DISSERTATION RESEARCH: Genomic basis of convergent phenotypic evolution in island populations of boa constrictors

岛屿往往包含独特的生态系统和生物体。动物生命树上的许多物种在岛屿上进化出了矮小的身体尺寸，其中一些物种，包括这项研究的重点物种蟒蛇，已经在多个独立的岛屿上多次进化出侏儒症。正常的大型大陆蟒蛇和它们近缘的矮小岛屿近亲之间的巨大差异表明，蟒蛇基因组中相对较少的遗传变异可能是岛矮症的基础，因此这一系统可能为脊椎动物的身体大小遗传学提供新的见解。该项目还利用蟒蛇矮小种群的复制进化来研究侏儒症的重复进化是否是由共享或独特的基因或跨多个独立进化的矮岛种群的功能途径驱动的。因此，这项工作将解决进化生物学中的基本问题，包括自然种群局部适应的遗传基础，以及检验进化收敛的遗传和形态基础之间的联系。进化驱动表型性状收敛进化的能力为选择和适应提供了一些最有力和最明确的证据。最近的工作特别感兴趣的是，遗传进化的渠化路径是否构成了收敛的表型进化的基础，或者相反，特殊和/或多样化的遗传路径和过程是否导致了收敛的表型解决方案。这项工作将首先利用全基因组单核苷酸多态性来描绘蟒蛇岛屿种群和大陆种群的种群结构和系统发育关系。这些相同的标记也将被用来寻找基因组中被认为处于选择之下的区域，以及在岛屿和大陆种群之间最具变异性的区域，这些区域代表着最有希望识别与体型矮小有关的基因的区域。从独立岛屿血统收集的数据将被用来测试身体大小的表型趋同是分子水平上的基因型趋同还是功能趋同的产物。因此，这项工作将回答关于适应的遗传学和关于收敛进化的分子基础的问题。

Islands often contain unique ecosystems and organisms. Numerous species across the animal tree-of-life have evolved a dwarfed body size on islands, and some, including Boa constrictor, the focal species for this work, have evolved dwarfism multiple times on multiple independent islands. The drastic variation between normal, large-sized mainland boas and their closely-related dwarfed island relatives suggests that a relatively small number of genetic variants in the B. constrictor genome may underlie island dwarfism, and that this system may therefore provide new insight into the genetics of body size in vertebrates. This project also leverages the replicated evolution of dwarf populations of Boa constrictor to investigate if repeated evolution of dwarfism is driven by shared or unique genes or functional pathways across multiple independently evolved dwarf island populations. This work will therefore address fundamental topics in evolutionary biology, including the genetic basis of local adaptation in natural populations and test for connections between the genetic and morphological basis for evolutionary convergence.The ability of evolution to drive the convergent evolution of phenotypic traits provides some of the strongest and clearest evidence for selection and adaptation. More recent work has become particularly interested in whether canalized paths of genetic evolution underlie convergent phenotypic evolution, or whether instead idiosyncratic and/or diverse genetic paths and processes lead to convergent phenotypic solutions. This work will use genome-wide single nucleotide polymorphisms to first delineate the population structure and phylogenetic relationships among island and mainland populations of Boa constrictor. These same markers will also be used to find regions of the genome that are putatively under selection and that are most variable between island and mainland populations, which represent the most promising regions in which to identify genes underlying body size dwarfism. Data collected from independent island lineages will be used to test whether phenotypic convergence in body size is the product of genotypic or functional convergence at the molecular level. This work will therefore answer questions about the genetics of adaptation and about the molecular basis of convergent evolution.