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

低温是限制许多生物地理分布的致命屏障；本研究将阐明抗冻性的演变及其意义。冻害耐受性的基因将从一种沼泽蜗牛（Melampus bidentatus）中分离出来，这种蜗牛发现于其属非典型的冰冻地区。将通过比较来自抗冻物种及其热带亲缘物种的这些基因的DNA序列，对北方物种的抗冻性进行自然选择试验。我们还将测量和比较耐冻和不耐冻物种冬季种群中耐冻基因的表达，以确定基因表达模式是否对低温生存有重要影响。总的来说，这些结果将测试耐寒性进化在允许范围从热带地区扩展到温带地区的重要性。一个多世纪以来，物种多样性的热带最大值已经被认识到，而避免冻结能力的罕见进化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极地范围扩张之间的相关性。这项研究将确定一个关键的生态特征——耐寒性的遗传和分子基础，并将更好地理解是什么决定了一个物种的范围。这项工作将测试一个假设的关键机制，该机制是主要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.