Chow Lai Him, Ahyong Shane T, Tsang Chandler T T, Lam Yu Fung, Naruse Tohru, Ng Peter K L, Tsang Ling Ming
Simon F.S. Li Marine Science Laboratory, School of Life Sciences, The Chinese University of Hong Kong, Shatin, Hong Kong, China.
Australian Museum Research Institute, 1 William St, Sydney, NSW 2010, Australia; School of Biological, Earth and Environmental Sciences, University of New South Wales, Kensington, NSW 2052, Australia.
Mol Phylogenet Evol. 2023 Nov;188:107904. doi: 10.1016/j.ympev.2023.107904. Epub 2023 Aug 12.
The pea crabs, superfamily Pinnotheroidea, are exceptional among brachyuran crabs in their diverse symbiotic associations involving both inquilinism and protective symbiosis. While this group presents a rare opportunity for evolutionary comparative study of host switching and morphological evolution in marine macroinvertebrates, previous phylogenetic studies have been focused on systematics. Here, we reconstructed the most extensive phylogeny of Pinnotheroidea based on two mitochondrial and six nuclear markers, with the aim of elucidating the host switching pathways and the correlation between symbiotic lifestyles and selected morphological adaptations. Ancestral state reconstruction of host association revealed a monophyletic origin of symbiosis in the form of inquilinism. Subsequent shifts in microhabitat preference for burrows or worm tubes, and the move to protective symbiosis, primarily in the switch to mollusc endosymbiosis, contributed to radiation in Pinnotheridae. Further parallel colonisations of echinoderms and tunicates occurred but did not lead to extensive diversification, except in the Clypeasterophilus + Dissodactylus lineage, which experienced a unique switch to echinoderm ectosymbiosis. The evolution of the third maxillipeds, carapace shape and ambulatory pereiopods suggests a rather strong coupling with the symbiotic lifestyle (whether inquilinism or protective symbiosis). Phenotypic diversity of these characters was higher among species engaged in protective symbiosis, with convergence in form (or function) among those sharing the same host affiliation. Species having different host affiliations or symbiotic lifestyles might also exhibit convergence in the form of the three morphological traits, suggesting a common adaptive value of the specialisations. Pinnotherid crabs overall exhibited a lower trait diversity than the also symbiotic palaemonid shrimps with comparable species diversity. This may plausibly be attributed to differences in potential for morphological modification to serve additional functions among the traits analysed in the two groups, the less frequent host switching and the less diverse host affiliations, and thus a less complicated evolutionary history in pinnotherids.
豌豆蟹超科（Pinnotheroidea）在短尾类螃蟹中很特别，它们具有多种共生关系，包括寄居共生和保护性共生。虽然这一群体为海洋大型无脊椎动物宿主转换和形态进化的进化比较研究提供了难得的机会，但以往的系统发育研究主要集中在系统分类学上。在这里，我们基于两个线粒体标记和六个核标记重建了最广泛的豌豆蟹超科系统发育树，目的是阐明宿主转换途径以及共生生活方式与选定形态适应之间的相关性。宿主关联的祖先状态重建揭示了以寄居共生形式存在的共生单系起源。随后对洞穴或虫管微生境偏好的转变，以及向保护性共生的转变，主要是在向软体动物内共生的转变中，促成了豆蟹科的辐射分化。对棘皮动物和被囊动物的进一步平行定殖也有发生，但除了在Clypeasterophilus + Dissodactylus谱系中经历了向棘皮动物外共生的独特转换外，并没有导致广泛的多样化。第三颚足、头胸甲形状和步足的进化表明与共生生活方式（无论是寄居共生还是保护性共生）有相当强的关联。这些特征的表型多样性在参与保护性共生的物种中更高，在共享相同宿主归属的物种中形态（或功能）趋同。具有不同宿主归属或共生生活方式的物种在这三个形态特征上也可能表现出趋同，这表明这些特化具有共同的适应性价值。总体而言，豆蟹比具有可比物种多样性的同样共生的长臂虾表现出更低的特征多样性。这可能合理地归因于两组分析特征中为实现额外功能而进行形态修饰的潜力差异、宿主转换频率较低和宿主归属较少样化，因此豆蟹的进化历史较不复杂。
