Multigenerational backcrossing and introgression between two woodrat species at an abrupt ecological transition

When organisms experience secondary contact after allopatric divergence, genomic regions can introgress differentially depending on their relationships with adaptation, reproductive isolation, recombination, and drift. Analyses of genome-wide patterns of divergence and introgression could provide insight into the outcomes of hybridization and the potential relationship between allopatric divergence and reproductive isolation. Here, we generate population genetic data (26,262 SNPs; 353 individuals) using a reduced-representation sequencing approach to quantify patterns of ancestry, differentiation, and introgression between a pair of ecologically distinct mammals – the desert woodrat (N. lepida) and Bryant’s woodrat (N. bryanti) – that hybridize at a sharp ecotone in southern California. Individual ancestry estimates confirmed that hybrids were rare in this bimodal hybrid zone, and entirely consisted of a few F1 individuals and a broad range of multigenerational backcrosses. Genomic clin...

当物种在地理隔离分化（allopatric divergence）后发生次生接触时，基因组区域的基因渐渗（introgression）模式会存在差异，这取决于其与适应性、生殖隔离（reproductive isolation）、重组及遗传漂变（genetic drift）的关联。对全基因组范围内的分化与渐渗模式进行分析，可助力解析杂交的演化结局，以及地理隔离分化与生殖隔离间的潜在关联。本研究采用简化基因组测序（reduced-representation sequencing）技术获取群体遗传数据：共得到26262个单核苷酸多态性（Single Nucleotide Polymorphisms, SNPs）位点，涵盖353个个体。我们借此量化了一对生态分化哺乳动物类群——荒漠林鼠（*Neotoma lepida*，N. lepida）与布莱恩特林鼠（*Neotoma bryanti*，N. bryanti）——的祖先成分、种群分化及基因渐渗模式。这两个类群在加利福尼亚州南部一处界限分明的生态交错带（ecotone）发生杂交。个体祖先成分分析结果证实，该双峰杂交带（bimodal hybrid zone）内的杂交个体较为稀少，且仅包含少量子一代（F₁）个体与多代回交（backcross）产生的各类杂交后代。基因组[……]