Corticosterone Plasma Levels of Embryo and Hatchling Broad-Snouted Caimans ( Caiman latirostris ) Incubated at Different Temperatures

Abstract

The temperature-sensitive period is the time during development at which sex determination occurs in temperature-dependent sex determination vertebrates, such as in caimans. The interplay among temperature and steroid hormones is also known, and that stress hormones (corticosterone) can influence sex ratios in some reptiles. To explore this, we measured the levels of corticosterone in Caiman latirostris, to determine if the incubation temperature affects plasma corticosterone levels. Caiman eggs, taken from wild nests just after laying, were incubated at different temperatures (31, 33 and 34°C) until hatching. Plasmatic corticosterone was determined by radioimmunoassay in embryos, after the temperature-sensitive period and in hatchlings. We obtained 100% of females at 31°C and 100% of males at 33 and 34°C incubation temperatures. Differences among nests were observed in plasma corticosterone. However, hormone levels showed no differences between sexes or incubation temperatures in Caiman latirostris embryos or hatchlings. Corticosterone levels in embryos incubated at 31°C ranged from 0.01 to 2.2 ng/ml, in those incubated at 33°C the levels ranged from 0.01 to 4.65 ng/ml and, finally embryos incubated at the highest temperature ranged from 0.01 to 6.31 ng/ml. Hatchlings presented higher levels of corticosterone: those produced at 31°C ranged from 1.11 to 39.18, at 33°C from 2.85 to 22.36 and 34°C 2.72 to 39.05 ng/ml.

El periodo termosensible es el momento durante el desarrollo embrionario en el cual ocurre la determinación sexual en vertebrados con DST, como sucede en los caimanes. Se conoce que la temperatura y las hormonas esteroideas pueden interactuar, y ha sido sugerido que la hormona de estrés (corticosterona) podría influenciar la proporción de sexos en algunos reptiles. Para explorar esto, medimos los niveles de corticosterona en Caiman latirostris, para poder determinar si la temperatura de incubación (31, 33 y 34°C) afecta los niveles de corticosterona plasmática. Se observaron diferencias en los niveles de corticosterona plasmática entre los nidos. Sin embargo, no se observaron diferencias significativas en los valores de corticosterona entre sexos o entre temperaturas de incubación en embriones y crías de Caiman latirostris. Los valores de corticosterona en embriones incubados a 31°C (100% hembras) variaron entre 0.01 hasta 2.2 ng/mL, en aquellos incubados a 33°C (100% machos) los niveles variaron desde 0.01 hasta 4.65 ng/mL, y finalmente los embriones incubados a temperatura más alta (100% machos) osciló desde 0.01 hasta 6.31 ng/mL. Las crías presentaron mayores niveles de corticosterona: aquellas producidas a 31°C variaron desde 1.11 hasta 39.18 ng/mL, a 33°C desde 2.85 hasta 22.36 ng/mL y a 34°C desde 2.72 hasta 39.05 ng/mL.