SIZE-DEPENDENT, SEX-DEPENDENT, AND SEASONAL-CHANGES IN INSULIN-LIKE GROWTH-FACTOR-I IN THE LOGGERHEAD SEA-TURTLE (CARETTA-CARETTA)

This study examines size-dependent, sex-dependent, and seasonal fluctu ations in plasma insufin-like growth factor-I (IGF-I) concentrations i n loggerhead sea turtles (Caretta caretta). Loggerhead turtles (n = 15 8) were captured in shrimp trawler nets during a 12-month survey in Ca pe Canaveral Channel, Florida. Plasma samples were analyzed using a va lidated heterologous radioimmunoassay. Large turtles (>75 cm straight- line carapace length) had significantly higher plasma IGF-I concentrat ions than small turtles (less than or equal to 75 cm; P < 0.0001). Pla sma IGF-I concentrations did not vary seasonally in small turtles, but large turtles had significantly higher plasma IGF-I concentrations du ring the spring and summer months (P < 0.005). Within the large turtle s, adult males had significantly lower IGF-I concentrations than femal es and subadult males (P < 0.05). These results and a review of logger head turtle natural history suggest that the seasonal fluctuations in plasma IGF-I of adult turtles are due to elevated IGF-I levels in repr oductively active female turtles. Further research is needed to examin e correlations between reproductive activities and plasma IGF-I concen trations in reptiles. (C) 1995 Academic Press, Inc.