Terai Yohey, Miyagi Ryutaro, Aibara Mitsuto, Mizoiri Shinji, Imai Hiroo, Okitsu Takashi, Wada Akimori, Takahashi-Kariyazono Shiho, Sato Akie, Tichy Herbert, Mrosso Hillary D J, Mzighani Semvua I, Okada Norihiro
Department of Evolutionary Studies of Biosystems, SOKENDAI (The Graduate University for Advanced Studies), Shonan Village, Hayama, Kanagawa, 240-0193, Japan.
Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8501, Japan.
BMC Evol Biol. 2017 Aug 22;17(1):200. doi: 10.1186/s12862-017-1040-x.
For Lake Victoria cichlid species inhabiting rocky substrates with differing light regimes, it has been proposed that adaptation of the long-wavelength-sensitive (LWS) opsin gene triggered speciation by sensory drive through color signal divergence. The extensive and continuous sand/mud substrates are also species-rich, and a correlation between male nuptial coloration and the absorption of LWS pigments has been reported. However, the factors driving genetic and functional diversity of LWS pigments in sand/mud habitats are still unresolved.
To address this issue, nucleotide sequences of eight opsin genes were compared in ten Lake Victoria cichlid species collected from sand/mud bottoms. Among eight opsins, the LWS and rod-opsin (RH1) alleles were diversified and one particular allele was dominant or fixed in each species. Natural selection has acted on and fixed LWS alleles in each species. The functions of LWS and RH1 alleles were measured by absorption of reconstituted A1- and A2-derived visual pigments. The absorption of pigments from RH1 alleles most common in deep water were largely shifted toward red, whereas those of LWS alleles were largely shifted toward blue in both A1 and A2 pigments. In both RH1 and LWS pigments, A2-derived pigments were closer to the dominant light in deep water, suggesting the possibility of the adaptation of A2-derived pigments to depth-dependent light regimes.
The RH1 and LWS sequences may be diversified for adaptation of A2-derived pigments to different light environments in sand/mud substrates. Diversification of the LWS alleles may have originally taken place in riverine environments, with a new mutation occurring subsequently in Lake Victoria.
对于栖息在光照条件不同的岩石基质上的维多利亚湖丽鱼科物种，有人提出长波长敏感（LWS）视蛋白基因的适应性变化通过颜色信号差异的感官驱动引发了物种形成。广泛且连续的沙/泥基质区域物种也很丰富，并且已有报道称雄性婚羽颜色与LWS色素的吸收之间存在相关性。然而，驱动沙/泥栖息地中LWS色素的遗传和功能多样性的因素仍未得到解决。
为了解决这个问题，我们比较了从沙/泥底部采集的10种维多利亚湖丽鱼科物种的8个视蛋白基因的核苷酸序列。在这8种视蛋白中，LWS和视杆视蛋白（RH1）等位基因是多样化的，并且每个物种中都有一个特定的等位基因占主导或固定存在。自然选择作用于每个物种中的LWS等位基因并使其固定下来。通过重组A1和A2衍生的视觉色素的吸收来测量LWS和RH1等位基因的功能。深水区域最常见的RH1等位基因的色素吸收大多向红色偏移，而在A1和A2色素中，LWS等位基因的色素吸收大多向蓝色偏移。在RH1和LWS色素中，A2衍生的色素更接近深水中的主导光，这表明A2衍生的色素有可能适应深度依赖的光照条件。
RH1和LWS序列可能因A2衍生的色素适应沙/泥基质中的不同光照环境而多样化。LWS等位基因的多样化可能最初发生在河流环境中，随后在维多利亚湖中出现了新的突变。
