Timing of reproductive behaviour in male musk turtles, Sternotherus odoratus: effects of photoperiod, temperature and testosterone

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.

Managing the Health of Captive Groups of Reptiles and Amphibians

Managing the health of reptile and amphibian collections is centered on providing appropriate environmental parameters, husbandry conditions, and nutrition as well as maintaining good welfare and careful collection planning. Disease transmission is reduced through quarantine, appropriate diagnostic testing, and annual veterinary health assessment."

Year-round plasma steroid hormone profiles and the reproductive ecology of gopher tortoises (Gopherus polyphemus) at the southernmost edge of their range

Populations of wide ranging ectotherms often exhibit variation in traits that are influenced by local environmental conditions. Although the gopher tortoise, Gopherus polyphemus, is well studied in pine flatwoods habitats across their range, little attention has been given to coastal populations existing in the southern extreme portion of the range. We examined the reproductive physiology of a coastal dune population in southwest Florida to determine if reproductive cycles vary across populations. Here we present the first year-round sex hormone profiles for a wild population of gopher tortoises. Male testosterone concentrations varied across the year (F_11,54 = 2.52, P = 0.015) with elevated values from September to December and minimal levels from April to July, with the exception of a secondary peak during the month of June. Female testosterone and estradiol concentrations varied across the sampling period (T: F_11,66 = 8.54, P < 0.001, E: F_11,66 = 4.57, P < 0.001) with highest values from August to February, and lowest levels from May to July. Female progesterone concentrations varied over the year (F_11,64 = 3.29, P = 0.002) and increased in late fall with a peak in March. These data suggest this population has an extended breeding season from fall through spring with mating likely occurring from September through March, and nesting in winter through spring. This pattern is similar to reproductive patterns described for tropical and sub-tropical chelonians but differs from that of gopher tortoise populations in northern portions of the range where hibernation may last for five months and a single clutch of eggs are deposited in late spring.

Rapid thermal immune acclimation in common musk turtles (Sternotherus odoratus)

As infectious diseases in ectothermic vertebrates increasingly threaten wild populations, understanding how host immune systems are affected by the environment is key to understanding the process of infection. In this study, we investigated how temperature change and simulated bacterial infection (via lipopolysaccharide [LPS] injection) interacted to regulate innate immunity, as measured by bactericidal ability (BA), phagocytosis rate, and heterophil:lymphocyte ratio (HLR) in common musk turtles (Sternotherus odoratus). We found that LPS stimulated an acute immune response, as measured by an increase in BA, phagocytosis rate, and HLR. When exposed to a 5 or 10°C temperature change for 48 hr, turtles rapidly acclimated to the new temperature by adjusting their immune output. This acclimation was compensatory as seen by elevated rates of immune output in colder animals and decreased rates of immune output in warmer animals. These results indicate that while temperature change may be a constraint on some animals, S. odoratus have the ability to rapidly adjust immunity to match environmental thermal demand. This rapid ability to adjust immunity may be related to the broad geographic distribution of musk turtles. Future research should focus on how immune acclimation in ectotherms varies both intraspecifically and interspecifically across regional scales and geographic distributions.

Characterization of seasonal reproductive and stress steroid hormones in wild Radiated Tortoises, Astrochelys radiata

