The research, conducted at the Ethological Station of the University of Bern in Switzerland, tracked 33 captive-bred tokay geckos from 16 breeding pairs across two breeding rounds. All eggs were incubated naturally within the parents’ enclosures, allowing temperature and humidity to vary around the clutches rather than being imposed by an incubator. Tiny waterproof data loggers called iButtons, tied close to each clutch, recorded temperature and humidity every 15 minutes for at least a week, giving the researcher a picture of the microclimate each embryo actually experienced. The average temperatures recorded across clutches ranged from about 26.1 to 29.6 degrees Celsius, a span of just 3.5 degrees.

That narrow range turned out to matter enormously. Warmer incubation temperatures were strongly associated with shorter incubation times, with hatching occurring anywhere between 78 and 138 days after eggs were laid. Bayesian statistical models, which estimate the probability that a predictor genuinely belongs in a model, gave strong support for this temperature effect. Higher temperatures were also linked to larger hatchlings, measured by snout-vent length, with very strong statistical support. Notably, no hatchlings in the study showed any of the deformities that are known to occur when reptile eggs are incubated at suboptimal temperatures, suggesting that the range experienced in the enclosures remained within a healthy developmental window.

Perhaps the most intriguing result concerns sex. Tokay geckos possess XX/XY sex chromosomes, which in textbook genetics should determine their sex. But the study found that a higher proportion of phenotypic males hatched at higher average incubation temperatures, and correspondingly more females at lower temperatures, a pattern echoing earlier observations in the closely related Schlegel’s Japanese gecko. The statistical evidence was comparatively weak, likely owing to the small sample size, but both the raw data and the model comparison pointed in the same direction. Sex was determined visually by the presence or absence of femoral glands, structures that males display prominently.

How can a species with sex chromosomes show a temperature-linked sex ratio? Herpetologists have documented similar puzzles before. Central bearded dragons, for instance, carry ZZ/ZW micro sex chromosomes, yet at incubation temperatures above 32 degrees Celsius genetically male embryos routinely reverse into functional females. For tokay geckos, two candidate explanations remain. One is temperature-dependent sex reversal, in which genetic males develop as phenotypic females at certain temperatures. The other is sex-biased embryo mortality: if female-producing temperatures kill male embryos, the surviving hatchlings skew female. In several clutches incubated at the cooler end of the range, mothers removed one of two eggs, leaving a single hatchling, an observation that could hint at selective mortality but could equally reflect simple disturbance. Without genetic sex testing, the study cannot distinguish between these mechanisms, and the author flags this as a priority for follow-up work.

Humidity, by contrast, showed no clear relationship with sex, incubation duration or hatchling size in the posterior estimates, even though model comparisons suggested the predictors deserved their place in the models. A recent meta-analysis across egg-laying reptiles found that wetter substrate conditions generally produce larger hatchlings, so a subtle humidity effect in tokay geckos cannot be ruled out with the current sample. What was unambiguous was nest choice. By placing loggers at matched but egg-free control locations in the same enclosures, the study showed that females consistently deposited their clutches at spots that were warmer and drier than the alternatives, with very strong statistical support. The same nest sites were even reused by different females across years, evidence that captive geckos actively seek out the microclimates that suit their embryos when given the choice.

The second half of the study asked whether the social environment after hatching matters as much as the environment before it. In commercial and laboratory settings, hatchling reptiles are typically raised in isolation, which simplifies cleaning and health monitoring but bears little resemblance to the lives of naturally social species. Tokay geckos are facultatively social, and adults perform biparental care of their offspring, making them an ideal species in which to test the costs and benefits of social rearing. The researchers therefore divided hatchlings between two treatments: some stayed in the family enclosure with their parents and zero, one or two siblings until six months of age, while others were removed immediately and raised entirely alone.

The outcome, at least for physical development, was a null result: group size had no detectable effect on snout-vent length, growth rate or body condition at six months, and tail loss from family interactions was observed in only two individuals. This contrasts with earlier work in other lizards. Juvenile veiled chameleons raised alone show deficits in social and feeding behaviour, while in tree skinks, housing with a social partner reduced growth and subordinate individuals were more likely to lose their tails. The author suggests that the spacious, naturalistic enclosures and scatter feeding used in the Swiss colony may have diluted competition, allowing family groups to develop without the resource conflicts seen in more confined setups. Notably, a companion study by the same researcher found that socially raised tokay geckos were bolder and more variable in their associative learning, hinting that the consequences of isolation may surface in behaviour rather than body size.

