Alligator Mississippiensis Research Articles

Crocodylian diversity during the early Eocene climatic optimum in the Golden Valley Formation of North Dakota, U.S.A.

ABSTRACT Rich bone beds from the lower Eocene strata of the Golden Valley Formation of Stark County, North Dakota reveal a speciose sympatric crocodylian fauna. However, analyses demonstrate limited phylogenetic diversity among these co-occurring taxa, and of the four species known for the locality, three are alligatorids and one is a crocodyloid. Phylogenetic hypotheses recover Chrysochampsa mylnarskii as a late lived member of Brachychampsini—a stem-based clade including Brachychampsa montana and all alligatorids more closely related to it than to Caiman crocodilus or Alligator mississippiensis—and a new genus and species, Ahdeskatanka russlanddeutsche groups with species of Allognathosuchus. The crocodylians, partitioned by body size and plan, would have occupied an array of ecological niches and feeding strategies. Whereas the large-bodied alligatorid Chrysochampsa mylnarskii preserves a generalist morphology, Ahdeskatanka russlanddeutsche bears a short, broad snout and globular distal teeth. Contemporaneous with a peak in alligatoroid diversity during this interval, Ahdeskatanka russlanddeutsche is an exemplar of a radiation of small-bodied alligatorids with crushing dentition and preserves the ancestral alligatorid feeding strategy. Trophic dynamics of the locality diverge from modern environments and the abundant crocodylians may have filled the ecological niche of large mammalian carnivores conspicuously absent here. This alligatorid-rich crocodylian fauna evolved in swampy lowlands and meandering streams flanked by subtropical forests during one of the hottest sustained intervals in Earth history. The lush, highly productive ecosystems preserved in the Golden Valley Formation inform the evolutionary history of North American alligatorids and preserve significant biodiversity following the Paleocene–Eocene Thermal Maximum.

There is no limitation for CO2 excretion across the lung in exercising American alligators (Alligator mississippiensis).

Vertebrates utilize various respiratory organs like gills, lungs, and skin in combination with diverse cardiovascular structures, including single, three, and four-chambered hearts, to enable oxygen delivery and carbon dioxide removal. They also exhibit differences in aerobic and anaerobic metabolism during exertion, but the cardiorespiratory gas transport of all vertebrates follow is a similar a four-step process governed by Fick's Principle and Fick's Law of Diffusion over the entire range of metabolic rates. Hillman et al. (2013) suggested that previous exercise studies have focused too narrowly on mammals and proposed that the cardiorespiratory system's excess capacity serves an evolutionary role in enhancing CO2 excretion in non-mammalian vertebrates. In contrast, an analysis by Hicks and Wang (2021) concluded that vertebrates maintain effective gas exchange even at peak activity, finding no evidence of arterial hypercapnia at maximal oxygen consumption and thus challenging the proposal of significant limitations to pulmonary or branchial CO2 efflux. In the present study, we investigate the limits for CO2 exchange in exercising American alligators (Alligator mississippiensis) and provide evidence that the cardiorespiratory system is adequately built to sustain CO2 excretion during strenuous exercise and maintain arterial PCO2 , with no evidence of diffusion limitation for pulmonary CO2 excretion.

Trends in American Alligator Pods in Arthur R. Marshall Loxahatchee National Wildlife Refuge

Abstract American alligators are an important component of the Greater Everglades, serving as ecosystem engineers, predator, and prey and are tightly tied to water depth patterns. Because of their importance to ecosystem function and link to hydrology, American alligators are an ecological indicator for Everglades restoration. I used data from fall nighttime spotlight surveys of American alligators in the Arthur R. Marshall Loxahatchee National Wildlife Refuge, Florida, to describe the trend in number of hatchling pods from 1998 to 2021 and relate that trend to hydrologic parameters hypothesized to influence American alligator production. I used an information-theoretic approach to evaluate 14 models created from combinations of year of observation and three hydrologic variables: average and range in water depth from 16 April of the previous year to 15 April of the nesting year (breeding potential window) and average water depth from 16 April to 31 May of the nesting year (courtship and mating window). Number of pods ranged from 16 in 1998 to 0 in 2011. Each of the four top models included year and one or more of the hydrologic variables as predictors and explained 26–34% (D-squared) of the variation in number of pods. Year was the predictor for which the 95% confidence interval (CI) did not contain 0 and indicated a declining trend (from −3 to −8%; 95% CI). I included all hydrologic variables in the top models, indicating that they contribute some information to explaining the trend; however, contrary to my hypotheses, there was not a clear relationship between any of the hydrologic variables and number of American alligator pods. I based my hypotheses on information synthesized in the American alligator production suitability index model used in Everglades restoration planning, and my results suggest the need for additional refinement of that model.

