A phylogenetic perspective on habitat shifts and diversity in the North American Enallagma damselflies

Community ecologists are increasingly aware that the regional history of taxon diversification can have an important influence on community structure. Likewise, systematists recognize that ecological context can have an important influence on the processes of speciation and extinction that create patterns of descent. We present a phylogenetic analysis of 33 species of a North American radiation of damselflies (Zygoptera: Coenagrionidae: Enallagma Selys), which have been well-studied ecologically, in order to elucidate the evolutionary mechanisms that have contributed to differences in diversity between larval habitats (lakes with and without fish predators). Analysis of molecular variation in 842 bp of the mitochondrial cytochrome oxidase I and II subunit and the intervening Leu-tRNA and 37 morphological characters resulted in three well-defined clades that are only partially congruent with previous phylogenetic hypotheses. Molecular and morphological data partitions were significantly incongruent. Lack of haplotype monophyly within species and small levels of sequence divergence (<1%) between related species in 3 of the 4 clades suggests that recent, and parallel, speciation has been an important source of community diversity. Reconstruction of habitat preference over the phylogeny suggests that the greater species diversity in fish-lake habitats is due to the recency of shifts into the fishless-lake habit, although a difference in speciation or extinction rates between the two habitats is difficult to exclude as an additional mechanism.

群落生态学家日益意识到，类群分化的区域历史对群落结构具有重要影响。同样，分类学家也认识到，生态背景对塑造谱系模式的物种形成与灭绝过程具有重要影响。本研究针对北美辐射演化的33种蜻蛉（束翅亚目Zygoptera：蟌科Coenagrionidae：蓝蟌属Enallagma Selys）开展系统发育分析——该类群已被充分开展生态学研究——以阐明驱动幼体生境（有鱼类捕食者的湖泊与无鱼类捕食者的湖泊）间多样性差异的演化机制。本研究对线粒体细胞色素氧化酶I、II亚基及其间插入的亮氨酸转运RNA（Leu-tRNA）共842 bp的分子变异，与37个形态性状进行分析，得到了3个界定清晰的进化枝，其与先前的系统发育假说仅部分吻合。分子数据与形态数据的分区结果存在显著不一致。在4个进化枝中的3个里，物种种内缺乏单倍型单系性，且近缘物种间的序列分歧度极低（<1%），这表明近期发生的平行物种形成是群落多样性的重要来源。基于系统发育的生境偏好重建结果显示，有鱼湖泊生境中更高的物种多样性，源于类群向无鱼湖泊生境的转移发生时间较晚；不过，两种生境间物种形成速率或灭绝速率的差异，仍无法被排除为额外的驱动机制。