Department of Biological Sciences, The Class of 1978 Life Sciences Center, Dartmouth College Hanover, NH, USA.
Department of Anthropology, Washington University, St. Louis MO, USA.
Front Integr Neurosci. 2014 Jul 25;8:61. doi: 10.3389/fnint.2014.00061. eCollection 2014.
The fovea is a declivity of the retinal surface associated with maximum visual acuity. Foveae are widespread across vertebrates, but among mammals they are restricted to haplorhine primates (tarsiers, monkeys, apes, and humans), which are primarily diurnal. Thus primates have long contributed to the view that foveae are functional adaptations to diurnality. The foveae of tarsiers, which are nocturnal, are widely interpreted as vestigial traits and therefore evidence of a diurnal ancestry. This enduring premise is central to adaptive hypotheses on the origins of anthropoid primates; however, the question of whether tarsier foveae are functionless anachronisms or nocturnal adaptations remains open. To explore this question, we compared the diets of tarsiers (Tarsius) and scops owls (Otus), taxa united by numerous anatomical homoplasies, including foveate vision. A functional interpretation of these homoplasies predicts dietary convergence. We tested this prediction by analyzing stable isotope ratios that integrate dietary information. In Borneo and the Philippines, the stable carbon isotope compositions of Tarsius and Otus were indistinguishable, whereas the stable nitrogen isotope composition of Otus was marginally higher than that of Tarsius. Our results indicate that species in both genera consumed mainly ground-dwelling prey. Taken together, our findings support a functional interpretation of the many homoplasies shared by tarsiers and scops owls, including a retinal fovea. We suggest that the fovea might function similarly in tarsiers and scops owls by calibrating the auditory localization pathway. The integration of auditory localization and visual fixation during prey detection and acquisition might be critical at low light levels.
中央凹是视网膜表面的一个凹陷，与最大视力有关。中央凹广泛存在于脊椎动物中，但在哺乳动物中，它们仅限于单孔类灵长类动物（眼镜猴、猴子、猿和人类），这些动物主要是昼行性的。因此，灵长类动物长期以来一直认为中央凹是对昼行性的功能适应。虽然眼镜猴是夜行性动物，但它们的中央凹被广泛解释为退化特征，因此是昼行性起源的证据。这一持久的前提是关于类人猿起源的适应性假说的核心；然而，关于眼镜猴的中央凹是否是无功能的遗迹或夜行性适应，这个问题仍然没有答案。为了探索这个问题，我们比较了眼镜猴（Tarsius）和角鸮（Otus）的饮食，这两个物种通过许多解剖学的同形现象联系在一起，包括中央凹视觉。这些同形现象的功能解释预测了饮食的趋同。我们通过分析整合饮食信息的稳定同位素比值来检验这一预测。在婆罗洲和菲律宾，Tarsius 和 Otus 的稳定碳同位素组成无法区分，而 Otus 的稳定氮同位素组成略高于 Tarsius。我们的结果表明，这两个属的物种主要以地面为食。总的来说，我们的研究结果支持了眼镜猴和角鸮之间许多同形现象的功能解释，包括视网膜中央凹。我们认为，中央凹可能通过校准听觉定位途径，在眼镜猴和角鸮中发挥类似的功能。在低光照水平下，听觉定位和视觉固定在猎物探测和获取过程中的整合可能至关重要。