Biotransformation of carbamazepine and nicotine in juvenile American alligator (Alligator mississippiensis) in vitro hepatic S9 vs. in situ perfused liver

American alligators (Alligator mississippiensis) are apex predators and sentinel species in the coastal wetland ecosystem along the Gulf of Mexico. There is concern for alligator exposure and susceptibility to chemical contaminants due to their high trophic level and lower metabolic capability. At present, their hepatic biotransformation capacity to metabolize or detoxify contaminants has not been comprehensively determined. In this study, the hepatic biotransformation capability of juvenile American alligators to metabolize two commonly found environmental pharmaceuticals: carbamazepine (CBZ) or nicotine (NCT) was evaluated. The formation of their respective primary metabolites, i.e., carbamazepine-10,11-epoxide (CBZ-E) and cotinine (CTN), was evaluated at 10 μM (within the human therapeutic range). The in vitro S9 and a novel in situ liver perfusion assays were used to characterize and compare metabolic ability in isolated hepatic enzymes vs. whole organ (liver). For CBZ, the perfused livers exhibited only 30% of intrinsic formation clearance (CLf,int) relative to the S9 assay. The metabolism of NCT was not detectable in the S9 assay and was only observed in the perfused liver assay. Compared to the corresponding rat models (S9 or perfused livers),alligators' CLf,int was 2060% for CBZ and 50% for NCT of rats. Additionally, NCT exposure increased lactate levels in perfused livers indicating metabolic stress. This study provides insight into the hepatic capability of alligators to metabolize CBZ and NCT using an established in vitro (S9) system and a newly developed in situ liver perfusion system.

Redescription of Dracovermis occidentalis (Digenea: Liolopidae) infecting American alligator, Alligator mississippiensis from the Bon-Secour River (Mobile–Tensaw River Delta, Alabama, USA) and a revised phylogeny for Liolopidae

We examined several American alligators, Alligator mississippiensis (Daudin, 1802) (Crocodilia: Alligatoridae) from Louisiana, Alabama, and South Carolina in August 2022. The intestine of one alligator from Alabama was infected by Dracovermis occidentalis Brooks and Overstreet, 1978 (Platyhelminthes: Digenea: Liolopidae Odhner, 1912), a seldom collected and incompletely described trematode that lacks a representative nucleotide sequence. Liolopidae comprises 5 genera and 15 species: Liolope spp. infect giant salamanders; Helicotrema spp. infect turtles and lizards; Harmotrema spp. infect snakes; Paraharmotrema spp. infect turtles; and Dracovermis spp. infect crocodilians. Based on our study of the newly collected specimens and the holotype of D. occidentalis, we redescribe D. occidentalis, correct errors in its original description, and provide an updated phylogeny for Liolopidae that, for the first time, includes Dracovermis Brooks and Overstreet, 1978. Our specimens were identified as D. occidentalis by having testes in the posterior 1/3 of the body, a pretesticular cirrus sac, a spined and eversible cirrus, a bipartite seminal vesicle, and a post-acetabular vitellarium. A phylogenetic analysis of the D1–D3 domains of the nuclear large subunit ribosomal DNA (28S) recovered Liolopidae as monophyletic; however, low taxon sampling in the group precludes hypothesis-testing about liolopid-vertebrate cophyly. This is the first collection for morphological study of the type species for Dracovermis since the genus was proposed 46 years ago, the first record of a liolopid from Alabama, and the first phylogenetic analysis that includes Dracovermis.

Optimization of an in situ liver perfusion method to evaluate hepatic function of juvenile American alligators (Alligator mississippiensis).