The body condition analysis did reveal some surprises of its own. Males at six months were in better condition than females, individuals from later clutches were in better condition than those from earlier ones, and hatchlings that began life larger tended to end their first half-year in better shape. Body condition was calculated using the scaled mass index, a method that adjusts an animal’s mass for its body length and is widely regarded as a robust measure of energetic reserves. An apparent difference in body condition across rearing group sizes in the raw data, backed up by model comparison, was tempered by the small and unbalanced sample, leaving the question open but tantalising.

For anyone breeding tokay geckos, the practical message is clear: provide options. Females that can choose among nest sites with a gradient of temperature and humidity will pick warmer, drier spots for their eggs, and those choices appear to influence how quickly embryos develop, how large hatchlings emerge and possibly what sex they become. For conservationists, the stakes extend beyond the terrarium. Captive breeding underpins reintroduction programmes for threatened reptiles worldwide, and animals raised under impoverished or unnatural conditions may be poorly prepared for life in the wild. The study also highlights a conspicuous gap in basic natural history: no one appears to have documented the natural range of nest temperatures for wild tokay geckos, information that would be essential for assessing how climate warming might affect this widespread but increasingly pressured species. Until that fieldwork is done, the humble cork bark panel on the back of a terrarium may be one of the best windows into what these geckos really need.

Subject of Research: Effects of incubation temperature and humidity and post-hatching social rearing on the development of captive-bred tokay geckos.

Article Title: The influence of the pre- and post-natal environment on Tokay gecko ( Gekko gecko , Squamata , Gekkonidae ) development in captivity

Article References: Szabo, B. (2026). The influence of the pre- and post-natal environment on Tokay gecko (Gekko gecko, Squamata, Gekkonidae) development in captivity. Herpetozoa, 39, 217-228. https://doi.org/10.3897/herpetozoa.39.e165454

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.39.e165454

Keywords: tokay gecko, Gekko gecko, incubation temperature, temperature-dependent sex determination, reptile captivity, nest site selection, humidity, social rearing, captive breeding, animal welfare, herpetology, gecko development

The study, published in the journal Discover Conservation, monitored seven olive ridley nests during the 2020–2021 nesting season, which runs from September through January in Ghana. Researchers led by Baidoo Abigail, Addo Samuel, and Agyekumhene Andrews deployed miniature HOBO U22 temperature data loggers directly into egg clutches as females were laying, positioning the devices near the center of the clutch where metabolic heat accumulates most. A second logger was buried roughly two meters from each nest at identical depth, acting as a control that recorded the background temperature of the surrounding beach sand. Both loggers recorded measurements every fifteen minutes for the entire incubation period, generating an unusually high-resolution record of the thermal environment experienced by developing embryos.

The most striking result concerns the moment when nest and sand temperatures part ways. For the first nineteen days of incubation, temperatures inside the eggs and in the adjacent sand tracked each other closely, with no statistically significant difference between them. But from day twenty onward—the period that coincides with the thermosensitive window during which hatchling sex is determined—nest temperatures rose consistently above sand temperatures and stayed elevated until the hatchlings emerged. The researchers attribute this divergence to metabolic heating: as embryos grow, their collective metabolic activity generates heat that warms the clutch from within, a phenomenon well documented in sea turtles but never before quantified at this West African site.

The numbers reveal how warm this rookery already runs. Mean nest temperatures across the seven nests ranged from 30.7 to 33.3 degrees Celsius, averaging 32.4 degrees, while adjacent sand temperatures averaged a cooler 31.7 degrees. When nest and sand temperatures diverged, the difference typically spanned 0.3 to 1.7 degrees Celsius, averaging about 0.9 degrees. These figures matter enormously because olive ridley turtles exhibit temperature-dependent sex determination: pivotal temperatures that produce equal numbers of males and females have been reported near 30.0 to 30.5 degrees Celsius, with anything warmer producing females. Since mean nest temperatures during the middle third of incubation—the critical sex-determining window—ranged from 31.5 to 32.9 degrees, the researchers conclude that the monitored nests exceeded pivotal thresholds for a substantial portion of development, strongly implying a female-biased hatchling output. Although sex ratios were not measured directly, the thermal signature alone is telling.

