Data from: Geographic body size variation in the periodical cicadas Magicicada: implications for life cycle divergence and local adaptation

Seven species in three species groups of periodical cicadas (Magicicada) occupy a wide latitudinal range in the eastern United States. To clarify how adult body size, a key trait affecting fitness, varies geographically with climate conditions and life cycle, we analyzed the relationships of population mean head width to geographic variables (latitude, longitude, altitude), habitat annual mean temperature, life cycle and species differences. Within species, body size was larger in females than males and decreased with increasing latitude (and decreasing habitat annual mean temperature), following the converse Bergmann rule. For the pair of recently diverged 13-y and 17-y species in each group, 13-y cicadas were equal in size or slightly smaller on average than their 17-y counterparts despite their shorter developmental time. This fact suggests that, under the same climatic conditions, 17-y cicadas have lowered growth rates compared to their 13-y counterparts, allowing 13-y cicadas with faster growth rates to achieve body sizes equivalent to those of their 17-y counterparts at the same locations. However, in the Decim group, which includes two 13-y species, the more southerly, anciently diverged 13-y species (M. tredecim) was characterized by a larger body size than the other, more northerly 13- and 17-y species, suggesting that local adaptation in warmer habitats may ultimately lead to evolution of larger body sizes. Our results demonstrate how geographic clines in body size may be maintained in sister species possessing different life cycles.