Female Alligators Research Articles

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.

The effects of endogenous FSH and its receptor on oogenesis and folliculogenesis in female Alligator sinensis

BackgroundThe precise mechanisms of hormone action responsible for the full course of events modulating folliculogenesis in crocodilian have not been determined, although histological features have been identified.ResultsThe Alligator sinensis ovarian morphological characteristics observed at 1, 15, 30, 60, 90, and 300 days post hatching(dph) revealed that the dynamic changes in germ cells varied in different meiotic and developmental stages, confirming that the processes of folliculogenesis were protracted and asynchronous. The presence of endogenous follicle-stimulating hormone(FSH) mRNA and protein expression within the cerebrum at 1 dph, in parallel with the increase in germ cells within the germ cell nests(Nest) from 1 dph to 15 dph, suggested that endocrine regulation of the pituitary-gonad axis is an early event in oogonia division. Furthermore, the endogenous expression of FSH showed a trend of negative feedback augmentation accompanied by the exhaustion of maternal yolk E2 observed at 15 dph. Such significant elevation of endogenous FSH levels was observed to be related to pivotal events in the transition from mitosis to meiosis, as reflected by the proportion of oogonia during premeiosis interphase, with endogenous FSH levels reaching a peak at the earliest time step of 1 dph. In addition, the simultaneous upregulation of premeiotic marker STRA8 mRNA expression and the increase in endogenous FSH further verified the above speculation. The strongly FSHr-positive label in the oocytes within Pre-previtellogenic follicles was synchronized with the significant elevation of ovarian cAMP detected at 300 dph, which suggested that diplotene arrest maintenance during early vitellogenesis might be FSH dependent. In addition, preferential selection in asynchronous meiotic initiation has been supposed to act on somatic supportive cells and not directly on germ cells via regulation of FSH that in turn affects downstream estrogen levels. This suggestion was verified by the reciprocal stimulating effect of FSH and E2 on the accelerated meiotic marker SYCP3 and by the inhibited cell apoptosis demonstrated in ovarian cell culture in vitro.ConclusionThe corresponding results contribute an expansion of the understanding of physiological processes and shed some light on the specific factors responsible for gonadotropin function in the early folliculogenesis of crocodilians.

Reproductive cycles of alligator snapping turtles (Macrochelys temminckii)

The alligator snapping turtle (Macrochelys temminckii) is a species for which captive propagation and reintroduction programs are well established; however, little is known about its reproductive behavior and physiology. In this study, we measured monthly plasma sex steroid hormone concentrations of androgen (T + DHT) estradiol-17B (E2), and progesterone (P4), and used ultrasonography to monitor annual reproductive cycles of a captive population of alligator snapping turtles that is maintained under semi-natural conditions in southeastern Oklahoma. Concurrently, we used automated radio telemetry to measure the relative activity levels of male and female alligator snapping turtles and examine these activity patterns in the context of their reproductive cycles. We also measured monthly concentrations of the glucocorticoid (GC) corticosterone (CORT). Seasonal variation was only detected for T in males, but was observed for T, E2, and P4 in females. Vitellogenesis began in August and ended in April and coincided with elevated E2. Ovulation took place 10–29 April and the nesting period lasted from 11 May – 3 June. Males exhibited greater relative activity levels than females in the fall, winter, and early spring, which coincided with the period when mature sperm would be available for mating. Females were more active than males during the peri-nesting period in the spring. Seasonal changes in CORT were detected and did not differ between males and females. CORT concentrations were elevated in the late spring and summer, coincident with the foraging season, and depressed in the fall, and winter, and at their nadir in the early spring.

Social structure and habitat design affect the impact of a novel feeding enrichment for alligators.

Providing enrichment that expands the range of behavioral opportunities associated with food acquisition and environmental exploration is an important contributing factor to the well-being of zoo animals. These behaviors can be difficult to promote in carnivores, given their foraging strategies and the logistical, ethical, and financial challenges of providing live prey. In this study, we introduced a novel feeding enrichment to Jacksonville Zoo and Gardens' five adult American alligators (Alligator mississippiensis) in an attempt to simulate a live prey organism within the exhibit and promote natural hunting behaviors like chasing and lunging, as well as increase daily activity levels. The enrichment promoted some behavioral goals for two of the alligators, but it did not promote behavioral goals for the other three alligators. This could have been due to a variety of factors including an existing dominance hierarchy amongst the group's females and the resulting spatial distribution of individuals across a habitat with only one water feature. Our results suggest that female alligators may carve out territories and avoid overlapping space usage with other females during the warmest months of the year. Given the outcomes and limitations of this enrichment strategy, we provide recommendations for this group specifically as well as future enrichment efforts in the general captive crocodilian population.