American alligators (Alligator mississippiensis) are a sentinel species whose health is representative of environmental quality. However, their susceptibility to various natural or anthropogenic stressors is yet to be comprehensively studied. Understanding hepatic function in such assessments is essential as the liver is the central organ in the metabolic physiology of an organism, and therefore influences its adaptive capability. In this study, a novel liver perfusion system was developed to study the hepatic physiology of juvenile alligators. First, a cannulation procedure was developed for an in situ liver perfusion preparation. Second, an optimal flow rate of 0.5 ml/min/g liver was determined based on the oxygen content in the effluent perfusate. Third, the efficacy of the liver preparation was tested by perfusing the liver with normoxic or hypoxic Tyrode's buffer while various biomarkers of hepatic function were monitored in the effluent perfusate. Our results showed that in the normoxic perfusion, the aspartate transferase (AST) and lactate/pyruvate ratio in the perfusate remained stable and within an acceptable physiological range for 6 h. In contrast, hypoxia exposure significantly increased the lactate/pyruvate ratio in the perfusate after 2 h, indicating an induction of anaerobic metabolism. These results suggest that the perfused liver remained viable during the perfusion period and exhibited the expected physiological response under hypoxia exposure. The liver perfusion system developed in this study provides an experimental framework with which to study the basic hepatic physiology of alligators and elucidate the effects of environmental or anthropogenic stressors on the metabolic physiology of this sentinel species.

The consequences of calcium: investigating intracortical reproductive signals in the American alligator for sex determination.

Identifying sex in extinct archosaurs has proven difficult due, in part, to low sample sizes, preservation biases, and methodology. While previous studies have largely focused on morphological traits, here we investigate intracortical signals of egg-shelling in extant alligators. Egg-shelling requires large mobilizations of calcium reserves. Aves utilize medullary tissue as a calcium reserve, whereas crocodylians mobilize calcium from cortical bone or osteoderms. If crocodylians derive calcium from bone cortices for egg-shelling, then egg-shelling events should be detectable in female crocodylian cortical bone. We examined mid-diaphyseal Alligator mississippiensis femoral bone cross-sections for signals of reproduction. Compaction and area of resorbed tissue were measured in femoral cross-sections from captive raised male (n = 10) and female (n = 29) A. mississippiensis of 26-27 years at age of death. This sample is more robust than previous studies, though reproductive history data is unknown. Femora from a small sample of wild caught male (n = 6) and female (n = 6) A. mississippiensis were also measured. Data were analyzed by pairwise t-tests between sex and captivity status. There was no significant difference in either compaction or resorbed tissue values between male and female alligators, regardless of habitat (wild or captive-raised). A reproductive signal was undetectable in this study and any quantifiable differences between sexes appears to be driven by size dimorphism. Cortical resorption rates in the femora of male and female alligators are reflective of normal aging processes and not indicative of egg-shelling during reproduction. Examination of younger alligators would clarify processes driving bone turnover during reproductively active years.

Estimation of maximum body size in fossil species: A case study using Tyrannosaurus rex.

Among extant species, the ability to sample the extremes of body size-one of the most useful predictors of an individual's ecology-is highly unlikely. This improbability is further exaggerated when sampling the already incomplete fossil record. We quantify the likelihood of sampling the uppermost limits of body size in the fossil record using Tyrannosaurus rex Osborn, 1905 as a model, selected for its comparatively well-understood life history parameters. We computationally generate a population of 140 million T. rex (based on prior estimates), modelling variation about the growth curve both with and without sexual dimorphism (the former modelled after Alligator mississippiensis), and building in sampling limitations related to species survivorship and taphonomic bias, derived from fossil data. The 99th percentile of body mass in T. rex has likely already been sampled, but it will probably be millennia before much larger giants (99.99th percentile) are sampled at present collecting rates. Biomechanical and ecological limitations notwithstanding, we estimate that the absolute largest T. rex may have been 70% more massive than the currently largest known specimen (~15,000 vs. ~8800 kg). Body size comparisons of fossil species should be based on ontogenetically controlled statistical parameters, rather than simply comparing the largest known individuals whose recovery is highly subject to sampling intensity.

