Monitoring bee health in European agro-ecosystems using wing morphology and fat bodies

Current global change substantially threatens pollinators, which directly impacts the pollination services underpinning the stability, structure and functioning of ecosystems. Amongst these threats, many synergistic drivers, such as habitat destruction and fragmentation, increasing use of agrochemicals, decreasing resource diversity, as well as climate change, are known to affect wild and managed bees. Therefore, reliable indicators for pollinator sensitivity to such threats are needed. Biological traits, such as phenotype (e.g. shape, size and asymmetry) and storage reserves (e.g. fat body size), are important pollinator traits linked to reproductive success, immunity, resilience and foraging efficiency and, therefore, could serve as valuable markers of bee health and pollination service potential.

This data paper contains an extensive dataset of wing morphology and fat body content for the European honeybee (Apis mellifera) and the buff-tailed bumblebee (Bombus terrestris) sampled at 128 sites across eight European countries in landscape gradients dominated by two major bee-pollinated crops (apple and oilseed rape), before and after focal crop bloom and potential pesticide exposure. The dataset also includes environmental metrics of each sampling site, namely landscape structure and pesticide use. The data offer the opportunity to test whether variation in the phenotype and fat bodies of bees is structured by environmental factors and drivers of global change. Overall, the dataset provides valuable information to identify which environmental threats predominantly contribute to the modification of these traits.

Distribution and predictors of wing shape and size variability in three sister species of solitary bees

Morphological traits can be highly variable over time in a particular geographical area. Different selective pressures shape those traits, which is crucial in evolutionary biology. Among these traits, insect wing morphometry has already been widely used to describe phenotypic variability at the inter-specific level. On the contrary, fewer studies have focused on intra-specific wing morphometric variability. Yet, such investigations are relevant to study potential convergences of variation that could highlight micro-evolutionary processes. The recent sampling and sequencing of three solitary bees of the genus Melitta across their entire species range provides an excellent opportunity to jointly analyse genetic and morphometric variability. In the present study, we first aim to analyse the spatial distribution of the wing shape and centroid size (used as a proxy for body size) variability. Secondly, we aim to test different potential predictors of this variability at both the intra- and inter-population levels, which includes genetic variability, but also geographic locations and distances, elevation, annual mean temperature and precipitation. The comparison of spatial distribution of intra-population morphometric diversity does not reveal any convergent pattern between species, thus undermining the assumption of a potential local and selective adaptation at the population level. Regarding intra-specific wing shape differentiation, our results reveal that some tested predictors, such as geographic and genetic distances, are associated with a significant correlation for some species. However, none of these predictors are systematically identified for the three species as an important factor that could explain the intra-specific morphometric variability. As a conclusion, for the three solitary bee species and at the scale of this study, our results clearly tend to discard the assumption of the existence of a common pattern of intra-specific signal/structure within the intra-specific wing shape and body size variability.

The Size But not the Symmetry of the Wings of Eulaema nigrita Lepeletier (Apidae: Euglossini) is Affected by Human-Disturbed Landscapes in the Brazilian Cerrado Savanna

Among other human-related activities, habitat loss and fragmentation are currently ranked as the most important environmental features affecting the persistence of animal and plant populations in landscapes, as well as the maintenance of ecological processes and services. Since these processes are also capable of affecting the ontogenetic development of species inhabiting those landscapes, here we measured the wing veins of male Eulaema nigrita Lepeletier (Apidae: Euglossini) bees in order to evaluate whether the bees sampled in agriculture (AG) areas suffer higher fluctuating asymmetry (FA) than those sampled in Cerrado (CE) areas in the Brazilian state of Goiás. We believe that individuals sampled in CE areas would be less asymmetric than those sampled in AG areas, given a potential higher exposure of these specimens to environmental stresses (mostly pesticides). However, we did not observe a significant trend in the FA measures we obtained, although three wing measures were bigger for bees from CE areas. The lack of significant effects of FA may be related to inherent bionomic features of E. nigrita. For instance, given their high individual dispersal abilities, the individuals we analyzed may have developed in different areas than those where they were sampled. Their generalist feeding behavior may also have given them a higher resistance to environmental perturbations, buffering the normal development of immatures even in areas with local high environmental stress. Nonetheless, higher death rates of individuals from anthropic areas may also have killed the developing immatures of E. nigrita before they reached adulthood consequently equalizing our sampled estimates.

