Fraija-Fernández Natalia, Fernández Mercedes, Raga Juan A, Aznar Francisco J
Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, Science Park, University of Valencia, PO Box 22085, 46071, Valencia, Spain.
Parasit Vectors. 2015 Dec 23;8:659. doi: 10.1186/s13071-015-1273-8.
Adults and larvae of generalist parasites are exposed to diverse hosts and local environmental conditions throughout their life cycles, thus local adaptation is expected to occur through phenotypic plasticity and/or natural selection. We investigated how the combined effect of cryptic host specificity and local selective pressures could shape reproductive traits of a putative generalist parasite in the oceanic realm.
The LSU rDNA, ITS2 and the mt-COI of individuals of the digenean Pholeter gastrophilus (Kossack, 1910) Odhner, 1914 (Heterophyidae Leiper, 1909) from oceanic striped dolphins, Stenella coeruleoalba Meyen, and coastal bottlenose dolphins, Tursiops truncatus Montagu, in the western Mediterranean were used to elucidate whether worms were conspecific. Infection parameters were compared between both dolphin species. General Linear Mixed Models were used to analyse the influence of host species on four reproductive traits of P. gastrophilus: body size, maturity stage (non-gravid/gravid), egg size, and number of eggs in utero. AIC values were used to rank competing models, and p-values to assess the effect of specific predictors.
Evidence indicated that worms collected from both dolphin species were conspecific. All worms collected were gravid and infection parameters did not differ between dolphin species. However, body size and egg size of individuals of P. gastrophilus were significantly larger in striped dolphins. The number of eggs in utero did not significantly differ between dolphin species but, for a given body size, worms in bottlenose dolphins harboured more eggs. A trade-off between egg size and egg number was found in worms from both dolphin species, with a higher slope in striped dolphins.
Apparently, striped dolphin is a more suitable host for P. gastrophilus, but reproductive investment seems to be adapted to the habitat where the life-cycle develops. Worms from striped dolphins likely face the problem of finding intermediate hosts in the oceanic realm and apparently invest into offspring size to enhance the early survival of larvae and the potential to multiply asexually within the first intermediate host. The small-sized worms from bottlenose dolphins would be adapted to reproduce early because of higher adult mortality, generating smaller and numerous eggs in a coastal habitat where chances of transmission are presumably higher.
广食性寄生虫的成虫和幼虫在其整个生命周期中会接触到多种宿主和当地环境条件，因此预期会通过表型可塑性和/或自然选择发生局部适应。我们研究了隐性宿主特异性和局部选择压力的综合作用如何塑造海洋领域中一种假定的广食性寄生虫的繁殖特征。
利用来自地中海西部海洋条纹海豚（Stenella coeruleoalba Meyen）和沿海宽吻海豚（Tursiops truncatus Montagu）的复殖吸虫胃嗜豆螺（Pholeter gastrophilus，Kossack，1910；Odhner，1914；异双盘科，Leiper，1909）个体的 LSU rDNA、ITS2 和 mt-COI 来阐明这些蠕虫是否为同种。比较了两种海豚物种之间的感染参数。使用广义线性混合模型分析宿主物种对胃嗜豆螺四种繁殖特征的影响：体型、成熟阶段（未怀孕/怀孕）、卵大小和子宫内卵的数量。AIC 值用于对竞争模型进行排名，p 值用于评估特定预测变量的效应。
有证据表明从两种海豚物种收集的蠕虫为同种。所有收集到的蠕虫均已怀孕，且海豚物种之间的感染参数没有差异。然而，条纹海豚体内胃嗜豆螺个体的体型和卵大小明显更大。两种海豚物种子宫内卵的数量没有显著差异，但对于给定的体型，宽吻海豚体内的蠕虫携带的卵更多。在两种海豚物种的蠕虫中都发现了卵大小和卵数量之间的权衡，条纹海豚中的斜率更高。
显然，条纹海豚是胃嗜豆螺更合适的宿主，但繁殖投入似乎适应了生命周期发育的栖息地。来自条纹海豚的蠕虫可能面临在海洋领域中寻找中间宿主的问题，并且显然会投入到后代大小上，以提高幼虫的早期存活率以及在第一中间宿主体内进行无性繁殖的潜力。由于成年死亡率较高，来自宽吻海豚的小型蠕虫会适应早期繁殖，在沿海栖息地产生更小且数量更多的卵，那里的传播机会可能更高。
