The Influence of Maternal Size on the Eggs and Hatchlings of Loggerhead Sea Turtles

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Our study examined variation in and correlation of reproductive traits for a population of Caretta caretta (Loggerhead Sea Turtle) nesting in Georgia and compared the results with those of other studies. We assessed variability in reproductive traits (i.e., maternal length, clutch size, egg diameter, egg mass, hatchling length, and hatchling mass) on the population level and individual level. At the population level, we investigated interannual and intraseasonal variation of these traits for 810 Loggerhead Sea Turtle nests in Georgia, on Wassaw National Wildlife Refuge (NWR) and Blackbeard Island NWR during 2000–2003 and 2001–2003, respectively. As the nesting season progressed, we observed a decrease in clutch size, mean egg diameter, mean egg mass per clutch, mean hatchling length per clutch, and mean hatchling mass per clutch. Further, we measured all previously mentioned traits on a subset of the female turtles encountered on the beach (n = 24) and used these data to examine the variability of the traits on the individual level. Generalized linear modeling using this more refined individual-level data set indicated that 55% of the variability in clutch size was explained by a combination of maternal length (47%) and hatchling length (8%). This model suggested that clutch size was positively related with maternal length (t = 4.79) and negatively related with hatchling length (t = -1.90). Greater maternal length resulted in larger clutch size, but not larger egg size; thus, egg size was relatively constant irrespective of maternal length. These results support optimal egg-size theory, indicating a trade-off between clutch size and hatchling size to produce the optimum maternal investment per offspring.