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Open Access Research article

A geographic cline induced by negative frequency-dependent selection

Yuma Takahashi1*, Satoru Morita2, Jin Yoshimura234 and Mamoru Watanabe1

Author affiliations

1 Division of Ecology and Evolutionary Biology, Graduate School of Life Sciences, Tohoku University, 6-3, Aoba, Aramaki, Aoba, Sendai, Miyagi 980-8578, Japan

2 Department of Systems Engineering, Shizuoka University, Naka, Hamamatsu 432-8561, Japan

3 Department of Environmental and Forest Biology, State University of New York College of Environmental Science and Forestry, Syracuse 13210, New York, USA

4 Marine Biosystems Research Center, Chiba University, Kamogawa, Chiba 299-5502, Japan

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Citation and License

BMC Evolutionary Biology 2011, 11:256  doi:10.1186/1471-2148-11-256

Published: 14 September 2011

Abstract

Background

Establishment of geographic morph frequency clines is difficult to explain in organisms with limited gene flow. Balancing selection, such as negative frequency-dependent selection (NFDS), is instead suggested to establish a morph frequency cline on a geographic scale at least theoretically. Here we tested whether a large-scale smooth cline in morph frequency is established by NFDS in the female-dimorphic damselfly, Ischnura senegalensis, where andromorphs and gynomorphs are maintained by NFDS.

Results

We found a large-scale latitudinal cline in the morph frequency: andromorph frequency ranged from 0.05 (South) to 0.79 (North). Based on the empirical data on the numbers of eggs, the number of ovariole, abdomen length and latitude, the potential fitness of andromorphs was estimated to be lower than that of gynomorphs in the south, and higher in the north, suggesting the gene-by-environment interaction. From the morph-specific latitudinal cline in potential fitness, the frequency of andromorphs was expected to shift from 0 to 1 without NFDS, because a morph with higher potential fitness wins completely and the two morphs will switch at some point. In contrast, NFDS led to the coexistence of two morphs with different potential fitness in a certain geographic range along latitude due to rare morph advantage, and resulted in a smooth geographic cline of morph frequency.

Conclusion

Our results provide suggestive evidence that the combination of NFDS and gene-by-environment interaction, i.e., multi-selection pressure on color morphs, can explain the geographic cline in morph frequency in the current system.