Department of Anthropology, Dartmouth College, Hanover, NH 03755, USA.
Proc Biol Sci. 2013 Mar 27;280(1759):20130189. doi: 10.1098/rspb.2013.0189. Print 2013 May 22.
Tarsiers are small nocturnal primates with a long history of fuelling debate on the origin and evolution of anthropoid primates. Recently, the discovery of M and L opsin genes in two sister species, Tarsius bancanus (Bornean tarsier) and Tarsius syrichta (Philippine tarsier), respectively, was interpreted as evidence of an ancestral long-to-middle (L/M) opsin polymorphism, which, in turn, suggested a diurnal or cathemeral (arrhythmic) activity pattern. This view is compatible with the hypothesis that stem tarsiers were diurnal; however, a reversion to nocturnality during the Middle Eocene, as evidenced by hyper-enlarged orbits, predates the divergence of T. bancanus and T. syrichta in the Late Miocene. Taken together, these findings suggest that some nocturnal tarsiers possessed high-acuity trichromatic vision, a concept that challenges prevailing views on the adaptive origins of the anthropoid visual system. It is, therefore, important to explore the plausibility and antiquity of trichromatic vision in the genus Tarsius. Here, we show that Sulawesi tarsiers (Tarsius tarsier), a phylogenetic out-group of Philippine and Bornean tarsiers, have an L opsin gene that is more similar to the L opsin gene of T. syrichta than to the M opsin gene of T. bancanus in non-synonymous nucleotide sequence. This result suggests that an L/M opsin polymorphism is the ancestral character state of crown tarsiers and raises the possibility that many hallmarks of the anthropoid visual system evolved under dim (mesopic) light conditions. This interpretation challenges the persistent nocturnal-diurnal dichotomy that has long informed debate on the origin of anthropoid primates.
眼镜猴是一种小型的夜行性灵长类动物，长期以来一直是关于类人猿灵长类动物起源和进化的争论焦点。最近，在两个姐妹种，即婆罗洲眼镜猴（Bornean tarsier）和菲律宾眼镜猴（Philippine tarsier）中，分别发现了 M 和 L 视蛋白基因，这被解释为存在祖先长到中（L/M）视蛋白多态性的证据，而这反过来又表明存在昼间或昼夜节律（不规则）的活动模式。这种观点与树栖眼镜猴是昼行性的假说相符；然而，中始新世时期眼眶的过度增大表明，在晚中新世时期婆罗洲眼镜猴和菲律宾眼镜猴分化之前，就已经发生了向夜行性的返祖现象。综上所述，这些发现表明，一些夜行性眼镜猴拥有高灵敏度的三色视觉，这一概念挑战了关于类人猿视觉系统适应性起源的主流观点。因此，探索三色视觉在眼镜猴属中的可能性和古老性非常重要。在这里，我们表明，苏拉威西眼镜猴（Tarsius tarsier），即菲律宾眼镜猴和婆罗洲眼镜猴的系统发育外群，具有一种 L 视蛋白基因，其与菲律宾眼镜猴的 L 视蛋白基因的非同义核苷酸序列更为相似，而与婆罗洲眼镜猴的 M 视蛋白基因的非同义核苷酸序列相比则不那么相似。这一结果表明，L/M 视蛋白多态性是冠眼镜猴的祖先特征状态，并提出了这样一种可能性，即许多类人猿视觉系统的特征是在暗淡（中间光）光照条件下进化而来的。这种解释挑战了长期以来一直影响关于类人猿起源的争论的持久的昼夜二分法。