Conquering the crush: A novel tool for holding crocodilian jaws open

AbstractCrocodilians have diverse snout shapes ranging from the long, narrow snouts of the Indian gharial (Gavialis gangeticus) to the broad snout of the American alligator (Alligator mississippiensis). In addition, crocodilians possess the strongest bite force of all extant animals, with recorded values for adult alligators exceeding 9 kilonewtons (kN). Jaw‐closing pressure poses a challenge and safety risk for people working with crocodilians, such as veterinarians, wildlife managers, and researchers who must safely access the oral cavity to perform veterinary procedures, health assessments, hook removals, or sample collection. Conventionally, polyvinyl chloride (PVC) or metal tubes (pipes) placed longitudinally into the mouth have been used to hold crocodilian jaws open for such operations. The short sections of opaque pipe can cause oral irritation, obscure the palate and tongue, and restrict access to the oral cavity and palatal valve. In conjunction with a project investigating the diet of alligators in the southeastern United States, we identified a need to create an efficient tool to allow safe and direct access to the alligator oral cavity. We built 2 versions of a device for holding alligator jaws open that are adjustable to accommodate different gape sizes. The device allows for safe positioning within the mouth, includes safety considerations for device failure, and is adaptable to both widen and collapse the gape of the mouth. We successfully deployed and recovered the device on 76 wild alligators ranging in total length from 120 to 329 cm. We also performed mechanical tests in the laboratory to assess the maximum force the devices and associated materials can safely withstand, as well as the conditions under which the devices fail. Our medium‐duty and heavy‐duty device designs withstood forces up to 6 kN and 18 kN, respectively. We observed no material fracture in the devices but did observe deformations of materials used during laboratory testing. The device is an inexpensive and effective tool for veterinarians, wildlife researchers, and managers who need to hold open the jaws of crocodilians safely.

Direct and pleiotropic effects of antimicrobial peptide transgene integration on reproductive, growth regulating, and non-coding loci in channel catfish (Ictalurus punctatus)

Antimicrobial peptides (AMPs) show promise in enhancing resistance against pathogens. Previously, we integrated two AMP genes, cathelicidin (Cath) from alligator (Alligator mississippiensis or Alligator sinensis) and cecropin (Cec) from moth (Hyalophora cecropia), into the channel catfish (Ictalurus punctatus) genome. This study examines the efficacy of exogenous AMP gene integration in improving bacterial resistance in transgenic channel catfish and assesses the direct and pleiotropic effects of gene replacement/knockout on survival and growth based on insertion site. Transgenic Cath- and Cec-expressing fish exhibited similar or higher survival rates (P ​> ​0.05) compared to controls during the initial culture. Integration of the Cec transgene doubled the survival rate when challenged with Edwardsiella ictaluri, with knock-in (KI) of Cath further increasing bacterial resistance. Coupling Cec KI with mstn knockout (KO) increased survival 3-fold after E. ictaluri infection and growth by 50% at 4 months post-fertilization (mpf). However, random integration of Cec had a minimal effect on disease resistance and did not enhance growth. Random integration of Cath increased survival 2.5-fold and 4-fold against E. ictaluri and Flavobacterium covae, respectively, without affecting growth. Cath KI at the lh locus increased survival 4-fold when challenged with F. covae and reduced growth by 10% (P ​> ​0.05) at 24 mpf, whereas Cath KI coupled with mc4r KO resulted in a 2.5-fold increase in survival following F. covae infection compared with controls, and increased growth by 80% at 3 mpf. Simultaneous KI of Cath and Cec, along with KO of mc4r and mstn, increased survival 4-fold against E. ictaluri, while increasing growth by 50% at 3 mpf. Dual insertion of AMP genes yielded the greatest resistance to disease. These direct and pleiotropic effects may increase comprehension and societal acceptance of genetic engineering in aquaculture.

Host-Feeding Behavior of Mosquitoes in the Florida Everglades.

Background: West Nile virus (WNV), Everglades virus (EVEV), and five species of Orthobunyavirus were isolated from mosquitoes collected in the Everglades in 2016-2017. Prior studies of blood meals of mosquitoes in southern Florida have related findings to acquisition and transmission of EVEV, St. Louis encephalitis virus, and WNV, but not the Orthobunyavirus viruses associated with the subgenus Melanoconion of the genus Culex. Materials and Methods: In the present study, blood-fed mosquitoes were collected in the Everglades in 2016, 2017, 2021, and 2022, and from an industrial site in Naples, FL in 2017. Blood meals were identified to host species by PCR assays using mitochondrial cytochrome b gene. Results: Blood meals were identified from Anopheles crucians complex and 11 mosquito species captured in the Florida Everglades and from 3 species collected from an industrial site. The largest numbers of blood-fed specimens were from Culex nigripalpus, Culex erraticus, Culex cedecei, and Aedes taeniorhynchus. Cx. erraticus fed on mammals, birds, and reptiles, particularly American alligator. This mosquito species could transmit WNV to American alligator in the wild. Cx. nigripalpus acquired blood meals primarily from birds and mammals and frequently fed on medium-sized mammals and white-tailed deer. Water and wading birds were the primary avian hosts for Cx. nigripalpus and Cx. erraticus in the Everglades. Wading birds are susceptible to WNV and could serve as reservoir hosts. Cx. cedecei fed on five species of rodents, particularly black and hispid cotton rats. EVEV and three different species of Orthobunyavirus have been isolated from the hispid cotton rat and Cx. cedecei in the Everglades. Cx. cedecei is likely acquiring and transmitting these viruses among hispid cotton rats and other rodents. The marsh rabbit was a frequent host for An. crucians complex. An. crucians complex, and other species could acquire Tensaw virus from rabbits. Conclusions: Our study contributes to a better understanding of the host and viral associations of mosquito species in southwestern Florida.

