Dichromatic vision in a fruit bat with diurnal proclivities: the Samoan flying fox (Pteropus samoensis)
A nocturnal bottleneck during mammalian evolution left a majority of species with two cone opsins, or dichromatic color vision. Primate trichromatic vision arose from the duplication and divergence of an X-linked opsin gene, and is long attributed to tandem shifts from nocturnality to diurnality and from insectivory to frugivory. Opsin gene variation and at least one duplication event exist in the order Chiroptera, suggesting that trichromatic vision could evolve under favorable ecological conditions. The natural history of the Samoan flying fox (Pteropus samoensis) meets these conditions—it is a large bat that consumes nectar and fruit and demonstrates strong diurnal proclivities. It also possesses a visual system that is strikingly similar to that of primates. To explore the potential for opsin gene duplication and divergence in this species, we sequenced the opsin genes of 11 individuals (19 X-chromosomes) from three South Pacific islands. Our results indicate the uniform presence of two opsins with predicted peak sensitivities of ca. 360 and 553 nm. This result fails to support a causal link between diurnal frugivory and trichromatic vision, although it remains plausible that the diurnal activities of P. samoensis have insufficient antiquity to favor opsin gene renovation.
KeywordsChiroptera Megachiroptera Pteropodidae Euarchontoglires Primate evolution
We acknowledge with gratitude the contributions of V. A. Brown, S. Kawamura, G. L. Moritz, N. P. Giannini, K. Kries, A. Miles, A. L. Russell, R. C. B. Utzurrum and M. Watsa. Funding was received from the Natural Sciences and Engineering Research Council of Canada (Postdoctoral Fellowship to ADM), the National Institutes of Health (Ruth L. Kirschstein National Research Service Award no. F32 GM064287 to NJD), and the David and Lucile Packard Foundation (Fellowship in Science and Engineering no. 2007-31754 to NJD). These procedures were approved by the Institutional Animal Care and Use Committee of the University of Tennessee, Knoxville (protocol no. 890).
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