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

进化辐射，即一个分支中物种多样性的增加，产生了大部分生物多样性。然而，形成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允许研究适应性分歧的基因组背景，包括网状进化过程。生态机会被认为是“适应性辐射”的主要驱动力，但似乎不足以解释为什么世系在适应和多样化的能力上存在差异。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群体分化，以响应不同的选择。在这里，我们测试假设的生态机会和杂交的作用，在一个单一的，小系统的适应性多样化密切相关的主要脊椎动物模式生物之一，青（Oryzias latipes）。三种Oryzias稻鱼的单系种群是印度尼西亚苏拉威西岛古波索湖特有的。我们测试，如果生态物种形成可以解释波索湖Oryzias的分歧，并假设竞争与同域但不密切相关的水稻鱼谱系限制了适应谱。我们进一步测试，如果杂交的湖泊鱼类与流种群影响湖泊鱼类的进化与生态机会的相互作用。在现场收集的试点数据表明，这三个Oryzias在很大程度上表现出不同的生态位，匹配的形态差异，营养相关的功能性状。这些数据还表明，它们的栖息地生态位是互补的同域性稻鱼谱系。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，田间工作揭示了一个潜在的杂交群体，这可能占基因组渐渗的信号。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与两个湖泊物种的相关性。提出的扩展采样和测序方法，涵盖潜在的亲本种群从栖息地靠近湖泊，将使适当的测试杂交假说受益于密切相关的Oryzias羊群的模式生物青。互补的深入的方法将提供一个全面的了解的进化历史，并在小湖波索Oryzias物种群的适应性分歧的驱动程序。

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.