The evolution of species' distributions:: Reciprocal transplants across the elevation ranges of Mimulus cardinalis and M. lewisii
The evolution of species' distributions:: Reciprocal transplants across the elevation ranges of Mimulus cardinalis and M. lewisii
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DOI：
10.1111/j.0014-3820.2005.tb01817.x
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发表时间：
2005-08-01
期刊：
影响因子：
3.3
通讯作者：
Schemske, DW
中科院分区：
文献类型：
--
作者：
Angert, AL;Schemske, DW
每个物种都占据有限的地理区域，但目前尚不清楚为什么限制分布的特征没有进化到允许范围扩大。关于地理范围进化稳定性的假设假设物种在范围边界处适应不良并且不适合超出当前范围，但这种假设很少得到检验。为了研究适应度在不同物种范围内的变化，我们在它们目前的海拔范围之内和之外相互移植了两种猴花，即Mimulus cardinalis和M. lewisii。我们使用从两个物种的海拔范围内收集的种群中已知血统的个体来检查种群是否适应该范围内的位置。对于这两个物种，我们发现在范围中心海拔处的平均适应度最大，在范围边缘的适应度降低，当移植到超出其当前海拔范围限制时，适应度为零或接近零。然而，不同物种之间适应性差异的根本原因有所不同。在超出其分布范围的高海拔地区，M. cardinalis 的生长和繁殖能力下降，而在低海拔地区，M. lewisii 的死亡率很高。在每个物种内的种群之间观察到性能上的微弱差异，并且这些差异与起源海拔无关。两个物种在其活动范围边缘的适应性较低，并且每个物种内种群之间的分化较弱，这表明对活动范围边缘和范围之外的环境的适应受到阻碍，这说明活动范围边缘提供了一个有趣的系统来研究适应的限制。
Every species occupies a limited geographic area, but it remains unclear why traits that limit distribution do not evolve to allow range expansion. Hypotheses for the evolutionary stability of geographic ranges assume that species are maladapted at the range boundary and unfit beyond the current range, but this assumption has rarely been tested. To examine how fitness varies across species' ranges, we reciprocally transplanted two species of monkeyflowers, Mimulus cardinalis and M. lewisii, within and beyond their present elevation ranges. We used individuals of known parentage from populations collected across the elevation ranges of both species to examine whether populations are adapted to position within the range. For both species we found the greatest average fitness at elevations central within the range, reduced fitness at the range margin, and zero or near-zero fitness when transplanted beyond their present elevation range limits. However, the underlying causes of fitness variation differed between the species. At high elevations beyond its range, M. cardinalis displayed reduced growth and fecundity, whereas at low elevations M. lewisii experienced high mortality. Weak differences in performance were observed among populations within each species and these were not related to elevation of origin. Low fitness of both species at their range margin and weak differentiation among populations within each species suggest that adaptation to the environment at and beyond the range margin is hindered, illustrating that range margins provide an interesting system in which to study limits to adaptation.