Data from: Patterns of size variation in bees at a continental scale: does Bergmann’s rule apply?

Body size latitudinal clines have been widley explained by the Bergmann’s rule in homeothermic vertebrates. However, there is no general consensus in poikilotherms organisms in particular in insects that represent the large majority of wildlife. Among them, bees are a highly diverse pollinators group with high economic and ecological value. Nevertheless, no comprehensive studies of species assemblages at a phylogenetically larger scale have been carried out even if they could identify the traits and the ecological conditions that generate different patterns of latitudinal size variation. We aimed to test Bergmann’s rule for wild bees by assessing relationships between body size and latitude at continental and community levels. We tested our hypotheses for bees showing different life history traits (i.e. sociality and nesting behaviour). We used 142,008 distribution records of 615 bee species at 50 km x 50 km (CGRS) grids across the West Palearctic. We then applied Generalized Least Squares fitted linear model (GLS) to assess the relationship between latitude and mean body size of bees, taking into account spatial autocorrelation. For all bee species grouped, mean body size increased with higher latitudes, and so followed Bergmann’s rule. However, considering bee genera separately, four genera were consistent with Bergmann’s rule, while three showed a converse trend, and three showed no significant cline. All life history traits used here (i.e. solitary, social and parasitic behaviour; ground and stem nesting behaviour) displayed a Bergmann’s cline. In general there is a main trend for larger bees in colder habitats, which is likely to be related to their thermoregulatory abilities and partial endothermy, even if a “season length effect” (i.e. shorter foraging season) is a potential driver of the converse Bergmann’s cline particularly in bumblebees.

恒温脊椎动物的体型纬度梯度格局长期以来均以贝格曼法则（Bergmann’s rule）作为主流解释。然而，变温动物类群，尤其是占野生生物绝大多数的昆虫类群中，学界尚未就其体型纬度梯度格局形成统一共识。其中，蜜蜂类群作为物种多样性极高的授粉昆虫，兼具重要的经济与生态价值。尽管此类研究可揭示驱动体型纬度变异格局差异的功能性状与生态条件，但目前学界尚未在更大系统发育尺度下开展针对蜜蜂类群组合的综合性研究。本研究旨在通过大陆与群落两个尺度下的体型-纬度相关性分析，验证野生蜜蜂类群是否符合贝格曼法则。我们针对具有不同生活史性状（即社会性与筑巢行为）的蜜蜂类群验证了研究假设。本研究整合了西古北界范围内50 km×50 km（CGRS）网格下的615种蜜蜂的142008条分布记录。随后，我们采用考虑空间自相关的广义最小二乘拟合线性模型（Generalized Least Squares, GLS），分析纬度与蜜蜂平均体型之间的相关性。对所有合并统计的蜜蜂物种而言，其平均体型随纬度升高而增大，符合贝格曼法则。但当按蜜蜂属级类群分别分析时，仅有4个属符合贝格曼法则，3个属呈现相反的体型纬度梯度趋势，另有3个属未表现出显著的纬度梯度格局。本研究所涉及的全部生活史性状（即独居、社会性与寄生行为；地面筑巢与茎秆筑巢行为）均表现出贝格曼型纬度梯度格局。总体而言，寒冷生境中的蜜蜂体型普遍更大，这可能与其体温调节能力及部分内温性特征相关；而“季节长度效应”（即较短的觅食季）则可能是部分类群（尤其是熊蜂）呈现反向贝格曼梯度格局的潜在驱动因素。