Embryonic Temperature Research Articles

Embryonic temperature shapes behavioural change following social experience in male leopard geckos, Eublepharis macularius

Individual variation in behavioural expression and behavioural plasticity exist in all species, and early experiences are critical determinants of both. The leopard gecko is a lizard with temperature-dependent sex determination, and in this species, embryonic incubation temperature (IncT) affects the display of social behaviours. For example, adult males hatched from eggs incubated at an IncT that produces predominantly males (male-biased IncT, 32.5°C) are more aggressive and less sexually active than males hatched from eggs at an IncT that produces predominantly females (female-biased IncT, 30°C). It is not known, however, whether IncT influences behavioural plasticity in adulthood. We assessed whether adult males hatched from eggs incubated at female- and male-biased IncTs showed different changes in territorial behaviour (scent marking in an empty test arena), anticipatory behaviours (activity, scent marking and tail vibrations in response to cues that predict the introduction of a female) and courtship behaviour following social interactions with females. We found that heterosexual social experiences increased territorial behaviour and the display of anticipatory behaviours in males from the female-biased IncT but not in males from the male-biased IncT. This difference was not due to differences in the amount of social experiences acquired, and the greater change in anticipatory behaviour in males from the female-biased IncT suggest that they acquired sexual conditioning more readily. Differences in sex steroid concentrations or neural metabolism caused by IncT could underlie this difference. These results highlight the profound implications of maternal nest site selection for offspring phenotype and plasticity in this species.Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Hybridization in the sea: gametic and developmental constraints on fertilization in sympatric species of Pseudechinus (Echinodermata: Echinoidea)

The constraints of gametic compatibility and developmental competence on hybrid production were examined in three sympatric species of the echinoid Pseudechinus in southern New Zealand. Differences were noted in embryonic temperature sensitivity between the species. Pseudechinus novaezealandiae embryos appeared to be better adapted to cooler temperatures than those of Pseudechinus huttoni, while Pseudechinus albocinctus embryos tolerated a wider range of temperatures than either of its sympatric congeners. Such differences were mirrored by the kinetics of gamete interaction between all possible reciprocal crosses of the three species. There appeared to be some physiological incompatibility between the eggs of P. novaezealandiae and the spermatozoa of the other two species. P. novaezealandiae spermatozoa were, however, capable of fertilizing both P. huttoni and, to a lesser extent, P. albocinctus ova. Hybrid echinoplutei resulting from the P. huttoni (female)× P. novaezealandiae (male) cross did not, however, become competent to metamorphose. The probabilities of settlement of echinoplutei resulting from the other reciprocal crosses involving the gametes of P. novaezealandiae were also low. It appears that a combination of physiological (gametic incompatibility) and genetic (developmental incompetence) factors contribute to maintaining the integrity of the P. novaezealandiae lineage. These factors were not useful in understanding how P. albocinctus and P. huttoni remain distinct species. This species-pair was characterized by reciprocal gamete compatibility as well as developmental competence to settlement. Thus, gamete incompatibility, while important for some groups, cannot provide the basis for speciation in the New Zealand members of the genus Pseudechinus.

Embryonic temperature and the relative timing of muscle-specific genes during development in herring (Clupea harengus L.).

Temperature influences many aspects of muscle development in herring (Clupea harengus). In Clyde herring, myofibril synthesis occurred later with respect to somite stage in embryos reared at 5 degrees C compared with 12 degrees C. The aim of the present study was to test the hypothesis that the relative timing of expression of myogenic regulatory factors (MRFs) and myosin heavy chain (MyHC) transcripts changes with developmental temperature. Reverse transcriptase/polymerase chain reaction (RT-PCR) was used to clone partial coding regions of MyoD, myogenin and MyHC from juvenile Clyde herring. Embryos were reared at 5, 8 and 12 degrees C, and the spatial and temporal expression patterns of transcripts were investigated using cRNA probes and in situ hybridisation. Antisense probes revealed a rostral-caudal progression of all three transcripts. MyoD transcription initially took place in the adaxial cells of the unsegmented, presomitic mesoderm, whereas myogenin transcription first occurred in newly formed somites. The MyHC gene transcript was not detected until approximately nine somites had formed. Since the somite stage at which the MRFs and MyHC were first expressed was independent of temperature, the hypothesis was rejected. We suggest that the effects of temperature on myofibril synthesis must occur downstream from MyHC transcription either at the level of translation or at the assembly stage.

