title: Size-dependent, sex-dependent, and seasonal changes in insulin-like growth factor I in the loggerhead sea turtle (Caretta caretta).
abstract: This study examines size-dependent, sex-dependent, and seasonal fluctuations in plasma insulin-like growth factor-I (IGF-I) concentrations in loggerhead sea turtles (Caretta caretta). Loggerhead turtles (n = 158) were captured in shrimp trawler nets during a 12-month survey in Cape Canaveral Channel, Florida. Plasma samples were analyzed using a validated heterologous radioimmunoassay. Large turtles (> 75 cm straight-line carapace length) had significantly higher plasma IGF-I concentrations than small turtles (< or = 75 cm; P < 0.0001). Plasma IGF-I concentrations did not vary seasonally in small turtles, but large turtles had significantly higher plasma IGF-I concentrations during the spring and summer months (P < 0.005). Within the large turtles, adult males had significantly lower IGF-I concentrations than females and subadult males (P < 0.05). These results and a review of loggerhead turtle natural history suggest that the seasonal fluctuations in plasma IGF-I of adult turtles are due to elevated IGF-I levels in reproductively active female turtles. Further research is needed to examine correlations between reproductive activities and plasma IGF-I concentrations in reptiles.
authors.affiliation: Department of Zoology, University of Florida, Gainesville 32611, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Crain
authors.forename: A B
authors.initials: AB
authors.lastname: Bolten
authors.forename: K A
authors.initials: KA
authors.lastname: Bjorndal
authors.forename: L J
authors.initials: LJ
authors.lastname: Guillette
authors.forename: T S
authors.initials: TS
authors.lastname: Gross
mesh_terms: D000818:Animals; D001824:Body Constitution; D005260:Female; D005431:Florida; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D008297:Male; D011863:Radioimmunoassay; D012621:Seasons; D012737:Sex Factors; D014426:Turtles / Q000378:metabolism*
chemical_list: D007334:Insulin-Like Growth Factor I