Velvet Gecko Research Articles

Consequences of Oviposition Site Choice for Geckos in Changing Environments.

Simple SummaryMost lizards lay eggs inside nests where developing embryos experience large temperature fluctuations. As females do not incubate eggs, the embryos can experience lethally high temperatures during heatwaves. Thus, future changes in the frequency and intensity of summer heatwaves may threaten lizard populations. However, variation in female nest site choice might buffer the embryos in some nests from high temperatures. In this study, we incubated eggs of the velvet gecko under two fluctuating temperature regimes to mimic the temperatures experienced inside currently used sun-exposed (“warm”: mean = 25.4 °C; range = 16.5–35.5 °C) and shaded (“cold”: mean = 23.3 °C; 17.5–30.5 °C) communal nest sites. We found that warm-incubated hatchlings hatched 15 days earlier, on average, and were smaller than their cold-incubated clutch mates. We released the hatchlings to the wild, and monitored their survival over six months. Egg incubation treatment did not influence the survival of hatchlings. This result is reassuring, because even if air temperatures increase by 2 °C in future, some currently used shaded nests will provide thermal regimes that are suitable for embryonic development. Variation in female nest site choice may therefore allow some populations of velvet geckos to persist in changing environments.Most lizards lay eggs inside nests where embryos experience daily fluctuations in temperature. As embryos are sensitive to exposure to high temperatures, increases in nest temperatures may pose a risk to lizards. In the velvet gecko Amalosia lesueurii, nest temperatures are positively correlated with air temperatures, so nests may get hotter in future. However, maternal variation in oviposition site choice might buffer populations from future warming. To evaluate the consequences of oviposition site choice, we incubated eggs under two fluctuating temperature regimes that mimicked temperatures experienced inside sun-exposed (“warm”: mean = 25.4 °C; range = 16.5–35.5 °C) and shaded (“cold”: mean = 23.3 °C; 17.5–30.5 °C) communal nests. We measured the phenotypic traits of hatchlings, released them to the wild, and monitored their survival over 6 months. Warm-incubated hatchlings hatched 15 days earlier, on average, and were smaller than their cold-incubated clutch mates. Incubation treatment did not influence the apparent survival of hatchlings. Hence, even if air temperatures increase by 2 °C in future, thermal regimes inside some currently used shaded nests will be suitable for embryo development. Maternal variation in nest site choice may therefore allow southern populations of the velvet gecko to persist in changing environments.

Nest site selection in a southern and northern population of the velvet gecko (Amalosia lesueurii).

In many oviparous reptiles, thermal conditions inside nests influence phenotypic traits of hatchlings that are linked to survival. Maternal nest-site selection can therefore have long-term implications for offspring and maternal fitness. We studied nest-site selection in a nocturnal lizard (Amalosia lesueurii) from south eastern Australia. Females of this species lay their eggs communally inside rock crevices, and previous studies have shown that maximum daily nest temperatures are positively correlated with maximum daily air temperatures. The incubation period extends for up to 100d, so during hot summers, embryos may be exposed to stressful thermal conditions. Potentially, mothers could buffer their eggs from thermal extremes via careful selection of nest sites. To evaluate this, we studied nest site selection in a southern population (Morton) and a northern population (Yengo) that experience mild and hot summers respectively. In the field, we measured the physical characteristics, orientation, canopy cover and incident radiation load, and thermal regimes of nest sites and randomly available crevices during one of the hottest Australian summers on record (2018-2019). We found strong inter population differences in the degree of canopy cover and solar radiation loads above nest sites. Nest sites from Morton were more open, and received higher radiation loads, than nest sites from Yengo. Mean nest temperatures were similar in Morton and Yengo, but nests from Yengo experienced higher daily temperatures than those from Morton. During heatwaves, temperatures in some nests exceeded the species critical thermal maximum (39.9°C) for several hours each day. Our results show that females can adjust nest-site choice to match local environments, but future research is necessary to clarify whether exposure to high temperatures influences hatching success or offspring phenotypes in this species.

