Drivers and dynamics of sex chromosome evolution in African cichlid fishes

性别决定的机制是多样的，尽管它们在定义物种内的男性和女性方面具有统一的功能。它们的范围从不同遗传性别决定系统上的一系列环境因素到外部和内部因素的复杂相互作用。这些机制在某些生物群体中是超级保守的(例如，所有哺乳动物都共享相同的性染色体系统)，然而，在其他群体中，即使是姐妹物种，性别决定的方式也不同。这个项目的重点是探索遗传性别决定，或者--换句话说--在进化生物学的模式系统--非洲池鱼--中调查性染色体。在坦噶尼喀湖这些鱼的辐射中，我之前发现了一个非常高的性染色体周转率，即用作性染色体的实际染色体的变化。这个项目将从三个新的角度研究性染色体的进化。第一个目标更深入非洲慈鱼的性染色体历史，目的是包括非洲所有主要血统的代表。在这个泛非洲数据集中识别性染色体，可以研究性染色体进化的速度和模式是否随着叶蝉科系统发育的不同而变化。这将回答如果快速的性染色体进化被限制在辐射的湖泊血统或池鱼的一般特征。第二个项目部分放大到特定物种的坦噶尼喀湖，在那里我之前识别了性染色体。这里的一个焦点是染色体，它在不同谱系的代表中反复进化为性染色体，目的是弄清相同基因的变化是否驱使性染色体进化趋同。在这个项目中，我们还将比较基因组序列，并在具有不同性别染色体系统的物种之间进行杂交，以确定性染色体之间转换的基因组特征。第三个项目项目调查与性染色体存在对应的性可塑性程度。在坦噶尼喀湖慈鱼辐射的一个特定谱系，即所谓的埃托迪尼，我们惊讶地发现，只有少数物种有性染色体。我们怀疑这些鱼的性可塑性水平增加：观察到没有性染色体的物种会将性别从雌性转变为雄性。该项目研究在相同条件下饲养的没有性染色体的物种是否比有性染色体的物种更容易变性。为了了解性别变化是如何在分子水平上实现的，我们将比较变性物种和非变性物种的基因表达以及激活和沉默基因表达的调控信号。

The mechanisms of sex determination are diverse despite their unifying function in defining male and female sex within a species. They range from an array of environmental factors over different genetic sex determination systems to a complex interplay of extrinsic and intrinsic factors. These mechanisms are ultra-conserved in some organismal groups (e.g. all mammals share the same sex chromosomal system), however, in other groups even sister species vary in their way how sex is determined. This project focuses on the exploration of genetic sex determination or -in other words- the investigation of sex chromosomes in a model system of evolutionary biology, the African cichlid fishes. Within the Lake Tanganyika radiation of these fishes, I previously identified an outstandingly high rate of sex chromosome turnover, i.e. change in the actual chromosome used as sex chromosome. This project will investigate sex chromosome evolution from three new perspectives. The first objective submerges deeper into the sex chromosome history of African cichlids with the aim to include representatives of all major African lineages. Identification of sex chromosomes in this pan-african dataset allows investigating if the speed and pattern of sex chromosome evolution varies along the cichlid phylogeny. This will answer if rapid sex chromosome evolution is restricted to radiating lake lineages or a general feature of cichlids.The second project part zooms into particular species of Lake Tanganyika in which I previously identified sex chromosomes. One focus is here on chromosomes, which repeatedly evolved as sex chromosomes in representatives of distinct lineages with the aim to disentangle if changes in the same genes drove sex chromosome evolution convergently. Within this project line, we will also compare genomic sequences and perform crosses between species that have different sex chromosomal systems to identify genomic signatures underlying transitions between sex chromosomes.The third project line investigates the degree of sexual plasticity in correspondence to the presence of sex chromosomes. Within a particular lineage of the Lake Tanganyika cichlid radiation, the so-called Ectodini, we were surprised to see that only a handful of species has sex chromosomes. We suspect that these fish have an increased level of sexual plasticity: Species that do not have sex chromosomes were observed to change sex from female to male. This project line investigates if when raised under the same conditions, species without sex chromosomes change sex more easily than species with sex chromosomes. To understand how sex change is achieved at the molecular level, we will compare gene expression as well as the regulatory signatures activating and silencing gene expression between males and females of species that change sex to those that do not.