Social Displays of the American Alligator (Alligator mississippiensis)

Adult alligators perform two conspicuous social displays, bellowsand headslaps. Both of these behaviors are performed from ahead oblique tail arched (HOTA) posture. Bellow displays,by both males and females, involve the production of a loud,roaring vocalization. Male alligators also produce a infrasonicsignal, termed subaudible vibrations, just prior to the audiblebellow. Bellowing occurs throughout the year but is most frequentduring the courting season, when alligators bellow daily inchoruses. Chorus length appears to be correlated with the sizeof the adult population. Chorusing is frequently initiated byfemales but seems to be perpetuated by male alligators. Bellowingmay serve to attract alligators of the opposite sex and possiblyto space out animals of the same sex. The headslap display is an assertion display consisting of eightcomponent behavioral acts: the elevated posture, HOTA posture,subaudible vibrations, headslap, jawclap, growl, inflated posture,and tail wag. Each act component is variable in presence andintensity producing a highly variable, graded signal. The alligatortypically remains motionless in the HOTA posture for about 16sec before executing the headslap/jawclap acts. The headslapdisplay involves a rapid clapping shut of the jaws as the undersurfaceof the head is slapped against the water surface. Headslappingis most common in early morning and afternoon hours. Analysisof 1,050 headslap displays by 91 known individuals indicatesthat 94.5% of the observed displays were performed by males.Headslap displays are generally performed from typical displaysites which the alligator seeks out prior to the display. Responsesto headslap displays include headslapping by others, lunges,approaches, and bellow growling. The headslap display functionsas a declaration of presence. A musky odor is commonly detected in association with both ofthese social displays, suggesting a possibly important, butlittle understood, pheromonal component of these behaviors. The displays both involve complex signals including visual,auditory, olfactory and possibly tactile channels of communication.Most of the behaviors described are shared with many other speciesof crocodilians.     

Biochemistry and Physiology of Alligator Metabolism in vivo

The metabolic rate of the alligator is a direct function ofthe volume of blood flowing through the capillaries/unit time/unitweight, which in turn, is determined by the heart rate and thestroke volume. For an animal with such a low metabolic rate,the heart rate is relatively rapid, in part because the heartis relatively small. Metabolic rate of the smallest alligatorexceeds that of the largest by about 25 to 1. Lowering the temperaturedecreases blood flow without decreasing the oxygen and substrateextracted from each liter. Metabolic rate (oxygen consumption)is expressed by the equation M.R. = F(A – V), where Fis the blood flow and A – V is the oxygen A – Vdifference. For the catabolism of compounds in which oxygenis not directly involved, the expression is V = KF[S], whereV is the velocity of the reaction, F is the blood flow, and[S] is the concentration of the substrate. K is a constant,differing for each catabolite, but having about the same valuefor any one catabolite in vertebrates, cold- or warm-blooded.Enzyme kinetics in a live vertebrate has little in common withthat determined in the usual experiments in vitro. A 70 kg alligatorat 28°C has a blood flow of 0.2 liters/min, a stroke volumeof 6.3 ml, a circulation time of 27 min, and it produces about72 kcal/day, or about 4% of that of a man of equal size.     

扬子鳄(Alligator sinensis)生态学研究进展

简要介绍了半个多世纪以来,扬子鳄自然种群的变化、种群衰落的原因、生活史对策、栖息地选择、行为生态、生理生态等方面的主要研究成果,并对将来的研究进行了展望。     

环境因素对圈养的扬子鳄营巢和产卵的影响

在2002～2004年的6-7月,每天观察扬子鳄的营巢行为,记录天气状况,得出扬子鳄的营巢时间受天气的影响,巢材湿度会影响鳄的产卵时间;在6月下旬末大雨天后,连续2～3天气温能保持在26～35℃时,鳄就会产卵;在整个产卵期巢受到严重破坏时,鳄不会产卵。     

Oogenesis and ovarian histology of the American alligator Alligator mississippiensis

