Wollschlager Jennifer, Folino-Rorem Nadine, Daly Marymegan
Department of Evolution, Ecology, and Organismal Biology, the Ohio State University, Columbus, OH 43210, USA.
Biol Bull. 2013 Apr;224(2):99-109. doi: 10.1086/BBLv224n2p99.
Although there is significant genetic diversity among populations of the hydroid Cordylophora caspia, the species has not been split into multiple species or subspecies, in part because its members also show great physiological and morphological plasticity. This plasticity makes new taxonomic units hard to define or identify and obscures the connection between historically used names and the genetically defined clades. We explore variation in nematocysts, a character system not previously assessed in Cordylophora but which has demonstrated phylogenetic signal in other cnidarian taxa. We measured more than 5000 capsules from 112 individuals belonging to 14 populations, including representatives of the major genetic lineages. We found no correlation between the size range of capsules and either clade or salinity. Thus, for C. caspia, nematocysts are neither phenotypically plastic with respect to salinity nor taxonomically informative. Nematocyst size and density in particular tissues may be correlated to other environmental factors (such as prey type, size, and abundance in the location of each population) and may aid in distinguishing more distantly related species.
尽管水螅虫类的里海棒螅种群间存在显著的遗传多样性，但该物种尚未被划分为多个物种或亚种，部分原因是其成员还表现出极大的生理和形态可塑性。这种可塑性使得新的分类单元难以定义或识别，也模糊了历史上使用的名称与基因定义的进化枝之间的联系。我们探究了刺细胞的变异情况，这是一个此前未在里海棒螅中评估过的特征系统，但在其他刺胞动物类群中已显示出系统发育信号。我们测量了来自14个种群的112个个体的5000多个刺丝囊，其中包括主要遗传谱系的代表。我们发现刺丝囊的大小范围与进化枝或盐度之间均无相关性。因此，对于里海棒螅来说，刺细胞在盐度方面既没有表型可塑性，也没有分类学信息价值。特定组织中的刺丝囊大小和密度可能与其他环境因素（如每个种群所在地的猎物类型、大小和丰度）相关，并且可能有助于区分亲缘关系更远的物种。
