Dissertation Research: The Evolution of Freeze Tolerance in a Historically Tropical Snail.

冰冻温度是一个致命的障碍，限制了许多生物的地理分布;这项研究将阐明抗冻性的进化和意义。 耐冻基因将从沼泽蜗牛（Melampus bidentatus）中分离出来，这种蜗牛在其属的非典型冰冻地区被发现。 将通过比较来自耐冻物种及其热带亲缘物种的这些基因的DNA序列，对北方物种的耐冻性进行自然选择试验。 还将测量耐冻基因的表达，并在耐冻和不耐冻物种的冬季种群之间进行比较，以确定基因表达模式是否对冷冻温度下的生存有重要贡献。 总的来说，这些结果将测试抗冻性进化的重要性，允许从热带到温带地区的范围扩展。 一个多世纪以来，人们一直认为热带地区的物种多样性达到了最大值，而避免冰冻的能力进化的罕见性可能是这种模式的基础。这项研究将直接测试耐寒性的进化与向极扩展的范围之间的相关性。这项研究将确定一个关键的生态特性，耐冻性的遗传和分子基础，并将导致更好地了解是什么决定了一个物种的范围。这项工作将测试一个关键的机制，假设是一个主要的全球多样性模式的基础，并将提供一个物种的详细案例研究？对全球气候变化的进化反应。

Freezing temperatures present a lethal barrier that limits the geographic distribution of many organisms; this research will illuminate the evolution and significance of freeze tolerance. The genes underlying freeze-tolerance will be isolated from a marsh snail (Melampus bidentatus) found in freezing regions atypical for its genus. Tests for natural selection for freeze tolerance in northern species will be made through comparison of DNA sequences of these genes from freeze-tolerant species and their tropical relatives. Expression of freeze-tolerance genes also will be measured and compared among winter populations of freeze-tolerant and non-tolerant species to determine if the pattern of gene expression contributes importantly to survival of freezing temperatures. Collectively, the results will test for the importance of evolution of freeze-tolerance in allowing range expansion from tropical to temperate regions. A tropical maximum in species diversity has been recognized for over a century, and the rarity of evolution of the ability to avoid freezing may underlie the pattern. This research will directly test for correlation between the evolution of freeze tolerance and a poleward range expansion. The research will identify the genetic and molecular basis of a key ecological trait, freeze tolerance, and will lead to a better understanding of what determines the range of a species. The work will test a key mechanism hypothesized to underlie a major global diversity pattern and will provide a detailed case study of one species? evolutionary responses to global climatic change.