Temperature exerted its clearest influence on the pace of development. Incubation duration ranged from 45 to 57 days across the seven nests, averaging about 48 days, and was strongly and negatively correlated with mean nest temperature, with a correlation coefficient of minus 0.88. Warmer nests hatched markedly sooner, and mean nest temperature explained roughly 78 percent of the variation in incubation duration among nests. This relationship is among the most robust in reptilian developmental biology, but its confirmation in Ghanaian sands underscores how powerfully thermal conditions govern the timeline from egg to emergence, even across a modest sample of nests.

Perhaps surprisingly, temperature told a much weaker story about reproductive success itself. Hatching success ranged widely, from 53.4 to 95.5 percent, with a mean of 81 percent, and emergence success ranged from 44.3 to 92.9 percent, averaging 75.2 percent. Yet neither measure showed a meaningful correlation with mean nest temperature, and incubation duration likewise bore no relationship to success rates. The authors interpret this variability as evidence that factors beyond temperature—sand moisture, gas exchange within the nest chamber, beach compaction, and disturbance—interact in complex ways to determine whether embryos survive. The finding is a caution against attributing nest outcomes to temperature alone, particularly in natural environments where multiple stressors overlap.

The hatchlings themselves offered additional clues about thermal stress. Morphological abnormalities, most frequently non-uniform carapace development, were observed in hatchlings from nests with mean temperatures ranging from 32.6 to 33.2 degrees Celsius, and the two hottest nests, averaging 33.0 and 33.2 degrees, produced the greatest number of anomalies. Locomotor performance, assessed through a self-righting test in which hatchlings were placed upside down on moist sand and timed as they flipped themselves upright, showed a moderate association with nest temperature, though the relationship did not reach statistical significance in the small sample. Such performance traits are closely linked to post-emergence survival, since hatchlings that cannot right themselves or crawl quickly are more vulnerable to predators on their frantic dash to the sea.

The study also carries practical implications for how scientists model the future of sea turtle populations under climate change. Many recent studies estimate nest temperatures from sand temperature data by adding a correction—typically 0.5 to 1.0 degrees Celsius—to account for metabolic heating. The Ghanaian measurements, showing an average nest-to-sand difference of about 0.9 degrees during divergence, provide direct empirical support for the magnitude of such corrections at a tropical site where incubation temperatures already press against pivotal thresholds. The researchers note that the beach at Songor was artificially nourished in 2010 as part of coastal erosion mitigation, a process known elsewhere to alter sand thermal properties, though sediment characteristics were beyond the scope of this study. With global climate change projected to raise sand temperatures further, and with local coastal development reshaping nesting microclimates, accurate in-nest measurements will become ever more critical for forecasting sex ratios and hatchling survival.

The work is not without limitations. Seven nests constitute a small sample, spanning a single nesting season, and the statistical power to detect subtle relationships was correspondingly limited; tendencies toward cooler deeper nests and warmer larger clutches matched published patterns but did not reach significance. Fine-scale thermal gradients within clutches were not assessed, and hatchling sex was never directly determined. Still, as the authors emphasize, this study delivers the first baseline characterization of olive ridley nest thermal dynamics anywhere in West Africa, filling a conspicuous geographic gap in global sea turtle science. As temperatures continue to climb at nesting beaches worldwide, understanding precisely what developing embryos experience inside their eggs—not just what the surrounding sand feels like—may prove decisive for conserving one of the ocean’s most vulnerable travelers, and for ensuring that Ghana’s beaches keep producing hatchlings capable of completing their ancient journey back to the sea.

Subject of Research: Effects of incubation temperature on olive ridley sea turtle nest success and hatchling development at the Songor Ramsar Site, Ghana

Article Title: Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana

Article References: Abigail, B., Samuel, A., & Andrews, A. (2026). Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana. Discover Conservation, 3(1), Article 40. https://doi.org/10.1007/s44353-026-00109-8

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00109-8

Keywords: olive ridley sea turtle, incubation temperature, metabolic heating, temperature-dependent sex determination, hatching success, Songor Ramsar Site, Ghana, climate change, nest temperature, hatchling performance, West Africa, conservation