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

冰冻温度是一道致命的屏障，限制了许多生物的地理分布；这项研究将阐明耐寒的进化和意义。耐冻性基因将从一种沼泽蜗牛(Melampus Bientatus)中分离出来，这种蜗牛是在冰冻地区发现的，这在其属中是非典型的。将通过比较耐冻物种及其热带近亲的这些基因的DNA序列，对北方物种的耐冻性进行自然选择测试。耐寒基因的表达也将在耐寒和不耐冻物种的冬季种群中进行测量和比较，以确定基因表达模式是否对冰冻温度的生存有重要影响。总的来说，这些结果将检验耐寒性进化在允许范围从热带地区扩大到温带地区方面的重要性。一个多世纪以来，人们已经认识到热带物种多样性的最大值，而避免冰冻的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演变与极地范围扩大之间的相关性。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，并将导致更好地理解是什么决定了物种的生存范围。这项工作将测试一种关键的机制，该机制被假设为构成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.