The role of physiological variation in delimiting geographical ranges of parapatric cryptic species

一个物种的地理范围是由多种因素决定的，包括扩散、生物相互作用、历史生物地理学和生理学。其中最主要的是温度造成的压力，但实验工作通常只测试温度的生理极限。在这里，我将论证生物体已经适应了一套多维的环境压力，并且这些压力可以以协同的方式影响生理耐受性。为了验证这一点，我建议研究两种部分重叠和高度分散能力的隐种之间的范围差异的生理和基因组基础。Melampus bidentatus nov. sp. N和M. bidentatus nov. sp. S是高潮间带沼泽蜗牛的隐种。总的来说，这两个物种跨越了近25个纬度，在这个纬度上，它们暴露在广泛的环境条件下；这两个物种都通过耐寒性在寒冷的冬天存活下来。有趣的是，它们有部分重叠的范围与不连续的异质区域和不同的北部范围。在它们的活动范围重叠的地方，它们在中等海洋盐度的地方被发现是完全同栖的，但在高盐度和低盐度的地方，它们之间是分开的。先前的耐寒性测试发现，这两个物种在耐寒程度上没有差异，这表明单凭寒冷并不能解释它们的范围差异。我建议采用全基因组比较、生理测试和实地调查相结合的方法来验证低温和海水盐度之间的相互作用可以解释这两个非常相似的物种之间的范围差异。这些结果将对理解环境在限制物种边界方面的作用、近亲之间适应性差异的基因组基础以及预测气候变化下潜在的范围变化具有重要意义。

A species’ geographic range is defined by a variety of factors, including dispersal, biotic interactions, historical biogeography, and physiology. Chief among these are the stresses imposed by temperature, but experimental work often tests the physiological limits of temperature alone. Here, I will argue that organisms have adapted to a multidimensional set of environmental stresses, and that these can impact physiological tolerance in a synergistic fashion. To test this, I propose a study of the physiological and genomic basis of range differences between two cryptic species with partially overlapping ranges and high dispersal abilities.Melampus bidentatus nov. sp. N and M. bidentatus nov. sp. S are cryptic species of high intertidal marsh snails. Collectively, the two species span nearly 25 latitudinal degrees, over which they are exposed to a wide range of environmental conditions; both species survive cold winters via freeze tolerance. Interestingly, they have partially overlapping ranges with discontinuous regions of allopatry and different northern range limits. Where their ranges overlap, they are found in complete sympatry at locales with intermediate ocean salinity, but at high- and low- salinity locales are segregated between the species. Previous tests of cold tolerance have found no difference in the degree to which both species are freeze tolerant, suggesting that cold alone does not explain their range differences. I propose using a combination of whole-genome comparisons, physiological tests, and field surveys to test the idea that interactions between low temperature and sea salinity will explain range differences between these two very similar species. These results would have important implications in understanding the role of the environment in limiting species boundaries, the genomic basis of adaptive differences among close relatives, and in predicting potential range shifts under climate change.