Embryonic temperature and gonadal sex organize male-typical sexual and aggressive behavior in a lizard with temperature-dependent sex determination.

Temperature during embryonic development determines gonadal sex in the leopard gecko, Eublepharis macularius. Moreover, both embryonic temperature and gonadal sex influence adult behavior. Yet it remains unclear whether the effects of embryonic temperature and gonadal sex on behavior are irreversibly organized during development. To address this question, we gonadectomized adult females and males generated from a temperature that produces mostly females (30 C) and a temperature that produces mostly males (32.5 C). Females and males from both temperatures were then treated with equivalent levels of various sex steroids. We found that both embryonic temperature and gonadal sex had persistent effects on the expression of male-typical sexual and aggressive behaviors. For example, adult females do not scent mark and display very little courtship and mounting behavior even when treated with levels of hormones (primarily androgens) that activate these behaviors in males. In contrast, species-typical aggressive displays were less sex specific and were activated by both dihydrotestosterone and testosterone (T) in males and by T in females. Nevertheless, the average duration of aggressive displays was significantly shorter in T-treated females than that in T-treated males. With regard to submissive behavior, androgens decreased flight behavior in males, but had no effect in females. Embryonic temperature had enduring effects on certain behaviors in males. For instance, males from a male-biased embryonic temperature scent-marked more than males from a female-biased embryonic temperature when treated with dihydrotestosterone or T. Conversely, and across hormone treatments, males from a female-biased embryonic temperature mounted more than males from a male-biased embryonic temperature. Finally, treatment with 17beta-estradiol decreased submissive behavior in males from a male-biased embryonic temperature compared with that in males from a female-biased embryonic temperature. Courtship and aggressive behavior were not influenced by temperature. These results strongly suggest that male-typical behaviors in the adult leopard gecko are permanently organized by both embryonic temperature and gonadal sex during development.

Embryonic Temperature and Gonadal Sex Organize Male-Typical Sexual and Aggressive Behavior in a Lizard with Temperature-Dependent Sex Determination

Embryonic Temperature and Gonadal Sex Organize Male-Typical Sexual and Aggressive Behavior in a Lizard with Temperature-Dependent Sex Determination

Embryonic temperature affects metabolic compensation and thyroid hormones in hatchling snapping turtles.

Temperature acclimation of adult vertebrates typically induces changes in metabolic physiology. During early development, such metabolic compensation might have profound consequences, yet acclimation of metabolism is little studied in early life stages. We measured the effect of egg incubation temperature on resting metabolic rate (RMR) and blood thyroid hormone levels of hatchling snapping turtles (Chelydra serpentina). Like many reptiles, snapping turtles have temperature-dependent sex determination (TSD), in which embryonic temperature determines sex. Therefore, we designed the experiments to separately measure effects of temperature and of sex on the response variables. We incubated eggs in the laboratory at 21. 5 degrees, 24.5 degrees, 27.5 degrees, and 30.5 degrees C, producing both sexes, all males, both sexes, and all females, respectively. Hatchling RMR, when measured at a common temperature (either 25 degrees or 31 degrees C), was negatively correlated with egg temperature in both males and females, such that RMR of turtles from 21.5 degrees C-incubated eggs averaged 160% that of turtles from 30.5 degrees C-incubated eggs. These results indicate that egg temperatures induced positive metabolic compensation in both sexes. Thyroid hormone levels of hatchlings showed similar correlations with egg temperature; thyroxine level of turtles from 21.5 degrees C-incubated eggs averaged 220% that of turtles from 30.5 degrees C-incubated eggs. To examine the possibility that thyroid hormones contribute to positive metabolic compensation, we added triiodothyronine to eggs during mid-incubation. RMR of hatchlings from these treated eggs averaged 131% that of controls, consistent with the previous possibility. Moreover, the effects of embryonic temperature on metabolic physiology, in combination with effects on sex, can result in differences in RMR and thyroid hormone levels between male and female hatchling turtles. Such differences may be important to the ecology and evolution of TSD.

