Juvenile American Alligators Research Articles

Febrile response to infection in the American alligator ( Alligator mississippiensis)

Temperature probes were inserted into the stomachs of juvenile American alligators ( Alligator mississippiensis) maintained outdoors at ambient fluctuating temperatures. Internal body temperatures ( T b) were measured every 15 min for two days, and then the alligators were injected with bacterial lipopolysaccharide (LPS), pyrogen-free saline, or left untreated. Alligators injected intraperitoneally with LPS exhibited maximum T bs 2.6 ± 1.1 °C and 3.5 ± 1.2 °C higher than untreated control animals on days one and two after treatment, respectively. T bs for these animals fell to within control ranges by day three postinjection. Similarly, mean preferred body temperatures (MPBTs) were significantly higher for LPS-injected alligators on days one (4.2 ± 1.8 °C) and two (3.5 ± 1.6 °C) after treatment. Intraperitoneal injection of heat-killed Aeromonas hydrophila, a gram-negative bacterium known to infect crocodilians, resulted in a fever while injection of Staphylococcus aureus (gram positive) did not elicit a febrile response. Injection of LPS in alligators maintained indoors in a constant temperature environment resulted in no increase in internal T b. These results indicate that alligators did not exhibit a febrile response in the absence of a thermal gradient, and suggest that febrile responses observed are probably behavioral in nature.

Hemodynamic consequences of eliminating right‐to‐left cardiac shunt in the American alligator

Cardiac shunting occurs in all non-avian reptiles and many hypotheses have been proposed to explain why it has evolved. However, no study to date has experimentally removed the ability to shunt. The morphology of the crocodilian heart, which has a completely divided ventricle, allows elimination of right-to-left (R-L) shunting by surgical occlusion of the left aortic arch (LAo) at its base, proximal to the foramen of Panizza. We eliminated R-L shunt in juvenile American alligators (Alligator mississippiensis) both acutely and chronically. In anaesthetized and artificially ventilated alligators, we measured blood flow and pressure in the pulmonary artery (PA), left aorta (LAo) and right ventricle (RV) before and after LAo occlusion. Anesthetized animals exhibited a substantial flow in the LAo. R-L shunt was confirmed with a hydrogen electrode. Acute occlusion of the LAo eliminated flow in the LAo, prevented R-L shunt, and produced a substantial rise in RV pressure and work. These effects could be reversed by removing the suture at the base of the LAo. Chronically LAo-occluded animals tested 8–12 months after surgery exhibited a similar absence of LAo-flow, lack of shunt, and increased RV pressure. Preliminary analysis of ventricles from these chronically LAo-occluded animals suggests alterations in myocardial protein composition which may result from chronic overload. Supported by NSF IOB grant #04445680 to JWH.

Contribution of the diaphragmaticus muscle to vital capacity in fasting and post-prandial American alligators (Alligator mississippiensis)

The importance of the diaphragmaticus muscle to vital capacity was investigated in juvenile American alligators by transection of this muscle. In both fasting and post-prandial animals a pneumotach was used to study vital capacity that was stimulated by either a hypercapnic-anoxic gas mixture or a hypercapnic-normoxic gas mixture in two types of control groups of animals (a shamoperated group and a group receiving no treatment) and in the experimental (transected) group. Transection did not significantly reduce vital capacity or affect time of inspiration or expiration in fasted animals. For both the experimental and control groups vital capacity was greatly reduced in post-prandial animals compared to the fasting state. Furthermore, alligators with a transected diaphragmaticus muscle showed a 16-18% greater drop in vital capacity in the post-prandial state than did alligators with an intact diaphragmaticus muscle. The post-prandial decrease in vital capacity for alligators with a transected diaphragmaticus occurred concomitantly with a significant increase in time to inspire and a decrease in maximum rate of inspiration when compared to control animals. The results from this study suggest that the diaphragmaticus muscle plays an important role in enabling large volumes of oxygen to be taken into the lungs in the post-prandial state.

