Geographic range limits and adaptation to changing climates: the effects of phenotypic lag, selection, and genetic variance

每一个物种都有有限的地理分布。换句话说，每个物种在景观上占据了有限的区域。进化允许地球上的生命以多种形式存在，占据了许多栖息地，那么是什么阻止了任何特定的物种适应他们范围之外的地区并无限期地传播？随着气候的变化，种群将面临哪些新的进化挑战，这些挑战将如何影响它们的地理分布？这些问题是我实验室研究的核心。在这里提出的工作中，我们将使用一种生长在北美西部的一年生野花作为我们的重点物种，测试几个假设，看看是什么限制了山脉边缘和气候变化的适应。一种可能性是，范围限制的出现是因为种群未能进化出在范围边缘或范围外茁壮成长所必需的特征。如果是这样的话，我们预计表型会比在射程中心偏离最佳近程边缘更远。我们还预计，在区间边缘的选择将是强劲和定向的，但在区间中心将是疲软和稳定的。然而，这些模式很少跨地理范围进行测量。我建议在牧场中心、北部牧场边缘和更远的地方，通过温室杂交和大田移植实验来描述它们的特征。关于牧场边缘为什么会出现的另一个假设是，牧场边缘的种群缺乏适应所必需的关键性状的遗传变异。然而，适合性取决于更多的特征，而不是可以测量的，所以我建议直接测量适合度的遗传差异，再次使用温室杂交和移植实验。我建议的设计将允许我们将人口素质(边缘与中心)的贡献与场地质量(边缘与中心)的贡献分离。我们还将研究种群是否能够适应他们在气候变化下可能经历的环境因素的新组合，或者遗传相关性是否限制了新特征组合的进化。这种类型的研究从根本上说很有趣，但对社会也很重要。具有经济和文化重要性的物种正在经历气候变化的影响。通过了解哪些物种在最近的分布受到限制，以及哪些物种在未来可能受到限制，我们将能够更好地规划重要物种的保护和栽培。

Every species has a limited geographic distribution. In other words, every species occupies a finite area on the landscape. Evolution has allowed life on earth to take many forms and occupy many habitats, so what prevents any particular species from adapting to areas outside their range and spreading indefinitely? As the climate changes, what new evolutionary challenges will populations face, and how will these affect their geographic distributions? These questions are central to research in my lab. In the work proposed here we will test several hypotheses for what constrains adaptation at range edges and under climate change, using an annual wildflower that grows in western North America as our focal species. One possibility is that range limits arise because populations fail to evolve the traits necessary to thrive at and beyond the range edge. If this is the case, we expect phenotypes to deviate further from the optimum near range edges than they do at the range centre. We also expect selection to be strong and directional at the range edge, but weak and stabilizing at the range centre. However, these patterns are rarely measured across geographic ranges. I propose to characterize them in the range centre, at the northern range edge, and beyond, with greenhouse crosses and field transplant experiments in Clarkia pulchella. An additional hypothesis for why range edges occur is that populations at range edges lack the genetic variance in key traits that is necessary to adapt. However, fitness depends upon more traits than can be measured, so I propose to directly measure genetic variance in fitness, again using greenhouse crosses and transplant experiments. My proposed design will allow us to decouple the contributions of population qualities (edge vs. centre) from site qualities (edge vs. centre). We will also examine whether populations are able to adapt to new combinations of environmental factors that they are likely to experience under climate change, or whether genetic correlations constrain the evolution of novel combinations of traits. This type of research is fundamentally interesting, but also important to society. Species of economic and cultural importance are experiencing the effects of climate change. By understanding what has limited distributions in the recent past and what is likely to be limiting in the future, we will be better able to plan conservation and cultivation of important species.