Floral Trait Preferences of Three Common wild Bee Species.

The interaction between bees and flowering plants is mediated by floral cues that enable bees to find foraging plants. We tested floral cue preferences among three common wild bee species: Lasioglossum villosulum, Osmia bicornis, and Bombus terrestris. Preferences are well studied in eusocial bees but almost unknown in solitary or non-eusocial generalist bee species. Using standardized artificial flowers altered in single cues, we tested preferences for color hue, achromatic contrast, scent complexity, corolla size, and flower depth. We found common attractive cues among all tested bees. Intensively colored flowers and large floral displays were highly attractive. No preferences were observed in scent complexity experiments, and the number of volatiles did not influence the behavior of bees. Differing preferences were found for color hue. The specific behaviors were probably influenced by foraging experience and depended on the flower choice preferences of the tested bee species. In experiments testing different flower depths of reward presentation, the bees chose flat flowers that afforded low energy costs. The results reveal that generalist wild bee species other than well-studied honeybees and bumblebees show strong preferences for distinct floral cues to find potential host plants. The diverse preferences of wild bees ensure the pollination of various flowering plants.

Forest structure, plants, arthropods, scale, or birds' functional groups: What key factor are forest birds responding to?

Forest birds respond to a diverse set of environmental factors, including those altered by forest management intensity, such as resource and habitat availability in the form of food or nesting sites. Although resource/habitat availability and bird traits likely mediate responses of bird diversity to global change drivers, no study has assessed the direct and indirect effects of changes in forest management and traits on bird assemblages jointly at large spatial scales. In this context the questions remain whether (1) the birds' response to forest management changes through alterations in structural properties and/or food availability, or (2) if birds' eco-morphological traits act as environmental filters in response to environmental factors. We audio-visually recorded birds at 150 forest plots in three regions of Germany and assessed the forest structure (LiDAR) as well as the diversity of the herbaceous layer and diversity and biomass of arthropods. We further assessed eco-morphological traits of the birds and tested if effects on bird assemblages are mediated by changes in eco-morphological traits' composition. We found that abundance and species numbers of birds are explained best by models including the major environmental factors, forest structure, plants, and arthropods. Eco-morphological traits only increased model fit for indirect effects on abundance of birds. We found minor differences between the three regions in Germany, indicating spatial congruency of the processes at the local and regional scale. Our results suggest that most birds are not specialized on a particular food type, but that the size, diversity and species composition of arthropods are important. Our findings question the general view that bird traits adapt to the resources available.

Land-use affects pollinator-specific resource availability and pollinator foraging behaviour.

Land-use management is a key factor causing pollinator declines in agricultural grasslands. This decline can not only be directly driven by land-use (e.g., habitat loss) but also be indirectly mediated through a reduction in floral resource abundance and diversity, which might in turn affect pollinator health and foraging. We conducted surveys of the abundance of flowering plant species and behavioural observations of two common generalist pollinator species, namely the bumblebee Bombus lapidarius and the syrphid fly Episyrphus balteatus, in managed grasslands of variable land-use intensity (LUI) to investigate whether land-use affects (1) resource availability of the pollinators, (2) their host plant selection and (3) pollinator foraging behaviour. We have found that the floral composition of plant species that were used as resource by the investigated pollinator species depends on land-use intensity and practices such as mowing or grazing. We have also found that bumblebees, but not syrphid flies, visit different plants depending on LUI or management type. Furthermore, LUI indirectly changed pollinator behaviour via a reduction in plot-level flower diversity and abundance. For example, bumblebees show longer flight durations with decreasing flower cover indicating higher energy expenditure when foraging on land-use intensive plots. Syrphid flies were generally less affected by local land use, showing how different pollinator groups can differently react to land-use change. Overall, we show that land-use can change resource composition, abundance and diversity for pollinators, which can in turn affect pollinator foraging behaviour and potentially contribute to pollinator decline in agricultural grasslands.

Nectar cardenolides and floral volatiles mediate a specialized wasp pollination system.

