title: Geographic body size variation in the periodical cicadas Magicicada: implications for life cycle divergence and local adaptation.
abstract: Seven species in three species groups (Decim, Cassini and Decula) 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 analysed the relationships of population mean head width to geographic variables (latitude, longitude, altitude), habitat annual mean temperature (AMT), life cycle and species differences. Within species, body size was larger in females than males and decreased with increasing latitude (and decreasing habitat AMT), following the converse Bergmann's rule. For the pair of recently diverged 13- and 17-year species in each group, 13-year cicadas were equal in size or slightly smaller on average than their 17-year counterparts despite their shorter developmental time. This fact suggests that, under the same climatic conditions, 17-year cicadas have lowered growth rates compared to their 13-years counterparts, allowing 13-year cicadas with faster growth rates to achieve body sizes equivalent to those of their 17-year counterparts at the same locations. However, in the Decim group, which includes two 13-year species, the more southerly, anciently diverged 13-year species (Magicicada tredecim) was characterized by a larger body size than the other, more northerly 13- and 17-year 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.
authors.affiliation: Department of Zoology, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Koyama
authors.affiliation: Graduate School of Science and Technology, Shizuoka University, Hamamatsu, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Ito
authors.affiliation: Graduate School of Science and Technology, Shizuoka University, Hamamatsu, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kakishima
authors.affiliation: Graduate School of Science and Technology, Shizuoka University, Hamamatsu, Japan.|Department of Environmental and Forest Biology, College of Environmental Science and Forestry, State University of New York, Syracuse, NY, USA.|Marine Biosystems Research Center, Chiba University, Uchiura, Kamogawa, Chiba, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Yoshimura
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, USA.
authors.forename: J R
authors.initials: JR
authors.lastname: Cooley
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Connecticut, Storrs, CT, USA.
authors.forename: C
authors.initials: C
authors.lastname: Simon
authors.affiliation: Department of Zoology, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sota
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D063147:Animal Distribution / Q000502:physiology*; D000818:Animals; D049628:Body Size / Q000502:physiology*; D005260:Female; D006430:Hemiptera / Q000502:physiology*; D008018:Life Cycle Stages / Q000502:physiology*; D008297:Male; D013045:Species Specificity
keywords: clinal variation; converse Bergmann cline; geographic variation; sexual dimorphism