Terrestrial habitats in Changxing Chinese Alligator Nature Reserve of Zhejiang and their effects on the egg laying of the female alligators

Terrestrial habitats in Changxing Chinese Alligator Nature Reserve of Zhejiang and their effects on the egg laying of the female alligators

Correlations between environmental salinity levels, blood biochemistry parameters, and steroid hormones in wild juvenile American alligators (Alligator mississippiensis)

American alligators (Alligator mississippiensis) inhabit freshwater wetlands that are vulnerable to salinization caused by anthropogenic alterations to freshwater flow, in addition to storm surges, sea level rise, and droughts. Salinization of coastal freshwater habitats is a growing concern in a changing climate due to increased frequency and intensity of storm surges and drought conditions. This study opportunistically sampled juvenile male and female wild alligators in various salinities each month excluding November, December, and January for one year at Rockefeller Wildlife Refuge in coastal Louisiana. Blood plasma biochemistry parameters including electrolyte levels were subsequently measured. In addition, levels of various renin–angiotensin–aldosterone system hormones, glucocorticoids, androgens, estrogens, and progestogens were analyzed using liquid chromatography and tandem mass spectrometry. Only males were sampled in hyperosmotic environments (> 10‰) during dry conditions in late summer 2018. In juvenile males, plasma Na+, Cl−, and the progestogen 17α,20β-dihydroxypregnenone were significantly and positively correlated with environmental salinity. However, variation in glucocorticoids, androgens, and estrogens were not associated with hypersaline water while sex steroids showed significant seasonal variation. This study demonstrated significant correlation of environmental salinity with electrolyte levels and a sex steroid in wild juvenile alligators, and to our knowledge represents the first measurement of 17α,20β-dihydroxypregnenone in alligators.

Effects of Egg Mass, Hatchling Size and Clutch on Growth of Female American Alligators ( Alligator mississippiensis )

Effects of Egg Mass, Hatchling Size and Clutch on Growth of Female American Alligators ( Alligator mississippiensis )

Multi-omics analysis reveals that natural hibernation is crucial for oocyte maturation in the female Chinese alligator

BackgroundHibernation in an appropriate environment not only is important for the survival of hibernators in winter, but also is crucial for breeding in the following season for many hibernating species. However, the genetic and epigenetic mechanism underlying this process remain unclear. In the current study, we performed an integrative multi-omics analysis of gonads collected from Chinese alligators that overwintered in wild cave and artificial warmroom to explore transcriptomic and epigenomic alternations in these organs.ResultsThe data revealed that in the breeding season, female alligators were more strongly affected in terms of gene expression than males by non-hibernation because of overwintering in a warm room, especially for genes related to oocyte maturation, and this effect commenced in winter with the downregulation of STAR, which is the rate limiting factor of steroid biosynthesis. Further, miRNAs were found to play essential roles in this negative effect of overwintering in the warm room on hibernation. The upregulated miRNAs likely were responsible for the suppression of oocyte maturation in the breeding season. Finally, DNA methylome changes, especially hypomethylation, were found to play an important role in the alterations in ovarian function-related gene expression induced by non-hibernation.ConclusionsOur study revealed the crucial role of hibernation quality for oocyte maturation in the Chinese alligator and the underlying genetic and epigenetic mechanisms, and highlights the importance of habitat, and especially, the overwintering site, in the conservation of not only the Chinese alligator, but also other endangered hibernators.

Estrogen-induced ovarian development is time-limited during the temperature-dependent sex determination of the American alligator

Many reptiles, including the American alligator, exhibit temperature-dependent sex determination (TSD), whose thermo-sensitive period for the female alligator begins at stages-15 and ends at stage-24. Estrogen signaling plays a central role in TSD, which can be overridden by an estrogen-exposure during the thermo-sensitive period. As some environmental contaminants are estrogenic, there is growing concern about their effects on the sex ratio and reproductive health of TSD-species. It is crucial to identify the timing of gonadal commitment to either ovary or testis for a better understanding of TSD and estrogen-signals. In the current study, eggs were exposed to 5 µg/g egg of 17β-estradiol (E2) or vehicle ethanol alone at three developmental stages-22, 24, and 26 at a male-promoting temperature, which produced 81% testis in all controls. E2-exposure at stages-22 and 24 induced more ovaries than the control group, whereas the exposure at stage-26 did not induce the same outcome. These results indicated that there is a critical commitment in the testicular development between the developmental stage 24 (100% ovary in E2 Exposure) and 26 (39% ovary with E2). Based on these results, we estimated a pivotal stage as stage-25.28. Thus, a gonadal commitment to testis could be later than a known temperature-sensitive period for promoting male in TSD.