The critically endangered Radiated Tortoise (Astrochelys radiata) is endemic to the southern coastlines of Madagascar. Once common, wild populations of this tortoise have undergone dramatic declines in recent years. Although there have been studies documenting reproductive activities, reproductive physiological parameters are unknown yet may be crucial in the recovery of the species. Over four research seasons in remote field locations native to A. radiata, we surveyed for, radio-tracked, and sampled wild, free ranging tortoises. We sampled and measured stress and reproductive parameters (corticosterone [CORT], testosterone [T], estradiol-17β [E2], and progesterone [P]) in 311 plasma samples from 203 wild A. radiata, capturing their active period. Generally, hormone concentrations were associated with body condition, temperature, and humidity. There was wide variation in CORT that varied monthly and by group. Juvenile tortoises maintained more than twice the mean basal CORT concentrations than either adult sex, with the most dramatic distinctions in the middle of the wet season. For adult sex hormones, the last months of the dry season and into the wet season when ground humidities are low and just begin to rise prior to temperature declines, male T concentrations gradually increased to a peak before returning to near undetectable values into the dry season. We had limited data for T concentrations in females, but found average T concentrations were much lower than in males and positively correlated with larger female home range sizes. For female hormone cycles, E2 also peaked in the early 1/3 of the wet season along with male T, and was followed by an uptick in P which correlates to the putative ovulatory cycle. Females tracked over four years showed variation in patterns of P, indicating that number and frequency of clutches vary. Our results suggest that 1) there is high species plasticity in response to stress; 2) A. radiata reproductive cycling is somewhat dissociated with courtship timing and is instead triggered by environmental cues; and 3) individual female reproductive output is irregular. This study is oone of the first to document and describe multi-year seasonal stress and reproductive hormones in a free-ranging Malagasy chelonian. These data may be used to identify key high-production habitats for conservation, and aide in captive management and reproduction in assurance colonies for species health and survival.

Effects of life-history requirements on the distribution of a threatened reptile

Survival and reproduction are the two primary life-history traits essential for species' persistence; however, the environmental conditions that support each of these traits may not be the same. Despite this, reproductive requirements are seldom considered when estimating species' potential distributions. We sought to examine potentially limiting environmental factors influencing the distribution of an oviparous reptile of conservation concern with respect to the species' survival and reproduction and to assess the implications of the species' predicted climatic constraints on current conservation practices. We used ecological niche modeling to predict the probability of environmental suitability for the alligator snapping turtle (Macrochelys temminckii). We built an annual climate model to examine survival and a nesting climate model to examine reproduction. We combined incubation temperature requirements, products of modeled soil temperature data, and our estimated distributions to determine whether embryonic development constrained the northern distribution of the species. Low annual precipitation constrained the western distribution of alligator snapping turtles, whereas the northern distribution was constrained by thermal requirements during embryonic development. Only a portion of the geographic range predicted to have a high probability of suitability for alligator snapping turtle survival was estimated to be capable of supporting successful embryonic development. Historic occurrence records suggest adult alligator snapping turtles can survive in regions with colder climes than those associated with consistent and successful production of offspring. Estimated egg-incubation requirements indicated that current reintroductions at the northern edge of the species' range are within reproductively viable environmental conditions. Our results highlight the importance of considering survival and reproduction when estimating species' ecological niches, implicating conservation plans, and benefits of incorporating physiological data when evaluating species' distributions.

Does testosterone influence activity budget in the male Greek tortoise (Testudo graeca graeca)?

The stimulatory effect of testosterone on male sexual activity is one of the clearest examples linking hormones and behaviors. However, this relationship is complex in Chelonians. We experimentally studied the influence of testosterone levels on the activity budget and space use in male Greek tortoises (Testudo graeca graeca) during the spring mating season. We first described the annual pattern of changes in plasma testosterone levels in free-ranging animals in Morocco. Two peaks, one in winter and one in summer, corresponded to periods of inactivity; whereas mating periods in spring and to a lesser extent in autumn were associated with low plasma testosterone levels. Second, we experimentally manipulated plasma testosterone levels in free-ranging males, and analyzed the behavioral consequences. The strong contrasts in plasma hormone levels induced by the experimental treatments did not result in changes in activity budget or space use, both in the short-term or more than one month after the beginning of the hormonal treatment. Our results suggest that testosterone levels did not influence directly behavioral activity in this species, either immediately or after a time delay of one month.