Specialization in plant pollination systems can arise from traits that function as filters of flower visitors. This may involve chemical traits such as floral volatiles that selectively attract favoured visitors and non-volatile nectar constituents that selectively deter disfavoured visitors through taste or longer-term toxic effects or both. We explored the functions of floral chemical traits in the African milkweed Gomphocarpus physocarpus, which is pollinated almost exclusively by vespid wasps, despite having nectar that is highly accessible to other insects such as honeybees. We demonstrated that the nectar of wasp-pollinated G. physocarpus contains cardenolides that had greater toxic effects on Apis mellifera honeybees than on Vespula germanica wasps, and also reduced feeding rates by honeybees. Behavioural experiments using natural compositions of nectar compounds showed that these interactions are mediated by non-volatile nectar chemistry. We also identified volatile compounds with acetic acid as a main component in the floral scent of G. physocarpus that elicited electrophysiological responses in wasp antennae. Mixtures of these compounds were behaviourally effective for attraction of V. germanica wasps. The results show the importance of both volatile and non-volatile chemical traits as filters that lead to specialization in plant pollination systems.

Macroevolution of floral scent chemistry across radiations of male euglossine bee-pollinated plantsMacroevolución de olores florales a través de radiaciones de plantas polinizadas por abejas euglosinas machosMacroevolução dos voláteis florais em radiações de plantas polinizadas por machos de abelhas Euglossini.

Floral volatiles play key roles as signaling agents that mediate interactions between plants and animals. Despite their importance, few studies have investigated broad patterns of volatile variation across groups of plants that share pollinators, particularly in a phylogenetic context. The "perfume flowers," Neotropical plant species exhibiting exclusive pollination by male euglossine bees in search of chemical rewards, present an intriguing system to investigate these patterns due to the unique function of their chemical phenotypes as both signaling agents and rewards. We leverage recently developed phylogenies and knowledge of biosynthesis, along with decades of chemical ecology research, to characterize axes of variation in the chemistry of perfume flowers, as well as understand their evolution at finer taxonomic scales. We detect pervasive chemical convergence, with many species across families exhibiting similar volatile phenotypes. Scent profiles of most species are dominated by compounds of either the phenylpropanoid or terpenoid biosynthesis pathways, while terpenoid compounds drive more subtle axes of variation. We find recapitulation of these patterns within two independent radiations of perfume flower orchids, in which we further detect evidence for the rapid evolution of divergent floral chemistries, consistent with the putative importance of scent in the process of adaptation and speciation.

Land-use-associated stressors interact to reduce bumblebee health at the individual and colony level.

In agricultural landscapes, bees face a variety of stressors, including insecticides and poor-quality food. Although both stressors individually have been shown to affect bumblebee health negatively, few studies have focused on stressor interactions, a scenario expected in intensively used agricultural landscapes. Using the bumblebee Bombus terrestris, a key pollinator in agricultural landscapes, we conducted a fully factorial laboratory experiment starting at nest initiation. We assessed the effects of food quality and insecticides, alone and in interaction, on health traits at various levels, some of which have been rarely studied. Pollen with a diluted nutrient content (low quality) reduced ovary size and delayed colony development. Wing asymmetry, indicating developmental stress, was increased during insecticide exposure and interactions with poor food, whereas both stressors reduced body size. Both stressors and their interaction changed the workers' chemical profile and reduced worker interactions and the immune response. Our findings suggest that insecticides combined with nutritional stress reduce bumblebee health at the individual and colony levels, thus possibly affecting colony performance, such as development and reproduction, and the stability of plant-pollinator networks. The synergistic effects highlight the need of combining stressors in risk assessments and when studying the complex effects of anthropogenic stressors on health outcomes.

Exposure to sublethal concentration of flupyradifurone alters sexual behavior and cuticular hydrocarbon profile in Heriades truncorum, an oligolectic solitary bee.

The aboveground oligolectic bee, Heriades truncorum, is a particularly good model for studying the impact of pesticides on sexual communication, since some aspects of its mating behavior have previously been described. We have tested (1) the interference of the pesticide flupyradifurone on male precopulatory behavior and male mating partner preferences, (2) the way that the pesticide interferes in male quality assessment by the female, and (3) the effects of the pesticide on the chemical compounds in the female cuticle. We exposed bees of both sexes to a sublethal concentration of flupyradifurone. Various behaviors were registered in a mating arena with two females (one unexposed and one exposed) and one male (either unexposed or exposed). Unexposed males were quicker to attempt to mate. Treatment also impacted precopulatory behavior and male quality assessment by females. Males approached unexposed females more quickly than insecticide-exposed ones. Females exposed to insecticide produced lower amounts of some cuticular hydrocarbons (sex pheromone candidates) and appeared less choosy than unexposed females. Our findings suggest that insecticide exposure affects sexual communication, playing a role both in male preference and in male quality assessment by the female.

Chemical ecology: Male orchid bees attract females with environmental-derived perfumes in courtship display.

