Department of Biology, University of Naples Federico II Naples, Naples, Italy.
PLoS One. 2019 Nov 11;14(11):e0224607. doi: 10.1371/journal.pone.0224607. eCollection 2019.
The ecological theory of island biogeography suggests that mainland populations should be more genetically divergent from those on large and distant islands rather than from those on small and close islets. Some island populations do not evolve in a linear way, but the process of divergence occurs more rapidly because they undergo a series of phenotypic changes, jointly known as the Island Syndrome. A special case is Reversed Island Syndrome (RIS), in which populations show drastic phenotypic changes both in body shape, skin colouration, age of sexual maturity, aggressiveness, and food intake rates. The populations showing the RIS were observed on islets nearby mainland and recently raised, and for this they are useful models to study the occurrence of rapid evolutionary change. We investigated the timing and mode of evolution of lizard populations adapted through selection on small islets. For our analyses, we used an ad hoc model system of three populations: wild-type lizards from the mainland and insular lizards from a big island (Capri, Italy), both Podarcis siculus siculus not affected by the syndrome, and a lizard population from islet (Scopolo) undergoing the RIS (called P. s. coerulea because of their melanism). The split time of the big (Capri) and small (Scopolo) islands was determined using geological events, like sea-level rises. To infer molecular evolution, we compared five complete mitochondrial genomes for each population to reconstruct the phylogeography and estimate the divergence time between island and mainland lizards. We found a lower mitochondrial mutation rate in Scopolo lizards despite the phenotypic changes achieved in approximately 8,000 years. Furthermore, transcriptome analyses showed significant differential gene expression between islet and mainland lizard populations, suggesting the key role of plasticity in these unpredictable environments.
岛屿生物地理学的生态理论表明，大陆种群与大型和遥远岛屿上的种群相比，应该具有更大的遗传差异，而不是与小型和近岛的种群相比。一些岛屿种群并没有以线性方式进化，而是因为经历了一系列表型变化而更快地发生了分化，这些变化统称为岛屿综合征。一个特殊的例子是反转岛屿综合征（RIS），在这种情况下，种群在体型、皮肤颜色、性成熟年龄、攻击性和食物摄入量等方面都发生了剧烈的表型变化。表现出 RIS 的种群在附近大陆和最近兴起的岛屿上被观察到，因此它们是研究快速进化变化发生的有用模型。我们研究了通过在小岛上选择而适应的蜥蜴种群的进化时间和模式。为了进行分析，我们使用了一个专门的模型系统，该系统由三个种群组成：来自大陆的野生型蜥蜴、来自大岛（意大利卡普里岛）的岛屿蜥蜴（未受该综合征影响的 Podarcis siculus siculus），以及正在经历 RIS 的岛屿蜥蜴种群（由于它们的黑色素沉着而称为 P. s. coerulea）。通过海平面上升等地质事件确定了大岛（卡普里岛）和小岛（斯科洛波岛）的分裂时间。为了推断分子进化，我们比较了每个种群的五个完整线粒体基因组，以重建系统发育地理，并估计岛屿和大陆蜥蜴之间的分化时间。我们发现，尽管在大约 8000 年内实现了表型变化，但斯科洛波岛蜥蜴的线粒体突变率较低。此外，转录组分析显示岛屿和大陆蜥蜴种群之间存在显著的差异基因表达，这表明可塑性在这些不可预测的环境中起着关键作用。
