Life in transition: the evolutionary consequences of ecological and habitat shifts

栖息地和生活方式特征的重大转变在生命史上占有重要地位，并塑造了地球上生物多样性的分布。有些种类的过渡已经独立地发生了无数次，例如在海洋和淡水之间，在捕食性和草食性摄食模式之间。以重复的、进化上独立的事件为代表的这种转变提供了宝贵的机会--即自然实验--来研究进化反应的可预测性。我的首要研究目标是阐明反复转变的进化原因和后果。 首先，我和我的学生将评估转变对分子进化速率随时间变化的影响程度，重点是昆虫和水生无脊椎动物。我们将量化分子进化速率的变异性，并测试分子进化速率是否与进化中的关键栖息地(例如海洋/淡水、底栖/浮游、陆地/水生)和生活方式(例如食肉/草食、共生/独居、寄生/自由生活)相关的系统变化。这项工作将代表着分子速率研究向前迈出了实质性的一步，通过对整个系统发育树上的速率变化进行建模，并同时在多变量背景下调查多种因素的强度。 其次，我们将研究与多种类型的水生栖息地转变相关的分子进化，每种类型代表着低灭绝与高灭绝环境之间的差异：古代湖泊与周围淡水、流动水域与死水、湖泊与池塘。使用不同栖息地占有率的系统发育配对姐妹谱系，这些不同的栖息地制度将被调查它们与提高的分子多样性、种群遗传结构、分子进化速度和遗传凝聚力的程度(与分散的分组相比)的潜在关联性。这项工作的结果将有助于理解栖息地转变对水生生物分子进化的影响。此外，通过明确研究灭绝对产生离散遗传分组的重要性这一假设，这项工作也将有助于解决为什么如此多的分类群表现出“条形码缺口”的谜题，这是在种内和种间成对DNA序列分歧之间经常观察到的脱节现象。 这些研究的结果将揭示这些转变是否会引发一般的分子进化反应。此外，了解系统的速率变异性对于所有依赖分子时钟为生命提供时间刻度的人至关重要，包括研究人员使用历史重建来研究宏观进化、生物地理和气候变化的影响。

Major transitions in habitat and lifestyle traits have featured prominently in the history of life and have shaped the distribution of biodiversity on Earth. Some kinds of transitions have occurred numerous times independently, such as between marine and fresh waters and between predatory and herbivorous feeding modes. Such transitions that are represented by repeated, evolutionarily independent events provide valuable opportunities -- i.e. natural experiments -- to study the predictability of evolutionary responses. My overarching research objective is to elucidate the evolutionary causes and consequences of repeated transitions. Firstly, my students and I will assess the degree to which transitions impact rates of molecular evolutionary change through time, with a focus upon insects and aquatic invertebrates. We will quantify variability in rates of molecular evolution and test whether rates vary systematically in association with key habitat (e.g. marine/freshwater, benthic/planktonic, terrestrial/aquatic) and lifestyle (e.g. carnivorous/herbivorous, eusocial/solitary, parasitic/free-living) transitions in evolution. This work will represent a substantial step forward in molecular rates research by modeling rate variation across entire phylogenetic trees and by simultaneously investigating the strength of multiple factors in a multivariate context. Secondly, we will study molecular evolution associated with multiple types of aquatic habitat transitions, each representing a difference between a lower-extinction vs. a higher-extinction environment: ancient lakes vs. surrounding freshwaters, flowing vs. standing waters, and lakes vs. ponds. Using phylogenetically paired sister lineages differing in habitat occupancy, these various habitat regimes will be investigated for their potential association with elevated molecular diversity, population genetic structure, molecular evolutionary rate, and extent of genetic cohesion (vs. clustering into discrete groupings). The results of this work will contribute to understanding the impacts of habitat transitions upon molecular evolution within aquatic life. Furthermore, by explicitly investigating the hypothesis that extinction is important for generating discrete genetic groupings, this work also will contribute towards resolving a puzzle as to why so many taxa exhibit a "barcode gap", which is the disjunction often observed between intraspecific vs. interspecific pairwise DNA sequence divergences. The results of these studies will reveal whether these transitions provoke general molecular evolutionary responses. Moreover, understanding systematic rate variability is crucial for all who rely upon the molecular clock to provide a timescale for life, including researchers studying macroevolution, biogeography, and climate change impacts using historical reconstructions.