Hatase Hideo, Omuta Kazuyoshi, Itou Koutarou, Komatsu Teruhisa
Atmosphere and Ocean Research Institute The University of Tokyo Kashiwa Chiba Japan.
Yakushima Sea Turtle Research Group Yakushima Kagoshima Japan.
Ecol Evol. 2018 Feb 27;8(6):3543-3555. doi: 10.1002/ece3.3938. eCollection 2018 Mar.
Exploring a trade-off between quantity and quality of offspring allows differences in the fitness between alternative life histories to be accurately evaluated. We addressed the mechanism that maintains alternative life histories (small oceanic planktivores vs. large neritic benthivores) observed in a loggerhead sea turtle () population, which has been suggested to be environmental, based on the lack of genetic structure and a large difference in reproductive output. We examined whether maternal foraging habitat affects offspring quality, by measuring the morphology, emergence success, and righting response of hatchlings following incubation in a common open sand area over the whole nesting season at Yakushima Island, Japan, and by recording early growth and survival of offspring that were reared in a common environment at a Japanese aquarium. Furthermore, we tested whether sea turtles adjust egg size in response to temporal shifts of the incubation environment. There were no significant differences in any hatchling traits between oceanic and neritic foragers (which were classified by stable isotope ratios), except for clutches laid during the warmest period of the nesting season. There were also no significant differences in the growth and survival of offspring originating from the two foragers. The size of eggs from both foragers significantly increased as the season progressed, even though the rookery had heavy rainfall, negating the need to counteract heat-related reduction in hatchling morphology. In comparison, the sizes of adult body and clutches from both foragers did not vary significantly. The results further support our previous suggestions that the size-related foraging dichotomy exhibited by adult sea turtles does not have a genetic basis, but derives from phenotypic plasticity. Adjustment in reproductive investment may be associated with: (1) predation avoidance, (2) founder effect, and/or (3) annual variation in egg size.
探索后代数量与质量之间的权衡，有助于准确评估不同生活史之间的适合度差异。我们研究了在蠵龟种群中观察到的维持不同生活史（小型海洋浮游生物食性与大型浅海底栖生物食性）的机制，基于缺乏遗传结构和生殖输出的巨大差异，此前有人认为这是环境因素导致的。我们通过测量在日本屋久岛整个筑巢季节于公共开阔沙地孵化后的幼龟的形态、出壳成功率和翻身反应，并记录在日本一家水族馆的共同环境中饲养的幼龟的早期生长和存活情况，来检验母体觅食栖息地是否会影响后代质量。此外，我们还测试了海龟是否会根据孵化环境的时间变化来调整卵的大小。除了在筑巢季节最温暖时期产下的窝卵外，海洋和浅海觅食者（根据稳定同位素比率分类）的幼龟在任何特征上均无显著差异。来自这两种觅食者的幼龟在生长和存活方面也没有显著差异。尽管繁殖地降雨量大，但随着季节的推进，两种觅食者的卵的大小均显著增加，这排除了抵消与热量相关的幼龟形态变化的必要性。相比之下，两种觅食者的成体大小和窝卵数没有显著变化。这些结果进一步支持了我们之前的观点，即成年海龟表现出的与大小相关的觅食二分法没有遗传基础，而是源于表型可塑性。生殖投资的调整可能与以下因素有关：（1）避免被捕食，（2）奠基者效应，和/或（3）卵大小的年度变化。
