Drivers and constraints of rapid adaptive diversification in Lake Poso ricefishes, an emerging model species flock

进化辐射，也就是一个分支中物种多样性的增加，已经产生了大部分生物多样性。然而，影响辐射的过程仍然是一个活跃的研究和有争议的讨论领域。栖息地岛屿特有的物种群体可以研究适应性分化的基因组背景，包括网状进化过程。相关谱系的杂交可以增加遗传和表型变异，这反过来又可以促进种群对不同选择的反应的分化。在这里，我们在一个与主要脊椎动物模式生物之一青蒿虫密切相关的单一小系统中测试生态机会和杂交在适应性多样化中的作用的假说。我们测试生态物种形成是否可以解释POSSO Oryzias湖的多样性，并假设与同域但关系不密切的稻鱼血统的竞争限制了适应的光谱。我们进一步测试了湖泊鱼类与溪流种群的杂交是否影响了湖泊鱼类的进化，并与生态机会相互作用。这些数据还表明，它们的栖息地生态位是对同域稻鱼世系的补充。我们将通过实施基于ROV的样带方法进一步扩展这些观测数据，以详细描述栖息地的使用情况--基于合理的样本大小，并涵盖深海和近海栖息地。此外，田野调查还揭示了一个潜在的杂交种群，这可能解释了基因组导入的信号。初步的RADseq数据区分了这三个湖泊物种，并表明潜在的杂交鱼类与其中两个湖泊物种有关。拟议的扩展采样和测序方法涵盖了湖边栖息地的潜在亲本种群，将使杂交假说能够得到适当的测试，这得益于稻群与模式生物青冈的密切关系。

Evolutionary radiations, that is the increase of species diversity in a clade, have given rise to the bulk of biodiversity. Yet the processes shaping radiations remain an area of active research and controversial discussion. Species flocks endemic to habitat islands allow studying the genomic background of adaptive divergence, including processes of reticulate evolution. Ecological opportunity is considered as the main driver of “adaptive radiation”, but appears insufficient to explain why lineages differ in their ability to adapt and diversify. Hybridization of related lineages can increase genetic and phenotypic variation, which in turn can facilitate population divergence in response to divergent selection. Here, we test hypotheses on the roles of ecological opportunity and hybridization in adaptive diversification in a single, small system closely related to one of the major vertebrate model organisms, the medaka (Oryzias latipes). The monophyletic species flock of three Oryzias ricefish species is endemic to ancient Lake Poso in Sulawesi, Indonesia. We test if ecological speciation can explain divergence of Lake Poso Oryzias, and hypothesize that competition with a sympatric but not closely related ricefish lineage constrained the spectrum of adaptation. We further test if hybridization of the lake fishes with stream populations affected lake fish evolution in interplay with ecological opportunity. Pilot data collected in the field suggest that the three Oryzias show largely distinct ecological niches, matching differences in their morphology, and in functional traits of trophic relevance. The data also suggest that their habitat niches are complementary to the sympatric ricefish lineage. We will further extend these observation data by implementing ROV-based transect methods, in order to characterize habitat use in in detail – based on sound sample sizes, and covering deep and offshore habitats. Fieldwork moreover revealed a potential hybrid population, which might account for signals of genomic introgression. Preliminary RADseq data distinguish the three lake species, and suggest relatedness of the potential hybrid fish with two of the lake species. The extended sampling and sequencing approach proposed, covering potential parental populations from habitats close by the lake, will enable appropriate testing of the hybridization hypothesis benefitting from the close relatedness of the Oryzias flock to the model organism medaka. The complementary in-depth approaches will deliver a comprehensive understanding of the evolutionary history, and the drivers of adaptive divergence in the small Lake Poso Oryzias species flock.