Incubation Temperature and Sex Affect Mass and Energy Reserves of Hatchling Snapping Turtles, Chelydra serpentina

Temperature during embryonic development irreversibly determines gonadal sex in many oviparous reptiles. Although embryonic temperature also influences a number of other traits in these species, it is unclear whether such effects are primarily due to incubation temperature or to gonadal sex. Here we dissociated these normally confounding effects via hormonal manipulations of snapping turtle embryos (Chelydra serpentina), a species with temperature-dependent sex determination. We then ascertained temperature and sex effects on residual yolk mass, abdominal fat body mass, and total mass in neonates shortly after hatching or after one month without feeding. Yolk mass was initially affected by incubation temperature, clutch identity. and their interaction, but not gonadal sex. Yolk mass was not influenced by any of these variables 30 d after hateching. Fat mass was initially affected by temperature and clutch, but not sex. Gonadal sex did, however, affect fat mass at 30 d of age as did temperature and clutch. Incubation temperature affected total mass in a complex manner. There were significant clutch by temperature interactions initially, but no main effect of temperature. These effects changed so that the temperature effect was significant but interaction effects were not detected at 30 d of age. Repeated measures analysis of total mass after hatching and at 30 d of age indicated that turtles from lower temperatures lost more mass than turtles from higher incubation temperatures. and that females lost more mass than males. These data indicate that some hatchling traits were influenced directly by incubation temperature, whereas others were independently affected by gonadal sex. These results are consistent with a leading hypothesis for the evolution of temperature-dependent sex determination.

Temperature during embryonic and juvenile development influences growth in hatchling snapping turtles, Chelydra serpentina

Embryonic temperature influenced subsequent growth in juvenile snapping turtles, Chelydra serpentina: incubation temperatures of 24 and 26.5°C enhanced growth relative to a temperature of 29°C. Although embryonic temperature normally determines gonadal sex in this species, experimental manipulations revealed that temperature effects on growth were independent of sex. Ambient temperature also affected growth: juvenile turtles grew slowly in a cool (19°C) versus a warm (28°C) environment. In a parallel experiment, turtles from different embryonic temperatures displayed different patterns of temperature choice in response to nutritional status or time of day. We tentatively conclude that embryonic temperature has both direct and indirect (i.e., through temperature choice) effects on growth in snapping turtles.

Embryonic temperature modulates muscle growth characteristics in larval and juvenile herring

The influence of embryonic and larval temperature regime on muscle growth was investigated in Atlantic herring (Clupea harengus L.). Eggs of spring-spawning Clyde herring were incubated at 5 degrees C, 8 degrees C or 12 degrees C until hatching and then reared until after metamorphosis at rising temperatures to simulate a seasonal warming. Metamorphosis to the juvenile stage was complete at 37 mm total length (TL), after an estimated 177 days as a larva at 5 degrees C, 117 days at 8 degrees C and 101 days at 12 degrees C. Growth rate and the development of median fins were retarded in relation to body length at 5 degrees C compared with 8 degrees C and 12 degrees C. Between hatching (at 8-9 mm TL) and 16 mm TL, there was a threefold increase in total muscle cross-sectional area, largely due to the hypertrophy of the embryonic red and white muscle fibres. The recruitment of additional white muscle fibres started at approximately 15 mm TL at all temperatures, and by 37 mm was estimated to be 66 fibres day-1 at 5 degrees C and 103 fibres day-1 at 8 degrees C and 12 degrees C. Peptide mapping studies revealed a change in myosin heavy chain composition in white muscle fibres between 20 and 25 mm TL. Embryonic red muscle fibres expressed fast myosin light chains until 24-28 mm TL at 5 degrees C and 22 mm TL at 12 degrees C, and new red fibres were added at the horizontal septum starting at the same body lengths. Following metamorphosis, the total cross-sectional area of muscle was similar at different temperatures, although the number of red and white fibres per myotome was significantly greater at the warmest than at the coldest regime. For example, the mean number of white muscle fibres per myotome in 50 mm TL juveniles was calculated to be 23.4 % higher at 12 degrees C (12 065) than at 5 degrees C (9775). In other experiments, spring-spawning (Clyde) and autumn-spawning (Manx) herring were reared at different temperatures until first feeding and then transferred to ambient seawater temperature and fed ad libitum for constant periods. These experiments showed that, for both stocks, the temperature of embryonic development influenced the subsequent rate of muscle fibre recruitment and hypertrophy as well as the density of muscle nuclei. Labelling experiments with 5'-bromo-2-deoxyuridine showed that both the hypertrophy and recruitment of muscle fibres involved a rapidly proliferating population of myogenic precursor cells. The cellular mechanisms underlying the environmental modulation of muscle growth phenotype are discussed.