Although folliculogenesis and oogenesis have been observed in numerous reptiles, these phenomena have not been described in detail in a crocodilian. Oogenesis and histological features of the adult ovary of Alligator mississippiensis are described. Using a complex process, the ovary develops telolecithal oocytes that attain a diameter of 38.8 +/- 2.4 mm. The morphology of yolk platelets shows gradual changes throughout the oogenic process. Initially, yolk platelets are seen surrounded by a vesicle. As vitellogenesis advances, the vesicles contain numerous yolk spheres, with slowly growing platelets. The yolk spheres continue to increase in size and number within the vacuoles. Differences in the animal and vegetal poles are seen based on the morphology and size of the yolk platelets. The ovary of A. mississippiensis shows a well-developed system of lacunae and bundles of smooth muscle around the follicles in all stages of development. Several features seen in the ovary of A. mississippiensis are similar to those observed in birds. In particular, the morphology of the yolk platelets, especially during the middle and late vitellogenic stages, and the presence of a ovarian system of lacunae and smooth muscle. These similarities in the reproductive biology of crocodilians and birds contribute to current studies of the evolution of archosaurian reproduction.     

Glutamine synthetase in liver of the American alligator, Alligator mississippiensis

Glutamine synthetase was shown to be localized in liver mitochondria of the American alligator, Alligator mississippiensis, by immunofluorescent staining of frozen liver sections and by the detection of enzymatic activity and immunoreactive protein in the mitochondrial fraction following subcellular fractionation of liver tissue by differential centrifugation. The primary translation product of alligator liver glutamine synthetase mRNA was shown to have an Mr = 45,000 which is similar if not identical in size to that of the mature subunit. This mRNA was found to be heterogeneous in size with a major form corresponding to 2.8-3.0 kb and a lesser form corresponding to around 2 kb. Both are in excess of the size required to code for the glutamine synthetase subunit. The synthesis and presumably the mitochondrial import of glutamine synthetase in alligator liver are thus very similar to the same processes in avian liver. Despite the excretion of a high percentage of nitrogen as ammonia, the demonstration of a mitochondrial glutamine synthetase indicates the alligator has the typical avian-type uricotelic ammonia-detoxification system in liver. This suggests that the transition to uricotelism occurred in the sauropsid line of evolution and has persisted through both the lepidosaurian (snakes, lizards) and archosaurian (dinosaurs, crocodilians, birds) lines.     

Growth dynamics in the American alligator (Alligator mississippiensis)

The growth dynamics of the American alligator ( Alligator mississippiensis ) were studied in the subtropical Florida Everglades using extensive mark-recapture data from over 2000 recaptures of known-aged and unknown-aged animals. A model based on the power curve best describes growth of Everglades alligators. The nonasymptotic character of this curve leads to rejection of the hypothesis that alligator growth is determinate. A model consisting of piece-wise linear equations better described growth in the first year, and suggested a period of arrested growth occurred in the first winter. A comparison of predictions from growth models derived from several populations indicated that Everglades alligators grew more slowly than did those in more temperate areas, leading to the rejection of the hypothesis that growth rates in subtropical Florida would be elevated because of the long growing season. We attribute this result to a combination of increased maintenance costs and a limited resource base in the Everglades.
Analyses considered the extent to which growth model evaluation and use can be affected by data selection. Mathematical constraints posed by negative growth data can be alleviated by including growth records over combined recapture intervals to achieve a positive growth increment. However, periods of no to negative growth may be real, and such deviations are obscured by fitting growth data to monotonically increasing models.     

Amphibious auditory responses of the American alligator (Alligator mississipiensis)

Animals that thrive both on land and underwater are faced with the task of interpreting stimuli in different media. This becomes a challenge to the sensory receptors in that stimuli (e.g., sound, motion) may convey the same type of information but are transmitted with different physical characteristics. We used auditory brainstem responses to examine hearing abilities of a species that makes full use of these two environments, the American alligator (Alligator mississipiensis). In water, alligators responded to tones from 100 Hz to 2,000 Hz, with peak sensitivity at 800 Hz. In air, they responded to tones from 100 Hz to 8,000 Hz, with peak sensitivity around 1,000 Hz. We also examined the contribution to hearing of an air bubble that becomes trapped in the middle ear as the animal submerges. This bubble has been previously implicated in underwater hearing. Our studies show that the trapped air bubble has no affect on auditory thresholds, suggesting the bubble is not an important adaptation for underwater hearing in this species.     