Plasma steroid and nutrient levels during the active season in wild Testudo horsfieldi

Plasma concentrations of sex steroids (testosterone and progesterone), proteins (total protein and albumin), lipids (phospholipids, cholesterol, and triglycerides), and minerals (calcium and phosphorus) were measured in wild Testudo horsfieldi in Uzbekistan, during the short, 3-month activity period (March-May, 1998). Testosterone concentration in males was highest (52 ng/ml) when they had just emerged from brumation (hibernation) in mid-March, which was also the beginning of the mating period, and fell in April. In females, progesterone peaked in mid-April (at 10 ng/ml), just before ovulation of the first clutches at the end of April and beginning of May. Testosterone levels in females and progesterone levels in males were low (<3 ng/ml) throughout the activity period. In general, the plasma concentrations of proteins, lipids, and phosphorus increased slowly in males, but more rapidly in females, during the activity season. These increases were particularly strong in females in the second half of April, coinciding with the peaks in female hormone levels. The changes in plasma hormones and nutrients reflected the timing of the different behaviours. The four first weeks of above-ground activity (mid-March to mid-April) by males, when they had high testosterone levels, were primarily allocated to fighting other males, courtship, and mating, while females spent much of that time feeding. Thereafter, both sexes concentrated on feeding. Females were probably preparing to ovulate in late-April, when their progesterone levels were highest and when plasma nutrient levels increased considerably.

Steroid levels and reproductive cycle of the Galápagos tortoise, Geochelone nigra, living under seminatural conditions on Santa Cruz Island (Galápagos)

The Galápagos Islands are home to 11 subspecies of large terrestrial tortoises (Geochelone nigra). All Galápagos tortoises are considered endangered and approximately 12,000 animals still exist. Until now, the reproductive cycle of the Galápagos tortoise has been studied only in captive animals, and no data from free-ranging tortoises have been available. During a one-year period, blood samples were collected from male and female G. nigra living under seminatural conditions on Santa Cruz Island, Galápagos. Plasma steroid hormones were measured by radioimmunoassays (RIAs). In males, plasma testosterone and corticosterone increased a few months before the onset of the mating season. Peak levels were observed while most copulations occurred and environmental temperatures were highest. Both testosterone and corticosterone showed low levels during the cold and dry nesting season and high levels during the hot and rainy mating season. In females, testosterone and corticosterone also rose during the hot and rainy mating season. Both hormones peaked during the second half of the mating season and decreased during the cooler dry season. Female estradiol levels increased at the onset of the mating season, reaching the highest level at the peak of the mating season, which coincided with the highest annual temperatures measured. Estradiol slowly decreased within the next months and rapidly dropped at the onset of the nesting season when temperatures decreased. Progesterone levels were high close to the time of ovulation and showed clearly elevated levels at the beginning of the nesting season after some females had laid their first clutch. Progesterone decreased during the nesting season, when ambient temperatures began to decrease, and reached minimal levels in the postbreeding period shortly before the onset of the next mating season. There were significant annual variations in plasma testosterone in both males and females. Plasma corticosterone was generally higher in males than in females and varied throughout the year in both sexes.

Seasonal changes in serum gonadal steroids associated with migration, mating, and nesting in the loggerhead sea turtle (Caretta caretta)

Adult male loggerhead sea turtles, Caretta caretta, exhibited a "prenuptial" spermatogenic cycle that was coincident with increased concentrations of serum testosterone (T). Serum T was high during the months when migration and mating have been recorded for males. In contrast to females, males appear to be annual breeders. Nine reproductively active female C. caretta (as verified through laparoscopy) were tagged with sonic transmitters and were repeatedly bled prior to migration. Four months prior to the nesting season, the ovaries of reproductively active females had hundreds of vitellogenic follicles of approximately 1.5 cm in diameter (i.e., half the size of ovulatory follicles). Approximately 4-6 weeks prior to migration from feeding grounds to mating and nesting areas, serum estradiol-17 beta (E2) concentrations increased significantly and remained high for approximately 4 weeks, suggesting a period of increased vitellogenesis. During a 1- to 2-week period prior to migration, serum E2 decreased significantly, while serum T concentrations increased (at least) until the time of migration. Serum T, E2, and progesterone (PRO) were elevated during nesting if a turtle was going to nest again during that nesting season. During the last nesting of a season, turtles had low serum concentrations of T, E2, and Pro. The prenuptial pattern of gonadal recrudescence and gonadal steroid production in both male and female C. caretta contrasts with those of many temperate freshwater turtles, and this type of reproductive pattern may have been facilitated by adaptation to a tropical marine environment.