A Edwards

Maternal basking behaviour determines offspring sex in a viviparous reptile.

Two primary dichotomies within vertebrate life histories involve reproductive mode (oviparity versus viviparity) and sex determination (genotypic sex determination versus environmental sex determination). Although reptiles show multiple evolutionary transitions in both parameters, the co–occurrence of viviparity and environmental–dependent sex determination have heretofore been regarded as incompatible. Our studies on the viviparous lizard Niveoscincus ocellatus show that the extent of basking by a female influences the sex of her offspring. Critically, our data reveal this effect both in the field (via correlations between date of birth and litter sex ratio) and in a laboratory experiment (females with reduced basking opportunities produced more male offspring). Changes in thermoregulatory behaviour thus allow pregnant female lizards to modify the sex of their offspring.

MULTIENNIAL REPRODUCTION IN FEMALES OF A VIVIPAROUS, TEMPERATE-ZONE SKINK, TILIQUA NIGROLUTEA

We examined the reproductive frequency in wild-caught and captive females of Tiliqua nigrolutea over five consecutive reproductive seasons. Reproductive frequency (0.38 ± SE 0.035) was clearly different from an annual pattern (1.0) in which all females reproduce every year. Individual females did not reproduce every year, but “skipped” seasons were staggered such that a proportion of the population produced a clutch each season. We attribute skipped reproductive opportunities to a combination of a long gestation, high relative clutch mass (0.43 ± SE 0.034), parturition late in the active season, a cessation of feeding in the latter stages of gestation, and low autumn temperatures that limited post-partum feeding opportunities.

Changes in Plasma Testosterone, Estrogen, and Progesterone Concentrations throughout the Annual Reproductive Cycle in Male Viviparous Blue-Tongued Skinks, Tiliqua nigrolutea, in Tasmania

Few published studies have detailed comprehensively the correlations between plasma steroid hormone peaks and the timing of reproductive events in male squamate reptiles. We examined the patterns of plasma testosterone (T), estrogen (E) and progesterone (P4) concentrations in males of the viviparous blue-tongued skink, Tiliqua nigrolutea, throughout the annual cycle. Plasma T concentrations varied through the annual cycle, peaking at 10.9 * 3.00 ng ml-1 during spermiogenesis, coincident with agonistic male-male interactions, but falling prior to the mating period. Mean plasma T concentrations were basal (2 - 3 ng ml-1) during reproductive quiescence. Mean plasma E concentrations were significantly elevated (778.0 * 120.00 pg ml-1) during the mating period, but basal (<300 pg ml-1) both before and after mating. Mean plasma P4 concentrations peaked during the mating period (1.1 * 0.17 ng ml-1) and declined significantly after mating. We propose a potential role for E and P4 in the stimulation of male reproductive behavior during the mating period.

Fecal Testosterone Concentrations May Not Be Useful for Monitoring Reproductive Status in Male Blue-Tongued Lizards ( Tiliqua nigrolutea : Scincidae)

Assessment of reproductive status in animals generally depends on monitoring hormone concentrations in plasma, but blood sampling often involves significant stress to the subject. Monitoring steroid profiles by assaying excreted steroids in urine and/or fecal samples is non-invasive, but does pose some problems.There are, however, only two published reports of the application of fecal steroid monitoring to reptiles. We compare the profile of fecal T with that for plasma T through the reproductive cycle of blotched blue-tongued lizards, and also examine the relative proportions of conjugated and free T in feces. Testosterone was detected in all samples assayed, and fecal T concentrations ranged from ~ 500 ng g-1 to ~1500 ng g-1 dry feces. Plasma hormone cycles were not reported, but the patterns of variation in fecal T concentrations appeared to show some correlation with reproductive activity. In contrast, our results suggest that there is an inverse relationship between concentrations of T in feces and in plasma of male blue-tongued skinks, with fecal T concentrations being highest during the non-breeding season, when plasma T levels are low. Our results suggest, therefore, that assay of fecal T concentrations may not be useful for assessing reproductive status in blue-tongued lizards because of the lack of correlation between T concentrations in feces and plasma.

A possible alternative to 17β-estradiol in a viviparous lizard, Tiliqua nigrolutea

We have detected an unusual polar steroid as a major end product of gonadal steroid biosynthesis in male and female blotched blue-tongued lizards, Tiliqua nigrolutea. In an investigation of the steroidogenic pathways in blue-tongued lizards, we incubated gonads of both male and female lizards with tritiated pregnenolone and identified the products of steroid biosynthesis using thin layer chromatography and high performance liquid chromatography with radiometric detection: gonads from both reproductively active and quiescent lizards were examined. The proportion of total radioactive substrate converted to the unknown polar steroid was greater in individuals with hypertrophied gonads (males (N=4) 28.1%; females (N=4) 45.3%) than in those with regressed gonads (males (N=4) 5.9%; females (N=4) 33.3%). Properties of the unknown steroid were identical across all incubations. Incubation time-course information, thin layer and high performance liquid chromatography properties of the polar steroid are presented. The steroid is more polar than 17beta-estradiol, which was not detected, but less polar than all tri-hydroxylated estrogens to which it was compared. The possibility of an alternative estrogen to 17beta-estradiol in some reptiles is discussed.

Calibration of the HemoCue point-of-care analyser for determining haemoglobin concentration in a lizard and a fish

Hemoglobin concentration is commonly measured by point-of-care systems for many animal studies. The HemoCue Hb 201+ overestimated hemoglobin in blue-tongued skinks and diploid and triploid Atlantic salmon. The overestimation was systematic in both species, and therefore hemoglobin determined by the HemoCue can be corrected using appropriate calibration equations.