Body temperature and time of day both affect nocturnal lizard performance: An experimental investigation.

The locomotor performance of reptiles is profoundly influenced by temperature, but little is known about how the time of day when the animal is usually active may influence performance. Time of day may be particularly relevant for studies on nocturnal reptiles that thermoregulate by day, but are active at night when ambient temperatures are cooler. If selection favours individuals that match their performance to activity times, then nocturnal species should perform better during the night, when they are normally active, than during the day. To test this hypothesis, we investigated how the time of day and body temperature affected the locomotor performance of adult females of the velvet gecko (Amalosia lesueurii). We measured the sprint speeds, running speeds and number of stops of 43 adult females at four different body temperatures (20, 25, 30 and 35 °C) during the day and at night. At night, sprint speeds were higher at 20 and 35 °C but sprint speeds were similar at 25 and 30 °C. By day, sprint speed increased with body temperature, peaking at 30 °C, before declining at 35 °C. However, gecko speeds over 1 m was higher at night at all four test temperatures than by day. Number of stops showed broadly similar patterns and females stopped almost twice as often on the racetrack during the day than they did at night. Furthermore, the thermal breadth of performance differed depending on when geckos were tested. Our results demonstrate that both body temperature and the time of day affects the behaviour and locomotor performance of female velvet geckos, with geckos running faster at night, the time of day when they are usually active. This study adds to evidence that both body temperature and the time of day are crucial for estimating the performance of ectotherms and evaluations and predictions of their vulnerability to climate warming should consider the context of laboratory experimental design.

A new velvet gecko (Oedura: Diplodactylidae) from Groote Eylandt, Northern Territory.

Over the last decade, the combination of biological surveys, genetic diversity assessments and systematic research has revealed a growing number of previously unrecognised vertebrate species endemic to the Australian Monsoonal Tropics. Here we describe a new species of saxicoline velvet gecko in the Oedura marmorata complex from Groote Eylandt, a large island off the eastern edge of the Top End region of the Northern Territory. Oedura nesos sp. nov. differs from all congeners in combination of moderate size, and aspects of tail morphology and colouration. It has not been reported from the nearby mainland regions (eastern Arnhem Land) suggesting it may be an insular endemic, although further survey work is required to confirm this. While Groote Eylandt is recognised as a contemporary ecological refuge for declining mammal species of northern Australia, newly detected endemic species suggest it may also be of significance as an evolutionary refuge for many taxa, especially those associated with sandstone escarpments.

Effects of incubation temperatures on learning abilities of hatchling velvet geckos.

Stressful environments in utero can have a profound influence on cognitive functions and learning ability. In lizards, thermal environments experienced by embryos can shape a range of traits, including sex, body size, and locomotor performance, which may influence fitness. Recent studies suggest that incubation temperatures may also influence brain development and learning ability of some lizard species. Therefore, predicted increases in nest temperatures of lizards may not only affect hatchling morphology and performance, but could also affect their learning ability. To investigate how incubation temperatures influence cognitive abilities of hatchlings, we incubated eggs of the velvet gecko, Amalosia lesueurii, under two fluctuating temperature regimes. The warm treatment mimicked the thermal profiles of currently used partly shaded communal nests (mean = 24.3°C, range 18.4-31.1°C), and the hot treatment simulated thermal profiles that could be experienced in sun-exposed nests in 2050 (mean = 28.9°C, range 19.1-38.1°C). At age three to four weeks, we measured the ability of hatchlings to locate an open shelter in a Y-maze choice test. Both hot and warm-incubated hatchlings successfully learned the task, but hatchlings from the warm-temperature treatment learned the task faster, and made fewer mistakes in the first five trials than hot-incubated hatchlings. These patterns were consistent for hatchlings from two geographic locations, suggesting that thermally stressful conditions in utero may alter the learning abilities of hatchling lizards. Because learning ability can affect the survival of hatchling velvet geckos, future increase in nest temperatures may have wide reaching impacts on populations.

