Patterns of size variation in bees at a continental scale: does Bergmann's rule apply?

Body size latitudinal clines have been widley explained by the Bergmann's rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann's rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142 008 distribution records of 615 bee species at 50 × 50 km (CGRS) grids across the West Palearctic. We then applied generalized least squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann's rule. However, considering bee genera separately, four genera were consistent with Bergmann's rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann's cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a ‘season length effect’ (i.e. shorter foraging season) is a potential driver of the converse Bergmann's cline particularly in bumblebees.     

Intraspecific queen parasitism in a highly eusocial bee

Insect societies are well-known for their advanced cooperation, but their colonies are also vulnerable to reproductive parasitism. Here, we present a novel example of an intraspecific social parasitism in a highly eusocial bee, the stingless bee Melipona scutellaris. In particular, we provide genetic evidence which shows that, upon loss of the mother queen, many colonies are invaded by unrelated queens that fly in from unrelated hives nearby. The reasons for the occurrence of this surprising form of social parasitism may be linked to the fact that unlike honeybees, Melipona bees produce new queens in great excess of colony needs, and that this exerts much greater selection on queens to seek alternative reproductive options, such as by taking over other nests. Overall, our results are the first to demonstrate that queens in highly eusocial bees can found colonies not only via supersedure or swarming, but also by infiltrating and taking over other unrelated nests.     

Global warming promotes biological invasion of a honey bee pest

Climate change and biological invasions are two major global environmental challenges. Both may interact, e.g. via altered impact and distribution of invasive alien species. Even though invasive species play a key role for compromising the health of honey bees, the impact of climate change on the severity of such species is still unknown. The small hive beetle (SHB, Aethina tumida, Murray) is a parasite of honey bee colonies. It is endemic to sub‐Saharan Africa and has established populations on all continents except Antarctica. Since SHBs pupate in soil, pupation performance is governed foremost by two abiotic factors, soil temperature and moisture, which will be affected by climate change. Here, we investigated SHB invasion risk globally under current and future climate scenarios. We modelled survival and development time during pupation (=pupal performance) in response to soil temperature and soil moisture using published and novel experimental data. Presence data on SHB distribution were used for model validation. We then linked the model with global soil data in order to classify areas (resolution: 10 arcmin; i.e. 18.6 km at the equator) as unsuitable, marginal and suitable for SHB pupation performance. Under the current climate, the results show that many areas globally yet uninvaded are actually suitable, suggesting considerable SHB invasion risk. Future scenarios of global warming project a vehement increase in climatic suitability for SHB and corresponding potential for invasion, especially in the temperate regions of the Northern hemisphere, thereby creating demand for enhanced and adapted mitigation and management. Our analysis shows, for the first time, effects of global warming on a honey bee pest and will help areas at risk to prepare adequately. In conclusion, this is a clear case for global warming promoting biological invasion of a pest species with severe potential to harm important pollinator species globally.     

Floral symmetry and nectar guides: ontogenetic constraints from floral development, colour pattern rules and functional significance

The accord between symmetries of flower shape (external contours) and nectar guides (internal contours) was examined using the bulbous flora of South Africa, and in the general floras of Britain, Alpine Colorado, Canadian Arctic and Israel. It was found that radially symmetrical flowers have radially symmetrical nectar guides whereas bilaterally symmetrical flowers have bilaterally symmetrical nectar guides. It is suggested that the complementarity between the external and the internal contours of the flower increases the probability that, and efficiency with which, a bee moves into the flower's centre and towards the sporophylls and access to floral rewards, regardless of the flower's form and the bee's previous experience. Patterns of coloration of tepals against background and nectar guides against tepals also accord with behavioural and sensory characteristics of pollinators. It is suggested that the complementarity of contours is probably constrained by floral development, but patterns of coloration of tepals against background and nectar guides against tepals is constrained by pollinators' sensory physiology.     

Life-cycle and foraging patterns of native <Emphasis Type="Italic">Bombus terrestris</Emphasis> (L.) (Hymenoptera,Apidae) in the Mediterranean region

