RELATEDNESS AND SEX-RATIO IN A PRIMITIVELY EUSOCIAL HALICTINE BEE

Lasioglossum laevissimum was studied in Calgary, Alberta, where it is eusocial with one worker brood. Estimates of relatedness were obtained among various categories of nestmate based upon four polymorphic enzy me loci, two of which exhibited significant levels of linkage disequil ibrium. Relatedness estimates among workers and among reproductive bro od females were very close to the expected 0.75 value that obtains whe n nests are headed by one, singly mated queen. However, relatedness be tween workers and the reproductive brood females they reared was signi ficantly lower than 0.75. A low frequency of orphaning with subsequent monopolisation of oviposition by one worker brood female in orphaned nests may explain these results. Workers were significantly more and q ueens significantly less closely related to male reproductives than ex pected if all males were to have resulted from queen-laid eggs. Orphan ing and worker-produced males contribute to this result. The sex inves tment ratio was 1:2.2 in favour of females, in excellent agreement wit h the predictions based upon relative relatednesses between workers an d reproductive brood males and females. Adaptive intercolony variation in investment ratios was detected: the sex ratio was more heavily fem ale-biased in nests in which the relative relatedness asymmetry betwee n workers and reproductive brood was more female-biased. The study spe cies is the most weakly eusocial hymenopteran for which relatedness es timates and sex ratio data are available. With high relatedness among nestmates and a strongly female-biased sex ratio, this study suggests the importance of indirect fitness contributions in the early stages o f social evolution.