Higher incubation temperatures produce long-lasting upward shifts in cold tolerance, but not heat tolerance, of hatchling geckos

ABSTRACTHeatwaves are a regular occurrence in Australia, and are predicted to increase in intensity and duration in the future. These changes may elevate temperatures inside lizard nests, shortening the incubation period, so that hatchlings are more likely to emerge during heatwaves. Potentially, developmental plasticity or heat hardening could buffer hatchings from future warming. For example, higher incubation temperatures could shift critical thermal maxima upwards, enabling lizards to withstand higher temperatures. To investigate whether developmental plasticity affects hatchling thermal tolerance, we incubated eggs of the velvet gecko Amalosia lesueurii under two fluctuating incubation treatments to mimic current (mean=24.3°C, range 18.4–31.1°C) and future ‘hot’ (mean=28.9°C, range 19.1–38.1°C) nest temperatures. We maintained the hatchlings under identical conditions, and measured their thermal tolerance (CTmax) aged 14 days and 42 days. We then released hatchlings at field sites, and recaptured individually marked lizards aged 6 months, to determine whether incubation induced shifts in thermal tolerance were transitory or long-lasting. We found that at age 14 days, hatchlings from hot-temperature incubation had higher CTmax [mean=39.96±0.25°C (s.d.)] than hatchlings from current-temperature incubation [mean=39.70±0.36°C (s.d.)]. Hatchlings from the current-incubation treatment also had significantly higher heat hardening capacity [mean=0.79±0.37°C (s.d.)] than hatchlings from hot-temperature incubation treatment [mean=0.47±0.17°C (s.d. )]. However, both of these incubation-induced effects did not persist into later life. By contrast, incubation treatment had significant and long-lasting effects on the cold tolerance of hatchlings. At age 14 days, current-incubated hatchlings tolerated colder temperatures [CTmin=11.24±0.41°C (s.d.)] better than hot-incubated hatchlings [CTmin=14.11±0.25°C (s.d.)]. This significant difference in cold tolerance persisted into the juvenile life stage, and was present in 6-month-old lizards that we recaptured from field sites. This finding indicates that upward shifts in cold tolerance caused by higher incubation temperatures might affect overwinter survival of lizards, but field studies linking fitness to thermal tolerance are necessary to test this idea. Overall, our results suggest that developmental plasticity for heat tolerance is unlikely to buffer lizard populations from higher temperatures.This article has an associated First Person interview with the first author of the paper.

A new species of velvet gecko (Diplodactylidae: Oedura) from sandstone habitats of inland north Queensland, Australia.

We describe a new species of velvet gecko (Diplodactylidae: Oedura) from the sandstone ranges of central-north Queensland, Australia. Oedura argentea sp. nov. is a medium-sized (SVL 61-80 mm) gecko that is distinguished from its congeners by a combination of its relatively small size, a pattern of 5-6 dark-edged pale transverse bands from neck to pelvis, a silvery iris, a slender tail, a single cloacal spur, and in possessing 14-22 pre-cloacal pores in males. Oedura argentea sp. nov. is a sandstone specialist currently known only from the Gregory Range and nearby sandstone outcropping at Bulleringa National Park. Further surveys are required to determine the limits of distribution through this region. Oedura argentea sp. nov. is the fifth described species of Oedura in north-eastern Queensland. We also assess the name O. fracticolor De Vis, 1884 because it is an unresolved name pertaining to this general region. Based on colour-pattern and locality in the original description, we conclude that O. fracticolor is a senior synonym of O. castelnaui (Thominot, 1889); however, we propose that priority be overturned under Articles 23.9.1.1 and 23.9.1.2 of the ICZN (1999) and that the name O. fracticolor be regarded as nomen oblitum and O. castelnaui a nomen protectum.

Localization of amylin-like immunoreactivity in the striped velvet gecko pancreas.

