Single mating in orchid bees (Euglossa, Apinae): implications for mate choice and social evolution

Neotropical orchid bees (Euglossini) are conspicuously different from other corbiculate bees (Apinae) in their lack of advanced sociality and in male use of acquired odors (fragrances) as pheromone-analogues. In both contexts, orchid bee mating systems, in particular the number of males a female mates with, are of great interest but are currently unknown. To assess female mating frequency in the genus Euglossa, we obtained nests from three species in Mexico and Panama and genotyped mothers and their brood at microsatellite DNA loci. In 26 out of 29 nests, genotypes of female brood were fully consistent with being descended from a singly mated mother. In nests with more than one adult female present, those adult females were frequently related, with genotypes being consistent with full sister-sister (r = 0.75) or mother-daughter (r = 0.5) relationships. Thus, our genetic data support the notions of female philopatry and nest-reuse in the genus Euglossa. Theoretically, single mating should promote the evolution of eusociality by maximizing the relatedness among individuals in a nest. However, in Euglossini this genetic incentive has not led to the formation of eusocial colonies as in other corbiculate bees, presumably due to differing ecological or physiological selective regimes. Finally, monandry in orchid bees is in agreement with the theory that females select a single best mate based on the male fragrance phenotype, which may contain information on male age, cognitive ability, and competitive strength.

Complex sociogenetic organization and the origin of unrelated workers in a eusocial sweat bee, Lasioglossum malachurum

Sweat bees (Halictidae) exhibit great interspecific and intraspecific diversity in their social organisation, yet there is remarkably little information on the sociogenetic organisation of any species. Lasioglossum malachurum is a eusocial sweat bee with an annual lifecycle that exhibits considerable variation in its social organisation across its wide geographic range from northern to southern Europe. We collected all adults from 31 L. malachurum nests at Eichkogl, Austria, near the latitudinal centre of its distribution, and genotyped 148 workers using 5 highly variable microsatellite loci developed for this species. Nests were often queenless (48% of nests) during the second phase of worker activity, when colonies were provisioning the sexual brood. Pedigree reconstruction and estimates of nestmate genetic relatedness demonstrated that nests often (32% of nests) contained alien workers, probably as a result of worker drifting from their natal to a foreign nest. Queen effective mating frequency was variable (harmonic mean m(e) = 1.24), but sometimes high (maximum 2.7). These data demonstrate that nests of L. malachurum do not have a classical eusocial sociogenetic organisation (monogyny, monandry) and thereby pose a challenge to exclusively relatedness based arguments for the evolution of eusociality in the taxon.

Body size differs in workers produced across time and is associated with variation in the quantity and composition of larval food in Nannotrigona perilampoides (Hymenoptera, Meliponini)

Although variation in body size has been recently reported in stingless bees (Meliponini), empirical evidence evaluating possible factors related to such variation is lacking, and thus it is not clear if it may have an adaptive significance. We evaluated if variation in the body size and weight of workers of stingless bees fluctuates across a seasonal pattern and if this could be related to characteristics of the food consumed during the larval stage. The weight of larval provisions, their protein, and sugar content were evaluated in four colonies of Nannotrigona perilampoides every 2 months across 1 year. Worker-destined larvae from the same combs were allowed to develop and were sampled as callow workers to determine their weight and size using morphometric data. The weight and size of workers were highly correlated and varied across the seasons in established colonies, suggesting that size variation cycles across the year in stingless bees. An increase in the protein content and, to a lesser degree, the quantity of larval food were positively linked to variation in body weight and size; food with richer protein content resulted in larger and heavier workers. This study provides the first evidence of an effect of the quantity and composition of larval food on the size of workers in stingless bees. Although body weight and size of workers differed across seasons, they were not readily noticeable as changes seem to occur as a continuum across the year. Since size polymorphism was of a larger magnitude across time but not within age cohorts and as it was highly determined by food resources, it may not be an adaptive feature in stingless bees. However, more studies are needed to determine the role of the cyclical change in worker body size on colony performance and thus its adaptive significance in stingless bees.