Structure and function of the esophagus of the American alligator(Alligator mississippiensis)

Esophageal structure and function were studied in juvenile American alligators (Alligator mississippiensis). The anatomy of alligators differs from humans in several important aspects: the crocodilian esophagus is more muscular and is composed entirely of smooth muscle. Functionally, the crocodilian esophagus is similar to that of mammals, but alligators have peak esophageal peristaltic pressures that are 2-3-fold greater than pressures in the human esophagus. As is found in humans, the incidence of esophageal reflux increased in postprandial animals compared with the fasting state. We observed a large increase in pressure in the lower esophageal sphincter (LES) during ventilation that ranged from 200% to 3000% of the pressures measured during apnea. These pressure changes appear to be intrinsic to the LES. Alligators lack a mammalian-type diaphragm; thus, there is no crural diaphragmatic contribution to LES pressure. These features recommend the alligator as a useful model for the study of regulation of the LES.

Seasonal variation in plasma thyroxine concentrations in juvenile alligators ( Alligators mississippiensis) from three Florida Lakes

Circulating concentrations of thyroxine (T 4) vary seasonally in many vertebrates. This study examined the seasonal variation in plasma concentrations of T 4 in juvenile American alligators ( Alligator mississippiensis) from three populations in central Florida, USA. One site, Lake Woodruff National Wildlife Refuge, is considered a reference site whereas the other two lakes, Lake Apopka and Orange Lake, are significantly impacted by human activity. Juvenile American alligators ranging from 75–150 cm in total length were hand-captured at night from November 2000–April 2002. Plasma thyroxine concentrations were analyzed using a radioimmunoassay (RIA) previously validated for alligator plasma. Juvenile American alligators display seasonal variation in circulating T 4 concentrations. Plasma T 4 concentrations decrease from August/September to November and then begin a slow rise until April, at which point they plateau. Sex of juveniles influenced plasma concentrations of T 4 in some months but did not appear to alter the pattern in seasonal variation. The pattern we observed in plasma T 4 concentrations is not directly related to an environmental factor such as ambient temperature but is similar to that seen in plasma sex steroid concentrations during the reproductive cycle of adult alligators. Although the pattern and plasma concentration of T 4 exhibits significant variation among the three lakes studied, the pattern in seasonal variation appears similar. Comparing the seasonal pattern in plasma T 4 with plasma concentrations of sex steroids (testosterone and estradiol-17β) or corticosterone could provide important information on the peripubescent life stage of the American alligator.

Variation in sex steroids and phallus size in juvenile American alligators ( Alligator mississippiensis) collected from 3 sites within the Kissimmee-Everglades drainage in Florida (USA)

This 3-year study was designed to examine variation in plasma sex steroids, phallus size, and the standard error (S.E.) associated with these endpoints in juvenile alligators collected from 3 sites within the Kissimmee-Everglades drainage (Florida, USA) with varying concentrations of sediment organochlorine contaminants. We hypothesized that decreased plasma sex steroid concentrations and phallus size would be observed in the higher contaminant site when compared to the intermediate and lower contaminant sites. Furthermore, we hypothesized that greater S.E. associated with these endpoints would be observed for the populations from more contaminated sites. We found that differences existed with females from the higher contaminant site exhibiting lower plasma estradiol-17β (E 2) and testosterone (T) concentrations. Males from the higher contaminant site exhibited smaller phallus sizes than males from the intermediate and lower contaminant sites. Smaller phallus size in this case differed from that reported in Lake Apopka male alligators [Gen. Comp. Endocrinol. 116 (1999) 356] in that a significant positive relationship between body size and phallus size existed. No difference among sites was observed in plasma T for males. Lower S.E. was associated with E 2 and T concentrations in females from the higher contaminant site and in phallus size in males from the higher contaminant site. This pattern was opposite to what we had hypothesized. We concluded that variation in plasma E 2 and T concentrations, phallus size, and the S.E. associated with these endpoints exists among the 3 sites with the patterns matching the patterns of organochlorine contamination, although S.E. patterns were opposite to what was predicted.

