Abstract
Reproductive conservation physiology research is essential to management of threatened wildlife populations. Florida manatees (Trichechus manatus latirostris) are a threatened species protected by the Endangered Species Act, Marine Mammal Protection Act, and the Florida manatee Sanctuary Act, but there are limited data available for Florida manatee reproductive physiology. This study aided to 1) measure plasma steroid hormones in Florida manatees of different reproductive status and gestational stage at Crystal River and Brevard County field sites and 2) determine the relationship between plasma progesterone concentrations and lipid biochemistry.
We developed an ultra-high performance liquid chromatography tandem mass spectrometry (UHPLC MS/MS) based approach to measure steroid hormones and lipids in the plasma of wild manatees. Plasma samples were collected from 8 male and 13 female healthy adult manatees from Crystal River, FL and 8 male and 5 female healthy adult manatees from Brevard County, FL (2010–2019). Morphometric data were collected on all manatees. Plasma hormones measured included cortisol, aldosterone, progesterone, 17-hydroxyprogesterone, estrone, 17β-estradiol, testosterone, and dihydrotestosterone. A total of 949 plasma lipid species were identified.
Pregnant manatees were morphometrically distinct from male and non-pregnant manatees, having a larger body weight and maximum girth. Progesterone was also elevated during early gestation versus late gestation as determined via ultrasonography. Cortisol was elevated in pregnant females, but not significantly different from the males and non-pregnant females. Aldosterone was elevated in manatees from Brevard County as compared to the Crystal River manatees; perhaps due to the salinity of the brackish water in Brevard County compared to the fresh spring water of Crystal River. Plasma concentrations of several glycerophospholipids, ceramides, non-hydroxy fatty acid-sphingosine (sphingolipids), and cholesterol esters (sterols) were related to pregnancy in the Florida manatee. This research contributes to the field of manatee physiology via parallel analysis of plasma steroid hormones in relation to reproductive status. Furthermore, this study generates a novel dataset of plasma lipids in healthy Florida manatees to shed light onto the importance of certain lipids during pregnancy. These data are expected to advance understanding of manatee physiology and improve pregnancy assessments.
Acknowledgements
EBR was supported by the National Science Foundation Graduate Research Fellowship (Program Grant No. 2019285699) (2019–2021). Any opinions, conclusions or recommendations expressed in this work are those of the author(s) and do not necessarily reflect the views of the National Science Foundation. EBR is now supported by the University of Florida Block Grant Fellowship funded in part by the Florida Fish and Wildlife Conservation Commission (2021–2025).