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显著地位，并塑造了地球上生物多样性的分布。有些类型的转变已经独立地发生了很多次，比如在海洋和淡水之间，在捕食和食草之间。这种由重复的、进化上独立的事件所代表的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重复过渡的进化原因和后果。***首先，我和我的学生将评估过渡对分子进化变化的影响程度，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化，并测试速率是否与主要栖息地（如海洋/淡水、底栖/浮游、陆生/水生）和生活方式（如食肉/食草、真社会/独居、寄生/自由生活）的进化转变有系统的关联。通过模拟整个系统发育树的速率变化，同时研究多因素在多变量背景下的强度，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。***其次，我们将研究与多种水生栖息地转变相关的分子进化，每种类型都代表了低灭绝与高灭绝环境之间的差异：古湖泊与周围淡水，流动与静水，湖泊与池塘。利用系统发育上不同栖息地占用的姐妹谱系，研究这些不同的栖息地制度与分子多样性、种群遗传结构、分子进化速率和遗传内聚程度（相对于聚类成离散类群）的潜在关联。这项工作的结果将有助于理解生境转变对水生生物分子进化的影响。此外，通过明确地研究灭绝对产生离散遗传类群很重要的假设，这项工作也将有助于解决一个难题，即为什么这么多分类群表现出“条形码缺口”，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。这些研究的结果将揭示这些转变是否会引起一般的分子进化反应。此外，理解系统速率变化率对于所有依赖分子钟为生命提供时间尺度的人来说都是至关重要的，包括使用历史重建来研究宏观进化、生物地理学和气候变化影响的研究人员

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.**