Faria Samuel Coelho, Provete Diogo Borges, Thurman Carl Leo, McNamara John Campbell
Departamento de Biologia, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto SP, Brazil.
Departamento de Ciências Ambientais, Universidade Federal de São Carlos, Sorocaba SP, Brazil.
PLoS One. 2017 Feb 9;12(2):e0171870. doi: 10.1371/journal.pone.0171870. eCollection 2017.
Salinity is the primary driver of osmoregulatory evolution in decapods, and may have influenced their diversification into different osmotic niches. In semi-terrestrial crabs, hyper-osmoregulatory ability favors sojourns into burrows and dilute media, and provides a safeguard against hemolymph dilution; hypo-osmoregulatory ability underlies emersion capability and a life more removed from water sources. However, most comparative studies have neglected the roles of the phylogenetic and environmental components of inter-specific physiological variation, hindering evaluation of phylogenetic patterns and the adaptive nature of osmoregulatory evolution. Semi-terrestrial fiddler crabs (Uca) inhabit fresh to hyper-saline waters, with species from the Americas occupying higher intertidal habitats than Indo-west Pacific species mainly found in the low intertidal zone. Here, we characterize numerous osmoregulatory traits in all ten fiddler crabs found along the Atlantic coast of Brazil, and we employ phylogenetic comparative methods using 24 species to test for: (i) similarities of osmoregulatory ability among closely related species; (ii) salinity as a driver of osmoregulatory evolution; (iii) correlation between salt uptake and secretion; and (iv) adaptive peaks in osmoregulatory ability in the high intertidal American lineages. Our findings reveal that osmoregulation in Uca exhibits strong phylogenetic patterns in salt uptake traits. Salinity does not correlate with hyper/hypo-regulatory abilities, but drives hemolymph osmolality at ambient salinities. Osmoregulatory traits have evolved towards three adaptive peaks, revealing a significant contribution of hyper/hypo-regulatory ability in the American clades. Thus, during the evolutionary history of fiddler crabs, salinity has driven some of the osmoregulatory transformations that underpin habitat diversification, although others are apparently constrained phylogenetically.
盐度是十足目动物渗透调节进化的主要驱动力，可能影响了它们向不同渗透生态位的多样化发展。在半陆生蟹类中，高渗调节能力有利于它们在洞穴和稀释介质中停留，并防止血淋巴稀释；低渗调节能力是其出露能力和远离水源生活的基础。然而，大多数比较研究忽略了种间生理变异的系统发育和环境成分的作用，阻碍了对系统发育模式和渗透调节进化适应性本质的评估。半陆生招潮蟹（Uca）栖息于淡水至高盐水域，美洲的物种占据比主要分布在低潮间带的印度-西太平洋物种更高的潮间带栖息地。在此，我们描述了巴西大西洋沿岸发现的所有十种招潮蟹的众多渗透调节特征，并采用系统发育比较方法，利用24个物种来检验：（i）亲缘关系密切的物种间渗透调节能力的相似性；（ii）盐度作为渗透调节进化的驱动力；（iii）盐摄取与分泌之间的相关性；以及（iv）高潮间带美洲谱系中渗透调节能力的适应性峰值。我们的研究结果表明，招潮蟹的渗透调节在盐摄取特征上呈现出强烈的系统发育模式。盐度与高/低调节能力不相关，但在环境盐度下驱动血淋巴渗透压。渗透调节特征已朝着三个适应性峰值进化，揭示了高/低调节能力在美洲类群中的显著贡献。因此，在招潮蟹的进化历史中，盐度驱动了一些支撑栖息地多样化的渗透调节转变，尽管其他一些转变显然受到系统发育的限制。
