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.在恒温脊椎动物中，体型的纬度梯度格局长期以来均以贝格曼法则（Bergmann’s Rule）进行解释。然而对于变温动物而言，学界尚未形成统一共识，在占野生生物绝大多数的昆虫类群中这一问题尤为突出。其中，蜂类是物种多样性极高的传粉昆虫类群，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，但截至目前尚无基于大尺度系统发育框架的蜂类物种集合综合研究。本研究旨在通过大陆与群落两个尺度下体型与纬度的关联分析，检验野生蜂类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）的蜂类开展了假设检验。本研究整合了西古北界范围内615个蜂类物种的142008条分布记录，这些记录均对应50 km × 50 km的（CGRS）网格单元。随后，我们采用考虑空间自相关效应的广义最小二乘线性模型（Generalized Least Squares，GLS），分析纬度与蜂类平均体型之间的关联。当对所有蜂类物种进行合并分析时，其平均体型随纬度升高而增大，符合贝格曼法则。但当按蜂属分别分析时，仅有4个属符合贝格曼法则，3个属呈现出相反的体型纬度梯度格局，另有3个属未表现出显著的纬度渐变特征。本研究所涉及的全部生活史性状（即独居、社会与寄生行为；地表筑巢与茎秆筑巢行为）均呈现出贝格曼型纬度梯度格局。总体而言，寒冷生境中的蜂类体型普遍更大，这一现象可能与其体温调节能力及兼性吸热特性相关；不过，‘季节长度效应’（即觅食季缩短）或为部分类群（尤其是熊蜂）呈现反向贝格曼格局的潜在驱动因素。