Abnormal bone composition in female juvenile American alligators from a pesticide-polluted lake (Lake Apopka, Florida).

Reproductive disorders have been found in pesticide-exposed alligators living in Lake Apopka, Florida (USA). These disorders have been hypothesized to be caused by exposure to endocrine- disruptive estrogen-like contaminants. The aim of this study was to expand our analysis beyond previous studies by investigating whether bone tissue, known to be affected by sex steroid hormones, is a potential target of endocrine disruptors. Long bones from 16 juvenile female alligators from Lake Apopka (pesticide-contaminated lake) and Lake Woodruff (control lake) were evaluated by peripheral quantitative computed tomography. We observed significant differences in bone composition, with female alligators from the contaminated lake having greater trabecular bone mineral density (BMD), total BMD, and trabecular mineral content compared with females from the control lake (p < 0.05). Increased trabecular and total BMD measurements suggest that juvenile female alligators from Lake Apopka were exposed to contaminants that created an internal environment more estrogenic than that normally observed. This estrogenic environment could be caused by both natural and anthropogenic compounds. Effects on BMD indicate interference with bone homeostasis. We hypothesize that contaminants present in the lake inhibit the natural and continuous resorption of bone tissue, resulting in increased bone mass. Although this is the only study performed to date examining effects of environmental estrogenic compounds on alligator bones, it supports previous laboratory-based studies in rodents. Further, this study is important in demonstrating that the alterations in morphology and physiology induced in free-ranging individuals living in environments contaminated with endocrine-active compounds are not limited to a few systems or tissues; rather, effects can be observed in many tissues affected by these hormones.

Seasonal variation in plasma sex steroid concentrations in juvenile American alligators

Seasonal variation in plasma sex steroid concentrations is common in mature vertebrates, and is occasionally seen in juvenile animals. In this study, we examine the seasonal pattern of sex hormone concentration in juvenile American alligators ( Alligator mississippiensis) and make a limited comparison of these seasonal patterns on two different lakes in Florida. Male juvenile alligators from a reference lake, Lake Woodruff, displayed temporal patterns in plasma testosterone (T) concentrations that appear to be seasonal. A similar pattern in plasma estradiol-17β (E 2) was observed in juvenile females from Lake Woodruff. Males had significantly elevated T concentrations during the spring and late summer, whereas females had elevated E 2 in the spring and late summer and significantly depressed E 2 concentrations during the winter. A limited 4-month survey of animals from contaminated Lake Apopka found a lack of such seasonality. These results suggest that: (1) healthy wild populations of juvenile alligators have a prolonged peripubescent period that is marked by seasonal hormonal cycles, (2) juvenile alligators exposed to environmental contaminants can lack such seasonal cyclicity, and (3) future studies of juvenile alligators should incorporate such seasonality into the experimental design.

Effect of acute stress on plasma β-corticosterone, estradiol-17β and testosterone concentrations in juvenile American alligators collected from three sites within the Kissimmee–Everglades drainage basin in Florida (USA)

The effect of acute stress on plasma β-corticosterone (B), testosterone (T) and estradiol-17β (E 2) concentrations in juvenile alligators collected from sites with varying sediment contaminants was examined in this study. Dramatic increases in plasma B concentrations were observed in alligators from all of the sites after 2 h of capture although females from the intermediate contaminant site exhibited a significantly lower percentage increase in B than females from the other two sites. Males from the site with the highest contaminant levels exhibited elevated initial B concentrations relative to the other sites. This pattern was not observed after 2 h of restraint. Females from the highest contaminant site exhibited depressed initial T when compared to the other sites although this pattern was not observed after 2 h of restraint. Neither E 2 nor T decreased after 2 h in females, whereas T concentrations decreased in all males over the same time period. The variance associated with these endpoints was also examined to determine whether it could serve as a more sensitive marker for perturbations of the endocrine system and stress response. Females from the higher and intermediate contaminant sites exhibited the lowest and highest standard errors (respectively) associated with 2 h plasma B concentrations with no differences among mean concentrations suggesting a perturbation of the stress response in these animals that was not detected by examining the means. We concluded that the environmental contaminants could be acting as stressors, leading to the observed differences.

