Data from: Ecological partitioning among parapatric cryptic species

Geographic range differences among species may result from differences in their physiological tolerances. In the intertidal zone, marine and terrestrial environments intersect to create a unique habitat, across which physiological tolerance strongly influences range. Traits to cope with environmental extremes are particularly important here because many species live near their physiological limits and environmental gradients can be steep. The snail Melampus bidentatus occurs in coastal salt marshes in the western Atlantic and the Gulf of Mexico. We used sequence data from one mitochondrial (COI) and two nuclear markers (histone H3 and a mitochondrial carrier protein, MCP) to identify three cryptic species within this broad-ranging nominal species, two of which have partially overlapping geographic ranges. High genetic diversity, low population structure, and high levels of migration within these two overlapping species suggest that historical range limitations do not entirely explain their different ranges. To identify microhabitat differences between these two species, we modeled their distributions using data from both marine and terrestrial environments. Although temperature was the largest factor setting range limits, other environmental components explained features of the ranges that temperature alone could not. In particular, the interaction of precipitation and salinity likely sets physiological limits that lead to range differences between these two cryptic species. This suggests that the response to climatic change in these snails will be mediated by changes to multiple environmental factors, and not just to temperature alone.

物种间地理分布范围的差异可能源于其生理耐受能力的不同。潮间带（intertidal zone）是海洋与陆地环境交汇形成的独特生境，在此类生境中，生理耐受对物种分布范围的塑造作用尤为显著。由于许多物种在此类生境中生存于其生理耐受极限附近，且环境梯度变化剧烈，应对极端环境的功能性状在此尤为关键。双齿锥脐螺（Melampus bidentatus）分布于西大西洋沿岸盐沼及墨西哥湾海域。本研究利用1个线粒体标记（COI）与2个核标记：组蛋白H3（histone H3）以及线粒体载体蛋白（mitochondrial carrier protein, MCP）的序列数据，在这一广布名义物种中鉴定出3个隐存种，其中2个隐存种的地理分布范围存在部分重叠。这两个重叠分布的隐存种呈现出较高的遗传多样性、较低的种群遗传分化水平以及高水平的种群迁移，表明历史分布范围限制无法完全解释二者分布范围的差异。为探究这两个隐存种的微生境差异，本研究结合海洋与陆地环境数据对其分布进行建模。尽管温度是决定分布范围边界的首要因素，但其他环境组分能够补充解释温度单独无法阐释的分布特征。尤为关键的是，降水与盐度的交互作用可能共同塑造了生理耐受极限，进而导致这两个隐存种的分布范围产生差异。这意味着，这些螺类对气候变化的响应将由多重环境因子的变化共同介导，而非仅受温度单一因素影响。