Population Contributions of Large Females May be Eroded by Contaminant Body Burden and Maternal Transfer: A Case Study of Alligator Gar

AbstractWithin a population, larger individuals tend to have higher fecundity and produce higher quality eggs. For this reason, larger, older females often disproportionately contribute to recruitment. However, increases in body size and age have also been shown to correlate with increased bioaccumulation of environmental contaminants, which negatively impact reproduction and larval survival. In this study, we tested for maternal age and size effects on fecundity, egg size and quality, contaminant body burden, and maternal transfer in Alligator Gar Atractosteus spatula to assess the potential for contaminant bioaccumulation to offset reproductive benefits of large females. We measured fecundity and egg quality (via lipid content) as well as tissue concentrations of mercury, polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) in female Alligator Gar from the Trinity River, Texas. Fecundity was positively correlated with body size, but egg lipid was not significantly correlated with body size or with fecundity. Total mercury (THg) in both liver and muscle was positively correlated with maternal body size, and egg THg was positively correlated with maternal body size and liver THg. All liver and egg samples contained detectable levels of PCBs and OCPs, which were positively correlated with body size. Concentrations of PCBs and OCPs were positively correlated between tissues for each female, with egg concentrations being generally higher than liver concentrations. Based on concentrations of Hg, PCBs, and OCPs known to cause biological impairment in adult and larval fishes, the concentrations observed in this study suggest that adult reproductive function and behavior—as well as egg hatching success, larval development, and survival—could be compromised. Our results provide data that are relevant for managing the lower Trinity River Alligator Gar population and also serve as a case study demonstrating that the reproductive benefits of larger, older females may be eroded by contaminant accumulation and maternal transfer.

Examining maternal and environmental transfer of mercury into American alligator eggs.

American alligators are exposed to mercury (Hg) throughout their natural range and may maternally transfer Hg into their eggs. Wildlife species are highly sensitive to Hg toxicity during embryonic development and neonatal life, and information on Hg transfer into eggs is critical when attempting to understand the effects of Hg exposure on developing oviparous organisms. To examine Hg transfer in alligators, the objectives of the present study were to 1) determine Hg concentrations in yolk (embryonic and neonatal food source) from wild alligator eggs collected from three locations - Yawkey Wildlife Center SC (YWC), Lake Apopka FL (LA), and Lake Woodruff FL (LW); 2) examine the relationship between THg concentrations in wild alligator nest material and egg yolk at Merritt Island National Wildlife Refuge, FL; 3) examine the Hg concentrations in wild maternal female alligators (blood) and the THg in corresponding egg yolks and embryos across three nesting seasons at a single location (YWC), and evaluate the relationship between nesting female THg concentrations (blood) and their estimated age and number of nesting years (YWC); and 4) assess the transfer of biologically-relevant Hg concentrations (based on Hg measured in maternal female blood) into embryos using an egg-dosing experiment. Mean total Hg (THg) concentrations observed at each site were 26.3ng/g±11.0ng/g (YWC), 8.8ng/g±5.1ng/g (LA), and 22.6ng/g±6.3ng/g (LW). No relationship was observed between THg in alligator nest material and corresponding yolk samples, nor between THg in maternal alligator blood and estimated age and number of nesting years of these animals. However, significant positive relationships were observed between THg in blood of nesting female alligators and THg in their corresponding egg yolk. We observed that 12.8% of the maternal blood THg is found in the corresponding egg yolk, and a highly significant correlation was observed between the two sample types (r=0.66; p<0.0001). The egg dosing experiment revealed that Hg did not transfer through the eggshell at developmental stage 19. Overall, this study provides new information regarding Hg transfer in American alligators which can improve biomonitoring efforts and may inform ecotoxicological investigations and population management programs in areas of high Hg contamination.

