Abstract
The loggerhead turtle (Caretta caretta) is an endangered marine reptile for whom assessing population health requires knowledge of demographic parameters such as individual growth rate. In Cape Verde, as within several populations, adult female loggerhead sea turtles show a size-related behavioral and trophic dichotomy. While smaller females are associated with oceanic habitats, larger females tend to feed in neritic habitats, which is reflected in their physiological condition and in their offspring. The ratio of RNA/DNA provides a measure of cellular protein synthesis capacity, which varies depending on changes in environmental conditions such as temperature and food availability. The purpose of this study was to evaluate the combined use of morphometric data and biochemical indices as predictors of the physiological condition of the females of distinct sizes and hatchlings during their nesting season and how temperature may influence the physiological condition on the offspring. Here we employed biochemical indices based on nucleic acid derived indices (standardized RNA/DNA ratio-sRD, RNA concentration and DNA concentration) in skin tissue as a potential predictor of recent growth rate in nesting females and hatchling loggerhead turtles. Our major findings were that the physiological condition of all nesting females (sRD) decreased during the nesting season, but that females associated with neritic habitats had a higher physiological condition than females associated with oceanic habitats. In addition, the amount of time required for a hatchling to right itself was negatively correlated with its physiological condition (sRD) and shaded nests produced hatchlings with lower sRD. Overall, our results showed that nucleic acid concentrations and ratios of RNA to DNA are an important tool as potential biomarkers of recent growth in marine turtles. Hence, as biochemical indices of instantaneous growth are likely temperature-, size- and age-dependent, the utility and validation of these indices on marine turtles stocks deserves further study.
Highlights
The impact of anthropogenic activity on biodiversity has been demonstrated throughout terrestrial and aquatic ecosystems [1,2]
We aimed to investigate the following hypotheses: regarding adult turtles, (i) Does the physiological condition of females decrease during the nesting season (A1)?; (ii) Is the physiological condition of ‘‘large’’ adult sea turtles associated with neritic habitats different to the physiological condition of ‘‘small’’ adult sea turtles associated with oceanic habitats (A2)? Regarding hatchling sea turtles, (i) Are the hatching and emergence successes of ‘‘small’’ adult sea turtles lower than in ‘‘large’’ adult sea turtles (O1)?; (ii) Are hatchlings produced by ‘‘large’’ females larger than the hatchlings produced by ‘‘small’’ females (O2)?; (iii) Is hatchling vigour correlated with physiological condition (O3)?; and (iv) Does incubation temperature influence the physiological condition of the hatchlings (O4)?
Hatching success was not correlated with the size of the nesting females, hatching success was positively correlated with the ecophysiological condition of the hatchlings (F1,52 = 4.282, p,0.05) (Fig. 4)
Summary
The impact of anthropogenic activity on biodiversity has been demonstrated throughout terrestrial and aquatic ecosystems [1,2]. The ratio of RNA to DNA (known as ‘standardized RNA/DNA ratio’- sRD) has been widely used as a biochemical index to assess potential survival and growth and in determining the ecophysiological condition of marine organisms [7]. This index has quickly become a promising biochemical tool that reflects physiological condition, and allows for the estimation of instantaneous growth rates in a great variety of organisms [8,9,10,11]
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