Adaptive radiation of land crabs from the Greater Antilles: ecological mechanisms and intraspecific plasticity

适应性辐射通常是物种形成过程中的一个基本踏脚石。当一个祖先分化成几个具有不同生态适应性以利用各种环境的谱系时，就会发生这种情况。这被认为发生在芝麻蟹在牙买加的陆地殖民期间，产生了9个目前公认的物种（Sesarma属和Metopaulias属）。今天，这些螃蟹可以在岛上各种不同的栖息地找到。虽然最近的一项研究表明，所有特有的芝麻属物种都是单系的，并给出了定殖和分化的时间估计，但它未能解决牙买加单系植物内部的物种形成事件。因此，在这一点上，适应性辐射的实际过程还不能从这个有趣的进化案例中得到结论性的信息。目前的项目将侧重于适应性辐射的机制，通过(i)使用新的分子标记来更好地解决牙买加特有螃蟹物种之间的系统发育关系，并通过（ii）研究导致适应性辐射的当前过程，重点是种群水平上的生态和遗传分化。为了比较，将研究其他大安的列斯群岛的假thelphids陆生蟹动物群。这个更古老的陆地殖民者谱系在生态和形态上比牙买加芝麻科分化更少。我们的研究将揭示在过去，假桫椤科种内可塑性的整体下降是否可能是适应性辐射缺乏的原因。

Adaptive radiation is often a fundamental stepping-stone in the process of speciation. It occurs when a single ancestor diverges into several lineages with different ecological adaptations to exploit a variety of environments. This is assumed to have occurred during the terrestrial colonization of Jamaica by sesarmid crabs, giving rise to nine currently recognized species (genera Sesarma and Metopaulias). Today, these crabs can be found in a variety of different habitats throughout the island. While a recent study showed that all the endemic sesarmid species are monophyletic and gave an estimate for the time of colonization and divergence, it failed to resolve speciation events within the Jamaican monophylum. Therefore, at this point no conclusive information on the actual process of adaptive radiation can be gained out of this interesting evolutionary case. The current project will focus on the mechanisms of adaptive radiation by (i) using new molecular markers to better resolve the phylogenetic relationships among the Jamaican endemic crab species and by (ii) studying current processes leading to adaptive radiation, with the emphasis on ecological and genetic divergence at the population level. For comparison, the pseudothelphusid terrestrial crab fauna of the other Greater Antilles will be studied. This older lineage of land colonisers is ecologically and morphologically less diverged than the Jamaican Sesarmidae. Our study shall reveal whether an overall decreased intraspecific plasticity in the Pseudothelphusidae might be the cause for the lack of adaptive radiations in the past.