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Zoological Science
Abstract
The occurrence of black fur, or melanism, in many mammalian species is known to be linked to DNA sequence variation in the agouti signaling protein (Asip) gene, which is a major determinant of eumelanin and pheomelanin pigments in coat color. We investigated 38 agouti (i.e., banded wildtype) and four melanistic Rattus rattus species complex (RrC) lineage II specimens from Okinawa Island, Ryukyu Islands, Japan, for genetic variation in three exons and associated flanking regions in the Asip gene. On Okinawa, a predicted loss-of-function mutation caused by a cysteine to serine amino acid change at p.124C>S (c.370T>A) in the highly conserved functional domain of Asip was found in melanistic rats, but was absent in agouti specimens, suggesting that the p.124C>S mutation is responsible for the observed melanism. Phylogeographic analysis found that Asip sequences from Okinawan RrC lineage II, including both agouti and melanistic specimens, differed from: 1) both agouti and melanistic RrC lineage I from Otaru, Hokkaido, Japan, and 2) agouti RrC lineages I and II from South Australia. This suggests the possibility of in-situ mutation of the Asip gene, either within the RrC lineage II population on Okinawa or in an unsampled RrC lineage II population with biogeographic links to Okinawa, although incomplete lineage sorting could not be ruled out.
We would like to thank deeply Stephen Donnellan, Hidetoshi Ikeda, Gohta Kinoshita and Kimiyuki Tsuchiya in collecting the animals and for providing valuable comments on an earlier manuscript in this study. This study was conducted as part of grants-in-aid for Scientific Research (C) to HS (no. 15K07177) supported by the Japan Society for the Promotion of Science (JSPS). We would like to thank Heiwa Nakajima Foundation for its generous support.
The authors have no competing interests to declare.
SS, ASW, VAT, MK and HS participated in the experimental design. SS, MK and HS carried out all experimental work and computational analyses. SS wrote the first draft of the manuscript. ASW, VAT and HS committed to complete the final version of manuscript. All authors contributed to the final version of the manuscript.
Supplementary material for this article is available online (URL: http://www.bioone.org/doi/suppl/10.2108/zs170027).
Supplementary Table 1. Rattus rattus species complex (RrC) lineage I and II samples used in this study.
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