Altered histology of the thymus and spleen in contaminant‐exposed juvenile American alligators

Morphological differences in spleen and thymus are closely related to functional immune differences. Hormonal regulation of the immune system has been demonstrated in reptilian splenic and thymic tissue. Spleens and thymus were obtained from juvenile alligators at two reference sites in Florida, USA: Orange Lake and a National Wildlife Refuge, Lake Woodruff, as well as from a contaminated lake, Lake Apopka. Lake Apopka has been extensively polluted with agricultural pesticides. Tissues were prepared for histological analysis to determine if previously detected endocrine abnormalities associated with contaminant exposure might also be reflected in morphological differences in splenic and thymic structures important for immunological response. Similar tissues were taken from captive-raised juvenile female alligators (3 years old) that were hatched from eggs collected on Lake Woodruff and Lake Apopka. Differences in thymic ratios (medulla/cortex) were found among alligators collected from the two lakes (P = 0.0051). Alligators from Lake Apopka had smaller thymic ratios than animals from either reference lake. Males from Lake Woodruff had significantly smaller lymphocyte sheaths in the spleen than females (P = 0.0009), indicative of a normal sexual dimorphism. Lymphocyte sheath width differed among females obtained from the three lakes, with females from Lake Apopka having the smallest sheath width and those from Orange Lake having the largest. Malpighian body area was largest in alligators from Orange Lake, intermediate in Lake Woodruff, and smallest in Lake Apopka. In contrast to that observed for wild-caught animals, no difference was found in the thymic medulla/cortex ratio of captive-raised female alligators (P = 0.378). Captive-raised female alligators from Lake Apopka and Lake Woodruff displayed lake-associated differences in lymphocyte sheath width as observed in wild animals; Lake Apopka alligators had smaller lymphocyte sheath width compared to Woodruff alligators (P = 0.0396). In contrast to wild-caught animals, area of the Malpighian bodies did not differ by lake in the captive-raised female alligators (P = 0.066). The enlarged thymic cortex suggests a change in T-lymphocyte maturation within the thymus of alligators from a contaminated environment, Lake Apopka. The results point to alterations in the histology of the thymus and spleen. Further studies are required to examine the functional significance of these observations.

Temporal and spatial variation in plasma thyroxine (T4) concentrations in juvenile alligators collected from lake Okeechobee and the northern Everglades, Florida, USA

We examined variation in plasma thyroxine (T4) in juvenile American alligators (Alligator mississippiensis) collected from three sites within the Kissimmee River drainage basin (FL, USA). Based on historical sediment data, Moonshine Bay served as the low contaminant exposure site, Water Conservation Area 3A served as an intermediate contaminant exposure site, and Belle Glade served as the high contaminate exposure site. In May 1999, alligators (n = 22) from Water Conservation Area 3A exhibited higher T4 concentrations than animals from both Belle Glade (n = 22; p = 0.0003) and Moonshine Bay (n = 33; p = 0.001). In May 2000, alligators (n = 29) Water Conservation Area 3A again exhibited higher T4 concentrations than those from Belle Glade (n = 49; p = 0.02) but not those from Moonshine Bay (n = 40). No sexual dimorphism was observed among mean T4 concentrations within any of the sites during either year (p > 0.05). Animals within all sites exhibited higher T4 concentrations in May 2000 when compared to May 1999. When variance was examined, animals from Water Conservation Area 3A exhibited higher variance in plasma T4 concentrations than those from either Moonshine Bay or Belle Glade. We concluded that mean plasma T4 concentrations did not match the sediment contaminant mixture data presently available to us, whereas variance seems to be a more reliable indicator of contaminant exposure.

