Neotropical stingless bees display a strong response in cold tolerance with changes in elevation

Authors: GONZALEZ, VICTOR - University Of Kansas; Oyen, Kennan; VITALE, NYDIA - Center For Applied Ecology Of The Coast(CECOAL):national Council For Scientific And Technical Resea; OSPINA, RODULFO - National University Of Colombia

Submitted to: Conservation Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2022
Publication Date: 12/21/2022
Citation: Gonzalez, V.H., Oyen, K.J., Vitale, N., Ospina, R. 2022. Neotropical stingless bees display a strong response in cold tolerance with changes in elevation. Conservation Physiology. 10(1). Article coac073. https://doi.org/10.1093/conphys/coac073.
DOI: https://doi.org/10.1093/conphys/coac073

Interpretive Summary: Tropical pollinators are likely vulnerable to the impacts of climate change. We tested whether tropical bees collected across elevational gradients exhibit differences in their ability to tolerate cold. We found that bees at higher elevations had more cold tolerance compared with bees from lower elevation. This suggests that long-distance relocations of bees may be unsuccessful due to local adaptation of natural colonies.

Technical Abstract: Tropical pollinators are expected to experience substantial effects due to climate change, but aspects of their thermal biology remain largely unknown. We investigated the thermal tolerance of stingless honey-making bees, the most ecologically, economically and culturally important group of tropical pollinators. We assessed changes in the lower (CTMin) and upper (CTMax) critical thermal limits of 17 species (12 genera) at two elevations (200 and 1500 m) in the Colombian Andes. In addition, we examined the influence of body size (intertegular distance, ITD), hairiness (thoracic hair length) and coloration (lightness value) on bees’ thermal tolerance. Because stingless beekeepers often relocate their colonies across the altitudinal gradient, as an initial attempt to explore potential social responses to climatic variability, we also tracked for several weeks brood temperature and humidity in nests of three species at both elevations. We found that CTMin decreased with elevation while CTMax was similar between elevations. CTMin and CTMax increased (low cold tolerance and high heat tolerance) with increasing ITD, hair length and lightness value, but these relationships were weak and explained at most 10% of the variance. Neither CTMin nor CTMax displayed significant phylogenetic signal. Brood nest temperature tracked ambient diel variations more closely in the low-elevation site, but it was constant and higher at the high-elevation site. In contrast, brood nest humidity was uniform throughout the day regardless of elevation. The stronger response in CTMin, and a similar CTMax between elevations, follows a pattern of variation documented across a wide range of taxa that is commonly known as the Brett’s heat-invariant hypothesis. Our results indicate differential thermal sensitivities and potential thermal adaptations to local climate, which support ongoing conservation policies to restrict the long-distance relocations of colonies. They also shed light on how malleable nest thermoregulation can be across elevations.