Short communication: Characterizing arterial and venous blood gases over the gas exchange surface, the chorioallantoic membrane, of embryonic American alligators (Alligator mississippiensis) at two points of development

Assessments of arterial and venous blood gases are required to understand the function of respiratory organs in animals at different stages of development. We measured blood gases in the arteries entering and veins leaving the chorioallantoic membrane (CAM) in embryonic alligators (Alligator mississippiensis). The CAM accounts for virtually all gas exchange in these animals, and we hypothesized that the CAM vasculature would be larger in eggs incubated in hypoxia (10% O2 for 50% or 70% of incubation), which would be reflected in a lower partial pressure of CO2 (PCO2). Contrary to this hypothesis, our measurements revealed no effects of hypoxic incubation on PCO2, and seemingly no increase in vascularization of the CAM in response to incubation in 10% O2. PCO2 was lower on the venous side, but only significantly different from arterial blood at 70% of incubation. The calculated blood flow to the CAM increased with development and was lower in both groups of alligators that had been incubated in hypoxia. Future studies should include measurements of blood parameters taken from embryos held in conditions that mirror incubation O2 levels, in combination with direct measurements of CAM artery blood flow.

Pathology of "double scale" skin defect in farmed American alligators (Alligator mississippiensis) and the possible association with hepatic fibrosis.

"Double scale" is a poorly characterized skin defect of crocodilians that drastically reduces the economic value of crocodilian skin. This study investigated the morphology and pathogenesis of double scale in a ranching farm of American alligators (Alligator mississippiensis). We compared the histopathology of skin and selected organs (liver, lung, kidney, heart, spleen, intestine, and brain) of alligators with double scale against healthy control animals, together with serum and liver vitamin and mineral levels. Skin affected with double scale had statistically significant hyperkeratosis, epidermal atrophy, and increased basal cell degeneration compared with control alligators (P < .0001). Interestingly, all alligators with double scale had varying degrees of hepatic fibrosis. Feed analysis showed that alligators that had double scale and hepatic fibrosis had prolonged dietary exposure to high levels of vitamin A, iron, and copper. Serum analysis indicated that levels of zinc (p < .0001), copper (P < .05), and vitamin E (P < .002) were significantly lower in alligators with hepatic fibrosis and double scale compared with controls. Finally, immunohistochemical analysis of skin with double scale showed a marked reduction in immunolabeling with the zinc-binding protein metallothionein. These results suggest that zinc deficiency, in combination with other micronutrient anomalies, may play a role in the pathogenesis of double scale in alligators with liver fibrosis.

Galleria mellonella Invertebrate Model Mirrors the Pathogenic Potential of Mycoplasma alligatoris within the Natural Host

Most mycoplasmal infections result in chronic, clinically silent disease. In direct contrast, Mycoplasma alligatoris elicits a fulminant, multisystem disease in the natural host, Alligator mississippiensis (American alligator). The goals of the study were to better understand the disease in the natural host and to determine if the invertebrate model G. mellonella could serve as a surrogate alternate host. The survival of alligators infected intratracheally was dose dependent (p=0.0003), ranging from no mortality (102 CFU) to 100% mortality (108 CFU), with 60% mortality at the 104 and 105 CFU infectious dose. Microbial load in blood, joints, and brain was dose dependent, regardless of whether alligators were infected intratracheally or intravenously (p &lt;0.002). Weight loss was similarly impacted (p &lt;0.001). Experimental infection of the invertebrate Galleria mellonella mirrored the result in the natural host. In a dose response infection study, both larval survival curves and successful pupation curves were significantly different (p≤0.0001) and dose dependent. Infected insects did not emerge as moths (p &lt;0.0001). Here, we describe the first study investigating G. mellonella as a surrogate model to assess the pathogenic potential of M. alligatoris. G. mellonella survival was dose dependent and impacted life stage outcome.

