Ewers-Saucedo Christine, Chan Benny K K, Zardus John D, Wares John P
Biol Bull. 2017 Jun;232(3):171-185. doi: 10.1086/693356. Epub 2017 Aug 14.
Symbiotic relationships are often species specific, allowing symbionts to adapt to their host environments. Host generalists, on the other hand, have to cope with diverse environments. One coping strategy is phenotypic plasticity, defined by the presence of host-specific phenotypes in the absence of genetic differentiation. Recent work indicates that such host-specific phenotypic plasticity is present in the West Pacific lineage of the commensal barnacle Chelonibia testudinaria (Linnaeus, 1758). We investigated genetic and morphological host-specific structure in the genetically distinct Atlantic sister lineage of C. testudinaria. We collected adult C. testudinaria from loggerhead sea turtles, horseshoe crabs, and blue crabs along the eastern U.S. coast between Delaware and Florida and in the Gulf of Mexico off Mississippi. We find that shell morphology, especially shell thickness, is host specific and comparable in similar host species between the Atlantic and West Pacific lineages. We did not detect significant genetic differentiation related to host species when analyzing data from 11 nuclear microsatellite loci and mitochondrial sequence data, which is comparable to findings for the Pacific lineage. The most parsimonious explanation for these parallel patterns between distinct lineages of C. testudinaria is that C. testudinaria maintained phenotypic plasticity since the lineages diverged 4-5 mya.
共生关系通常具有物种特异性，这使得共生体能够适应其宿主环境。另一方面，宿主泛化者则必须应对多样化的环境。一种应对策略是表型可塑性，它由在缺乏遗传分化的情况下存在宿主特异性表型来定义。最近的研究表明，这种宿主特异性表型可塑性存在于共栖藤壶龟甲藤壶（Chelonibia testudinaria，林奈，1758年）的西太平洋谱系中。我们研究了龟甲藤壶在遗传上不同的大西洋姐妹谱系中的遗传和形态宿主特异性结构。我们从美国东海岸特拉华州和佛罗里达州之间以及密西西比州附近墨西哥湾的蠵龟、鲎和蓝蟹身上采集了成年龟甲藤壶。我们发现，壳形态，尤其是壳厚度，具有宿主特异性，并且在大西洋和西太平洋谱系的相似宿主物种之间具有可比性。当分析来自11个核微卫星位点和线粒体序列数据的数据时，我们没有检测到与宿主物种相关的显著遗传分化，这与太平洋谱系的研究结果相当。对龟甲藤壶不同谱系之间这些平行模式最简约的解释是，自400 - 500万年前谱系分化以来，龟甲藤壶一直保持着表型可塑性。