Sex‐Specific Dynamic Rates in the Alligator Gar: Implications for Stock Assessment and Management

AbstractGrowth and mortality are commonly estimated for fish populations; however, potential differences between males and females receive less attention. Quantifying sex‐specific dynamic rates can be important as they can lead to differential exploitation, altered sex ratios, and reduced reproductive potential. We examined sex‐specific growth, size and age structure, maximum observed age, longevity, and total mortality using total length (TL), age, and sex collected from 549 Alligator Gar Atractosteus spatula from multiple Texas systems. Males (n = 324) ranged from 353 to 2,051 mm TL and 1–61 years of age, whereas females (n = 225) were 385 to 2,420 mm TL and 1–60 years old. We found significant differences in population‐specific size and age distributions between sexes. Greater than 91% of males were less than 1,500 mm TL, whereas over 63% of females sampled were greater than this length. Sixty‐four percent of males were ≤ 10 years old as compared with only 20% of females. Sex‐specific estimates of longevity and total mortality indicated that females lived 10–15 years longer than males and exhibited 25% to 40% lower total mortality. Despite similar growth rates for males and females prior to age 3, female Alligator Gar growth was greater than males at older age‐classes, resulting in a 617‐mm difference in theoretical maximum length based on the double von Bertalanffy growth model. The considerable differences we observed between sexes have important implications for population sampling and stock assessment and highlight the importance of collecting sex‐specific data.

Allometric and Biphasic Allometric Growth of Major Organs in Hatchling Female Alligators (Alligator mississippiensis)

Allometric equations represent relationships between a morphological size (e.g., organ size) or physiological rate (e.g., metabolic rate) and body mass using the equation Y=aMb, where Y is morphological size or physiological rate, a is elevation or y‐intercept, b is slope and M is animal body mass. Vertebrate organ growth relative to body mass varies between allometric (b&lt;1.0 or b&gt;1.0) and isometric (b=1.0), depending on the organ and species. In mammals and reptiles, heart and lungs have been shown to grow isometrically, whereas in mammals, the kidneys and liver have been shown to grow with negative allometry. Most allometric studies of organ growth focus on changes that span orders of magnitude achieved between juvenile and adult life stages or between various species of widely divergent size. This may ignore or possibly ‘wash out’ trends that occur during rapid growth in very early life stages. Large avian species and reptiles grow most rapidly during their early life history, and there can be significant genetic or ‘clutch’ effects for reptiles with different parentage. Large crocodilians, like the American alligator, can increase in size by a factor of &gt;10 during their first year post‐hatching and show physiological differences between clutches that persist at least through the first year post‐hatching. We measured organ growth in hatchling female alligators from 5 clutches at 8–10 time points during their first order of magnitude of growth (~45 g to ~500 g). We tracked each individual alligator (N&gt;90) from their original egg identity (clutch and egg mass). Animals were anesthetized and sacrificed, and their organs carefully dissected. Organ and animal wet masses (±0.1 mg and ±0.1 g, respectively) were measured upon sacrifice, and dry masses were measured after organs and the animal's carcass had fully dried (2d ‐ several weeks at 70°C) so that mass did not change by &gt;1% between &gt;18‐h spaced measurements. Slopes and intercepts for regressions of organ mass against body mass were compared among clutches using ANCOVA. Breakpoint analyses determined the intersection with minimum residual sum of squares or the intersection where the differences of the residual variances were smallest. Preliminary data showed that dry kidney and liver size increased in relative proportion to body mass (b~1.0), and heart size (b~0.9) and lung size (b~0.75) decreased in relative proportion. Dry masses showed less variation compared to wet masses. Within the first order of magnitude of growth, breakpoint analyses revealed that kidney and liver mass grew more quickly during the hatchlings first weeks‐to‐months post‐hatching, and our study is the first to document biphasic organ growth in hatchlings of a large, long‐lived reptile. Hatchling alligators appear to undergo a very early period of rapid kidney and liver growth following hatching, and these two organs grow with different kinetics than lung or heart tissue. Reasons for this disparity will be an area of further research.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

A new species of leech of the genus Placobdella (Hirudinida, Glossiphoniidae) from the American alligator (Alligator mississippiensis) in Mississippi, USA.