Alterations in Sexually Dimorphic Biotransformation of Testosterone in Juvenile American Alligators (Alligator mississippiensis) from Contaminated Lakes

The goal of this study was to determine whether hepatic biotransformation of testosterone is normally sexually dimorphic in juvenile alligators and whether living in a contaminated environment affects hepatic dimorphism. Lake Woodruff served as our reference site. Moonshine Bay, located on the west side of Lake Okeechobee, served as an intermediate site. Lake Apopka, the Belle Glade area located at the south end of Lake Okeechobee, and Water Conservation Area 3A, in the northern Everglades, served as our contaminated sites (all lakes are in Florida). Normal testosterone hydroxylase activity exhibited sexually dimorphic patterns of expression, with reference animals from Lake Woodruff exhibiting a female:male ratio of 1.44. This pattern was perturbed in all of the intermediate and contaminated sites investigated. Normal testosterone oxido-reductase activity exhibited sexually dimorphic expression (Lake Woodruff female:male ratio of 1.45). This pattern was altered in all contaminated sites investigated. UDP-Glucuronosyltransferase activity exhibited no sexually dimorphic pattern in animals collected from our reference site, with Lake Woodruff animals exhibiting a female:male ratio of 1.06. This pattern was perturbed in animals from Water Conservation Area 3A, which exhibited a female:male ratio of 0.65. Sulfotransferase activity demonstrated no sexual dimorphism at any of the sites investigated, although elevated activity was observed in males from the Lake Okeechobee watershed compared to those from Lake Woodruff. These data demonstrate different patterns of hepatic androgen biotransformation in animals living in contaminated environments.

Alterations in sexually dimorphic biotransformation of testosterone in juvenile American alligators (alligator mississippiensis) from contaminated lakes.

The goal of this study was to determine whether hepatic biotransformation of testosterone is normally sexually dimorphic in juvenile alligators and whether living in a contaminated environment affects hepatic dimorphism. Lake Woodruff served as our reference site. Moonshine Bay, located on the west side of Lake Okeechobee, served as an intermediate site. Lake Apopka, the Belle Glade area located at the south end of Lake Okeechobee, and Water Conservation Area 3A, in the northern Everglades, served as our contaminated sites (all lakes are in Florida). Normal testosterone hydroxylase activity exhibited sexually dimorphic patterns of expression, with reference animals from Lake Woodruff exhibiting a female:male ratio of 1.44. This pattern was perturbed in all of the intermediate and contaminated sites investigated. Normal testosterone oxido-reductase activity exhibited sexually dimorphic expression (Lake Woodruff female:male ratio of 1.45). This pattern was altered in all contaminated sites investigated. UDP-Glucuronosyltransferase activity exhibited no sexually dimorphic pattern in animals collected from our reference site, with Lake Woodruff animals exhibiting a female:male ratio of 1.06. This pattern was perturbed in animals from Water Conservation Area 3A, which exhibited a female:male ratio of 0.65. Sulfotransferase activity demonstrated no sexual dimorphism at any of the sites investigated, although elevated activity was observed in males from the Lake Okeechobee watershed compared to those from Lake Woodruff. These data demonstrate different patterns of hepatic androgen biotransformation in animals living in contaminated environments.

Plasma Dihydrotestosterone Concentrations and Phallus Size in Juvenile American Alligators (A. mississippiensis) from Contaminated and Reference Populations

Evidence increasingly suggests that some environmental pollutants are able to permanently affect development of the endocrine system in wildlife. Embryonic and neonatal exposure to these endo- crine-disrupting contaminants can cause structural and functional abnormalities of the reproductive system. It has recently been hypothesized that demasculinization of a population of male juvenile American alli- gators (Alligator mississippiensis) from Lake Apopka, Florida, could result from exposure to antiandrogenic contaminants. The persistent pesticide contaminant p.p'-DDE interacts with the mammalian androgen recep- tor and antagonizes androgen action in vivo. Wildlife from Lake Apopka, which has been contaminated through agriculture and an industrial accident, exhibit elevated levels of p.p.'-DDE, among other pesticide residues. This study provides further evidence of reproductive dysfunction in Lake Apopka juvenile alli- gators by comparison with a reference population from a relatively uncontaminated lake nearby, Lake Woodruff National Wildlife Refuge. Phallus size correlated strongly with plasma dihydrotestosterone (DHT) concentrations or body size in juvenile males from Lake Woodruff In contrast, males from Lake Apopka had significantly smaller phalli (adjusted for body size) than those from Lake Woodruff, and correlations with body size or plasma DHT concentrations were weak or absent. Plasma DHT concentrations did not differ significantly between juvenile males from the two lakes. In contrast, plasma DHT concentrations were significantly higher in females from Lake Apopka compared to those from Lake Woodruff This is the first report of masculinized female juvenile alligators from Lake Apopka and suggests that juveniles of both sexes exhibit altered endocrine and reproductive parameters.

