DISSERTATION RESEARCH: Spatial sorting and Postglacial population dynamics in Plethodon dunni and P. vehiculum.

虽然自然选择是一种具有良好特征的进化力量，但它可能不是进化变化的唯一机制--特别是在某些种群发生快速进化适应期间。在经历地理范围迅速扩大的物种中，假设那些具有增强扩散能力的表型特征的个体将代表扩张的前沿，并将与拥有相似特征的个体交配。从理论上讲，这种分类交配应该会导致与增强扩散能力相关的特征的进化。这个项目将在两种关系密切的火蜥蜴身上测试这种“空间分类假说”。这两个物种的扩散能力有限，在上一次冰川盛峰期仅限于南部避难区，在过去20,000年里一直以不同的速度向北部扩张。研究人员将收集遗传、环境和形态数据，使他们能够测量扩张速度，确定扩张是否正在进行，并识别由于空间排序而进化的特征。更广泛地说，加强对应对气候变暖的山脉演化的理解，将对保护温带物种具有重要意义。本项目致力于一个检验空间排序假说的理想系统。空间排序预计将在范围突然扩大期间发生，即在扩展物种边缘的快速分散的个体在空间上被隔离，从而与相似的个体繁殖。一旦范围扩展达到其极限(由环境条件或可用栖息地设定)，产生空间排序表型的分类交配将停止，随机交配将在整个种群中返回。因此，记录空间分选需要一个系统，在这个系统中，与扩散相关的表型可以被量化，并且扩展还没有达到其极限。这项拟议的工作将在一个人口持续扩张和分散率较低的系统中量化这些表型。研究人员收集的初步遗传数据表明，在最后一次冰盛期结束时，这两个重点物种被限制在一个单一的避难种群中，物种分布模拟(SDM)表明，这个避难所位于俄勒冈州南部。研究人员将进行进一步的研究，以确定任何合适的无人居住的栖息地，并完善冰川避难所和扩张路线的位置。研究人员将测量与扩散能力相关的表型特征，并通过标记-重新捕获方法测量直接扩散，最终量化证据以支持或驳斥空间排序假说。

While natural selection is a well-characterized evolutionary force, it may not be the only mechanism for evolutionary change -- particularly during rapid evolutionary adaptations occurring in some populations. In species that experience rapid expansion of their geographic range, it is hypothesized that those individuals with phenotypic traits that enhance dispersal ability will represent the leading edge of the expansion, and will mate with individuals that possess similar traits. In theory, this assortative mating should lead to the evolution of traits associated with enhanced dispersal ability. This project will test this "spatial sorting hypothesis" in two closely related species of salamanders. These two salamander species have limited dispersal abilities, were restricted to southern refugial ranges during the last glacial maximum, and have been expanding to the north at different rates for the last 20,000 years. The researchers will collect genetic, environmental, and morphological data that will allow them to measure rates of expansion, determine if expansion is ongoing, and identify the traits that are evolving due to spatial sorting. More broadly, an enhanced understanding of range evolution in response to a warming climate will have important implications for the conservation of temperate species. This project focuses on an ideal system for testing the spatial sorting hypothesis. Spatial sorting is expected to occur during sudden range expansions, when fast-dispersing individuals at the margins of an expanding species are spatially segregated, and thus reproduce with similar individuals. Once the range expansion reaches its limits (set by environmental conditions or available habitat), the assortative mating that produced spatially-sorted phenotypes will cease, and random mating will return throughout the population. Documentation of spatial sorting thus requires a system where phenotypes associated with dispersal can be quantified and where expansion has not reached its limit. The proposed work will quantify such phenotypes in a system where population expansion is ongoing and dispersal rates are low. Preliminary genetic data collected by the researchers indicate that the two focal species were confined to a single refugial population at the close of the last glacial maximum and species distribution modeling (SDM) suggests that this refuge was located in southern Oregon. The researchers will conduct additional research to identify any suitable habitat that is unoccupied and to refine the location of glacial refugia and expansion routes. The researchers will measure phenotypic traits associated with dispersal ability and measure direct dispersal via mark-recapture methods, ultimately quantifying evidence to support or refute the spatial sorting hypothesis.