Abstract:

【Aim】 As an important group of pollinators in the natural environment, bumblebees are covered with brightly coloured hairs that form distinctive colour patterns. This study aims to investigate the geographical distribution pattern of the colour-pattern polymorphism of Bombus breviceps inYunnan, southwestern China to provide basic data for the study of genetic evolution and environmental adaptability of bumblebees. 【Methods】 A total of 957 B. breviceps specimens including 898 female adults (103 queens and 795 workers) and 59 male adults collected from 127 sampling sites inYunnanandGuizhoufrom 2017 to 2021 were examined. The colour patterns of these specimens were scored and the colour pattern groups and their relative abundance were analyzed. Clustering analysis was conducted based on the pubescence colour composition of different elements and the geographical distribution pattern of the colour patterns was analyzed based on their distribution in grid cells of 0.5° longitude × 0.5° latitude. 【Results】 The colours of the thoracic dorsum pubescence of B. breviceps include black, grey yellow, and orange yellow, while those of the abdominal dorsum pubescence include black, grey yellow, yellow and dark brown. All the 1st abdominal segments are covered with yellow pubescence, which can extend up to the abdominal tergum 3. Gastral terga 2 and 3 are covered with yellow, black, or grey yellow pubescence and the dark brown pubescence can stretch from gastral tergum 6 forward to the lower part of gastral tergum 3. A total of 81 colour patterns were identified in female adults of B. breviceps. Eighty different colour patterns were detected in workers and 13 colour patterns were identified in queens. The workers and queens shared 12 colour patterns. The male adults of B. breviceps exhibited 37 different colour patterns, 28 of which were similar to those of female adults. The 81 colour patterns of female adults of B. breviceps include 2 dominant, 5 abundant, 10 common and 64 sparse colour patterns. The colour patterns of female adults of B. breviceps were clustered into three body colour groups: group A (black thoracic dorsum with dark brown abdominal segments), group B-1 (dark brown thoracic dorsum with dark abdominal segments), and group B-2 (dark brown thoracic dorsum and abdominal segments).  The geographical distribution of the colour patterns of B. breviceps inYunnancould be grouped into two regions: western Yunnan Plateau (I) and eastern Yunnan Plateau (II). Region I could be further divided into subtropical plateau basin region in central Yunnan (I1) and tropical low mountain and wide valley region in southwest Yunnan (I2). Region II could be further divided into tropical karst mountain valley area in Southeast Yunnan (II1) and subtropical mid-mountain valley area in Northeast Yunnan (II2). Group A colour pattern is only distributed in subregion I1 and group B-2 was only distributed in subregion I2. Group B-1 colour pattern is only distributed in region II, where group B-2 colour pattern is also distributed. There was no significant correlation between the polymorphisms of the colour pattern and the latitude and longitude of distribution area. There were up to 18 colour patterns distributed in the central Yunnan Plateau (24.00°-24.50°N, 102.50°-103.00°E), representing the greatest colour-pattern polymorphism area. The average altitude of group A colour pattern [(1 951±311) m] was extremely significantly higher than those of group B-1 colour pattern [(1 568±352) m] and group B-2 colour pattern [(1 556±534) m]. 【Conclusion】 B. breviceps exhibits a striking intraspecific polymorphism of colour patterns inYunnan. The colour patterns can be divided into three main groups, and their distribution is related to climatic zoning, geomorphology and land use type. The distribution of the colour patterns has obvious geographical division characteristics and their polymorphisms in the same domain converge to the dominant colour patterns. The results of this study are of great significance for the in-depth exploration of local bumblebee resources and the conservation of species diversity inChina, and provide technical support for the utilization and development of bumblebees in different habitats.

Key words: Bombus breviceps')">

Bombus breviceps, pubescence, colour pattern, clustering analysis, geographical distribution