Serum concentrations of various environmental contaminants and their relationship to sex steroid concentrations and phallus size in juvenile American alligators.

Recent studies have reported a number of abnormalities in the hatchling and juvenile alligators of Lake Apopka, FL (USA). These abnormalities include modifications of plasma concentrations of sex steroids in males and females as well as abnormalities in gonadal morphology, gonadal enzyme activity, and steroidogenesis. Embryonic exposure to environmental contaminants in the eggs has been hypothesized to be the causal agent for these changes. However, posthatchling exposure can also contribute to changes in reproductive and endocrine functioning. We have detected serum concentrations of 16 of 18 organochlorine pesticides or metabolites (OCs) and 23 of 28 congener-specific polychlorinated biphenyls (PCBs) examined in juvenile alligators from Lake Apopka, Orange Lake, and Lake Woodruff National Wildlife Refuge. Lake Apopka juveniles had significantly elevated serum concentrations of p,p'-DDE, dieldrin, endrin, mirex, oxychlordane, SigmaDDTs, and SigmaPCBs compared to juveniles from the other lakes. Further, we observed no correlations between serum contaminant concentrations and sex steroid concentrations (estradiol-17beta and testosterone). However, serum testosterone was significantly lower in males from Lake Apopka and Orange Lake compared to Lake Woodruff NWR. We did not observe relationships between phallus size or other body parameters and serum contaminant levels. Phallus size was smaller in males from Lake Apopka even after adjustment for body size. We suggest that the observations previously reported for juvenile alligators-and observed again in this study-are apparently not associated with the current serum levels of the environmental contaminants we measured, but could be due to exposures during embryonic development to these or other pollutants. Future studies must determine if a causal relationship exists between the contaminants found in alligator eggs and abnormalities observed in the hatchlings and persisting in juveniles.

Gular pumping responses by juvenile American alligators (Alligator mississippiensis) to meat scents

Gular pumping responses by juvenile American alligators (<i>Alligator mississippiensis</i>) to meat scents

Glycolysis and Swimming Performance in Juvenile American Alligators

Glycolysis and Swimming Performance in Juvenile American Alligators

Food Habits of Juvenile American Alligators in the Upper Lake Pontchartrain Estuary

Food habits of juvenile (0.49-1.21 m total length) American alligators (Alligator mississippiensis) from an area in southeastern Louisiana were investigated. One-hundred and one stomach samples were obtained by stomach-pumping. Crustaceans (crayfish; blue crabs, Callinectes sapidus; grass shrimp, Palaemonetes sp.), insects (hemipterans, coleopterans), and small fish (least killifish, Heterandria formosa; mosquitofish, Gambusia affinis) constituted the majority of prey items taken. Fish consumption was significantly more frequent during April and May than during June through September (P<0.025). This differential use of prey species may be due to seasonally fluctuating water levels in the study area. Comparisons of juvenile alligator food habits revealed dietary differences between Louisiana and Florida (P<0.001), possibly due to the different prey available at the two areas. Prey utilization was not significantly different between larger alligators (0.9-1.2 m total length) and smaller alligators (0.3·0.9 m total length) (P>0.25).

Late Summer Diet of Juvenile American Alligators

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Serum Concentration and Disposition Kinetics of Gentamicin and Amikacin in Juvenile American Alligators

Serum Concentration and Disposition Kinetics of Gentamicin and Amikacin in Juvenile American Alligators