Jones Conor M, Miller Terrence L, Grutter Alexandra S, Cribb Thomas H
School of Integrative Biology, University of Queensland, St. Lucia, Qld 4072, Australia.
Int J Parasitol. 2008 Mar;38(3-4):477-91. doi: 10.1016/j.ijpara.2007.07.013. Epub 2007 Aug 14.
Cymothoid isopods are parasites that have a biphasic life cycle comprised of free-swimming micropredatory stages that eventually attach permanently to fishes, on which they change sex and morphology. Thus, matching free-swimming and permanently attached life-history stages is difficult. We attempted to identify natatory-stage cymothoids by seeking matches of partial 16S rRNA gene sequences from these stages and described adult cymothoids. Natatory cymothoids were collected from light traps at Lizard Island, Great Barrier Reef and adult females were collected from fishes from several sites along the east coast of Australia. A 488bp alignment of 16S mtDNA was compared for nine species of adult cymothoids and 10 natatory-stage morphotypes. Sequences from five natatory morphotypes were similar or identical to described specimens. Sequences identical to those of Anilocra nemipteri and Cymothoa indica were collected and these are considered definitive identifications. Sequences of three other morphotypes were highly similar (97.1-99.8% homologous) to described species; the differences may reflect a low level of sequencing error, intra-specific variation or the presence of complexes of species. Figures and descriptions are provided for identified and unidentified natatory cymothoids. The sequences were also used to explore the phylogenetic relationships of these taxa using minimum evolution, maximum parsimony, maximum likelihood and Bayesian inference analyses. Topologies from each of the four phylogenetic analyses did not differ significantly. Bayesian inference and maximum likelihood methods produced identical topologies with the highest resolution. These analyses showed that some morphological characters (pereopods and uropods) of natatory stages were distributed consistently on these molecular phylogenies, raising the possibility of identifying some natatory stages to genus. Our results suggest that ancestral cymothoids attached in the buccal or gill cavity and that external attachment, as seen in Anilocra and Renocila is a derived condition that has arisen more than once.
缩头水虱类等足动物是寄生虫，具有双相生命周期，包括自由游动的微型捕食阶段，这些阶段最终会永久附着在鱼类身上，并在鱼身上发生性别和形态变化。因此，很难将自由游动阶段和永久附着阶段的生活史匹配起来。我们试图通过寻找这些阶段的部分16S rRNA基因序列的匹配来识别游动阶段的缩头水虱类，并描述成年缩头水虱类。游动阶段的缩头水虱类是从大堡礁蜥蜴岛的灯光诱捕器中收集的，成年雌性则是从澳大利亚东海岸多个地点的鱼类身上收集的。对9种成年缩头水虱类和10种游动阶段形态型的16S线粒体DNA进行了488bp的比对。5种游动形态型的序列与已描述的标本相似或相同。收集到了与印度缩头水虱和尼氏缩头水虱序列相同的样本，这些被认为是确定性鉴定。其他三种形态型的序列与已描述物种高度相似（同源性为97.1 - 99.8%）；这些差异可能反映了测序误差水平较低、种内变异或物种复合体的存在。提供了已识别和未识别的游动缩头水虱类的图片和描述。这些序列还被用于通过最小进化、最大简约法、最大似然法和贝叶斯推断分析来探索这些分类单元的系统发育关系。四种系统发育分析的拓扑结构没有显著差异。贝叶斯推断和最大似然法产生了分辨率最高的相同拓扑结构。这些分析表明，游动阶段的一些形态特征（步足和尾足）在这些分子系统发育树上分布一致，这增加了将一些游动阶段鉴定到属的可能性。我们的结果表明，祖先的缩头水虱类附着在口腔或鳃腔中，而在尼氏缩头水虱属和雷氏缩头水虱属中所见得外部附着是一种衍生状态，已经出现不止一次。
