Valentine A. Lance

Is regulation of aromatase expression in reptiles the key to understanding temperature-dependent sex determination?

A brief review of our current understanding (or lack of understanding) of the molecular basis of temperature-dependent sex determination (TSD) in reptiles is presented. Current theories are discussed: yolk steroids as sex determinants, the brain as the driver for TSD and the enzyme aromatase and estrogen production as the possible determinants of sex. There is little evidence to support the first two theories, but enough evidence to keep the third theory in play. As yet, however, we have no molecular understanding of how a two-degree difference in temperature during the temperature-sensitive phase of egg incubation can initiate the molecular cascade that determines whether the indifferent gonad develops as an ovary or a testis.

ECOLOGICAL CONSEQUENCES OF AGONISTIC INTERACTIONS IN LIZARDS

It is relatively easy to document direct agonistic interactions among or within species that lead to exclusion of subordinate animals from preferred habitats. It is more difficult to measure the competitive effects of that exclusion on the loser. Thus, much behavioral research assumes that the intensity of agonistic interactions is correlated with their cost to performance, but does not directly measure such a cost. We examined fitness- associated traits of pregnant viviparous scincid lizards ( Eulamprus heatwolei) in outdoor enclosures under three conditions: alone, with a conspecific, or with a larger and more aggressive heterospecific (Egernia saxatilis, a sympatric scincid species). As in previous laboratory studies, Egernia saxatilisattacked Eulamprus heatwoleiand excluded individuals of the smaller species from warmer shelter sites. However, Eulamprus heatwoleiwere able to maintain normal schedules of body temperatures and food intake, apparently by modifying their behavior to minimize encounters with their aggressive cage mates. Ac- cordingly, the subordinate animals showed no overt ill effects in spite of strong agonistic interactions: the body condition, locomotor performance, and corticosterone levels of sub- ordinate Eulamprus housed with Egernia were indistinguishable from those of lizards kept in solitary cages or with conspecifics only. Similarly, the offspring of these pregnant females were born at the same time, and with similar phenotypic traits, as the offspring of control females. Thus, even in situations of intense interspecific aggression and consequent habitat exclusion, behavioral flexibility of the subordinate animals may decrease or eliminate the inferred ecological consequences of that interaction.

Sperm Storage in the Oviduct of the American Alligator

Oviducts of the American alligator (Alligator mississippiensis) were examined histologically for the presence of stored sperm. Two regions containing sperm were identified, one at the junction of the posterior uterus and the vagina (UVJ) and the other at the junction of the tube and isthmus (TIJ). In these areas, sperm were found in the lumina of oviductal glands. The glands in these areas of the oviduct are diffuse and shallow and appear to allow better access to sperm than glands located elsewhere. Histochemically, the glands of the UVJ reacted weakly for carbohydrates and proteins, whereas those of the TIJ reacted strongly for these same two components, secretions of which are associated with sperm storage structures in other reptiles. Sperm were not in contact with the glandular epithelium, and glands at the UVJ contained more sperm than those at the TIJ. Oviductal sperm storage was observed not only in recently mated females but in all females possessing uterine eggs as well as all females known to be associated with a nest. We conclude that female alligators are capable of storing sperm in their oviductal glands, but not from one year to the next.

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 temperature-sensitive period (TSP) during incubation of broad-snouted caiman (Caiman latirostris) eggs

All crocodiles studied to date exhibit temperature-dependent sex determination. During the many weeks from egg laying to hatch there is a period of 10 to 15 d in the middle third of incubation (in the American alligator) during which the sex of the embryo is irreversibly fixed, referred to as the temperature-sensitive period or TSP. In this work we investigated the TSP in Caiman latirostris eggs incubated at female-inducing and male-inducing temperatures (29 ◦ C and 33 ◦ C respectively) by switching eggs from 29 ◦ Ct o 33 ◦ C and vice versa at timed interval throughout incubation. Compared to Alligator mississippiensis the duration of TSP was longer, and the onset of TSP was at an earlier stage of incubation.

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.

Heavy Metal Contamination in Phrynops geoffroanus (Schweigger, 1812) (Testudines: Chelidae) in a River Basin, São Paulo, Brazil

The Piracicaba River basin is considered the most disturbed river basin in the state of São Paulo. Considerable amounts of agricultural residues are seasonally drained into the river, and the region is also highly urbanized and industrialized with an incipient sewage treatment system. The presence of heavy metals has been previously reported for the water and riverbed in Piracicaba river basin. In this study we evaluated 13 heavy metals in the blood of 37 Geoffroy’s side-necked turtles, Phrynops geoffroanus, from Piracicaba River and Piracicamirim Creek, one of its tributaries. Blood levels of As, Co, Cr, Se and Pb varied among sites, whereas Sn varied between males and females. However, no obvious pathology was detected. Serum level of Cu (2,194xa0ngxa0g−1) and Pb (1,150xa0ngxa0g−1) found in this study are the highest ever described for any reptile; however, no clinical symptoms have been detected in the present study. There is no information about the time scale of such contamination, which could be currently subclinical and yet lead to a breakdown in the population reproductive success in a few years. Based on the present study, legal enforcement is urged in order to locate and extirpate heavy metal sources in the Piracicaba River basin. In addition, monitoring should include humans and commercial fish consumed in local markets.

Long-Distance Movement by American Alligators in Southwest Louisiana

Abstract n 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).