Life-cycle and foraging patterns of native Bombus terrestris populations were investigated at two sites in the Mediterranean region of Turkey, Phassalis (0 – 100 m above sea level [a.s.l.]) and Termessos (500 – 700 m a.s.l.). Bumble-bee activity was recorded during standard bee walks from November 2003 until the end of October 2004, each site being visited three times every month during the one-year period. The yearly dynamics of flight, the flowering plant species visited, and the visitation frequencies of these plants were recorded during every bee walk at both sites. There were considerable differences between the two populations with regard to the dates when the queens emerged from diapause (the emerging season), the timing of the appearance of sexuals (young queens and males), and the total number of plant species visited. Bombus terrestris queens emerged from diapause in November-December at the Phassalis site (coastal area) and in February-March at the Termessos site. The queens aestivated at the Phassalis site, whereas they hibernated at the Termessos site. Only one generation per year was produced at each site. The duration of the queens’ diapause lasted 5 – 8 months and length of the life cycle 190 – 215 days. Native B. terrestris populations were noted to forage on 47 flowering plant species from 20 families (10 at the Phassalis site and 40 at the Termessos site) during the study period. Two of the plant species (Arbutus unedo L. and Vitex agnus-castus L.) have long flowering periods and play a crucial role in the life cycle of native B. terrestris populations. The emergence of queens at the aestivation site was synchronized with the flowering of Arbutus unedo L., while the emergence of sexuals coincided with the flowering of Vitex agnus-castus L. at both sites. Received 30 May 2007; revised 5 December 2007; accepted 8 January 2008.     

Characterization of the native honey bee (Apis mellifera jemenitica) in the south western region of Saudi Arabia using morphometric and genetic (mtDNA COI) characteristics

Apis mellifera jemenitica incorporates a few perceived subspecies that vary in their natural properties and farming qualities. Mitochondrial COI gene sequence (mtCOI) has not been used before for bee identification in the southwestern region of Saudi Arabia. The aim of this work was to study the morphometry and analyzing the mtCOI of all collected bees. The nucleotide sequence of the mtCOI gene was analyzed. Similarity searches and distances between each obtained DNA and sequences available in GenBank were made. Morphometric analysis revealed close similarities among the studied bees, but these similarities are different from those previously indicated in earlier studies of the same region. Molecular studies revealed that the collected bees are similar to each other and some other sequences found in GenBank, but these bees are a new hybrid or subspecies that are different from those previously reported in the same region, indicating the emergence of a new hybrid.     

Genes versus environment: geography and phylogenetic relationships shape the chemical profiles of stingless bees on a global scale

Chemical compounds are highly important in the ecology of animals. In social insects, compounds on the body surface represent a particularly interesting trait, because they comprise different compound classes that are involved in different functions, such as communication, recognition and protection, all of which can be differentially affected by evolutionary processes. Here, we investigate the widely unknown and possibly antagonistic influence of phylogenetic and environmental factors on the composition of the cuticular chemistry of tropical stingless bees. We chose stingless bees because some species are unique in expressing not only self-produced compounds, but also compounds that are taken up from the environment. By relating the cuticular chemistry of 40 bee species from all over the world to their molecular phylogeny and geographical occurrence, we found that distribution patterns of different groups of compounds were differentially affected by genetic relatedness and biogeography. The ability to acquire environmental compounds was, for example, highly correlated with the bees'' phylogeny and predominated in evolutionarily derived species. Owing to the presence of environmentally derived compounds, those species further expressed a higher chemical and thus functional diversity. In Old World species, chemical similarity of both environmentally derived and self-produced compounds was particularly high among sympatric species, even when they were less related to each other than to allopatric species, revealing a strong environmental effect even on largely genetically determined compounds. Thus, our findings do not only reveal an unexpectedly strong influence of the environment on the cuticular chemistry of stingless bees, but also demonstrate that even within one morphological trait (an insect''s cuticular profile), different components (compound classes) can be differentially affected by different drivers (relatedness and biogeography), depending on the functional context.     

Clinal variability of oil and nectar rewards in Monttea aphylla (Plantaginaceae): relationships with pollinators and climatic factors in the Monte Desert

Monttea aphylla flowers simultaneously produce oil and nectar, rewards known to differentially attract ecologically and functionally distinct pollinators. We examined whether geographical differentiation occurred for rewards, and whether this could be explained by spatially heterogeneous pollinator guilds and climate. Rewards were measured across the entire species range. Geographical patterns of reward quantity and their relationships with biotic and abiotic factors were examined using uni‐ and multivariate analyses. Latitude significantly explained population variation in nectar and oils, although in contrasting ways. Pollinator assemblages showed a prevalence of oil‐collecting Centris bees. Centris vardyorum, specialized on M. aphylla, showed a latitudinal pattern of visits. Oil production was not higher where plants associated with ecologically specialized bees (i.e. C. vardyorum), but this occurred instead where they were less frequent and co‐occurred with other bees that used many floral sources, including other plant species that produce oil. The multivariate analysis showed that the prevalence of C. vardyorum was the factor that contributed most significantly to the combined patterns of rewards. We suggest that large‐scale variation in rewards involves local optima throughout the species range, related to processes that operate in each ecoregion with their particular biotic and abiotic scenarios. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 314–328.