Immunohistochemical techniques were employed to investigate the distribution of amylin-like immunoreactive cells in the pancreas of gecko Homopholis fasciata. Four types of endocrine cells were distinguished: insulin immunoreactive (B cells), pancreatic polypeptide immunoreactive (PP cells), glucagon and pancreatic polypeptide immunoreactive (A/PP cells) and somatostatin immunoreactive cells (D cells). Pancreatic islets contained B, A/PP and D cells, whereas extrainsular regions contained B, D and PP cells. In the pancreatic islets, amylin-like immunoreactive cells corresponded to B cells, but not to A/PP or D cells. In the extrainsular regions, amylin-like immunoreactive cells corresponded to either B or PP cells. Amylin secreted from intrainsular B cells may regulate pancreatic hormone secretion in an autocrine and/or a paracrine fashion. On the other hand, amylin secreted from extrainsular PP and B cells, and/or intrainsular B cells may participate in the modulation of calcium homoeostasis in an endocrine fashion.

Hotter nests produce hatchling lizards with lower thermal tolerance.

In many regions, the frequency and duration of summer heatwaves is predicted to increase in future. Hotter summers could result in higher temperatures inside lizard nests, potentially exposing embryos to thermally stressful conditions during development. Potentially, developmentally plastic shifts in thermal tolerance could allow lizards to adapt to climate warming. To determine how higher nest temperatures affect the thermal tolerance of hatchling geckos, we incubated eggs of the rock-dwelling velvet gecko, Amalosia lesueurii, at two fluctuating temperature regimes to mimic current nest temperatures (mean 23.2°C, range 10-33°C, 'cold') and future nest temperatures (mean 27.0°C, range 14-37°C, 'hot'). Hatchlings from the hot incubation group hatched 27 days earlier and had a lower critical thermal maximum (CTmax 38.7°C) and a higher critical thermal minimum (CTmin 6.2°C) than hatchlings from cold incubation group (40.2 and 5.7°C, respectively). In the field, hatchlings typically settle under rocks near communal nests. During the hatching period, rock temperatures ranged from 13 to 59°C, and regularly exceeded the CTmax of both hot- and cold-incubated hatchlings. Because rock temperatures were so high, the heat tolerance of lizards had little effect on their ability to exploit rocks as retreat sites. Instead, the timing of hatching dictated whether lizards could exploit rocks as retreat sites; that is, cold-incubated lizards that hatched later encountered less thermally stressful environments than earlier hatching hot-incubated lizards. In conclusion, we found no evidence that CTmax can shift upwards in response to higher incubation temperatures, suggesting that hotter summers may increase the vulnerability of lizards to climate warming.

The effects of incubation temperature on locomotor performance, growth and survival in hatchling velvet geckos

AbstractThe thermal environment that lizard eggs experience during incubation can affect the size, shape and performance of hatchlings. Summer heatwaves are predicted to increase in frequency and duration in the future, and could produce higher temperatures inside lizard nests. Increase in nest temperatures may influence offspring sex, body size, growth and locomotor performance, which in turn can affect fitness. We investigated whether incubation temperatures influenced the locomotor performance of hatchlings of the velvet gecko (Amalosia lesueurii), a nocturnal gecko that lays eggs in communal nests inside rock crevices. We incubated eggs at two fluctuating temperature regimes that mimicked current nest temperatures (mean = 23.2°C, range 10–33°C, ‘current’) and predicted future nest temperatures (mean = 27.0°C, 14–37°C, ‘future’). We measured the locomotor performance of hatchlings at four temperatures (20, 25, 30 and 35°C), and released them at two field sites (Nowra and Dharawal National Park, ‘DNP’) to estimate their growth and survival over 10 months. Hot‐incubated hatchlings were smaller, and ran more slowly than current‐incubated hatchlings at all four test temperatures. Incubation temperature did not affect the growth rates of lizards from Nowra, but at DNP, hot‐incubated lizards grew more slowly than current‐incubated lizards. Survival analyses revealed that future‐incubated hatchlings had lower survival than current‐incubation hatchlings over 10 months of life, but selection on hatchling traits differed between study sites. For hatchlings from DNP, there was evidence for directional selection on body mass, but little support for selection on SVL or speed. At Nowra, there was equivalent evidence for selection on mass, SVL and speed. These results demonstrate that incubation induced differences in morphology and locomotor performance can influence the survival of hatchlings. In the absence of maternal plasticity in nesting behavior, future increase in nest temperatures, by altering offspring morphology, performance and survival, have the potential to influence the viability of gecko populations.

