Loggerhead turtle (Caretta caretta) offspring size does not vary with maternal alternative foraging behaviors: support for their phenotypic plasticity

Abstract

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.

Nest site selection in loggerhead sea turtles that use different foraging areas: do less fecund oceanic foragers nest at safer sites?

“…These results suggested that the proportion of nests damaged or lost by natural causes (e.g., inundation, beach erosion) is similar for oceanic and neritic foragers. When taken together with the comparable quality (morphology, emergence success and activity levels) of hatchlings derived from the two foragers (Hatase et al ., , ), our results indicated that the survival rate of offspring on land is very similar between the two foragers. Thus, the 2.5‐fold lower fecundity of oceanic foragers is unlikely to be offset by differences in offspring survival due to differential nest site selection.…”

“…δ 13 C and δ 15 N were expressed as deviations from the standard, as defined by the following equation: δ 13 C or δ 15 N = ( R sample / R standard – 1) × 1000 (‰), where R is 13 C/ 12 C or 15 N/ 14 N. Vienna Pee Dee Belemnite (VPDB) and atmospheric nitrogen were used as the carbon and nitrogen isotope standards, respectively. Analytical precision was ≤0.15‰ for both δ 13 C and δ 15 N. Females producing yolks with a δ 13 C of <–18.0‰ and a δ 15 N of <12.0‰ were classified as oceanic planktivores, and females with a δ 13 C of ≥–18.0‰ or a δ 15 N of ≥12.0‰ were classified as neritic benthivores (Watanabe et al ., ; Hatase et al ., , ) following the findings of a previous study in which stable isotope analysis and satellite telemetry were simultaneously conducted on the same females and isotope ratios were compared between potential prey and females (Hatase et al ., ). To justify this method of classification, linear discriminant analysis was also conducted (see electronic supplementary material: Appendix ).…”

“…Less fecund females can improve offspring survival in two ways: directly, by investing more reproductive resources into individual offspring, as larger offspring may have better chances of survival (Janzen, ), or indirectly, via selection of nesting environments that enhance embryonic development and post‐hatching survival (Shine & Harlow, ). Previous studies failed to show that less fecund female sea turtles improve the survival of offspring directly (Hatase, Omuta & Komatsu, , ). Here, we considered whether less fecund females try to improve offspring survival indirectly through nest site selection.…”

Effect of maternal foraging habitat on offspring quality in the loggerhead sea turtle (Caretta caretta)

“…The hatchlings sampled from some nests included hatchlings that emerged over several nights, because few hatchlings emerged during the first night. The morphology did not differ significantly between hatchlings that emerged on the first night and those that emerged on subsequent nights within nests (Hatase et al., ).…”

“…Sea turtles generally nest from late April to early August on the island (Yakushima Sea Turtle Research Group ). To encompass the whole nesting season, nightly patrols looking for nesting turtles were conducted from 15 to 24 May 2013 (Hatase et al., ), 22 May to 5 June 2014 (Hatase et al., ), 25 June to 4 July 2015, and 4 to 9 July 2016. Although the nesting season continues until early August, it is difficult to obtain enough samples due to the decrease in nesting females late in the nesting season.…”