Embryonic Temperature Influences Juvenile Temperature Choice And Growth Rate In Snapping Turtles Chelydra Serpentina

Snapping turtles (Chelydra serpentina) demonstrate temperature-dependent sex determination (TSD): intermediate egg incubation temperatures (23-27 degreesC) produce males, while extreme temperatures produce females. Snapping turtles are also sexually dimorphic: adult males are typically larger than females. Previous researchers hypothesized that male-producing egg temperatures enhanced the growth rate of juvenile turtles, resulting in the adult dimorphism and potentially providing an adaptive benefit for TSD. In reptiles, the choice of ambient temperature can also influence growth. I measured the effect of egg incubation temperature on juvenile growth rate and water temperature choice of C. serpentina. Eggs were incubated in the laboratory at 21.5, 24.5, 27.5 or 30.5 degreesC to produce both sexes, all males, both sexes or all females, respectively. Egg temperature was linearly and negatively correlated with growth rate of both male and female juveniles. Thus, growth was enhanced, but not maximized, by male-producing egg temperatures. Egg temperature was also negatively correlated with juvenile temperature choice such that, on average, turtles from 21.5 degreesC eggs selected 28 degreesC water, while turtles from 30.5 degreesC eggs chose 24.5 degreesC water. Additionally, these temperature choices were highly repeatable, even following a 6 month hibernation period at 7 degreesC. Thus, while male egg temperatures do not directly maximize growth, multiple effects of embryonic temperature may combine to create long-lasting differences in the behavioral physiology of male and female C. serpentina. Such differences could be important to the ecology and evolution of TSD.

Embryonic Thermosensitivity of the Ascidian, Ciona savignyi

Embryonic temperature sensitivity of the solitary ascidian, Ciona savignyi, was examined with special reference to acclimatization to seasonal change in seawater temperature. This ascidian spawns throughout the year; its life span is completed within six months and depends on the cumulative environmental temperature. The optimal temperature range for development from early cleavage stage to metamorphosis in embryos produced by individuals raised in warmer seasons differed significantly from that of individuals raised in colder seasons. Within the common optimal temperature range, developmental times at any given temperature were the same for both groups of embryos. The thermal acclimation of ascidian embryos is discussed and compared with that of echinoid embryos.

Hyperthermia, teratogenesis and the heat shock response in mammalian embryos in culture.

Hyperthermia is a recognized teratogen in animals and there is strong evidence that it also causes significant damage to human embryos. Studies with induced hyperthermia in pregnant animals defined the defects which are produced, the susceptible stages of development, and threshold doses of heat required to cause defects. The in vivo experiments lacked precision because of variability of embryonic development at a given conceptual age, varying maternal responses to agents causing temperature elevations, the difficulty in measuring embryonic temperature and the possibility that defects were caused by toxic changes in maternal metabolism. These variables were eliminated by the use of postimplantation whole rat and mouse embryo cultures, which were exposed to various doses of heat at closely defined stages of development. The studies showed that heat acts directly on embryos and that elevations of 2 degrees C and greater sustained over early rat organogenesis cause defects mainly by causing apoptotic cell death especially in the developing central nervous system. A moderate, non damaging exposure is followed within 15 min by protection for up to 8 h against a more severe and otherwise teratogenic exposure. The protective heat shock response is accompanied by a reduction of normal protein synthesis and concurrent synthesis of heat shock proteins (HSP90, 71, 47, 27). Most HSP in these families are also present constitutively in embryos, probably having important roles in protecting newly synthesized proteins from aggregation and facilitating folding into their normal functional configurations. The appearance of induced HSP and hsp mRNA at known sites of thermal damage suggests a protective role. Heat induced cell death by apoptosis is a feature of teratogenic damage to the developing brain. Apoptosis could be a by-product of a damaging heat exposure because of a priority favoring induction of the heat shock response over the normal gene program for organogenesis, survival being achieved at the expense of normal development.

In vivo assessment of embryonic cardiovascular dimensions and function in day-10.5 to -14.5 mouse embryos.

