Pallarés Susana, Arribas Paula, Bilton David T, Millán Andrés, Velasco Josefa, Ribera Ignacio
Department of Ecology and Hydrology, Facultad de Biología, University of Murcia, Murcia, Spain.
Island Ecology and Evolution Research Group, IPNA-CSIC, Santa Cruz de Tenerife, Spain.
Mol Ecol. 2017 Oct;26(20):5614-5628. doi: 10.1111/mec.14334. Epub 2017 Sep 14.
Transitions from fresh to saline habitats are restricted to a handful of insect lineages, as the colonization of saline waters requires specialized mechanisms to deal with osmotic stress. Previous studies have suggested that tolerance to salinity and desiccation could be mechanistically and evolutionarily linked, but the temporal sequence of these adaptations is not well established for individual lineages. We combined molecular, physiological and ecological data to explore the evolution of desiccation resistance, hyporegulation ability (i.e., the ability to osmoregulate in hyperosmotic media) and habitat transitions in the water beetle genus Enochrus subgenus Lumetus (Hydrophilidae). We tested whether enhanced desiccation resistance evolved before increases in hyporegulation ability or vice versa, or whether the two mechanisms evolved in parallel. The most recent ancestor of Lumetus was inferred to have high desiccation resistance and moderate hyporegulation ability. There were repeated shifts between habitats with differing levels of salinity in the radiation of the group, those to the most saline habitats generally occurring more rapidly than those to less saline ones. Significant and accelerated changes in hyporegulation ability evolved in parallel with smaller and more progressive increases in desiccation resistance across the phylogeny, associated with the colonization of meso- and hypersaline waters during global aridification events. All species with high hyporegulation ability were also desiccation-resistant, but not vice versa. Overall, results are consistent with the hypothesis that desiccation resistance mechanisms evolved first and provided the physiological basis for the development of hyporegulation ability, allowing these insects to colonize and diversify across meso- and hypersaline habitats.
从淡水生境到咸水生境的转变仅限于少数昆虫谱系，因为咸水的定殖需要专门的机制来应对渗透胁迫。先前的研究表明，对盐度和干燥的耐受性在机制和进化上可能存在联系，但对于单个谱系而言，这些适应性的时间顺序尚未明确确立。我们结合分子、生理和生态数据，以探究水甲虫属Enochrus亚属Lumetus（水龟虫科）的抗干燥能力、低渗调节能力（即在高渗介质中进行渗透调节的能力）以及生境转变的进化过程。我们测试了增强的抗干燥能力是在低渗调节能力增强之前进化，还是反之，或者这两种机制是并行进化的。推断Lumetus的最近祖先具有较高的抗干燥能力和中等的低渗调节能力。在该类群的辐射过程中，不同盐度水平的生境之间存在反复的转变，向盐度最高的生境转变通常比向盐度较低的生境转变更快。在整个系统发育过程中，低渗调节能力的显著且加速的变化与抗干燥能力较小且更渐进的增加并行进化，这与全球干旱事件期间中盐度和高盐度水域的定殖有关。所有具有高渗调节能力的物种也都具有抗干燥能力，但反之则不然。总体而言，结果与以下假设一致：抗干燥机制首先进化，并为低渗调节能力的发展提供了生理基础，使这些昆虫能够在中盐度和高盐度生境中定殖并多样化。
