Data from: Population admixture and high larval viability among urban toads

In terms of evolutionary biology, a population admixture of more than two distinct lineages may lead to strengthened genetic variation through hybridization. However, a population admixture arising from artificial secondary contact poses significant problems in conservation biology. In urban Tokyo, a population admixture has emerged from two lineages of Japanese common toad: native Bufo japonicus formosus and nonnative B. japonicus japonicus, of which the latter was introduced in the early 20th century. To evaluate the degree of genetic disturbance in the admixed population of these two subspecies, we analyzed genotypes of toads distributed within and outside Tokyo by assessing mtDNA and seven microsatellite loci. We found that the introduced B. japonicus japonicus genotype dominates six local populations in the Tokyo admixture zone and was clearly derived from past introgressive hybridization between the two subspecies. These observations were supported by morphological assessments. Furthermore, the average larval survival rate in Tokyo was significantly higher than that outside Tokyo, suggesting that the temporary contribution of introduced toads occurred through introgression. The fitness of toads in urban Tokyo may thus be increasing with the assistance of nonnative individuals.

从进化生物学视角来看，两个及以上不同谱系的种群混合可通过杂交作用提升遗传变异水平。然而，由人工二次接触引发的种群混合，却会给保护生物学带来诸多棘手问题。
在东京都市圈，日本普通蟾蜍（Japanese common toad）的两个遗传谱系——本土的日本蟾蜍（Bufo japonicus formosus）与20世纪早期引入的外来亚种日本蟾蜍指名亚种（B. japonicus japonicus）——已形成种群混合现象。
为评估这两个亚种的混合种群所受的遗传扰动程度，我们通过分析线粒体DNA（mtDNA）与7个微卫星位点（microsatellite loci），对东京都内外分布的蟾蜍基因型进行了分析。研究发现，在东京混合种群区域的6个本地种群中，外来的B. japonicus japonicus基因型占据主导地位，且该基因型显然源自两个亚种此前发生的渐渗杂交（introgressive hybridization），这一结果得到了形态学评估的佐证。
此外，东京都内蟾蜍幼体的平均存活率显著高于东京都外，这表明引入的外来蟾蜍类群曾通过基因渐渗（introgression）产生了暂时性的适应性贡献。综上，东京都市圈中蟾蜍的适合度或许可借助外来个体的辅助作用逐步提升。