The reproductive hormone cycle of adult female American alligators from a barrier island population

Abstract

Comparatively, little data are available detailing the geographic variation that exists in the reproductive endocrinology of adult alligators, especially those living in barrier islands. The Merritt Island National Wildlife Refuge (MI) is a unique barrier island environment and home to the Kennedy Space Center (FL, USA). Seasonal patterns of sex steroids were assessed in adult female American alligators from MI monthly from 2008 to 2009, with additional samples collected at more random intervals in 2006, 2007, and 2010. Plasma 17b-estradiol and vitellogenin concentrations peaked in April, coincident with courtship and mating, and showed patterns similar to those observed in adult female alligators in other regions. Plasma concentrations of progesterone, however, showed patterns distinctly different than those reported for alligator populations in other regions and remained relatively constant throughout the year. Plasma DHEA peaked in July around the time of oviposition, decreased in August, and then remained constant for the remaining months, except for a moderate increase in October. Circulating concentrations of DHEA have not been previously assessed in a female crocodilian, and plasma concentrations coincident with reproductive activity suggest a reproductive and/or behavioral role. Interestingly, plasma testosterone concentrations peaked in May of 2008, as has been shown in female alligator populations in other regions, but showed no peak in 2009, demonstrating dramatic variability from year to year. Surveys showed 2009 to be particularly depauperate of alligator nests in MI, and it is possible that testosterone could serve as a strong indicator of breeding success.

Variations in hepatic biomarkers in American alligators ( Alligator mississippiensis ) from three sites in Florida, USA

“…Interestingly, no differences existed among sites in MT concentrations, nor were sexually dimorphic patterns of expression observed in adult alligators collected from Lakes Woodruff and Apopka. These observations suggest that differences in life stage specific expression, circulating hormone concentrations among age groups (Guillette et al, 1997; Hamlin et al, 2010; Hamlin et al, 2014; Lance, 2003; Rooney et al, 2004), contaminant exposure, or dietary shifts impact MT concentrations in alligators. Ontogenetic dietary shifts — from freshwater and estuarine diets among females and juveniles to a predominantly marine diet among large adult males — have been described in the Merritt Island NWR alligator population (Boggs et al, 2016).…”

Urinary iodine and stable isotope analysis to examine habitat influences on thyroid hormones among coastal dwelling American alligators

“…Increased feeding on estuarine prey trapped by receding water in marshes from reduced rainfall could increase UI. However, there were no significant differences in mean UI concentrations among the years studied despite a drought in May 2008 and a dramatic increase in rainfall in May 2009 (a difference of approximately 30 cm between the years) (Hamlin et al, 2014). Therefore, it is not likely that increased prey density due to drought is the cause of increased urinary iodine in this study.…”

“…Therefore, it is not likely that increased prey density due to drought is the cause of increased urinary iodine in this study. Alternatively, an increase in UI concentrations could be related to reproductive activities as April and May are the courtship and breeding season for alligators in this region (Hamlin et al, 2011; Hamlin et al, 2014). There is anecdotal evidence for courtship activities occurring in the marine environments as males have been seen bellowing at MINWR in the marine environments.…”

“…These categories were defined as juveniles (snout-vent length [SVL] < 100 cm, n = 29), small adults (100 cm < SVL < 135 cm, n = 50), and large adults (SVL > 135 cm, n = 143). These size classes were determined by previous studies on the reproductive hormone cycles of A. mississippiensis which illustrated differences in steroid hormones according to size (Hamlin et al, 2011; Hamlin et al, 2014). …”

Integrative and comparative reproductive biology: From alligators to xenobiotics

“…Dr. Guillette and colleagues have identified seasonal reproductive hormone profiles for a variety of species including mosquitofish, Florida gar, loggerhead turtle, white ibis and every life stage of the American alligator from a number of locales (Bermudez et al, 2005; Edwards et al, 2006b, 2013b, 2010; Guillette et al, 1991, 1997; Hamlin et al, 2011, 2014; Heath et al, 2003; Kristensen et al, 2007; Orlando et al, 2007, 2003; Rooney et al, 2004). His laboratory has used hormone assessments to answer questions fundamental to reproductive physiology, including the endocrine control of parturition and oviposition, gonadotropin regulation of hormone synthesis, gene regulation of steroidogenesis, and has used this information to address concerns related to human health (Crain et al, 1997; Edwards et al, 2004; Guillette et al, 1991; Hamlin and Guillette, 2010; Jones and Guillette, 1982).…”