Morphology and life history divergence in cave and surface populations of <i>Gammarus lacustris</i> (L.)

Cave animals provide a unique opportunity to study contrasts in phenotype and life history in strikingly different environments when compared to surface populations, potentially related to natural selection. As such, we compared a permanent cave-living Gammarus lacustris (L.) population with two lake-resident surface populations analyzing morphology (eye- and antennal characters) and life-history (size at maturity, fecundity and egg-size). A part of the cytochrome c oxidase subunit I gene in the mitochondrion (COI) was analyzed to contrast genetic relationship of populations and was compared to sequences in GenBank to assess phylogeography and colonization scenarios. In the cave, a longer life cycle was implied, while surface populations seemed to have a shorter life cycle. Egg size, and size at maturity for both sexes, were larger in the cave than in surface populations, while fecundity was lower in the cave than in surface populations. The cave population had longer first- and second antennae with more articles, longer first- and second peduncles, and fewer ommatidia than surface populations. The cold low-productive cave environment may facilitate different phenotypic and life-history traits than in the warmer and more productive surface lake environments. The trait divergences among cave and surface populations resembles other cave-surface organism comparisons and may support a hypothesis of selection on sensory traits. The cave and Lake Ulvenvann populations grouped together with a sequence from Slovenia (comprising one genetic cluster), while Lake Lille Lauarvann grouped with a sequence from Ukraine (comprising another cluster), which are already recognized phylogenetic clusters. One evolutionary scenario is that the cave and surface populations were colonized postglacially around 9 000–10 000 years ago. We evaluate that an alternative scenario is that the cave was colonized during an interstadial during the last glaciation or earlier during the warm period before onset of the last glaciation.洞穴动物相较于地表种群，为在极具差异的环境中研究表型与生活史的差异提供了独特契机，这类差异可能与自然选择相关。有鉴于此，本研究将永久栖息于洞穴的湖沼钩虾（Gammarus lacustris）种群与2个湖泊栖息的地表种群进行对比，分析其形态学特征（眼部与触角性状）及生活史指标（成熟个体体型、繁殖力与卵径）。本研究对线粒体细胞色素c氧化酶亚基I基因（cytochrome c oxidase subunit I, COI）的一段序列进行分析，以明确种群间的遗传关系，并将其与GenBank中的序列进行比对，进而评估种群的系统地理学格局与定殖历史场景。研究结果显示，洞穴种群的生活周期更长，而地表种群的生活周期相对更短。洞穴种群的卵径以及雌雄个体的成熟体型均大于地表种群，但其繁殖力却低于地表种群。相较于地表种群，洞穴种群的第一、第二触角更长且分节更多，第一、第二柄节也更长，但其小眼面数量更少。相较于温暖且生产力更高的地表湖泊环境，寒冷且生产力较低的洞穴环境可能塑造出与之不同的表型与生活史特征。洞穴与地表种群间的性状分化模式与其他洞穴-地表生物的对比研究结果相似，这可为感官性状受到自然选择的假说提供支撑。洞穴种群与乌尔文万湖（Lake Ulvenvann）种群与来自斯洛文尼亚的序列聚为一支，构成一个遗传簇；而里尔劳阿尔万湖（Lake Lille Lauarvann）种群则与来自乌克兰的序列聚为另一支，这两个簇均为已被确认的系统发育簇。一种演化场景认为，洞穴与地表种群均是在约9000至10000年前的冰期后完成定殖的。本研究认为另一种可能的场景是，洞穴种群的定殖发生在末次冰期的间冰阶，或是更早的末次冰期开始前的温暖时期。