To date, the only species of leech reported from the American Alligator, Alligator mississippiensis is Placobdella multilineata. Seven specimens of a previously undescribed species of Placobdella were collected from the feet and lower jaw of a single female alligator from the Pascagoula River Wildlife Management Area, George County, Mississippi. The new species was named Placobdella siddalli Richardson & Moser, sp. n., in honor of the contributions of Dr. Mark Siddall to our understanding of the biology of leeches. Placobdella siddalli Richardson & Moser is similar to other papillated members of the genus Placobdella, but differs from Placobdella ali Hughes & Siddall, 2007, Placobdella rugosa (Verrill, 1874), Placobdella multilineata Moore, 1953, and Placobdella papillifera (Verrill, 1872) in coloration, papillation, ventral striping, and in the possession of a relatively large caudal sucker. In addition, molecular comparison of 626 nucleotides of CO-I between the new species and other papillated leeches (P. ali, P. multilineata, Placobdella ornata, P. papillifera, P. rugosa) revealed interspecific differences of 14.0–18.0% (88–113 nucleotides).

Improved genome assembly of American alligator genome reveals conserved architecture of estrogen signaling.

The American alligator, Alligator mississippiensis, like all crocodilians, has temperature-dependent sex determination, in which the sex of an embryo is determined by the incubation temperature of the egg during a critical period of development. The lack of genetic differences between male and female alligators leaves open the question of how the genes responsible for sex determination and differentiation are regulated. Insight into this question comes from the fact that exposing an embryo incubated at male-producing temperature to estrogen causes it to develop ovaries. Because estrogen response elements are known to regulate genes over long distances, a contiguous genome assembly is crucial for predicting and understanding their impact. We present an improved assembly of the American alligator genome, scaffolded with in vitro proximity ligation (Chicago) data. We use this assembly to scaffold two other crocodilian genomes based on synteny. We perform RNA sequencing of tissues from American alligator embryos to find genes that are differentially expressed between embryos incubated at male- versus female-producing temperature. Finally, we use the improved contiguity of our assembly along with the current model of CTCF-mediated chromatin looping to predict regions of the genome likely to contain estrogen-responsive genes. We find that these regions are significantly enriched for genes with female-biased expression in developing gonads after the critical period during which sex is determined by incubation temperature. We thus conclude that estrogen signaling is a major driver of female-biased gene expression in the post-temperature sensitive period gonads.

Determinate Growth and Reproductive Lifespan in the American Alligator (Alligator mississippiensis): Evidence from Long-term Recaptures

The perception that crocodilians exhibit indeterminate growth is common in the general reptilian literature. However, this assumption is frequently based on observations of immature and young adult animals and therefore lacks a complete understanding of adult growth patterns. Long-term mark-recapture studies appear to be the most certain method of determining growth patterns of adult crocodilians. From 1979–2015, we conducted a mark-recapture study of an American Alligator (Alligator mississippiensis) population on the Tom Yawkey Wildlife Center (YWC) in coastal South Carolina to examine long-term growth patterns and the influence of age on multiple reproductive parameters. We found no discernible linear growth in 19 of 31 adult female and 7 of 19 adult male alligators over periods of 5–33 years. The mean maximum reproductive lifespan for female alligators on the study site was 46 years, and females continued to reproduce for an extended period of time after reaching maximum size. The Schnute growth model...

Variation in perfluoroalkyl acids in the American alligator (Alligator mississippiensis) at Merritt Island National Wildlife Refuge

This study aimed to quantify concentrations of fifteen perfluoroalkyl acids (PFAAs) in the plasma of American alligators (Alligator mississippiensis) inhabiting wetlands surrounding the Kennedy Space Center (KSC) in Florida, USA located at Merritt Island National Wildlife Refuge (MINWR). Approximately 10 male and 10 female alligators (ntotal = 229) were sampled each month during 2008 and 2009 to determine if seasonal or spatial trends existed with PFAA burden. PFOS represented the highest plasma burden (median 185 ng/g) and PFHxS the second highest (median 7.96 ng/g). While no significant seasonal trends were observed, unique spatial trends emerged. Many of the measured PFAAs co-varied strongly together and similar trends were observed for PFOS, PFDA, PFUnA, and PFDoA, as well as for PFOA, PFHxS, PFNA, PFTriA, and PFTA, suggesting more than one source of PFAAs at MINWR. Higher concentrations of PFOS and the PFAAs that co-varied with PFOS were collected from animals around sites that included the Shuttle Landing Facility (SLF) fire house and the Neil Armstrong Operations and Checkout (O&C) retention pond, while higher concentrations of PFOA and the PFAA that co-varied with PFOA were sampled from animals near the gun range and the old fire training facility. Sex-based differences and snout-vent length (SVL) correlations with PFAA burden were also investigated.

