Bee Guilds’ Responses to Urbanization in Neotropics: A Case Study

The consequent deforestation of urban sprawl is one of the causes of the decline of wild bee communities. In this context, urban green areas (UGA) may play an important role and constitute refuge areas for bees. This study analyzed the influence of UGA conditions and their surroundings in bee guilds’ responses in a medium-sized Brazilian city (Campos dos Goytacazes, RJ). The bees were sampled for 12 months (2017–2018) in 12 UGAs, and bee abundance and species richness were evaluated in guilds considering: nesting behavior, nesting site, and trophic specialization. We used as explanatory variables conditions of UGAs—the number of trees (NT), diameter at breast height (DBH), flower cover (FC), plant richness (PR), percentage of paving (PV)—and of their surroundings—paving (SPV) and the number of buildings (NB). Results showed 80% of eusocial bees, 82% nest in cavities, and 99% were generalists. FC, DBH, and NB mainly explained the responses of different guilds in study areas from all explanatory variables. Thus, this study confirms different responses associated with bee guilds’ attributes. In order to conserve bee diversity, city planning must include more green areas with large flower covers and avoid long corridors of high buildings that can impact bee dispersion.

Spontaneous choices for insect-pollinated flower shapes by wild non-eusocial halictid bees

The majority of angiosperms require animal pollination for reproduction and insects are the dominant group of animal pollinators. Bees are considered one of the most important and abundant insect pollinators. Research into bee behaviour and foraging decisions has typically centred on managed eusocial bee species, Apis mellifera and Bombus terrestris. Non-eusocial bees are understudied with respect to foraging strategies and decision-making, such as flower preferences. Understanding whether there are fundamental foraging strategies and preferences which are features of insect groups can provide key insights into the evolution of flower-pollinator co-evolution. In the current study, Lasioglossum (Chilalictus) lanarium and L. (Parasphecodes) sp., two native Australian generalist halictid bees, were tested for flower shape preferences between native insect-pollinated and bird-pollinated flowers. Each bee was presented with achromatic images of either insect-pollinated or bird-pollinated flowers in a circular arena. Both native bee species demonstrated a significant preference for images of insect-pollinated flowers. These preferences are similar to those found in A. mellifera, suggesting that flower shape preference may be a deep-rooted evolutionary occurrence within bees. With growing interest in the sensory capabilities of non-eusocial bees as alternative pollinators, the current study also provides a valuable framework for further behavioural testing of such species.

An exploration of the relationship between recruitment communication and foraging in stingless bees

Social information is widely used in the animal kingdom and can be highly adaptive. In social insects, foragers can use social information to find food, avoid danger or choose a new nest site. Copying others allows individuals to obtain information without having to sample the environment. When foragers communicate information they will often only advertise high quality food sources, thereby filtering out less adaptive information. Stingless bees, a large pantropical group of highly eusocial bees, face intense inter- and intra-specific competition for limited resources, yet display disparate foraging strategies. Within the same environment there are species that communicate the location of food resources to nest-mates and species that do not. Our current understanding of why some species communicate foraging sites while others do not is limited. Studying freely foraging colonies of several co-existing stingless bee species in Brazil, we investigated if recruitment to specific food locations is linked to (1) the sugar content of forage, (2) the duration of foraging trips and (3) the variation in activity of a colony from one day to another and the variation in activity in a species over a day. We found that, contrary to our expectations, species with recruitment communication did not return with higher quality forage than species that do not recruit nestmates. Furthermore, foragers from recruiting species did not have shorter foraging trip durations than those from weakly-recruiting species. Given the intense inter- and intraspecific competition for resources in these environments, it may be that recruiting species favour food resources that can be monopolised by the colony rather than food sources that offer high-quality rewards.

Diversity of Eusocial Bees in Natural and Anthropized Areas of a Tropical Dry Forest in the Parque da Sapucaia (Montes Claros, Minas Gerais, Brazil)

In the present study we inventoried the diversity of eusocial bees (Hymenoptera: Apidae) in preserved and anthropized areas of a tropical dry forest in the Parque da Sapucaia (Montes Claros, Minas Gerais, Brazil). We tested the hypothesis that the diversity of bee species would: 1) be greater in the preserved areas, 2) respond positively to the structure of the vegetation and 3) decrease during the dry season. We sampled eusocial bee species in 18 plots of 10 x 10 m distributed throughout the park, being nine plots in anthropized areas and nine plots in areas with preserved vegetation. In total we recorded 382 individuals and eight species of eusocial bees. The most abundant species was Oxytrigona tataira (Smith) (N = 233) and the most common species was Trigona spinipes (Fabricius) recorded in 72.2% of the plots. As expected, we found that eusocial bee diversity (Shannon diversity) was higher in preserved plots than in anthropized plots. Tree species richness positively affected bee species richness and abundance, while tree abundance positively influenced the bee abundance and tree height positively affected the bee Shannon diversity, corroborating our expectations. On the other hand, we detected no differences in the diversity of eusocial bees between dry and rainy seasons. Our findings suggest that both natural (vegetation structure) and anthropogenic (habitat modification) factors are important predictors of the diversity of eusocial bee species in tropical dry forests.