Are male orchid bees the 'chemical peacocks' of the insect world? A new study on orchid bees shows that perfumes of males do indeed have a comparable function as a peacock's tail to increase male mating success and paternity.

Global change may make hostile - Higher ambient temperature and nitrogen availability increase ant aggression.

Behaviour is a response of organisms to internal and external stimuli and comprises various activities such as searching for food. Aggression is important in such activities, for example, improving the chances of winning competition for food, but animals differ in their level of aggression. This behavioural plasticity allows individuals to respond to environmental changes and is important for the survival of animals. It may be an important asset in facing global changes, which affect all organisms, for example, via rising temperature and eutrophication. The latter have steadily increased since 1900, especially in high elevations. Their effects may first become visible in stationary organisms such as ants because their nests are strictly associated with the conditions on site. Here, we analysed eight populations of the high-elevation ant Tetramorium alpestre along several elevations spanning the European Alps. We conducted a correlative approach and analysed several genetic and environmental proxies, namely within- and across-colony genetic relatedness, cuticular hydrocarbons, body size, across-colony geographic distance, air temperature, and worker nitrogen values additionally to within-population aggressive behaviour. We hypothesised that a) these proxies and aggressive behaviour differ among populations and that b) one or more of these proxies influence aggression. We found that a) some environmental proxies and aggression differed among populations but not the genetic proxies and that b) air temperature and worker nitrogen-isotope values correlated positively with worker aggression. The results indicate an environmental but not social-structural influence on this ant's aggressive behaviour, even though social structure varied among populations (single- and multiple-queened colonies). We infer that global change affects aggression in our study system and propose five mutually non-exclusive scenarios to explain the behavioural change mechanistically. Using the space-for-time principle, we speculate that aggression may increase due to future increases in temperature and nitrogen availability in this ant and other species living in high elevations.

The supply of multiple ecosystem services requires biodiversity across spatial scales.

The impact of local biodiversity loss on ecosystem functioning is well established, but the role of larger-scale biodiversity dynamics in the delivery of ecosystem services remains poorly understood. Here we address this gap using a comprehensive dataset describing the supply of 16 cultural, regulating and provisioning ecosystem services in 150 European agricultural grassland plots, and detailed multi-scale data on land use and plant diversity. After controlling for land-use and abiotic factors, we show that both plot-level and surrounding plant diversity play an important role in the supply of cultural and aboveground regulating ecosystem services. In contrast, provisioning and belowground regulating ecosystem services are more strongly driven by field-level management and abiotic factors. Structural equation models revealed that surrounding plant diversity promotes ecosystem services both directly, probably by fostering the spill-over of ecosystem service providers from surrounding areas, and indirectly, by maintaining plot-level diversity. By influencing the ecosystem services that local stakeholders prioritized, biodiversity at different scales was also shown to positively influence a wide range of stakeholder groups. These results provide a comprehensive picture of which ecosystem services rely most strongly on biodiversity, and the respective scales of biodiversity that drive these services. This key information is required for the upscaling of biodiversity-ecosystem service relationships, and the informed management of biodiversity within agricultural landscapes.

Water Deficit, Nitrogen Availability, and Their Combination Differently Affect Floral Scent Emission in Three Brassicaceae Species.

Floral scent plays a central role in plant-pollinator interactions, as flower visitors can discriminate between scent differences to recognize and forage on rewarding flowers. Changes in scent compositions might therefore lead to recognition mismatches between host plants and flower visitors. An understanding of the phenotypic plasticity of floral scent, especially in crop species, is becoming important because of climate change, e.g., increasing drought periods, and other anthropogenic influences, e.g., nitrogen (N) deposition. We have investigated the effects of the combination of progressive water deficits (dry-down) and N supplementation on floral scent emission in three Brassicaceae species (cultivated vs. wild). Individuals were randomly assigned to one of four treatments: (1) well-watered without N supplementation; (2) well-watered with N supplementation; (3) dry-down without N supplementation; (4) dry-down with N supplementation. We collected scent on day 0, 2, 7, and 14 after the commencement of the watering treatment. All samples were analyzed using gas chromatography coupled with mass spectrometry. We found that the highly cultivated Brassica napus had the lowest overall emission rate; its scent composition was affected by the interaction of watering treatment and N supplementation. Scent bouquets of the cultivated Sinapis alba also changed under these treatments. Scent bouquets of the common weed Sinapis arvensis were affected by watering treatment, but not by time and N supplementation. Furthermore, the influence of treatments on the emission rate of single compounds was highly compound-specific. Nonetheless, our study revealed that especially terpenes were negatively affected by drought-stress.

