Ecogeographical patterns of body size differ among North American paper wasp species

Species with widespread distributions frequently show clines in body size
across broad geographic areas. These clines may be the result of
“ecogeographical rules” that describe spatial patterns of phenotypic
diferences driven by environmental variation. Intraspeciic variation in
body size, and the mechanisms causing this variation, have been poorly
described in social wasps. This study examined ecogeographical patterns of
body size for 12 native species and one non-native species of North
American paper wasps (genus: Polistes) using body size
measurements from > 14,000 pinned museum specimens. Intraspeciic
body size was correlated with latitude, elevation, and broadscale climate
variation. However, the direction of this relationship was idiosyncratic
across species, with Bergmann’s clines and converse Bergmann’s clines
equally represented. There was no evidence of a phylogenetic signal in the
direction of the cline between body size and the environment. Within
species, the worker caste and the reproductive caste showed the same
direction of response between body size and latitude, although for most
species the reproductive caste was larger than the worker caste.
Intraspeciic variation in body size appears to be driven by diferences in
the response among species to similar environmental variables but the
mechanisms causing this variation remain unknown.

分布范围广泛的物种，在广阔的地理区域内往往呈现出体型渐变群（cline）特征。这类渐变群可能源于“生态地理规则”——该规则描述了由环境变异驱动的表型差异的空间分布模式。社会性胡蜂的种内体型变异及其驱动机制，目前仍鲜有系统研究报道。
本研究以北美12种本土马蜂（Polistes属）及1种外来马蜂为研究对象，利用超过14000份馆藏针插标本的体型测量数据，分析了其体型的生态地理分布模式。种内体型与纬度、海拔及大尺度气候变异相关。然而，这种关联的方向在不同物种间具有特异性，贝格曼渐变群（Bergmann's clines）与反贝格曼渐变群的占比相当。体型与环境间的渐变群方向未呈现显著的系统发育信号（phylogenetic signal）。在物种内部，工职蜂与生殖职蜂的体型对纬度的响应方向一致，尽管多数物种的生殖职蜂体型大于工职蜂。
种内体型变异似乎源于不同物种对相似环境变量的响应差异，但该变异的具体驱动机制仍有待阐明。