Embryonic cardiovascular function has been extensively studied in vivo in the chick embryo. However, the geometry of mammalian and avian hearts differs; the mammalian cardiovascular system is coupled to both yolk sac and placental circulations, and unique murine genetic models associated with structural and functional cardiovascular defects are now available. We therefore adapted techniques validated for the chick embryo to define cardiovascular dimensions and function in the mouse embryo. We bred C3HeB female and C57B1/J6 male mice and ICR pairs for experiments on embryonic days (EDs) 10.5 to 14.5 (n = 130 dams). After maternal anesthesia (pentobarbital, 60 mg/kg IP), laparotomy, and sequential regional hysterotomy, we exposed and then imaged individual embryos at 60 Hz (video) in the ventral and/or left anterior oblique views while maintaining uteroplacental continuity. We measured epicardial chamber dimensions and then calculated right and left ventricular elliptical volumes from ares. In addition, we measured pulsed-Doppler blood velocity across the atrioventricular cushions and ventricular outflow tract. We maintained embryonic temperature with a heated surgical platform, topical oxygenated and warmed buffer, and warming lamps. Embryonic heart rate increased from 124.7 +/- 5.2 to 194.3 +/- 13.2 bpm from EDs 10.5 to 14.5 (P < .01). Right and left ventricular end-diastolic and end-systolic dimensions increased (P < .05 by ANOVA for each). Maximal ventricular mean inflow and outflow velocities increased from 62.33 +/- 4.06 to 106.23 +/- 11.59 and from 55.79 +/- 6.11 to 91.61 +/- 6.93 mm/s, respectively (P < .05 by ANOVA for each). Thus, as has been done for chick and rat embryos, the maturation of murine embryonic cardiovascular function can be quantified in vivo, setting the stage for the investigation of structure-function relations in mouse models of cardiovascular development and disease.

Variation in Embryonic Temperature Sensitivity among Groups of the Sea Urchin, Hemicentrotus pulcherrimus, which Differ in their Habitats

Abstract The sea urchin, Hemicentrotus pulcherrimus, spawns during winter and spring in Kagoshima, Aomori and Kanagawa. The seawater temperature during the spawning season ranges from about 16 to 19°C at Sendai, Kagoshima, from about 12 to 15°C at Misaki, Kanagawa, and from about 5 to 7°C in Mutsu Bay, Aomori. Among the groups of this species differing in their habitats, optimal temperature ranges for development were found to differ significantly and the difference corresponded to the difference in seawater temperature during the spawning season. Despite the difference in the optimal temperature range for development among the groups, the relationship between developmental speed and temperature within the common optimal temperature range for these groups was nearly constant. The thermotolerance of embryos produced by cross-fertilization between the group from Kagoshima and that from Aomori was also examined. These embryos showed maternal inheritance of embryonic thermotolerance.

Benign Neglect of Terminal Eggs in Herring Gulls

Terminal-egg neglect arises in Herring Gulls (Larus argentatus) when parents begin to feed and brood the first two (a-, b-) newly hatched young, thereby disrupting incubation of the third (c-) egg. Mean temperature of pipped c-eggs dropped to 33.4?C, significantly below that of the pipped a(37.6?C) and b(36.6?C) eggs. Experimental manipulation of neglect by placement of pipped c-eggs at chronologically earlier nests showed that both hatchability and time to hatch were unaffected by natural levels of neglect. Laboratory incubation confirmed that chilling pipped eggs to 33?C does not affect hatching. Further chilling to 30?C lowered hatchability and increased hatching times. Development was arrested at 27?C. Although Herring Gulls clearly neglected terminal eggs during the final stages of incubation, it was entirely benign in that mean embryonic temperatures were maintained above levels that would cause damage. Last-hatched eggs in this species are evidently well-adapted, physiologically, to withstand chilling down to at least 33?C, thereby enabling them to maintain full viability despite moderate levels of neglect during the hatching period.

Medical sonography: Reproductive effects and risks

While it is clear that the levels and types of medical sonography that have been used in the past have no measurable risks, it would be inaccurate to label the modality of ultrasound as totally safe regardless of exposure. Most agents have reproductive risks and even teratogenic risks if the exposure is raised sufficiently. Thus the prudent use of sonography means that clinicians and designers of equipment have to maintain exposures far below the risks that have been demonstrated in animal studies and from the knowledge obtained about the physical changes that can be produced in humans as the absorbed dose is elevated. The reproductive risks were evaluated using five criteria: 1) human epidemiology, 2) secular trend data, 3) animal experiments, 4) dose response relationships, and 5) biologic plausibility. The analysis reveals that the human epidemiology does not indicate that diagnostic ultrasound presents a measurable risk to the developing embryo or fetus. Animal studies also indicate that diagnostic levels of ultrasound are safe and do not elevate the fetal temperature into the region where deleterious embryonic and fetal effects will occur. Because higher exposures of ultrasound can elevate the temperature of the embryo, the use of diagnostic procedures and the design of sonographic equipment should take into consideration the hyperthermic potential of higher exposures of ultrasound and the hypothetical additional risk of performing sonography on pregnant patients who are febrile. It would appear that if the embryonic temperature never exceeds 39 degrees C, then there is no measurable risk. We suggest that sonography (the field) and sonogram (the procedure) are the most appropriate and least anxiety provoking terms.