Amoebacidal effects of serum from the American alligator (Alligator mississippiensis)

Treatment of axenic Naegleria gruberi cultures with alligator serum resulted in time-dependent amoebacidal activity, with measurable activity at 5 min and maximal activity occurring at 20 min. The amoebacidal activity was concentration dependent, with measurable activity at 25% serum, whereas treatment of amoebas with undiluted serum resulted in only 16% survival. The efficacy was dependent on the concentration of amoebas, with higher survival rates at high amoeba densities and lower survival rates at low amoeba densities. The amoeba-killing effects of alligator serum were broad in spectrum because the serum was effective against 3 strains of Naegleria species tested and 4 Acanthamoeba species, which have been reported to be resistant to human serum complement-mediated lysis. The amoebacidal effects of alligator serum were temperature dependent, with optimal activity at 15-30 C and a decrease in activity below 15 C and above 30 C. The amoebacidal activity of alligator serum was heat labile and protease sensitive, indicating the proteinaceous nature of the activity, and was also inhibited by ethylenediaminetetraacetic acid, which indicated a requirement for divalent metal ions. These characteristics strongly suggest that the amoebacidal properties of alligator serum are because of complement activity.     

Habitat Quality Affects Early Physiology and Subsequent Neuromotor Development of Juvenile Black-Capped Chickadees

In songbirds, the ability to learn and render the species-specific song is influenced by the development of both the song nuclei in the brain and the syrinx (bird''s vocal apparatus) early in the bird''s life. In black-capped chickadees (Poecille atricapillus), habitat quality is known to affect song structure, with birds in high-quality habitat (mature forest) having a higher song consistency than birds in low-quality habitat (young forest). Although this difference is suspected to stem from differences in development, the developmental status of juvenile birds in either habitat remains unexplored. In this study, we used ptilochronology and feather corticosterone to compare the conditional state of juvenile chickadees in young and mature forest during two distinct periods of song learning - the sensory phase, which occurs prior to settlement, and the sensorimotor phase, which occurs post-settlement. A sample of juvenile males was captured and euthanized several weeks prior to their first breeding season to compare the development of song center nuclei and syrinx in both habitats. The corticosterone levels of natally-grown feathers were greater among birds that settled in mature than young forests - as these feathers were grown pre-settlement, they reflect differences in physiology during the sensory phase. This difference in conditional state is reflected by differences in syrinx and song center nuclei development later during the sensorimotor phase - birds in young forest have smaller syrinx, and moderately-larger RA, than birds in mature forest. Those differences could be responsible for the difference in consistency in song structure observed across habitats. The difference in physiological state across habitats, combined with potential compounding effect of differences in winter resources between habitats, could influence the difference in syrinx and neural development seen in juvenile males during the early spring, and influence the male''s ability to learn and render their species-specific song.     

Antibacterial properties of serum from the American alligator (Alligator mississippiensis)

Treatment of alligator (Alligator mississippiensis) and human serum samples with Escherichia coli resulted in a time- and concentration-dependent inhibition of bacterial proliferation. When inoculated with E. coli, alligator serum exhibited 10-fold lower bacterial survival rates after 1 h than human serum. In addition, the antibacterial spectrum of alligator serum was shown to be much broader than that of human serum, with growth inhibition occurring in 100% of bacterial strains tested (compared to only 35% for human serum). Additional results showed that the antimicrobial activities of alligator serum could be completely inhibited by preincubation with proteases, indicating the proteinaceous nature of the antimicrobial activities. Furthermore, incubation of alligator serum at 56 degrees C for 30 min (classical human serum complement inactivation conditions) obliterated all antimicrobial properties of the alligator serum. The antibacterial activities occurred relatively quickly in vitro, with significant activity occurring within 5 min of inoculation with E. coli and maximal activity at 20 min. Also, the antimicrobial activity exhibited temperature dependence, with a substantial decrease in activity below 15 degrees C. These data suggest that the antimicrobial properties of alligator serum may be due to an active serum complement system.     

Isolation of Aeromonas hydrophila from the American alligator, Alligator mississippiensis.

