Linck Ethan B, Celi Jorge E, Sheldon Kimberly S
Department of Ecology & Evolutionary Biology University of Tennessee, Knoxville Knoxville TN USA.
Biogeography and Spatial Ecology Research Group Universidad Regional Amazónica Ikiam Tena Ecuador.
Ecol Evol. 2020 Apr 12;10(9):4143-4155. doi: 10.1002/ece3.6185. eCollection 2020 May.
Janzen's seasonality hypothesis predicts that organisms inhabiting environments with limited climatic variability will evolve a reduced thermal tolerance breadth compared with organisms experiencing greater climatic variability. In turn, narrow tolerance breadth may select against dispersal across strong temperature gradients, such as those found across elevation. This can result in narrow elevational ranges and generate a pattern of isolation by environment or neutral genetic differentiation correlated with environmental variables that are independent of geographic distance. We tested for signatures of isolation by environment across elevation using genome-wide SNP data from five species of Andean dung beetles (subfamily Scarabaeinae) with well-characterized, narrow thermal physiologies, and narrow elevational distributions. Contrary to our expectations, we found no evidence of population genetic structure associated with elevation and little signal of isolation by environment. Further, elevational ranges for four of five species appear to be at equilibrium and show no decay of genetic diversity at range limits. Taken together, these results suggest physiological constraints on dispersal may primarily operate outside of a stable realized niche and point to a lower bound on the spatial scale of local adaptation.
詹曾的季节性假说预测，与经历更大气候变异性的生物相比，栖息在气候变异性有限环境中的生物将进化出更窄的热耐受性广度。反过来，狭窄的耐受性广度可能不利于生物跨越强烈的温度梯度扩散，比如在海拔梯度上发现的温度梯度。这可能导致海拔分布范围狭窄，并产生一种环境隔离模式或与独立于地理距离的环境变量相关的中性遗传分化。我们使用来自五种安第斯蜣螂（金龟子亚科）的全基因组SNP数据，测试了海拔梯度上环境隔离的特征，这些蜣螂具有特征明确、狭窄的热生理特性和狭窄的海拔分布。与我们的预期相反，我们没有发现与海拔相关的种群遗传结构的证据，也几乎没有环境隔离的信号。此外，五个物种中的四个物种的海拔分布范围似乎处于平衡状态，并且在分布范围边界处没有显示出遗传多样性的衰减。综上所述，这些结果表明，对扩散的生理限制可能主要在稳定的实际生态位之外起作用，并指出了局部适应空间尺度的下限。
