| dc.description.abstract | American alligators (Alligator mississippiensis) inhabit freshwater wetlands but are vulnerable to salt stress during storm surges and droughts. Anthropogenic alterations to freshwater system hydrology, runoff of coal mine spoils, and road de-icing using salt can further contribute to salinization of freshwater habitats. Juvenile alligators are especially vulnerable to salt stress due to their thinner integument and lower mobility and ability to avoid saltwater. Little is known about how crocodilian physiological systems respond to environmental stressors such as salinity.
To better understand the effects of saltwater on alligators, juvenile alligators were exposed to 12‰ saltwater for 5-week and 1-week periods and blood plasma biochemistry, components of the renin-angiotensin-aldosterone system, steroidogenesis, and behavior were assessed. Furthermore, to correlate findings in laboratory-based studies with conditions in the wild, juvenile male and female wild alligators in various salinities were opportunistically sampled each month excluding November, December, and January for one year at Rockefeller Wildlife Refuge in coastal Louisiana.
Compared to freshwater-kept alligators, 5-week exposure to 12‰ saltwater significantly elevated plasma corticosterone, 11-deoxycortisol, 17α-hydroxyprogesterone, testosterone, estrone, 17β-estradiol, and estriol. Conversely, alligators exposed to 12‰ saltwater for 1 week had significantly reduced estrone and 17β-estradiol, while corticosterone and 11-deoxycortisol were elevated and histology showed alterations in gonad tissues. Additionally, the progestogen 17α,20β-dihydroxypregnenone was significantly, positively correlated with environmental salinities wild juvenile male alligators were found in. Angiotensin II was significantly reduced after 5- and 1-week exposure, which correlated with low renin and angiotensin-converting enzyme expression in kidney and lung tissues of alligators exposed for 1 week. Na+ and Cl- were significantly elevated after 5- and 1-week exposure, which corresponded well with Na+ and Cl- being strongly, positively correlated with environmental salinities wild juvenile male alligators were found in. Additionally, saltwater-exposed alligators largely ceased feeding within 1 week and spent significantly less time basking compared with pre-salinity observations.
This dissertation demonstrates behavioral changes and time-dependent, dynamic changes in physiology of juvenile alligator exposed to saltwater. This work further shows significant correlation of environmental salinity with electrolyte levels and a sex steroid in wild juvenile alligators, and to my knowledge represents the first measurement of 17α,20β-dihydroxypregnenone in alligators. | en |
