Loggerhead turtle (Caretta caretta) offspring size does not vary with maternal alternative foraging behaviors: support for their phenotypic plasticity
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Revealing the causes and consequences of differential habitat use among previously untrackable species will help advance our understanding of how organisms have survived and adapted during their evolutionary histories. Among loggerhead sea turtles (Caretta caretta) nesting on one Japanese beach, small females tend to forage on planktonic prey in oceanic waters (depth >200 m) as the juveniles do, while large females tend to forage on benthic prey in neritic waters (depth <200 m). These alternative foraging behaviors are presumably maintained by a strategy depending on growth conditions during oceanic early life, and each tactic would be consistently used throughout the adult stage. To verify whether the morphology of emerged hatchlings varies with maternal alternative foraging behaviors, the clutches of similar egg characteristics derived from oceanic and neritic foragers were incubated in a common beach area (30°24′N, 130°26′E), Yakushima Island, Japan, 2014. There were no significant differences in straight carapace length and width and body mass of emerged hatchlings between the two foraging groups, which were classified based on stable isotope ratios, suggesting that the development process of hatchling tissue from yolk and albumen is genetically similar between the two groups. Egg size and mass significantly increased with female body size only in neritic foragers that laid larger clutches than oceanic foragers, whereas hatchling size and mass significantly increased with egg mass in both groups. This suggested that larger females produced larger hatchlings within neritic foragers, and indeed, there was a significant positive correlation in body size between females and hatchlings only within neritic foragers. However, significant negative correlations between the number of eggs reburied per nest and emergence success that might explain the above phenomenon were not found in either oceanic or neritic foragers. Effects of a seasonal rise in ambient temperature on embryonic development and hatchling morphology were also similar between the two foraging groups, implying their genetic similarity in thermal response, consistent with their phenotypic plasticity.
KeywordsClutch Size Green Turtle Female Body Size Loggerhead Turtle Incubation Duration
We thank T. Hidaka, the staff (M. Ono, N. Omuta, T. Araishi, S. Koide, and M. Uchida) and volunteers (R. Shimizu, N. Sugio, R. Kawasaki, K. Nakajima, K. Yamada, and others) of the Yakushima Sea Turtle Research Group for field assistance and logistical support. The Associate Editor, G.C. Hays, and one anonymous reviewer provided constructive criticism. Field sampling was conducted under licenses issued by the municipalities of Kagoshima Prefecture (Nos. 11-2 and 11-3) and Yakushima Town (No. 981) and in accordance with the Animal Care Authorization (No. P14-1) of The University of Tokyo. This work was supported by JSPS KAKENHI Grant Number 25870141 to H.H.
Compliance with ethical standards
This study was funded by JSPS KAKENHI (Grant Number 25870141) to the first author, Hideo Hatase.
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in this study involving animals were in accordance with the Animal Care Authorization (No. P14-1) of The University of Tokyo.
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