern populations of these
species were not markedly different from southern populations. Selection for
female-biased sex allocation and high reproductive skew in
Exoneura probably stems from strong benefits from
cooperative nesting, and our results suggest that opportunities for sib
rearing (and eusociality) in these species may depend on latitudinally
mediated brood development rates, and are unrelated to levels of sex bias and
relatedness.
Sex Allocation Patterns across Cooperatively Breeding Birds Do Not Support Predictions of the Repayment Hypothesis