Fruit scent as an honest signal for fruit quality.

BACKGROUND: Fleshy fruits evolved to be attractive to seed dispersers through various signals such as color and scent. Signals can evolve through different trajectories and have various degrees of reliability. The strongest substrate on which reliable signals can evolve is when there is an inherent link between signal and reward, rendering cheating costly or impossible. It was recently proposed that aliphatic esters in fruit scent may be predictive of sugar content due to their synthesis from products of sugar fermentation. We test this hypothesis on a case study of wild fig species (Ficus tiliifolia) from Madagascar, which relies on seed dispersal by lemurs. RESULTS: We found a strong positive correlation between signal (esters) and reward (sugar). We also found that non-esters, including direct fermentation products, in fruit scent do not indicate sugar levels, which implies that this relationship is not simply a product of fruit maturation wherein more mature fruits emit more scent and contain more sugar. CONCLUSIONS: While based on a single taxon, these results strongly support the hypothesis that a biochemical link between ester synthesis and sugar may render the ester fraction of fruit scent an honest signal for fruit quality, with consequences for animal sensory and feeding ecology, and the evolution of plants in the context of seed dispersal.

Linking bacteria, volatiles and insects on carrion: the role of temporal and spatial factors regulating inter-kingdom communication via volatiles.

Multi-kingdom community complexity and the chemically mediated dynamics between bacteria and insects have recently received increased attention in carrion research. However, the strength of these inter-kingdom interactions and the factors that regulate them are poorly studied. We used 75 piglet cadavers across three forest regions to survey the relationship between three actors (epinecrotic bacteria, volatile organic compounds (VOCs) and flies) during the first 4 days of decomposition and the factors that regulate this interdependence. The results showed a dynamic bacterial change during decomposition (temperature-time index) and across the forest management gradient, but not between regions. Similarly, VOC emission was dynamic across a temperature-time index and the forest management gradient but did not differ between regions. However, fly occurrence was dynamic across both space and time. The strong interdependence between the three actors was mainly regulated by the temperature-time index and the study regions, thereby revealing regulation at temporal and spatial scales. Additionally, the actor interdependence was stable across a gradient of forest management intensity. By combining different actors of decomposition, we have expanded our knowledge of the holistic mechanisms regulating carrion community dynamics and inter-kingdom interactions, an important precondition for better describing food web dynamics and entire ecosystem functions.

Artificial Nesting Hills Promote Wild Bees in Agricultural Landscapes.

The availability of nesting resources influences the persistence and survival of bee communities. Although a positive effect of artificial nesting structures has frequently been shown for aboveground cavity-nesting wild bees, studies on below ground-nesting bees are rare. Artificial nesting hills designed to provide nesting habitats for ground-nesting bees were therefore established within the BienABest project in 20 regions across Germany. Wild bee communities were monitored for two consecutive years, accompanied by recordings of landscape and abiotic nest site variables. Bee activity and species richness increased from the first to the second year after establishment; this was particularly pronounced in landscapes with a low cover of semi-natural habitat. The nesting hills were successively colonized, indicating that they should exist for many years, thereby promoting a species-rich bee community. We recommend the construction of nesting hills on sun-exposed sites with a high thermal gain of the substrate because the bees prefer south-facing sites with high soil temperatures. Although the soil composition of the nesting hills plays a minor role, we suggest using local soil to match the needs of the local bee community. We conclude that artificial nesting structures for ground-nesting bees act as a valuable nesting resource for various bee species, particularly in highly degraded landscapes. We offer a construction and maintenance guide for the successful establishment of nesting hills for bee conservation.

Land-use stress alters cuticular chemical surface profile and morphology in the bumble bee Bombus lapidarius.

Pollinators and other insects are currently undergoing a massive decline. Several stressors are thought to be of importance in this decline, with those having close relationships to agricultural management and practice seemingly playing key roles. In the present study, we sampled Bombus lapidarius L. workers in grasslands differing in their management intensity and management regime across three different regions along a north-south gradient in Germany. We analyzed the bees with regard to (1) their cuticular hydrocarbon profile (because of its important role in communication in social insects) and amount of scent by using gas chromatography and (2) the size of each individual by using wing distances as a proxy for body size. Our analysis revealed changes related to land-use intensity and temperature in the cuticular scent profile of bumble bees. Decreasing body size and increasing total scent amount were explained by an interaction of land-use intensity and study region, but not by land-use intensity alone. Thus, land-use intensity and temperature influence intracolonial communication and size, both of which can have strong effects on foraging. Land management and climate are therefore probably detrimental for colony maintenance and the reproductive success of bumble bees.