Morphometric and genetic differentiation of two sibling gossamer-wing damselflies, Euphaea formosa and E. yayeyamana, and adaptive trait divergence in subtropical East Asian islands

Insular species frequently demonstrate different tendencies to become smaller or larger than their continental relatives. Two sibling gossamer-wing damselflies, Euphaea formosa (Odonata: Euphaeidae) from Taiwan and E. yayeyamana from the Yaeyama Islands of Japan, have no clear structural differentiation, and can only be recognized by their geographical distribution, sizes, and subtle differences in wing shape and coloration. This study combined morphometric and genetic techniques to investigate the adaptive significance of trait divergence and species status in these two Euphaea damselflies. Phylogenetic analyses of the mitochondrial cox2 sequences demonstrated that the two damselflies are monophyletic lineages and constitute valid phylogenetic species. The landmark-based geometric morphometrics indicated that the two damselflies are different morphological species characterized by distinctive wing shapes. The larger E. formosa exhibited broader hind wings, whereas E. yayeyamana had narrower and elongated forewings. The body size and wing shape variations among populations of the two species do not follow the expected pattern of neutral evolution, suggesting that the evolutionary divergence of these two traits is likely to be subjected to natural or sexual selection. The decreased body size, elongated forewings, and narrower hind wings of E. yayeyamana may represent insular adaptation to limited resources and reduced territorial competition on smaller islands.

Wing shape and its influence on the outcome of territorial contests in the damselfly Calopteryx virgo

Male mating success is often determined by territory ownership and traits associated with successful territory defense. Empirical studies have shown that the territory owner wins the majority of fights with challenging males. Several physical and physiological traits have been found to correlate with resource holding potential. In addition, in aerial insects, wing design may also have a strong influence on resource holding potential, since it determines efficiency and precision during flight. However, this possibility has not yet been thoroughly evaluated using the modern technique of geometric morphometrics to analyze shape. Therefore, this study examined whether wing shape affects the outcome of male-male contests in the territorial damselfly, Calopteryx virgo (L.) (Odonata: Calopterygidae). Wing shape and also traditional flight-related morphological measures were compared between 27 pairs of winners and losers from experimental territorial contests. Contrary to expectations, there were no differences between winners and losers in all studied wing traits (shape, length, width, total surface, aspect ratio, and wing loading). However, highly significant differences in wing shape and size were detected between the fore- and hindwing. It is currently not known how these differences relate to flight performance, since previous biomechanical studies in damselflies assumed fore- and hindwings to have an identical planform.

Frequency-dependent variation in mimetic fidelity in an intraspecific mimicry system

Contemporary theory predicts that the degree of mimetic similarity of mimics towards their model should increase as the mimic/model ratio increases. Thus, when the mimic/model ratio is high, then the mimic has to resemble the model very closely to still gain protection from the signal receiver. To date, empirical evidence of this effect is limited to a single example where mimicry occurs between species. Here, for the first time, we test whether mimetic fidelity varies with mimic/model ratios in an intraspecific mimicry system, in which signal receivers are the same species as the mimics and models. To this end, we studied a polymorphic damselfly with a single male phenotype and two female morphs, in which one morph resembles the male phenotype while the other does not. Phenotypic similarity of males to both female morphs was quantified using morphometric data for multiple populations with varying mimic/model ratios repeated over a 3 year period. Our results demonstrate that male-like females were overall closer in size to males than the other female morph. Furthermore, the extent of morphological similarity between male-like females and males, measured as Mahalanobis distances, was frequency-dependent in the direction predicted. Hence, this study provides direct quantitative support for the prediction that the mimetic similarity of mimics to their models increases as the mimic/model ratio increases. We suggest that the phenomenon may be widespread in a range of mimicry systems.