Vocal regulation of temperature by avian embryos: a laboratory study with pipped eggs of the American white pelican

When exposed to temperatures above or below normal mean incubation temperature, embryonic American white pelicans, Pelecanus erythrorhynchos, at the pipped egg stage called quickly and strongly in a graded fashion, then soon stopped calling when temperatures were returned to normal. The ability of pelican embryos to regulate their own body temperature by calling was examined by subjecting pipped eggs to an incubation temperature that was either above (50°C) or below (20°C) normal in a surrogate incubation apparatus that automatically returned incubation temperature to near-normal levels for a brief 4-min period whenever an experimental embryo called in response to heating or cooling. Under these conditions, embryonic temperatures initially drifted about 2°C from normal, then stabilized until the end of a 2-h experimental period. When a return to normal incubation temperature was controlled by calls of an embryo held in another room (yolked control), body temperature drifted erratically, and tended towards ambient, indicating that temperature regulation could not be achieved simply by random calling. Results show that late-stage pelican embryos are capable of vocal regulation of temperature provided a parent or surrogate responds appropriately to the embryo's calls. Vocal regulation of embryonic temperature by calling to cooperative parents is potentially operative in a wide range of precocial and some altricial species of birds.

Correlation of embryonic temperature sensitivity of sea urchins with spawning season

In the coastal waters of Japan, from the subtropical area to the subfrigid area, there are several species of sea urchin with a different biogeographic distribution. The present study investigated the temperature sensitivity, as represented by the range of temperature optima for the embryos, and the dependence of developmental velocity on temperature within that range, for each of eight species of sea urchin, Echinometra mathaei, Diadema setosum, Anthocidaris crassispina, Clypeasterjaponicus, Pseudocentrotus depressus, Hemicentrotus pulcherrimus, Strongylocentrotus nudus and Strongylocentrotus intermedius. For all of these species, the optimal temperature range was confirmed to correspond well with the range of seawater temperature during the spawning season. The distributions of these sea urchins were generally correlated with their embryonic temperature sensitivities but exceptions to this correlation were found. This departure from the correlation as well as the flexibility of embryonic temperature sensitivity are discussed.

Embryonic Development and Temperature Tolerance in Diploid and Polyploid Salamanders (Genus Ambystoma)

-The effects of polyploidy on embryonic developmental rate and temperature tolerance of salamanders in the Ambystoma laterale-texanum hybrid complex were examined. Neither initial size, genotype nor ploidy of eggs affected embryonic rates and tolerance limits. Larger eggs gave rise to larger hatchlings at cold temperatures only, and body size of hatchlings from large and small eggs was larger at cold temperatures than at warm temperatures. Although polyploidy does not affect embryonic development, one selective benefit of polyploidy is large egg size.

Embryonic temperature determines adult sexuality in a reptile

Gonadal differentiation in amniote vertebrates is controlled by one of two mechanisms: genotypic sex determination (GSD) or environmental sex determination (ESD). After differentiation the fetal gonad produces sex steroid hormones which govern the development of other components of sexuality. Thus, the primary sex determiner is thought to operate solely as a trigger that initiates a cascade of events culminating in adult sex differences. In the leopard gecko (Eublepharis macularius), gonadal and morphological sex is determined by incubation temperature, with relatively 'hot' temperatures (32 degrees C) resulting in mostly male offspring and relatively 'cold' temperatures (26 degrees C) resulting in only female offspring. We report here that the reproductive behaviour and endocrine physiology of an adult is influenced by the temperature experienced as an embryo. Also, the perception of a female to courtship by a male is influenced by incubation temperature. These data indicate that incubation temperature, the primary determiner of sex in this species, has differential effects on adult sexuality.