Aeromonas hydrophila was isolated from the internal organs of nine adult alligators, Alligator mississippiensis, which died without apparent cause, suggesting the bacterium may have been a factor. One hundred and twenty-three alligators ranging in age from six months to over 10 years were captured from five locations in the southeastern United States and sampled for A. hydrophila. The bacterium was isolated from the oral cavity of 85% of the animals, on the external jaw area from over 50% and from 70% of the internal tissue samples. A. hydrophila is ubiquitous with alligators in their natural habitats, but apparently does not cause clinical disease. However, stress factors such as trapping, handling, and warm water temperatures may be conducive to the rapid proliferation of the bacteria, thereby facilitating disease.     

Intestinal brush border membrane-bound disaccharidases of the American alligator, Alligator mississippiensis

1. The disaccharidase activities of the small intestines of American alligators (Alligator mississippiensis) were studied in epithelial scrapes and brush-border membrane preparations. 2. Maltase, isomaltase and trehalase activities were found. Activities of these enzymes were higher in the proximal small intestine and decreased distally. 3. Disaccharidase activities were enriched 12-15 times in brush-border membrane preparations, compared with mucosa/enterocyte crude homogenates and were co-enriched with the brush-border membrane marker alkaline phosphatase. 3. The pH optima were: maltase 6.5; isomaltase 5.6; and trehalase 5.8. The Q10 of maltase, the most active enzyme, was equal to 1.82. 4. In reptiles, as in mammals, disaccharidase activities may be correlated with feeding habits. The co-occurrence of sucrase and isomaltase may not be a common feature of vertebrates.     

Formation and regression of the corpus luteum of the American alligator (Alligator mississippiensis)

Luteal morphology of the American alligator is unique when compared to other reptiles but is similar to that of its phylogenetic relatives, the birds. The theca is extensively hypertrophied, but the granulosa never fills the cavity formed following the ovulation of the ovum. The formation of the corpus luteum (CL) is correlated with elevated plasma progesterone concentrations, which decline dramatically after oviposition with the onset of luteolysis. Unlike those of most other reptiles, the central luteal cell mass is composed of two cell types; one presumably is derived from the granulosa, whereas the other is from the theca interna. Both cell types are present throughout gravidity but only one cell type is seen during mid to late luteolysis. A significant decline in luteal volume occurs following oviposition and continues throughout the post-oviposition period. The fastest decline in luteal volume occurs in the month immediately after oviposition; this rate then slows. Luteolysis appears to continue for a year or more following oviposition, as distinct structures of luteal origin can still be identified in animals 9 months after oviposition. The size of persistent CL can be used to determine whether a given female oviposited during the previous nesting season. Females with CL having volumes greater than 0.2 cm² or CL diameters greater than 0.4 cm were active the previous season. © 1995 Wiley-Liss, Inc.     

Multiyear multiple paternity and mate fidelity in the American alligator, Alligator mississippiensis

We examined multiple paternity during eight breeding events within a 10-year period (1995–2005) for a total of 114 wild American alligator nests in Rockefeller Wildlife Refuge in south-west Louisiana. Our goals included examining (i) within population variation in multiple paternity among years, (ii) variation in multiple paternity in individual females and (iii) the potential for mate fidelity. To accomplish this, in the current study, eggs were sampled from 92 nests over 6 years and analysed along with 22 nests from a previous 2-year study. Genotypes at five microsatellite loci were generated for 1802 alligator hatchlings. Multiple paternity was found in 51% of clutches and paternal contributions to these clutches were highly skewed. Rates of multiple paternity varied widely among years and were consistently higher in the current study than previously reported for the same population. Larger females have larger clutches, but are not more likely to have multiply sired nests. However, small females are unlikely to have clutches with more than two sires. For 10 females, nests from multiple years were examined. Seven (70%) of these females exhibited long-term mate fidelity, with one female mating with the same male in 1997, 2002 and 2005. Five females exhibiting partial mate fidelity (71%) had at least one multiple paternity nest and thus mated with the same male, but not exclusively. These patterns of mate fidelity suggest a potential role for mate choice in alligators.     