Environmentally relevant concentrations of nitrate increase plasma testosterone concentrations in female American alligators (Alligator mississippiensis)

Anthropogenic nitrogen is a ubiquitous environmental contaminant that is contributing to the degradation of freshwater, estuarine, and coastal ecosystems worldwide. The effects of environmental nitrate, a principal form of nitrogen, on the health of aquatic life is of increasing concern. We exposed female American alligators to three concentrations of nitrate (0.7, 10 and 100mg/L NO3-N) for a duration of five weeks and five months from hatch. We assessed growth, plasma sex steroid and thyroid hormone concentrations, and transcription levels of key genes involved in steroidogenesis (StAR, 3β-HSD, and P450scc) and hepatic clearance (Cyp1a, Cyp3a). Exposure to 100mg/L NO3-N for both five weeks and five months resulted in significantly increased plasma testosterone (T) concentrations compared with alligators in the reference treatment. No differences in 17β-estradiol, progesterone, or thyroid hormones were observed, nor were there differences in alligator weight or the mRNA abundance of steroidogenic or hepatic genes. Plasma and urinary nitrate concentrations increased with increasing nitrate treatment levels, although relative plasma concentrations of nitrate were significantly lower in five month, versus five week old animals, possibly due to improved kidney function in older animals. These results indicate that environmentally relevant concentrations of nitrate can increase circulating concentrations of T in young female alligators.

In ovo treatment with an estrogen receptor alpha selective agonist causes precocious development of the female reproductive tract of the American alligator (Alligator mississippiensis)

The molecular signaling processes involved the differentiation of the Müllerian duct (MD) into the female reproductive tract, or oviduct, in non-mammalian vertebrates are not well understood. Studies in mammals and birds indicate that steroid hormones play a role in this process, as the embryonic MD has been shown to be vulnerable to exogenous estrogens and progestins and environmental endocrine disrupting contaminants. In a previous study, developmental treatment with an estrogen receptor α (ERα) agonist, 4,4′,4″-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT), induced significant enlargement of the MD in alligator embryos incubated at a male-producing temperature, which was not observed in embryos treated with an estrogen receptor β (ERβ) agonist, 7-bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol (WAY 200070), or with 17β-estradiol (E2). In order to understand the role of estrogen signaling in female alligator oviduct development, we incubated eggs at a female-producing temperature and treated them with E2 and these ER selective agonists, PPT and WAY 200070, just prior to the thermosensitive window of sex determination. At stage 27, one stage prior to hatching, PPT induced significant enlargement of the MD with precocious development of secretory glands and connective tissue differentiation similar to characteristics of mature adult oviduct. PPT treatment in ovo increased mRNA expression of ERβ, progesterone receptor, androgen receptor and insulin-like growth factor 1 in MD at stage 27, while expression of ERα was decreased. Neither WAY 200070 nor E2 treatment induced these effects seen in PPT-treated MD. The results of this study provide insight into the critical factors for healthy reproductive system formation in this sentinel species, although further investigation is needed to determine whether the observed phenomena are directly due to selective stimulation of ERα or related to some other aspect of PPT treatment.

Fallen Nestlings and Regurgitant as Mechanisms of Nutrient Transfer from Nesting Wading Birds to Crocodilians

Positive interspecific interactions can shape fundamental wetland ecosystem dynamics, including energy transfer and spatial distribution of nutrients. Birds, by foraging in one location and nesting in another, commonly act as between-ecosystem nutrient vectors. However, the distribution of nutrients within nesting areas and mechanisms of transfer to other trophic levels are poorly understood. We report on measurements of available food transferred from nesting long-legged wading birds to American alligators (Alligator mississippiensis) in the Everglades of Florida, USA. Using throughfall traps, a historic dataset on nesting success and a literature-parameterized alligator energy budget, we estimated the potential food available to alligators via regurgitant and nestling carcasses, and compared that to alligator food requirements. Although dropped regurgitant is of little importance to scavenging alligators, we estimate that nestling carcasses throughout the ecosystem could support the energetic requirements of hundreds of alligators for periods of several months. This resource occurs during the dry season, when alligator thermoregulatory opportunities are relatively scarce and female alligators are mobilizing resources for egg-laying. Our results indicate that through fallen nestlings, wading bird nesting colonies have strong potential to benefit alligators. This facilitative exchange may be globally widespread, forming a keystone process in many tropical and subtropical wetlands.