The genetic and developmental basis of a novel pigment pattern in cichlid fishes

自然界中存在着种类繁多的物种。它们在许多属性(特征)上有所不同，如形状、大小、颜色、栖息地和行为。生物学的一个核心问题一直是：究竟是什么机制推动了物种之间的这种差异？对这种变化很重要的遗传单位(基因)是什么？在早期胚胎事件中有什么不同，使得物种如此之多。最大的限制是，即使是关系最密切的物种，通常也仍然是遥远的亲缘关系，即使不是数百万年的进化，也是数十万年的相隔。因此，物种之间的密切比较可能是困难的。一组鱼类物种--慈鱼--为这项研究提供了一个独特的机会。它们主要生活在三个非洲湖泊(马拉维、维多利亚和坦噶尼喀湖)，每个湖泊中都有数千种非常接近的物种，在形状、大小、颜色、栖息地和行为上表现出巨大的多样性。这为观察非常接近的物种之间的形态进化提供了一个独特的机会。在这个项目中，我们将专注于一种特殊的色素沉积特征--数百种慈鱼的肛鳍上出现的五颜六色的斑点。之所以这样选择，是因为它们起源于一组被称为色素细胞的细胞。这些细胞起源于早期发育，然后经历变化并迁移到成年鱼的肛鳍，形成不同物种中存在的卵斑图案。因此，我们的目标是将胚胎发育的变化导致不同鱼种的色素差异联系起来。我们将通过几种方法来实现这一点：1)我们将比较不同属性物种的卵斑发育，以寻找与卵斑形态差异的相关性；2)我们将具有不同卵斑的密切相关鱼类进行杂交，然后寻找与属性变化相关的基因；3)我们将测试基因与野生鱼类种群中不同卵斑的相关性；4)我们将观察基因(基因表达)在早期发育中的作用，以确定哪些基因对这种特征的发展是重要的；5)最后，我们将删除或添加鱼类基因组中任何感兴趣的基因，以测试它们是否确实在卵斑形成中起作用。在项目结束时，我们希望确定这一重要特征的物种之间的差异是如何产生的。由于在所有脊椎动物中都发现了色素细胞，我们的结果将对该小组产生更大的影响，并将使我们走上更好地理解脊椎动物进化和多样性背后的机制的道路。

In nature there is a huge diversity of species present. They vary in many attributes (traits), such as shape, size, colour, habitat, and behaviour. A central question of biology has always been: exactly what are the mechanisms that drive this variation between species? What are the units of inheritance (genes) that are important for this change? And what are the differences in early embryonic events that make this immense variety of species. The biggest limitation is that even the most closely related species are often still distantly related and separated by hundreds of thousands, if not millions, of years of evolution. Therefore close comparison between species can be difficult. One group of fish species, the cichlids, provide a unique opportunity to allow this study to happen. They mainly live in three African lakes (Malawi, Victoria and Tanganyika) and in each lake there are several thousands of very closely related species that show a huge range of diversity in shape, size, colour, habitat and behaviour. This provides a unique opportunity for looking at the evolution of morphologies between very closely related species. In this project we will focus on a specific pigmentation character - the colourful spots that are present in the anal fins of hundreds of cichlid species. The reason for this choice is that they originate from a group of cells called the pigment cells. These cells originate in early develop and then undergo change and migrate to the anal fin of the adult fish to form the egg-spot pattern present in the different species. Thus we are aiming to link what changes in embryonic development result in differences in pigmentation in the different fish species.We will do this in a number of ways: 1) We will compare development of egg-spots between species with different attributes to look for correlation with differences in egg-spot morphology; 2) We will make crosses between closely related fish species that have different egg-spots, and then look for genes that correlate with changes in attributes; 3) We will test for correlations between genes and different egg-spots in wild fish populations; 4) We will look at the action of genes (gene expression) during early development to identify which are important for the development of this trait; 5) Finally, we will remove or add any genes of interest in the fish genomes to test if they do in fact have a role in egg-spot formation.At the end of the project we hope to have identified how the variation between species in this important trait is generated. Since pigment cells are found in all vertebrates, our results will have larger implications for the group and will set us on the path towards a greater understanding of the mechanisms underlying vertebrate evolution and diversity.