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.
Highlights
American alligators (Alligator mississippiensis)[1] do not tolerate saline environments for prolonged periods of time without access to freshwater[2,3,4,5]
Our working hypothesis was that endocrine effects observed in laboratory-kept juvenile alligators exposed to 12‰ salinity would be reflected in wild juvenile alligators found in hyperosmotic environments
We anticipated that while salinity varies throughout the environment, even short-term exposure to environmental salinity would correlate with physiological changes in wild-caught juvenile alligators
Summary
American alligators (Alligator mississippiensis)[1] do not tolerate saline environments for prolonged periods of time without access to freshwater[2,3,4,5]. Short-term (1 week) exposure to 12‰ seawater elevated Na+ and Cl− and glucocorticoid levels in juvenile alligators while estrogen levels decreased and androgen levels were largely unaffected[5] These studies demonstrated that exposure to high salinity can cause time-dependent changes in sex steroids important for growth and reproduction. While we have significant knowledge on anthropogenic compounds, little information exists as to the effects of a natural stressor (e.g., salinization) on alligator endocrine physiology This information is especially pertinent as changes in hydrology and saline environments have been demonstrated to negatively impact alligator populations by reducing body condition, growth, and reproductive success[32,33,34]. We anticipated that while salinity varies throughout the environment, even short-term exposure to environmental salinity would correlate with physiological changes in wild-caught juvenile alligators
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