In the dry tropics, foraging bees face significant thermal constraints as a result of high ambient temperatures and direct insolation. In order to determine the potential importance of body size and body coloration in heat gain and heat loss, passive warm-up and cooling rates were measured for freshly killed workers of 24 stingless bee species. Results accorded with biophysical principles. Small bees reached lower temperature excesses ( T(exc)) and warmed up and lost heat much more rapidly than larger bees. In addition to body size, body coloration had a clear effect on thermal parameters. Light-coloured bees warmed up less rapidly and had lower T(exc) than dark bees. An intraspecific comparison of Melipona costaricensis and Cephalotrigona capitata colour morphs confirmed that body coloration influences thermal characteristics. This study is the first to indicate that abdominal coloration in stingless bees might be involved in the regulation of body temperature in extreme thermal conditions. However, body temperatures of foraging bees of colour morphs were not very different. This is probably due to behavioural adaptations (e.g. foraging strategies) or differences in convective and evaporative heat loss or the production of metabolic heat during flight, that all mask the effect of body colour. Notwithstanding such effects and potential thermoregulatory capabilities, stingless bees show niche differentiation and biogeographic distributions that correlate with body coloration and body size. This also suggests that, in general, light bees have an advantage over black bees in hot open lowland habitats, whereas black bees might have an advantage in wet habitats and mountains. The origin, occurrence and function of flavinism (yellow integument colouring) are discussed.

To better understand human and chimpanzee personality evolution, we obtained trait ratings of personality for 154 captive bonobos (~80% of the U.S. and European population). We found factors that we labeled Assertiveness, Conscientiousness, Openness, Agreeableness, Attentiveness, and Extraversion. The interrater reliabilities and test-retest reliabilities for these factors were comparable to those found in humans and other species. Using orthogonal targeted Procrustes rotations, we compared the bonobo dimensions with those of three samples of captive chimpanzees. Overall congruence coefficients indicated a fair degree of similarity; at the factor level, there was good evidence for Assertiveness, Conscientiousness, Openness, and Agreeableness in the chimpanzee samples; evidence for Attentiveness and Extraversion was poor. These findings suggest that, as expected given their close phylogenetic relationship, bonobo personality structure resembles chimpanzee personality structure in some respects. However, divergent evolution, perhaps as a result of socioecological differences between bonobos and chimpanzees, also appears to have shaped personality structure in these species.

Understanding how a single genome can produce a variety of different phenotypes is of fundamental importance in evolutionary and developmental biology. One of the most striking examples of phenotypic plasticity is the female caste system found in eusocial insects, where variation in reproductive (queens) and non-reproductive (workers) phenotypes results in a broad spectrum of caste types, ranging from behavioural through to morphological castes. Recent advances in genomic techniques allow novel comparisons on the nature of caste phenotypes to be made at the level of the genes in organisms for which there is little genome information, facilitating new approaches in studying social evolution and behaviour. Using the paper wasp Polistes canadensis as a model system, we investigated for the first time how behavioural castes in primitively eusocial insect societies are associated with differential expression of shared genes. We found that queens and newly emerged females express gene expression patterns that are distinct from each other whilst workers generally expressed intermediate patterns, as predicted by Polistes biology. We compared caste-associated genes in P. canadensis with those expressed in adult queens and workers of more advanced eusocial societies, which represent four independent origins of eusociality. Nine genes were conserved across the four taxa, although their patterns of expression and putative functions varied. Thus, we identify several genes that are putatively of evolutionary importance in the molecular biology that underlies a number of caste systems of independent evolutionary origin.

Investigating how differential gene expression underlies caste determination in the social Hymenoptera is central to understanding how variation in gene expression underlies adaptive phenotypic diversity. We investigated for the first time the association between differential gene expression and queen-worker caste determination in the bumble-bee Bombus terrestris. Using suppression subtractive hybridization we isolated 12 genes that were differentially expressed in queen-and worker-destined larvae. We found that the sets of genes underlying caste differences in larvae and adults failed to overlap greatly. We also found that B. terrestris shares some of the genes whose differential expression is associated with caste determination in the honeybee, Apis mellifera, but their expression patterns were not identical. Instead, we found B. terrestris to exhibit a novel pattern, whereby most genes upregulated (i.e. showing relatively higher levels of expression) in queen-destined larvae early in development were upregulated in worker-destined larvae late in development. Overall, our results suggest that caste determination in B. terrestris involves a difference not so much in the identity of genes expressed by queen-and worker-destined larvae, but primarily in the relative timing of their expression. This conclusion is of potential importance in the further study of phenotypic diversification via differential gene expression.