Cuticular hydrocarbons of alpine bumble bees (Hymenoptera: Bombus) are species-specific, but show little evidence of elevation-related climate adaptation

Abstract

Alpine bumble bees are the most important pollinators in temperate mountain ecosystems. Although they are used to encounter small-scale successions of very different climates in the mountains, many species respond sensitively to climatic changes, reflected in spatial range shifts and declining populations worldwide. Cuticular hydrocarbons (CHCs) mediate climate adaptation in some insects. However, whether they predict the elevational niche of bumble bees or their responses to climatic changes remains poorly understood. Here, we used three different approaches to study the role of bumble bees’ CHCs in the context of climate adaptation: using a 1,300 m elevational gradient, we first investigated whether the overall composition of CHCs, and two potentially climate-associated chemical traits (proportion of saturated components, mean chain length) on the cuticle of six bumble bee species were linked to the species’ elevational niches. We then analyzed intraspecific variation in CHCs of Bombus pascuorum along the elevational gradient and tested whether these traits respond to temperature. Finally, we used a field translocation experiment to test whether CHCs of Bombus lucorum workers change, when translocated from the foothill of a cool and wet mountain region to (a) higher elevations, and (b) a warm and dry region. Overall, the six species showed distinctive, species-specific CHC profiles. We found inter- and intraspecific variation in the composition of CHCs and in chemical traits along the elevational gradient, but no link to the elevational distribution of species and individuals. According to our expectations, bumble bees translocated to a warm and dry region tended to express longer CHC chains than bumble bees translocated to cool and wet foothills, which could reflect an acclimatization to regional climate. However, chain lengths did not further decrease systematically along the elevational gradient, suggesting that other factors than temperature also shape chain lengths in CHC profiles. We conclude that in alpine bumble bees, CHC profiles and traits respond at best secondarily to the climate conditions tested in this study. While the functional role of species-specific CHC profiles in bumble bees remains elusive, limited plasticity in this trait could restrict species’ ability to adapt to climatic changes.

Cuticular hydrocarbon profiles of Himalayan bumble bees (Hymenoptera:BombusLatreille) are species-specific and show local and elevation related variation

“…Bees of the genus Lasioglossum changed the composition of their CHC profiles similar to the bumblebees investigated in the present study (Mayr et al 2021). In contrast, a study on bumble bees from an elevational gradient in the Alps did not reveal an adaptation of the CHC profiles to potential drought stress in higher altitudes (Maihoff et al 2023). The elevational gradient of 1000 m studied might have been too small to cause pronounced changes in the environmental conditions and thus, the selection pressure might not be strong enough to change the compositional features of the CHC profiles in the selected bumble bee species.…”

“…Due to their importance as pollinators of many flowering plants, bumble bees and other wild bees became a model system to better understand their vulnerability and resilience against climate changes (Soroye et al 2020;Maebe et al 2021;Warrit et al 2023). Possible mechanisms of adaptation include, for example, pilosity (Hines et al 2022), cuticular hydrocarbons (Maihoff et al 2023), temperature tolerance (Pimsler et al 2020;Martinet et al 2021), respiratory and neural systems (Jackson et al, 2020).…”

Warming up through buildings and roads: what we know and should know about the urban heat island effect on bees

“…In bees, studies are still rare. In one study on alpine Bombus, Maihoff et al (2023) showed that workers translocated to a warm region tended to possess longer hydrocarbon chains than bumblebees translocated to cool regions. In addition, Mayr et al (2021) found that Lasioglossum species (Halictidae) at higher elevations along Mount Kilimanjaro (Tanzania) possess higher proportions of alkanes.…”