Constitutive Innate Immunity and Systemic Responses to Infection of the American Alligator (Alligator mississippiensis).

Uninfected alligators (Alligator mississippiensis) exhibited high constitutive levels of hepatic gene expression related to immune function, whereas the highest-expressed hepatic genes of uninfected mice were related to metabolism. Intraperitoneal challenge of mice with bacterial lipopolysaccharide results in dramatic inflammatory effects including peritoneal ascites, febrile response, dramatic alterations in electrophoretic serum profile, and mortality. In contrast, coelomic injection of alligators with 200× the murine LD50 of intraperitoneal bacterial lipopolysaccharide resulted in no changes in serum protein profiles, behavioral effects, mortality, and no coelomic ascites. However, injection of juvenile alligators with live bacteria resulted in a titer-dependent decrease in metabolic rate, as measured by oxygen consumption. These results are the opposite of those observed for mammalian and avian species. The decreased oxygen consumption was not accompanied by changes in heart or respiration rate, indicating that this phenomenon was not due to bradycardia or bradypnea. Interestingly, challenge of alligators with bacteria resulted in the complete expulsion of digestive tract contents within four hours. We interpret these activities as temporary minimization of other biological systemic activities to redirect and devote energy to immune function. The reallocation of resources within an organism to fight infection without increases in metabolic rate has not been described in other animals.

Ecological implications of allometric relationships in American alligators (Alligator mississippiensis)

Morphometric allometry, the effect of size on morphological variation, has been of great interest for evolutionary biologist and is currently used in fields such as wildlife ecology to inform management and conservation. We assessed American alligator (Alligator mississippiensis) morphological static allometry across the Greater Everglades ecosystem in South Florida, United States using a robust dataset (~ 22 years) and investigated effects of sex, habitat, and sampling area on morphological relationships. Regression models showed very strong evidence of a linear relationship between variables explaining equal to or above 92% of the variation in the data. Most trait–size relationships (8 out of 11 assessed) showed hyperallometry (positive allometry) with slope deviations from isometry between 0.1 and 0.2 units while the other three relationships were isometric. Sampling area, type of habitat, and in a lesser extent sex influenced allometric coefficients (slope and intercept) across several relationships, likely as result of differing landscapes and ecosystem dynamic alterations and sexual dimorphism. We discuss our findings in terms of the biology of the species as well as the usefulness of our results in the context of ecosystem restoration and conservation of the species. Finally, we provide recommendations when using trait–length relationships to infer population nutritional—health condition and demographics.

Lipids in the American Alligator stratum corneum provide insights into the evolution of vertebrate skin

In terrestrial vertebrates, the outermost layer of the skin, the stratum corneum (SC), provides a durable and flexible interface with the environment and is comprised of corneocytes embedded in lipids. However, the morphology and lipid composition of the SC varies throughout evolutionary history. Because crocodilians and birds phylogenetically bracket the Archosaurian clade, lipid composition in crocodilian SC may be compared with that of birds and other vertebrates to make inferences about broader phylogenetic patterns within Archosaurs while highlighting adaptations in vertebrate skin. We identified and quantified lipid classes in the SC of the American Alligator (Alligator mississippiensis) from three skin regions varying in mobility. Our results find similarities in lipid composition between alligator and avian SC, including a high percentage of cerebrosides, a polar lipid previously found only in the SC of birds and bats. Furthermore, polar lipids were more abundant in the most mobile region of the SC. Because polar lipids bind with water to increase skin hydration and therefore its pliability under physical stress, we hypothesize that selection for lipids in Archosaurian SC was driven by the unique distribution of proteins in the SC of this clade, and cerebrosides may have served as pre-adaptations for flight.

The Crocodylian proatlas functions to redistribute venous blood and cerebrospinal fluid.