Sociality sculpts similar patterns of molecular evolution in two independently evolved lineages of eusocial bees

While it is well known that the genome can affect social behavior, recent models posit that social lifestyles can, in turn, influence genome evolution. Here, we perform the most phylogenetically comprehensive comparative analysis of 16 bee genomes to date: incorporating two published and four new carpenter bee genomes (Apidae: Xylocopinae) for a first-ever genomic comparison with a monophyletic clade containing solitary through advanced eusocial taxa. We find that eusocial lineages have undergone more gene family expansions, feature more signatures of positive selection, and have higher counts of taxonomically restricted genes than solitary and weakly social lineages. Transcriptomic data reveal that caste-affiliated genes are deeply-conserved; gene regulatory and functional elements are more closely tied to social phenotype than phylogenetic lineage; and regulatory complexity increases steadily with social complexity. Overall, our study provides robust empirical evidence that social evolution can act as a major and surprisingly consistent driver of macroevolutionary genomic change.

Exploitative competition and displacement mediated by eusocial bees: experimental evidence in a wild pollinator community

Eusocial bees are likely to be ecologically important competitors for floral resources, although competitive effects can be difficult to quantify in wild pollinator communities. To investigate this, we excluded honeybees (HBE treatment), bumblebees (BBE) or both (HB&BBE) from wild-growing patches of bramble, Rubus fruticosus L. agg., flowers in two eight-day field trials at separate locations, with complementary mapping of per-site local floral resource availability. Exclusions increased per-flower volume of nectar and visitation rates of non-excluded bees, compared to control patches with no bee exclusions (CON). There was a large increase in average nectar standing crop volume both at Site 1 (+ 172%) and Site 2 (+ 137%) in HB&BBE patch flowers, and no significant change in HBE or BBE, compared to CON patches. Foraging bee responses to exclusion treatments were more pronounced at Site 2, which may be due to lower local floral resource availability, since this is likely to increase the degree of exploitative competition present. Notably, at Site 2, there was a 447% increase in larger-bodied solitary (non-Apis/Bombus) bees visiting HB&BBE patches, suggesting ecological release from competition. Hoverflies showed no response to bee removals. Numbers of other non-bee insect groups were very small and also showed no clear response to exclusions. Our findings reveal patterns of competitive exclusion between pollinator groups, mediated by resource depletion by eusocial bees. Possible long-term implications of displacement from preferred flowers, particularly where alternative forage is reduced, are discussed. Significance statement Understanding patterns of exploitative competition and displacement is necessary for pollinator conservation, particularly for vulnerable or threatened species. In this research, experimental methods reveal underlying patterns of resource competition exerted by eusocial bees in a wild pollinator community. We show that honeybees and bumblebees competitively displace each other and particularly solitary (non-Apis/Bombus) bees from bramble, an important native nectar and pollen source. Effects were stronger where local floral resource availability was identified to be limited. Notably, following experimental exclusion of both honey- and bumblebees from flowers, visitation by solitary bees increased by up to 447%, strongly suggesting ecological release from competition. These results highlight the need for informed landscape management for pollinator wellbeing, including appropriate honeybee stocking densities and improved floral resource availability.

Octopamine increases individual and collective foraging in a neotropical stingless bee

The biogenic amine octopamine (OA) is a key modulator of individual and social behaviours in honeybees, but its role in the other group of highly eusocial bees, the stingless bees, remains largely unknown. In honeybees, OA mediates reward perception and affects a wide range of reward-seeking behaviours. Thus, we tested the hypothesis that OA increases individual foraging effort and collective food source exploitation in the neotropical stingless bee Plebeia droryana . OA treatment caused a significant increase in the number of bees at artificial sucrose feeders and a 1.73-times higher individual foraging frequency. This effect can be explained by OA lowering the sucrose response threshold and, thus, increasing the perceived value of the food source. Our results demonstrate that, similar to its effects on honeybees, OA increases both individual and collective food source exploitation in P. droryana . This suggests that, despite having evolved many complex behaviours independently, OA might have similar regulatory effects on foraging behaviours in the two groups of highly eusocial bees.

A small family business: synergistic and additive effects of the queen and the brood on worker reproduction in a primitively eusocial bee

The mechanisms that maintain reproductive division of labor in social insects are still incompletely understood. Most studies focus on the relationship between adults, overlooking another important stakeholder in the game – the juvenile offspring. Recent studies from various social species show that not only the queen, but also the brood regulates reproductive division of labor between females, but how the two coordinate to maintain reproductive monopoly remained unexplored.Our study aims at disentangling the roles of the brood and the queen in regulating worker reproduction in primitively eusocial bees. We examined the effects induced by the brood and queen, separately and together, on the behavioral, physiological and brain gene expression of Bombus impatiens workers. We found that young larvae induce a releaser effect in workers, decreasing egg laying and aggressive behaviors, while the queen induces both releaser and primer effects, modifying worker aggressive and egg laying behavior and reproductive physiology. The expression of reproduction- and aggression-related genes was altered in the presence of both queen and brood, but the effect was stronger or the same in the presence of the queen.We identified two types of interactions between the queen and the brood in regulating worker reproduction: (1) synergistic interactions regulating worker physiology, where the combined effect of the queen and the brood was greater than each of them separately; (2) additive interactions regulating worker behavior, where the combined effects of the queen and the brood are the gross sum of their separated effects. In these interactions the brood acted in a manner similar to the queen but to a much smaller extent and improved the quality of the effect induced by the queen. Our results suggest that the queen and the brood of primitively eusocial bees coordinate synergistically, additively, and sometimes even redundantly to regulate worker behavior and reproduction, and the interaction between them exists in multiple regulatory levels.