Cuticular Hydrocarbon Profiles of Himalayan Bumble Bees (Hymenoptera: Bombus Latreille) are Species-Specific and Show Elevational Variation

Abstract

Bumble bees are important pollinators in natural environments and agricultural farmlands, and they are in particular adapted to harsh environments like high mountain habitats. In these environments, animals are exposed to low temperature and face the risk of desiccation. The Eastern Himalayas are one of the recognized biodiversity hotspots worldwide. The area covers subtropical rainforest with warm temperature and high precipitation as well as high mountain ranges with peaks reaching up to 7,000 m, shaping a diverse floral and faunal community at the different elevational zones. To identify possible adaptation strategies, we investigated the cuticular hydrocarbon profiles of four bumble bee species occurring at different elevational ranges in Arunachal Pradesh, the northeastern most state in India. At 17 locations along an elevational gradient, we collected workers of two species from lower elevations (B. albopleuralis and B. breviceps; ~ 100 m - 3,000 m asl) and two species from higher elevations (B. prshewalskyi and B. mirus; ~ 2,800 m - 4,500 m asl). The CHC profiles of all four species showed a significant degree of variation in the composition of hydrocarbons, indicating species specificity. We also found clear correlation with elevation. The weighted mean chain length of the hydrocarbons significantly differed between the low and high elevation species, and the proportion of saturated hydrocarbons in CHC profiles significantly increased with the elevational range of the bumble bee species. Our results indicate that bumble bees living at high elevations reduce the risk of water loss by adapting their CHC composition on their cuticle, a phenomenon that has also been found in other insects like ants and fruit flies.

Keywords: Adaptation; CHC Profiles; Climatic Conditions; Desiccation Stress.

Fig. 1

Sampling locations in Arunachal Pradesh.Overview map of the region with an overlay of the elevation profile of the Himalayan Mountain range. The red box indicates the enlarged part of Arunachal Pradesh shown at the bottom. Sampling locations (N = 17) are shown as black dots. Color refers to elevation above sea level. Elevation data from Jarvis et al. (2008), country borders from Runfola et al. (2020) and Himalaya range borders from Liu and Zhu (2022). (For detailed information about the location and number of collected specimens see Suppl. Table 1)

Fig. 2

CHC profile diversity of four Himalayan bumble bee species with different elevational ranges. (A). Phylogenetic position of the study species embedded in the subgeneric classification of the bumble bees (Sun et al. , Williams et al., 2022). (B) Elevational range of collected bumble bee specimens (box indicating first and third quartile and median and whiskers the total range). (C) Diversity of CHC profiles of bumble bees displayed in a two-dimensional graph by non-metric multidimensional scaling (NMDS) based on Bray-Curtis distances. Distance between symbols indicates the degree of similarity among the CHC profiles. Each symbol represents the CHC profile of an individual bumble bee worker. Circles: species with lower elevational ranges, triangles: species with higher elevational ranges. Colors indicate the species

Fig. 3

Differences in elevation associated chemical traits of CHC profiles in the four bumble bee species. Differences in (A) weighted mean chain lengths of the hydrocarbons and (B) the proportion of saturated hydrocarbons in the CHC profiles. Significance values refer to the results of Dunn’s test for multiple comparisons (***, p < 0.001; see main text and Suppl. Tables 4 & 5)