The proatlas, a bone located between the skull and the neural spines of the cervical vertebrae, is best known from reptiles. Most previous studies of the proatlas have centered on its developmental, debating the relationship between the proatlas and the cervical neural arches. The present study was intended as a description of the proatlas in the American alligator (Alligator mississippiensis) and an experimental test of its hypothesized role in venous blood and cerebrospinal fluid (CSF) distribution. In Alligator, the proatlas is chevron-shaped; ventrally it has a loose connection to the dorsal surface of the first cervical vertebrae, dorsally it has a robust elastic tissue tether on the otoccipital and supraoccipital bones. The ventral surface of the proatlas parallels the dorsal margin of the foramen magnum and rests on the dorsal surface of the spinal venous sinus. Experimental manipulation of the proatlas demonstrated that displacement of the proatlas causes pressure changes in both the spinal venous sinus and the enclosed spinal CSF. The results of this study represent the first demonstration of an explicit functional role for the proatlas, the circulation of fluids between the cranial and spinal compartments of the central nervous system.

Testing androgen-induced immunosuppression: Environmental androgens as a model system for steroid-immune interaction.

It is well known that hormones influence and direct most facets of physiology; however, there is still contention regarding the directions of certain relationships, for example, between gonadal hormones and immunity. Among the many proposed relationships relating to gonadal-immune interactions, support for immunosuppressive effects of androgens remains prominent within physiological literature. Although ample study has been directed towardthe immunosuppressive effects of androgens, considerable disagreement remains regarding their influence on immune function. In this study, we test the hypothesis that androgens inhibit immunocompetence in the American alligator (Alligator mississippiensis). Developing alligators were incubated at female-producing temperatures with a subset of individuals being exposed to 17-α-methyltestosterone (MT) before sexual determination. 17-α-methyltestosterone is a potent androgen, not aromatizable by crocodilians, that has been found to exert masculinizing effects in exposed crocodilian populations in vivo and in vitro. Additionally, a subset of animals was exposed to a novel antigen to quantify innate and acquired immune function. We recovered no significant differences in leukocyte ratios or proportions between groups and found no significant differences in innate immune function as measured by hemolysis-hemagglutination. However, we did find significant differences in acquired immune function, where masculinized individuals expressed greater antibody titers. Our findings reject the hypothesis that androgens suppress immune function; rather, androgens may be immunoenhancing to acquired humoral responses and neutral to innate humoral immunity in crocodilians.

Fauna Associated with American Alligator (Alligator mississippiensis) Nests in Coastal South Carolina, USA.

Crocodilians are considered to be "ecosystem engineers" because their modification of habitats provides opportunities for feeding, drinking, breeding, and other vital life activities to a wide variety of other animals. One such habitat modification is the construction of nest mounds during the breeding season by most crocodilian species, including American alligators (Alligator mississippiensis). While many reports exist describing wildlife associated with alligator nests, no studies have quantified faunal associates and their corresponding behaviors while visiting nests. To address this data gap, we used automated game cameras to monitor wildlife and their behaviors at alligator nests during the egg incubation period (June-September) in coastal South Carolina, USA (2016-2021). We documented a total of 81 species (79 vertebrates and 2 invertebrates) at 78 alligator nests representing six taxonomic groups, including 48 birds (59.2%), 9 mammals (11.1%), 19 reptiles (23.4%), 3 amphibians (3.7%), 1 malacostracan (1.2%), and 1 insect (1.2%). Collectively, faunal associates primarily used alligator nests for feeding/foraging (51.8%), traveling (29.3%), and loafing (19.9%) and to a much lesser extent basking, burrowing/shelter, breeding, and nesting. However, trends in alligator nest use varied among faunal associate groups (birds, mammals, reptiles, amphibians, etc.), subgroups (e.g., passerines, raptors, wading birds, and waterfowl), and species. Several novel behaviors by some nest associates were also noted during the study, including the first observations of Virginia oppossum (Didelphis virginiana) opening and predating nests, bobcat (Lynx rufus) consuming alligator hatchlings, and Carolina wren (Thryothorus ludovicianus) feeding on the contents of a recently predated alligator egg. The results of this study indicate that a diverse assemblage of vertebrates (and some invertebrates) use alligator nest sites in coastal South Carolina for a variety of life activities during the egg incubation period, and the proportion of the behaviors exhibited varies among animal groups and species. This study provides a first step for investigations regarding the net impacts of alligator nest-faunal associate interactions and ultimately the greater ecological role of alligators and other crocodilians.