Domènech Francesc, Tomás Jesús, Crespo-Picazo José Luis, García-Párraga Daniel, Raga Juan Antonio, Aznar Francisco Javier
Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, Valencia, Spain.
Veterinary Services, Biology Department, Oceanogràfic, Valencia, Spain.
PLoS One. 2017 Jan 23;12(1):e0170789. doi: 10.1371/journal.pone.0170789. eCollection 2017.
Species of Balaenophilus are the only harpacticoid copepods that exhibit a widespread, obligate association with vertebrates, i.e., B. unisetus with whales and B. manatorum with marine turtles and manatees. In the western Mediterranean, juveniles of the loggerhead sea turtle, Caretta caretta are the only available hosts for B. manatorum, which has been found occurring at high prevalence (>80%) on them. A key question is how these epibionts are transmitted from host to host. We investigated this issue based on experiments with live specimens of B. manatorum that were cultured with turtle skin. Specimens were obtained from head-started hatchlings of C. caretta from the western Mediterranean. Hatched nauplii crawled only on rough substrates and lacked the ability to swim. Only copepodites IV and V, and adults, were able to perform directional swimming. Legs 2, 3 and 4 played a major role in swimming and were only well-developed in these stages. Nauplii reared in wells with turtle skin readily fed on this item. Late copepodites and adults also fed on turtle skin but did not consume other potential food items such as fish skin, baleen plates or planktonic algae. Evidences suggest that the transmission of B. manatorum should rely on hosts' bodily contacts and/or swimming of late developmental stages between spatially close hosts. The possibility of long-ranged dispersal is unlikely for two reasons. First, all developmental stages seem to depend on turtle skin as a food resource. Second, the average clutch size of ovigerous females was small (< 70 eggs) for free-living phases to successfully contact turtles that occur at very low densities (< 0.6 turtles·km-2) in the western Mediterranean. The high prevalence of B. manatorum in loggerhead turtles in this area raises the question whether these turtles have contacts, or tend to closely aggregate, more than is currently believed.
巴拉诺菲洛斯属的物种是仅有的与脊椎动物呈现广泛且专性共生关系的猛水蚤目桡足类动物，即单刚毛巴拉诺菲洛斯与鲸鱼共生，而海龟巴拉诺菲洛斯与海龟和海牛共生。在西地中海，蠵龟（Caretta caretta）的幼龟是海龟巴拉诺菲洛斯唯一可利用的宿主，人们发现该寄生虫在蠵龟幼龟身上的感染率很高（>80%）。一个关键问题是这些体表寄生虫如何在宿主之间传播。我们基于用蠵龟皮肤培养的海龟巴拉诺菲洛斯活体标本进行实验，对这个问题展开了研究。标本取自西地中海人工养殖的蠵龟孵化幼体。孵化出的无节幼体只在粗糙基质上爬行，没有游泳能力。只有IV期和V期桡足幼体以及成体能进行定向游泳。第2、3和4对足在游泳中起主要作用，且仅在这些阶段发育良好。在装有蠵龟皮肤的培养皿中饲养的无节幼体很容易以其为食。后期桡足幼体和成体也以蠵龟皮肤为食，但不吃其他潜在食物，如鱼皮、鲸须板或浮游藻类。有证据表明，海龟巴拉诺菲洛斯的传播应依赖宿主间的身体接触和/或发育后期阶段在空间上接近的宿主之间的游动。远距离扩散的可能性不大，原因有两个。第一，所有发育阶段似乎都依赖蠵龟皮肤作为食物来源。第二，产卵雌体的平均产卵量较小（<70枚卵），使得自由生活阶段的个体难以成功接触到在地中海西部密度极低（<0.6只·平方公里）的蠵龟。该地区蠵龟上海龟巴拉诺菲洛斯的高感染率引发了一个问题，即这些蠵龟之间的接触或聚集程度是否比目前认为的更高。
