Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720, USA.
National Institute of Fundamental Studies, Hantana Road, Kandy 20000, Sri Lanka.
Curr Biol. 2018 Mar 19;28(6):941-947.e3. doi: 10.1016/j.cub.2018.01.083. Epub 2018 Mar 8.
Insular adaptive radiations in which repeated bouts of diversification lead to phenotypically similar sets of taxa serve to highlight predictability in the evolutionary process [1]. However, examples of such replicated events are rare. Cross-clade comparisons of adaptive radiations are much needed to determine whether similar ecological opportunities can lead to the same outcomes. Here, we report a heretofore uncovered adaptive radiation of Hawaiian stick spiders (Theridiidae, Ariamnes) in which different species exhibit a set of discrete ecomorphs associated with different microhabitats. The three primary ecomorphs (gold, dark, and matte white) generally co-occur in native forest habitats. Phylogenetic reconstruction mapped onto the well-known chronosequence of the Hawaiian Islands shows both that this lineage colonized the islands only once and relatively recently (2-3 mya, when Kauai and Oahu were the only high islands in the archipelago) and that the distinct ecomorphs evolved independently multiple times following colonization of new islands. This parallel evolution of ecomorphs matches that of "spiny-leg" long-jawed spiders (Tetragnathidae, Tetragnatha), also in Hawaii [2]. Both lineages are free living, and both have related lineages in the Hawaiian Islands that show quite different patterns of diversification with no evidence of deterministic evolution. We argue that repeated evolution of ecomorphs results from a rugged adaptive landscape, with the few peaks associated with camouflage for these free-living taxa against the markedly low diversity of predators on isolated islands. These features, coupled with a limited genetic toolbox and reduced dispersal between islands, appear to be common to situations of repeated evolution of ecomorphs.
在经历多次物种分化后产生表型相似的分类单元的岛屿适应性辐射,突出了进化过程中的可预测性[1]。然而,这种重复事件的例子很少。为了确定相似的生态机会是否能导致相同的结果,非常需要对跨进化枝的适应性辐射进行交叉比较。在这里,我们报告了一个迄今为止尚未被发现的夏威夷刺蛛(Theridiidae,Ariamnes)适应性辐射,其中不同的物种表现出与不同微生境相关的一系列离散的生态型。这三个主要的生态型(金色、深色和哑光白色)通常共同出现在原生森林栖息地中。基于夏威夷群岛著名的年代序列构建的系统发育重建表明,该谱系仅在 2-3 百万年前(当考艾岛和瓦胡岛是群岛中仅有的两个高岛时)一次相对较近地殖民了这些岛屿,并且在殖民新岛屿后,这些独特的生态型独立进化了多次。这种生态型的平行进化与夏威夷的“刺腿长颚蛛”(Tetragnathidae,Tetragnatha)相似[2]。这两个谱系都是自由生活的,在夏威夷群岛中都有相关的谱系,它们的多样化模式截然不同,没有证据表明存在确定性进化。我们认为,生态型的反复进化是由崎岖的适应景观导致的,与这些自由生活的类群的伪装相关的少数高峰与孤立岛屿上显著低多样性的捕食者有关。这些特征,加上有限的遗传工具箱和岛屿间扩散的减少,似乎是多次进化生态型的共同特征。