Phillip L. Trosclair

Seasonal acclimatisation of muscle metabolic enzymes in a reptile (Alligator mississippiensis)

SUMMARY Reptiles living in heterogeneous thermal environments are often thought to show behavioural thermoregulation or to become inactive when environmental conditions prevent the achievement of preferred body temperatures. By contrast, thermally homogeneous environments preclude behavioural thermoregulation, and ectotherms inhabiting these environments (particularly fish in which branchial respiration requires body temperature to follow water temperature) modify their biochemical capacities in response to long-term seasonal temperature fluctuations. Reptiles may also be active at seasonally varying body temperatures and could, therefore, gain selective advantages from regulating biochemical capacities. Hence, we tested the hypothesis that a reptile (the American alligator Alligator mississippiensis) that experiences pronounced seasonal fluctuations in body temperature will show seasonal acclimatisation in the activity of its metabolic enzymes. We measured body temperatures of alligators in the wild in winter and summer (N=7 alligators in each season), and we collected muscle samples from wild alligators (N=31 in each season) for analysis of metabolic enzyme activity (lactate dehydrogenase, citrate synthase and cytochrome c oxidase). There were significant differences in mean daily body temperatures between winter (15.66±0.43°C; mean ± S.E.M.) and summer (29.34±0.21°C), and daily body temperatures fluctuated significantly more in winter compared with summer. Alligators compensated for lower winter temperatures by increasing enzyme activities, and the activities of cytochrome c oxidase and lactate dehydrogenase were significantly greater in winter compared with summer at all assay temperatures. The activity of citrate synthase was significantly greater in the winter samples at the winter body temperature (15°C) but not at the summer body temperature (30°C). The thermal sensitivity (Q10) of mitochondrial enzymes decreased significantly in winter compared with in summer. The activity of mitochondrial enzymes was significantly greater in males than in females, but there were no differences between sexes for lactate dehydrogenase activity. The differences between sexes could be the result of the sex-specific seasonal demands for locomotor performance. Our data indicate that biochemical acclimatisation is important in thermoregulation of reptiles and that it is not sufficient to base conclusions about their thermoregulatory ability entirely on behavioural patterns.

Body Temperature Null Distributions in Reptiles with Nonzero Heat Capacity: Seasonal Thermoregulation in the American Alligator (Alligator mississippiensis)

Regulation of body temperature may increase fitness of animals by ensuring that biochemical and physiological processes proceed at an optimal rate. The validity of current methods of testing whether or not thermoregulation in reptiles occurs is often limited to very small species that have near zero heat capacity. The aim of this study was to develop a method that allows estimation of body temperature null distributions of large reptiles and to investigate seasonal thermoregulation in the American alligator (Alligator mississippiensis). Continuous body temperature records of wild alligators were obtained from implanted dataloggers in winter (n = 7, mass range: 1.6–53.6 kg) and summer (n = 7, mass range: 1.9–54.5 kg). Body temperature null distributions were calculated by randomising behavioural postures, thereby randomly altering relative animal surface areas exposed to different avenues of heat transfer. Core body temperatures were predicted by calculations of transient heat transfer by conduction and blood flow. Alligator body temperatures follow regular oscillations during the day. Occasionally, body temperature steadied during the day to fall within a relatively narrow range. Rather than indicating shuttling thermoregulation, however, this pattern could be predicted from random movements. Average daily body temperature increases with body mass in winter but not in summer. Daily amplitudes of body temperature decrease with increasing body mass in summer but not in winter. These patterns result from differential exposure to heat transfer mechanisms at different seasons. In summer, alligators are significantly cooler than predictions for a randomly moving animal, and the reverse is the case in winter. Theoretical predictions show, however, that alligators can be warmer in winter if they maximised their sun exposure. We concluded that alligators may not rely exclusively on regulation of body temperature but that they may also acclimatise biochemically to seasonally changing environmental conditions.