Sex and season influence gonadal steroid biosynthetic pathways, end-product production and steroid conjugation in blotched blue-tongued lizards (Tiliqua nigrolutea).

We examined differences in gonadal steroid production and biosynthetic pathway activity with changing reproductive condition and between sexes in the scincid lizard, Tiliqua nigrolutea. We observed clear seasonal and sexual variation in the production of androgens and steroid conjugates, but detected no 17beta-estradiol or 5alpha-dihydrotestosterone produced by the gonads. An alternative steroid, more polar than estradiol, was detected: an investigation of this steroid is reported separately [Gen. Comp. Endocrinol. 129 (2002) 114]. There were seasonal and sex-related differences in steroid biosynthetic pathway activity. The Delta5 pathway metabolite, dehydroepiandrosterone, was detected only in males, and only from incubations using regressed testicular tissue. There was also a seasonal difference between the sexes in rates of progesterone accumulation, although the absence of corresponding elevated plasma concentrations suggests that the role of progesterone switches from a directly acting hormone to a precursor for others during the reproductive cycle in females. These results suggest that within the traditional view that vertebrate biosynthetic pathway activity and end-products are phylogenetically conserved, there is likely to be considerably species- and/or genus-specific variation.

Pregnancy limits lung function during exercise and depresses metabolic rate in the skink Tiliqua nigrolutea

ABSTRACT High gestational loads have been associated with a range of ecological costs, such as decreased locomotor ability; however, the physiological mechanisms that underpin these changes are poorly understood. In this study, breathing patterns, metabolic rates, lung volume and lung diffusing capacity were measured at rest and during exercise in the pregnant skink Tiliqua nigrolutea. Breathing patterns were largely unaffected by gestation; however, decreases in metabolic rate (rate of oxygen consumption) in the late stages of pregnancy induced a relative hyperventilation. The reductions in metabolic rate during late pregnancy prevent the calculation of the maintenance cost of pregnancy based on post-partum and neonatal metabolic rates. Despite the high relative litter mass of 38.9±5.3%, lung diffusing capacity was maintained during all stages of pregnancy, suggesting that alterations in diffusion at the alveolar capillary membrane were not responsible for the relative hyperventilation. Lung volume was increased during pregnancy compared with non-pregnant females, but lung volume was significantly lower during pregnancy compared with post-partum lung volume. Pregnant females were unable to produce the same metabolic and ventilatory changes induced by exercise in non-pregnant females. This lack of ability to respond to increased respiratory drive during exercise may underpin the locomotor impairment measured during gestation in previous studies. Highlighted article: Pregnancy depresses metabolic rate in blotched blue tongue lizards and limits exercise ability. Despite the developing fetuses compressing the lungs, gas diffusion ability was not altered.

Interpopulational variation in costs of reproduction related to pregnancy in a viviparous lizard

Interpopulational variation in reproductive costs may affect variation in life history traits including reproductive investment (i.e. clutch mass relative to either maternal body mass or length). While the relationships between reproductive investment and costs of reproduction, especially costs to mobility, have been well studied in squamate reptiles, how these costs relate to investment and explain patterns within and between populations is not always straightforward. In the present study, we examined the relationship between reproductive investment and costs of reproduction (gravid and postpartum sprint speeds and maternal postpartum body condition) in two populations of a viviparous skink, Pseudemoia entrecasteauxii living in different habitat types. We found that costs of reproduction (i.e. impact on gravid and postpartum sprint speeds) depended on the interaction between relative reproductive burden (RRB) and population. There was no link between relative clutch mass (RCM) and maternal sprint speeds. Maternal postpartum body condition was not related to either RRB or RCM for either population. Gravid females living in the open habitat population showed significantly slower sprint speed compared with the same females immediately postparturition, and other gravid females living in a closed habitat population. Such females are likely to experience a higher cost of reproduction in terms of changes in sprint speed as well as exposure to predators and may show a behavioural shift to crypsis in order to compensate for locomotor impairment and to reduce the risk of predation. We suggest that factors which relate to costs of reproduction (i.e. sprint speeds) are complex and may involve multiple factors such as reproductive investment and habitat characteristics.

Response to gonadotropin-releasing hormone challenge: Seasonal variation in steroid production in a viviparous lizard, Tiliqua nigrolutea

The hypothalamic-pituitary-gonadal axis plays a central role in the regulation of gamete maturation, sex steroid production and the stimulation of reproductive behaviours in vertebrates. In seasonal breeders, the timely activation and deactivation of this control system is important to ensure successful reproduction: this process is not well understood in species which breed irregularly. Males of the viviparous blotched blue-tongued lizard, Tiliqua nigrolutea, breed annually, while females display a multiennial cycle. We investigated seasonal variation in hypothalamic-pituitary-gonadal axis responsiveness in both sexes of T. nigrolutea. We measured changes in plasma concentrations of testosterone and estrogen in response to a single intraperitoneal injection of a GnRH agonist, chicken-II LH-RH, at three reproductively distinct times of year. Plasma testosterone concentrations in males were significantly increased during gonadal quiescence, but not initial or final spermatogenesis. There was no estrogen response in males at any time of year. Conversely, in females, there was an increase in plasma testosterone, but not estrogen, concentration, in reproductively quiescent females several months in advance of a successful pregnancy. These results indicate clear variation in HPG axis activity with sex, season and reproductive condition in this seasonally breeding viviparous lizard. This study opens the way for further investigation into the mechanisms by which internal (body condition) and external seasonal cues (temperature and photoperiod) are coordinated to regulate reproduction in irregularly-breeding reptiles.