Population genetics and fitness correlates of colour vision in wild sifaka lemurs

虽然我们普遍接受自然选择塑造了生物体的外观和行为，但是，精确地指出DNA序列的变化与解剖学、生理学或行为上的有利变化相对应的情况，仍然是生物学的主要挑战。我们可以确定DNA序列与生理/行为之间的明确联系的罕见案例之一是灵长类动物的颜色视觉系统。灵长类动物是已知唯一拥有完整（三色）视觉的胎盘哺乳动物，这种能力在灵长类动物中的分布特别有趣。除了偶尔的色盲个体，所有的人类、猿类和旧大陆的猴子都有完全的彩色视觉。但在大多数新大陆猴和一些狐猴中，个体的色觉能力是不同的——所有雄性和一些雌性都是红绿色盲（二色），但其他雌性有与人类相似的全彩色视觉。此外，色盲个体在辨别颜色的范围上也会有所不同。这就产生了一个有趣的情况，生活在同一社会群体中的个体看待世界的方式截然不同。但是自然选择是如何维持这种“多态”系统的呢？拥有全彩色视觉的好处有很多：它可以让灵长类动物在绿色森林树叶的背景下找到成熟的红色水果，或者在成熟的、营养不足的绿叶中发现富含蛋白质的嫩叶，这些嫩叶通常是红色的。然而，有推测认为红绿色盲也可能带来优势。对人类的研究表明，色盲的人在发现伪装图案方面往往比那些具有全彩色视觉的人更好。因此，红绿色盲灵长类动物在发现伪装的猎物或捕食者，或寻找不显眼的水果方面可能有优势。这项对野生狐猴的研究将首次系统地研究野生灵长类动物种群的进化适应性（生存和繁殖）与色觉状态之间的联系。这是一项与马达加斯加Beza-Mahafaly特别保护区狐猴野外研究人员的国际合作。自1984年以来，人们一直在研究这个地点的狐獴，所有年龄超过1岁的狐獴都被捕获并取样进行基因分析。这提供了一个特殊的数据集，其中包含了20多年来狐猴个体行为生物学的记录。我们将通过光色素（视蛋白）基因的DNA测序，确定100个人的色觉状态。然后，我们将检查颜色视觉状态是否单独或与社会因素（如群体大小）和生态因素（如栖息地质量）相结合，是适合度的预测因子。具体来说，我们解决三种类型的问题：1。在人群中，色觉类型是如何分布的？群体和/或繁殖对在色觉状态方面是否以非随机方式结合？在人群中，某些光色素变体是否比其他变体更常见？2. 色觉状态能预测一个人的健康吗？拥有全彩色视觉的个体是否比红绿色盲的个体更有可能存活更长时间并拥有更多的后代？这是否也受到社会和/或生态因素的影响？3. 属于一个拥有不同色觉类型的社会群体是否有益？混合色盲群体的个体平均寿命和繁殖成功率是否高于所有色盲群体（与个体色觉状态无关）？通过研究微小的遗传变化如何影响个体适应性，我们将更好地理解自然选择如何驱动和维持自然种群的生物多样性。

Although we generally accept that natural selection has shaped the appearance and behaviour of organisms, pin-pointing cases where a change in DNA sequence corresponds to an advantageous change in anatomy, physiology or behaviour remains a primary challenge for biology. One of the rare cases in which we can identify a clear link between DNA sequences and physiology / behaviour is the colour vision system of primates. Primates are the only placental mammals known to possess full (trichromatic) colour vision, and the distribution of this ability within the primate order is particularly interesting. Excluding the occasional colour-blind individuals, all humans, apes, and Old World monkeys have full colour vision. But in most New World monkeys and some lemurs, colour vision capacities of individuals can differ - all males and some females are red-green colour blind (dichromatic), but other females have full colour vision similar to that of humans. Moreover, colour blind individuals can differ in the range of colours that they discriminate. This creates an interesting situation in that individuals living in the same social group can see the world rather differently. But how does natural selection maintain this 'polymorphic' system? The possible advantages of having full colour vision are numerous: It may allow primates to find ripe reddish fruit against the background of green forest foliage or to spot young protein-rich leaves, which are often reddish, among the mature, less-nutritious, green leaves. However, there is speculation that red-green colour blindness might also confer an advantage. Studies in humans have demonstrated that colour-blind men are often better than those with full colour vision at detecting camouflaged patterns. Thus, red-green colour blind primates may have advantages in detecting camouflaged prey or predators, or in finding inconspicuous fruits. This study of wild Verreaux's sifaka lemurs will be the first to systematically examine links between evolutionary fitness (survival and reproduction) and colour vision status in a population of wild primates. This is an international collaboration with researchers at the sifaka field site at Beza-Mahafaly Special Reserve, Madagascar. The sifakas at this site have been studied since 1984 and all individuals over the age of one have been captured and sampled for genetic analysis. This provides an exceptional dataset with over two decades of records on the behavioural biology of individual sifaka. We will identify, through DNA sequencing of photopigment (opsin) genes, the colour vision status of 100 individuals. We will then examine whether colour vision status, alone or in combination with social factors (e.g. group size) and ecological factors (e.g. habitat quality), is a predictor of fitness. Specifically, we address three types of questions: 1. How are colour vision types distributed across the population? Do groups and/or breeding pairs associate in a non-random way with respect to colour vision status? Across the population, are some photopigment variants more common than others? 2. Does colour vision status predict an individual's fitness? Are individuals with full colour vision likely to survive longer and have more offspring than individuals who are red-green colour blind? Is this also influenced by social and/or ecological factors? 3. Is it beneficial to belong to a social group whose members have a variety of colour vision types? Is average lifespan and reproductive success greater for individuals in groups of mixed composition than for those in all colour blind groups (independent of individual colour vision status)? By examining how small genetic changes can influence individual fitness, we will better understand how natural selection can drive and maintain biodiversity in natural populations.