Ecological Mechanisms of Diversification in Hyalella Amphipods

9815059俄克拉荷马大学加里·威尔伯恩博士的Wellborne研究将研究淡水端足类Hyallela Azteca复合体内进化多样化的生态和行为基础，以确定适应捕食者的作用和生殖隔离的附带进化机制。Hyallela是一类分布广泛、表型可变且在分类学上有问题的淡水甲壳类动物，在新大陆各栖息地的形态和生活史上表现出很大的生态型差异。Hyallela的一个显著模式是，小体、早期繁殖的生态型出现在有大小选择性捕食性鱼类的生境中，而大身体、后期繁殖的生态型出现在没有捕食性鱼类的生境中。这些表型差异是遗传的，自然种群之间的体型和生活史差异符合适应特定栖息地捕食制度的假设。在对干扰作用的初步研究中，发现不同生态型的个体被生殖隔离。然而，在初步的等位酶分析中发现，遗传多样性与生态型差异并不相关；然而，在该物种复合体的种群中，遗传多样性总体上似乎是中等到高度的。被测试的假说是，两足类反复分化为大小生态型，生殖隔离(因此，物种形成)与生态型分化并行进化。与捕食有关的对个体大小或年龄成熟的选择可能会引起交配行为的差异，作为一种偶然或附带的影响，从而加强生殖隔离，从而形成物种形成。北美的观测工作和实验室实验将检验这一假说的各种遗传、行为和生活史方面的情况。这种被称为复制适应性辐射或平行物种形成的多样化模式可能在淡水类群中很常见，尽管到目前为止还很少有人认识到这一点。

9815059Wellborn Research by Dr. Gary Wellborn at the University of Oklahoma will examine the ecological and behavioral bases of evolutionary diversification within the freshwater amphipod Hyallela azteca complex, to determine the role of adaptation to predators and the mechanism of collateral evolution of reproductive isolation. Hyallela is a widespread, phenotypically variable, and taxonomically problematic group of freshwater crustaceans, that exhibits substantial ecotypic variation in morphology and in life history across New World habitats. A salient pattern in Hyallela is that small-bodied, early-reproducing ecotypes occur in habitats that contain size-selective predatory fish, and large-bodied, late-reproducing ecotypes occur in habitats lacking predatory fish. These phenotypic differences are genetic, and the body size and life history differences among natural populations are consistent with the hypothesis of adaptation to habitat-specific predation regimes. In preliminary studies on interfertility, individuals of the different ecotypes were found to be reproductively isolated. Genetic diversity, however, as revealed in preliminary allozyme analyses, did not correlate with ecotypic differences; still, genetic diversity appears to be moderate to high overall in populations of this species complex. The hypothesis under test is that the amphipods have diversified into large and small ecotypes repeatedly, and that reproductive isolation (hence, speciation) has evolved collaterally with ecotypic divergence. Predation-related selection on body size or on age-to-maturation may induce, as an accidental or collateral effect, differences in mating behaviors that reinforce reproductive isolation, and hence speciation. Observational work in North America and laboratory experiments will test various genetic, behavioral, and life-history aspects of the hypothesis. This diversification mode, termed replicate adaptive radiation or parallel speciation, may be common in freshwater taxa, although little appreciated until now.