Abstract：
Adaptive evolution can facilitate species\' range expansions across environmentally heterogeneous landscapes. However, serial founder effects can limit the efficacy of selection, and the evolution of increased dispersal during range expansions may result in gene flow swamping local adaptation. Here, we study how genetic drift, gene flow and selection interact during the cane toad\'s (Rhinella marina) invasion across the heterogeneous landscape of Australia. Following its introduction in 1935, the cane toad colonised eastern Australia and established several stable range edges. The ongoing, more rapid range expansion in north-central Australia has occurred concomitant with an evolved increase in dispersal capacity. Using reduced representation genomic data of Australian cane toads from the expansion front and from two areas of their established range, we test the hypothesis that high gene flow constrains local adaptation at the expansion front relative to established areas. Genetic analyses indicate the three study areas are genetically distinct but show similar levels of allelic richness, heterozygosity and inbreeding. Markedly higher gene flow or recency of colonisation at the expansion front have likely hindered local adaptation at the time of sampling, as indicated by reduced slopes of genetic-environment associations (GEAs) estimated using a novel application of geographically weighted regression that accounts for allele surfing; GEA slopes are significantly steeper in established parts of the range. Our work bolsters evidence supporting adaptation of invasive species post-introduction and adds novel evidence for differing strengths of evolutionary forces among geographic areas with different invasion histories.
摘要：
适应性进化可以促进跨环境异质景观的物种范围扩展。然而,连续创始人效应会限制选择的效力，范围扩展过程中扩散增加的进化可能会导致基因流淹没局部适应。这里,我们研究遗传漂移，在甘蔗蟾蜍（Rhinellamarina）入侵澳大利亚异质景观期间，基因流和选择相互作用。在1935年引入后，甘蔗蟾蜍在澳大利亚东部定居，并建立了几个稳定的范围边缘。正在进行的，随着扩散能力的不断增加，澳大利亚中北部地区的范围扩展更加迅速。使用澳大利亚甘蔗蟾蜍从扩展前沿和其既定范围的两个区域的简化表示基因组数据，我们检验了这样的假设，即相对于已建立的区域，高基因流量限制了扩展前沿的局部适应。遗传分析表明，这三个研究区域在遗传上是不同的，但显示出相似的等位基因丰富度水平。杂合性和近亲繁殖。在扩增前沿明显较高的基因流或最近的定殖可能阻碍了采样时的局部适应，正如使用地理加权回归的新应用估计的遗传-环境关联（GEA）斜率降低所表明的那样，该应用考虑了等位基因冲浪；GEA斜率在该范围的既定部分明显更陡。我们的工作支持了支持入侵物种在引入后适应的证据，并为具有不同入侵历史的地理区域之间进化力量的不同优势增加了新的证据。