Telomere Length Shortens with Body Length in Alligator mississippiensis

Abstract In Alligator mississippiensis (American Alligator), body length increases with age, but body length can be used as an accurate estimator of age only up to about 6–7 years, when growth rates slow considerably. Telomeres are repetitive DNA sequences that cap the ends of each chromosome. Telomeres shorten with age in most animals, but telomere shortening has not been examined in reptiles. We measured telomere length in erythrocytes of A. mississippiensis varying between ≈ 5 and 240 cm in body length and found a negative relationship between telomere length and body length (P < 0.01). Assuming that erythrocyte telomeres continue to shorten with time, even after growth rate declines, those individuals with the shortest telomeres should be the oldest members of the population. This method of estimating age, even in animals of similar body size, should allow questions about age structure and senescence to be addressed.

Ultrasonography of reproductive structures and hormonal correlates of follicular development in female American alligators, Alligator mississippiensis, in southwest Louisiana.

Ultrasonography has been used effectively to study reproduction in a variety of reptile species, but its application to crocodilians has been relatively limited. We present results from a study testing the efficacy of using ultrasonography to monitor reproduction in the American alligator, Alligator mississippiensis. Ultrasound results were then compared with plasma hormone levels. A total of 124 females were examined during March, April, May, and early June (2001-2003). Ultrasound results were validated on a series of reproductive females (n=14) necropsied for other studies. Previtellogenic follicles, vitellogenic follicles, recently shelled eggs, fully developed well-calcified eggs, and atretic follicles were readily discernible with ultrasound in mature females. Reproductive structures were observed in 57 females of which 43 were actively reproductive, while 14 were non-reproductive, but contained large atretic follicles from prior years. Oviducts were discernible in females with eggs. Ovarian state was also correlated with hormone levels. These results are in agreement with previous studies that showed that 50% or less of the adult female alligator population is reproductively active in a given year. Ultrasonography can be used to make an accurate assessment of reproductive condition in wild alligator populations.

The American Alligator as a Predator of Mottled Ducks

Abstract Mottled Ducks (Anas fulvigula) are widely distributed in southeastern coastal marshes, as are American Alligators (Alligator mississippiensis). Although the alligator has been noted to prey upon Mottled Ducks, evidence of Mottled Duck consumption is rare in numerous studies of alligator food habits. This may be due to the season and habitat from which alligators were collected for evaluation (often autumn samples from deep water habitats preferred by adult alligators). We examined stomach contents of alligators in summer (when Mottled Duck broods and molting adults are flightless) from shallow water habitats preferred by Mottled Ducks. Mottled Duck remains were found in 20.9% of 43 alligator stomachs examined, far more than the highest frequency occurrence previously reported (1.27%). Unexpectedly, three relatively small alligators (1.51–1.70 m total length) consumed Mottled Ducks and the sixteen largest alligators did not. This study underscores the importance of season and location of collections when evaluating stomach content data.

The effects of Hurricane Rita and subsequent drought on alligators in southwest Louisiana

Hurricane Rita struck the coast of southwest Louisiana in September 2005. The storm generated an enormous tidal surge of approximately four meters in height that inundated many thousands of acres of the coastal marsh with full strength seawater. The initial surge resulted in the deaths of a number of alligators and severely stressed those who survived. In addition, a prolonged drought (the lowest rainfall in 111 years of recorded weather data) following the hurricane resulted in highly saline conditions that persisted in the marsh for several months. We had the opportunity to collect 11 blood samples from alligators located on Holly Beach less than a month after the hurricane, but were unable to collect samples from alligators on Rockefeller Wildlife Refuge until February 2006. Conditions at Rockefeller Refuge did not permit systematic sampling, but a total of 201 samples were collected on the refuge up through August 2006. The blood samples were analyzed for sodium, potassium, chloride, osmolality, and corticosterone. Blood samples from alligators sampled on Holly Beach in October 2005, showed a marked elevation in plasma osmolality, sodium, chloride, potassium, corticosterone, and an elevated heterophil/lymphocyte ratio. Blood samples from alligators on Rockefeller Refuge showed increasing levels of corticosterone as the drought persisted and elevated osmolality and electrolytes. After substantial rainfall in July and August, these indices of osmotic stress returned to within normal limits.

