Data from: Spatio-temporal changes in the structure of an Australian frog hybrid zone: a 40 year perspective

Spatio-temporal studies of hybrid zones provide an opportunity to test evolutionary hypotheses of hybrid zone maintenance and movement. We conducted a landscape genetics study on a classic hybrid zone of the south-eastern Australian frogs, Litoria ewingii and L. paraewingi. This hybrid zone has been comprehensively studied since the 1960s, providing the unique opportunity to directly assess changes in hybrid zone structure across time. We compared both mtDNA and male advertisement call data from two time periods (present and 1960s). Clinal analysis of the coincidence (same centre) and concordance (same width) of these traits indicated that the centre of the hybrid zone has shifted 1 km south over the last 40 years, although the width of the zone and the rate of introgression remained unchanged. The low frequency of hybrids, the strong concordance of clines within a time period and the small but significant movement across the study period despite significant anthropogenic changes through the region, suggest the hybrid zone is a tension zone located within a low density trough. Hybrid zone movement has not been considered common in the past but our findings highlight that it should be considered a crucial component to our understanding of evolution.

杂交带（hybrid zone）的时空研究为检验杂交带维持与动态演化的进化假说提供了绝佳契机。我们针对澳大利亚东南部的经典蛙类杂交带——尤氏雨滨蛙（Litoria ewingii）与拟尤氏雨滨蛙（L. paraewingi）——开展了景观遗传学（landscape genetics）研究。该杂交带自20世纪60年代起便得到系统性研究，为我们直接评估不同时期杂交带的结构变化提供了独特条件。我们对比了两个时间节点（当代与20世纪60年代）的线粒体DNA（mtDNA）与雄性求偶鸣曲（male advertisement call）数据。通过对这些性状开展渐变群分析（clinal analysis），并评估其重合性（中心位置一致）与一致性（梯度宽度一致），结果显示：在过去40年间，该杂交带的中心位置向南偏移了1公里，尽管杂交带的宽度与基因渐渗（introgression）速率未发生改变。杂交个体出现频率偏低、同一时期内各性状的渐变群高度一致，且尽管研究区域内发生了显著的人为活动改变，杂交带在整个研究周期内仍出现了小幅但显著的位移——这些结果表明该杂交带属于一处位于种群低密度槽（low density trough）内的张力带（tension zone）。过往学界普遍认为杂交带位移并非普遍现象，但我们的研究结果凸显了将其纳入进化认知框架的关键必要性。