Correlations between environmental salinity levels, blood biochemistry parameters, and steroid hormones in wild juvenile American alligators (Alligator mississippiensis)

Abstract

American alligators (Alligator mississippiensis) inhabit freshwater wetlands that are vulnerable to salinization caused by anthropogenic alterations to freshwater flow, in addition to storm surges, sea level rise, and droughts. Salinization of coastal freshwater habitats is a growing concern in a changing climate due to increased frequency and intensity of storm surges and drought conditions. This study opportunistically sampled juvenile male and female wild alligators in various salinities each month excluding November, December, and January for one year at Rockefeller Wildlife Refuge in coastal Louisiana. Blood plasma biochemistry parameters including electrolyte levels were subsequently measured. In addition, levels of various renin–angiotensin–aldosterone system hormones, glucocorticoids, androgens, estrogens, and progestogens were analyzed using liquid chromatography and tandem mass spectrometry. Only males were sampled in hyperosmotic environments (> 10‰) during dry conditions in late summer 2018. In juvenile males, plasma Na+, Cl−, and the progestogen 17α,20β-dihydroxypregnenone were significantly and positively correlated with environmental salinity. However, variation in glucocorticoids, androgens, and estrogens were not associated with hypersaline water while sex steroids showed significant seasonal variation. This study demonstrated significant correlation of environmental salinity with electrolyte levels and a sex steroid in wild juvenile alligators, and to our knowledge represents the first measurement of 17α,20β-dihydroxypregnenone in alligators.

Blood Biochemical Reference Intervals of Black Caimans (Melanosuchus niger) and Spectacled Caimans (Caiman crocodilus) in the Brazilian Amazon Region

“…Additionally, Na + and K + concentrations were higher in males than in females of the spectacled caiman. Higher Na + concentrations were also found in wild juvenile males of American alligator ( Alligator mississippiensis ; Faulkner et al 2021). In Nile crocodile ( Crocodylus niloticus ), K + concentration was higher in females than in males (Lovely et al 2007).…”

“…In Nile crocodile ( Crocodylus niloticus ), K + concentration was higher in females than in males (Lovely et al 2007). The slightly higher and significant difference in electrolyte(Na + and K + ) intervals may be related to the concentration of androgen hormones and different dietary habits (Birukawa et al 2005) or hydration status (Faulkner et al 2021) because of their role in hydroelectrolytic balance. These results suggest that the hydro electrolyte profile may vary between species and between sexes and should be investigated in the future.…”