Nest-site Fidelity in American Alligators in a Louisiana Coastal Marsh

Abstract Little is known about nest-site fidelity in wild Alligator mississippiensis (American Alligator). As part of a long-term study on multiple paternity and mate fidelity that required capture and marking of nesting female alligators, we documented several instances of nest-site reuse by individual females. In one case, the female nested at the same site seven years after initial capture, demonstrating long-term nest-site fidelity. Another female used one nest site in 2000, 2002, and 2004. Herein, we provide data on minimum nesting intervals for recaptured alligators, including three cases of females nesting in two consecutive years. Despite tremendous habitat alteration and storm surge from Hurricane Rita in 2005 and a catastrophic drought precluding nesting in 2006, we found female alligators in 2007 at nests within 20 m and 170 m of their nest sites from seven years and three years, respectively, prior to those events.

Long-Distance Movement by American Alligators in Southwest Louisiana

Abstract As part of an ongoing study on growth and sexual maturation of Alligator mississippiensis (American Alligator) on Rockefeller Wildlife Refuge, LA, 3601 specimens, ranging in total length from 28 to 361 cm, were captured from June 2000 through August 2004. Additionally, 70 alligators were collected opportunistically as part of a teaching exercise in August 2005, and 248 more were collected in 2006 (and one in January 2007) as part of a study evaluating the effects of Hurricane Rita on alligators. Representative samples from size classes greater than 60 cm were collected in most months of the year between 2000 and 2004. Each animal was tagged, measured, sexed, and released immediately at the site of capture. A large number of these marked alligators were recaptured outside the refuge boundaries during annual alligator hunts in September. Of the 286 recaptured alligators, 214 were males, 68 were females, and four were of undetermined sex. From each recaptured alligator, total body length and date of recapture were recorded, and minimum distance from initial capture site estimated. From these preliminary data, we calculated the time interval between captures, and plotted minimum distance moved. The number of days between first capture and recapture ranged from 29 to 3336 days (9.1 years). Distance moved from initial capture site to final capture site ranged from 0.3 to 90.2 km. Eleven alligators moved between 30.0 and 39.9 km, and eight moved ≥40 km. Six of these moved between 40.0 and 49.9 km, and the others moved 87.4 and 90.2 km. These results greatly extend previous estimates of long-distance movement by alligators and demonstrate that both sub-adult and sexually mature animals move considerable distances. These data also showed that smaller alligators moved greater distances than larger alligators (P = 0.0002), and that the longer the time between captures, the greater the distance moved (P < 0.0001).

Sexual Maturity in Male American Alligators in Southwest Louisiana

Abstract. Very little is known about the attainment of puberty in reptiles. In the American alligator (Alligator mississippiensis) males are assumed to be sexually mature at about 1.8 m in total length, but it is not clear at what size they produce testosterone, spermatozoa and mate successfully. We re-examined this question by studying plasma testosterone levels in blood samples from a large sample of alligators (∼1,500) collected every month of the year and ranging in size from approximately 61 cm (2 ft) to 360 cm (11.5 ft). Testosterone values ranged from 0.05–115.41 ng/mL. All size classes of alligators exhibited a seasonal cycle in testosterone levels, but the concentrations were size-dependent: the larger the alligator the higher the testosterone. In all size-classes testosterone reached a peak in the breeding season (March–May). Mean testosterone in the largest size-class during breeding was 75 ng/mL whereas in the smallest size-class peak testosterone was less than 3 ng/mL. The smallest size-class (59–89 cm) showed an additional rise in testosterone in late summer. The attainment of sexual maturity in alligators appears to be closely associated with growth and is a gradual process lasting several years. Sexually immature alligators show a seasonal pattern of testosterone secretion similar to that of adults, but the values are significantly lower.

The Use of an Unmanned Aerial Vehicle to Locate Alligator Nests

Abstract Coastal marshes of Louisiana provide nesting habitat for Alligator mississippiensis (American Alligator). Helicopters are typically used to locate Alligator nests in remote interior marshes. We tested the use of an unmanned aerial vehicle (UAV) to detect Alligator nests on Rockefeller Wildlife Refuge in Grand Chenier, LA. Three brief flights with a combined search time of approximately 25 minutes and 9 seconds were conducted in a single afternoon, covering 28.2 ha. While in the field, we observed 6 Alligator nests with the UAV, and later review of video imagery recorded allowed us to detect an additional 6 Alligator nests. The use of UAVs may be a useful tool for detecting Alligator nests.