Floral Scent Chemistry and Pollinators of a Sexually Dimorphic Neotropical Orchid.

Catasetum is a speciose Neotropical orchid genus of which male and female flowers emit scents acting both as attractant and reward for their exclusive pollinators, male orchid bees (Euglossini: Apidae). In Catasetum, it is well known that flowers display a remarkably morphological sexual dimorphism. However, it remains poorly investigated whether this is also true for floral scents. Here, we investigated the pollination ecology and floral scent traits (chemistry and total emission) of C. maranhense, a species endemic to the Brazilian N/NE region. Males of Euglossa securigera are the only pollinators of C. maranhense. The floral scent of C. maranhense is composed of 29 volatile compounds, with eucalyptol, indole, (E)-Methyl p-methoxycinnamate, and (Z)-Methyl p-methoxycinnamate accounting for more than 80% of the scent bouquet. No sexual dimorphism was detected in any of the traits investigated. We discuss the ecological and evolutionary significance of our findings to Catasetum species and other unisexual perfume plants.

Pheromone communication among sexes of the garden cross spider Araneus diadematus.

Chemical communication plays a fundamental role in many aspects of an animal's life from assessing habitat quality to finding mating partners. Behavioural observations show that chemical communication likewise plays an important role in spiders, but the contexts and the substances involved are little explored. Here, we investigate the chemical communication in the garden cross spider Araneus diadematus (Clerck, 1757) between and within the sexes. Using choice trials, we demonstrate that males are attracted to odours of adult females, but not to those of subadult females. Our data further suggest that adult females avoid odours of conspecific adult females, possibly in order to reduce reproductive competition with other females. Cuticle and silk extracts as well as headspace samples of subadult and adult virgin females were analysed via GC-MS. Available candidate compounds for the female sex pheromone were tested via electroantennography on palps (electropalpography) of adult virgin females and on females in behavioural trials. We propose sulcatone (6-methyl-5-hepten-2-one) as a candidate substance for the female volatile pheromone and several long-chained alkanes and alcohols as candidates for contact pheromones. Apart from demonstrating that attraction of males to females depends on the latter's developmental stage, our study suggests that pheromones can also play an important role between females, an aspect that requires further attention.

Differential Evolutionary History in Visual and Olfactory Floral Cues of the Bee-Pollinated Genus Campanula (Campanulaceae).

Visual and olfactory floral signals play key roles in plant-pollinator interactions. In recent decades, studies investigating the evolution of either of these signals have increased considerably. However, there are large gaps in our understanding of whether or not these two cue modalities evolve in a concerted manner. Here, we characterized the visual (i.e., color) and olfactory (scent) floral cues in bee-pollinated Campanula species by spectrophotometric and chemical methods, respectively, with the aim of tracing their evolutionary paths. We found a species-specific pattern in color reflectance and scent chemistry. Multivariate phylogenetic statistics revealed no influence of phylogeny on floral color and scent bouquet. However, univariate phylogenetic statistics revealed a phylogenetic signal in some of the constituents of the scent bouquet. Our results suggest unequal evolutionary pathways of visual and olfactory floral cues in the genus Campanula. While the lack of phylogenetic signal on both color and scent bouquet points to external agents (e.g., pollinators, herbivores) as evolutionary drivers, the presence of phylogenetic signal in at least some floral scent constituents point to an influence of phylogeny on trait evolution. We discuss why external agents and phylogeny differently shape the evolutionary paths in floral color and scent of closely related angiosperms.

Contrasting responses of above- and belowground diversity to multiple components of land-use intensity.

Land-use intensification is a major driver of biodiversity loss. However, understanding how different components of land use drive biodiversity loss requires the investigation of multiple trophic levels across spatial scales. Using data from 150 agricultural grasslands in central Europe, we assess the influence of multiple components of local- and landscape-level land use on more than 4,000 above- and belowground taxa, spanning 20 trophic groups. Plot-level land-use intensity is strongly and negatively associated with aboveground trophic groups, but positively or not associated with belowground trophic groups. Meanwhile, both above- and belowground trophic groups respond to landscape-level land use, but to different drivers: aboveground diversity of grasslands is promoted by diverse surrounding land-cover, while belowground diversity is positively related to a high permanent forest cover in the surrounding landscape. These results highlight a role of landscape-level land use in shaping belowground communities, and suggest that revised agroecosystem management strategies are needed to conserve whole-ecosystem biodiversity.