Hind limb movements of the American alligator (Alligator mississippiensis) and postural grades

Middle ear ontogeny in Monodelphis domestica is investigated to understand better both the immediate consequences for suckling in a neonate marsupial and the epigenetic factors that constrain morphogenesis. Neonates of Monodelphis possess neither mammalian (dentarysquamosal) nor reptilian (quadrate-articular) jaw articulations, nor does the contact between the incus and crista parotica offer a joint surface ( contra Maier, 1987). Elasticity in Meckel's cartilage allows minimal deflection of the lower jaw. Observation of the developmental rate of the individual elements reveals that mandibular arch derivatives (malleus, incus and tensor tympani) are on a slightly faster ontogenetic schedule than hyoid arch derivatives (stapes and m. stapedius).     

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(b)s 2.6+/-1.1 degrees C and 3.5+/-1.2 degrees C higher than untreated control animals on days one and two after treatment, respectively. T(b)s 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 degrees C) and two (3.5+/-1.6 degrees 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.     

Animal-Borne Imaging Reveals Novel Insights into the Foraging Behaviors and Diel Activity of a Large-Bodied Apex Predator,the American Alligator (Alligator mississippiensis)

Large-bodied, top- and apex predators (e.g., crocodilians, sharks, wolves, killer whales) can exert strong top-down effects within ecological communities through their interactions with prey. Due to inherent difficulties while studying the behavior of these often dangerous predatory species, relatively little is known regarding their feeding behaviors and activity patterns, information that is essential to understanding their role in regulating food web dynamics and ecological processes. Here we use animal-borne imaging systems (Crittercam) to study the foraging behavior and activity patterns of a cryptic, large-bodied predator, the American alligator (Alligator mississippiensis) in two estuaries of coastal Florida, USA. Using retrieved video data we examine the variation in foraging behaviors and activity patterns due to abiotic factors. We found the frequency of prey-attacks (mean = 0.49 prey attacks/hour) as well as the probability of prey-capture success (mean = 0.52 per attack) were significantly affected by time of day. Alligators attempted to capture prey most frequently during the night. Probability of prey-capture success per attack was highest during morning hours and sequentially lower during day, night, and sunset, respectively. Position in the water column also significantly affected prey-capture success, as individuals’ experienced two-fold greater success when attacking prey while submerged. These estimates are the first for wild adult American alligators and one of the few examples for any crocodilian species worldwide. More broadly, these results reveal that our understandings of crocodilian foraging behaviors are biased due to previous studies containing limited observations of cryptic and nocturnal foraging interactions. Our results can be used to inform greater understanding regarding the top-down effects of American alligators in estuarine food webs. Additionally, our results highlight the importance and power of using animal-borne imaging when studying the behavior of elusive large-bodied, apex predators, as it provides critical insights into their trophic and behavioral interactions.     

Isolation of faecal coliform bacteria from the American alligator (Alligator mississippiensis)

Aims: To determine whether American alligators (Alligator mississippiensis) are an unrecognized poikilothermic source of faecal coliform and/or potential pathogenic bacteria in South Carolina’s coastal waters. Methods and Results: Bacteria from the cloaca of American alligators, as well as bacteria from surface water samples from their aquatic habitat, were isolated and identified. The predominant enteric bacteria identified from alligator samples using biochemical tests included Aeromonas hydrophila, Citrobacter braakii, Edwardsiella tarda, Escherichia coli, Enterobacter cloacae, Plesiomonas shigelloides and putative Salmonella, and these were similar to bacteria isolated from the surface waters in which the alligators inhabited. Based on most‐probable‐number enumeration estimates from captive alligator faeces, faecal coliform bacteria numbered 8·0 × 10⁹ g^?1 (wet weight) of alligator faecal material, a much higher concentration than many other documented endothermic animal sources. Conclusions: A prevalence of enteric bacteria, both faecal coliforms and potential pathogens, was observed in American alligators. The high faecal coliform bacterial density of alligator faeces may suggest that alligators are a potential source of bacterial contamination in South Carolina coastal waters. Significance and Impact of the Study: These findings help to increase our understanding of faecal coliform and potential pathogenic bacteria from poikilothermic reptilian sources, as there is the potential for these sources to raise bacterial water quality levels above regulatory thresholds.