title: Lack of genetic variation prevents adaptation at the geographic range margin in a damselfly.
abstract: What limits a species' distribution in the absence of physical barriers? Genetic load due to asymmetric gene flow and the absence of genetic variation due to lack of gene flow are hypothesized to constrain adaptation to novel environments in marginal populations, preventing range expansion. Here, we examined the genetic structure and geographic variation in morphological traits in two damselflies (Ischnura asiatica and I. senegalensis) along a latitudinal gradient in Japan, which is the distribution centre of I. asiatica and the northern limit of I. senegalensis. Genomewide genetic analyses found a loss of genetic diversity at the edge of distribution in I. senegalensis but consistently high diversity in I. asiatica. Gene flow was asymmetric in a south-north direction in both species. Although body size and wing loading showed decreasing latitudinal clines (smaller in north) in I. asiatica in Japan, increasing latitudinal clines (larger in north) in these phenotypic markers were observed in I. senegalensis, particularly near the northern boundary, which coincided well with the location where genetic diversity began a sharp decline. In ectothermic animals, increasing latitudinal cline in these traits was suggested to be established when they failed to adapt to thermal gradient. Therefore, our findings support the possibility that a lack of genetic variation rather than geneflow swamping is responsible for the constraint of adaptation at the margin of geographic distribution.
authors: Frontier Research Institute for Interdisciplinary Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba, Sendai, Miyagi, 980-8578, Japan. takahashi.yum@gmail.com.|Division of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba, Sendai, Miyagi, 980-8578, Japan. takahashi.yum@gmail.com.
authors: Yuma
authors: Y
authors: Takahashi
authors: Field Science Center, Graduate School of Agricultural Science, Tohoku University, 232-3 Yomogida, Naruko-onsen, Osaki, Miyagi, 989-6711, Japan.
authors: Yoshihisa
authors: Y
authors: Suyama
authors: Field Science Center, Graduate School of Agricultural Science, Tohoku University, 232-3 Yomogida, Naruko-onsen, Osaki, Miyagi, 989-6711, Japan.
authors: Yu
authors: Y
authors: Matsuki
authors: Department of Cell Proliferation, United Center for Advanced Research and Translational Medicine, Graduate School of Medicine, Tohoku University, 2-1 Seiryo, Aoba, Sendai, 980-8575, Japan.
authors: Ryo
authors: R
authors: Funayama
authors: Department of Cell Proliferation, United Center for Advanced Research and Translational Medicine, Graduate School of Medicine, Tohoku University, 2-1 Seiryo, Aoba, Sendai, 980-8575, Japan.
authors: Keiko
authors: K
authors: Nakayama
authors: Division of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, 6-3 Aoba, Aramaki, Aoba, Sendai, Miyagi, 980-8578, Japan.
authors: Masakado
authors: M
authors: Kawata
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D000818:Animals; D049628:Body Size; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D007564:Japan; D063191:Odonata / Q000235:genetics*; D014921:Wings, Animal
keywords: adaptation; damselfly; distribution range; genetic diversity; migration load; range margin