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

虽然自然选择是一种特征鲜明的进化力量，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的过程中。在经历地理范围迅速扩张的物种中，假设那些具有增强扩散能力的表型性状的个体将代表扩张的前沿，并将与具有相似性状的个体交配。从理论上讲，这种选择性交配应该会导致与增强扩散能力相关的性状的进化。这个项目将在两种关系密切的蝾螈中检验这种“空间分类假说”。这两种蝾螈物种的扩散能力有限，在末次冰期最大期仅限于南部的避难所范围，在过去的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、环境和形态学数据，以测量扩张速率，确定扩张是否正在进行，并确定由于空间排序而进化的特征。更广泛地说，加强对气候变暖引起的范围演变的理解，将对温带物种的保护产生重要影响。这个项目的重点是一个理想的系统来测试空间排序假设。空间排序预计会发生在突然的范围扩张，当快速分散的个人在一个不断扩大的物种的边缘空间隔离，从而复制与类似的个人。一旦范围扩张达到其极限（由环境条件或可用栖息地设定），产生空间排序表型的重复交配将停止，随机交配将在整个种群中恢复。因此，空间排序的文件需要一个系统，在该系统中，与扩散相关的表型可以量化，并且扩展尚未达到其极限。拟议的工作将量化这样的表型在一个系统中，人口扩张正在进行中，扩散率低。研究人员收集的初步遗传数据表明，这两个焦点物种在末次冰期最大期结束时仅限于一个避难所种群，物种分布模型（SDM）表明这个避难所位于俄勒冈州南部。研究人员将进行额外的研究，以确定任何合适的栖息地是无人居住，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性状，并通过标记重捕获方法测量直接扩散，最终量化证据以支持或反驳空间分类假说。

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.