Predicting the effect of climate change on a range-restricted lizard in southeastern Australia.

Climate change is ranked as one of the most severe threats to global biodiversity. This global phenomenon is particularly true for reptiles whose biology and ecology are closely linked to climate. In this study, we used over 1,300 independent occurrence points and different climate change emission scenarios to evaluate the potential risk of changing climatic conditions on the current and future potential distribution of a rock-dwelling lizard; the velvet gecko. Furthermore, we investigated if the current extent of protected area networks in Australia captures the full range distribution of this species currently and in the future. Our results show that climate change projections for the year 2075 have the potential to alter the distribution of the velvet gecko in southeastern Australia. Specifically, climate change may favor the range expansion of this species to encompass more suitable habitats. The trend of range expansion was qualitatively similar across the different climate change scenarios used. Additionally, we observed that the current network of protected areas in southeast Australia does not fully account for the full range distribution of this species currently and in the future. Ongoing climate change may profoundly affect the potential range distribution of the velvet gecko population. Therefore, the restricted habitat of the velvet geckos should be the focus of intensive pre-emptive management efforts. This management prioritization should be extended to encompass the increases in suitable habitats observed in this study in order to maximize the microhabitats available for the survival of this species.

Incubation under climate warming affects learning ability and survival in hatchling lizards.

Despite compelling evidence for substantial individual differences in cognitive performance, it is unclear whether cognitive ability influences fitness of wild animals. In many animals, environmental stressors experienced in utero can produce substantial variation in the cognitive abilities of offspring. In reptiles, incubation temperatures experienced by embryos can influence hatchling brain function and learning ability. Under climate warming, the eggs of some lizard species may experience higher temperatures, which could affect the cognitive abilities of hatchlings. Whether such changes in cognitive abilities influence the survival of hatchlings is unknown. To determine whether incubation-induced changes in spatial learning ability affect hatchling survival, we incubated velvet gecko, Amalosia lesueurii, eggs using two fluctuating temperature regimes to mimic current (cold) versus future (hot) nest temperatures. We measured the spatial learning ability of hatchlings from each treatment, and released individually marked animals at two field sites in southeastern Australia. Hatchlings from hot-incubated eggs were slower learners than hatchlings from cold-incubated eggs. Survival analyses revealed that hatchlings with higher learning scores had higher survival than hatchlings with poor learning scores. Our results show that incubation temperature affects spatial learning ability in hatchling lizards, and that such changes can influence the survival of hatchlings in the wild.

Communal nesting under climate change: fitness consequences of higher incubation temperatures for anocturnal lizard.

Communal nesting lizards may be vulnerable to climate warming, particularly if air temperatures regulate nest temperatures. In southeastern Australia, velvet geckos Oedura lesueurii lay eggs communally inside rock crevices. We investigated whether increases in air temperatures could elevate nest temperatures, and if so, how this could influence hatching phenotypes, survival, and population dynamics. In natural nests, maximum daily air temperature influenced mean and maximum daily nest temperatures, implying that nest temperatures will increase under climate warming. To determine whether hotter nests influence hatchling phenotypes, we incubated eggs under two fluctuating temperature regimes to mimic current 'cold' nests (mean=23.2°C, range 10-33°C) and future 'hot' nests (27.0°C, 14-37°C). 'Hot' incubation temperatures produced smaller hatchlings than did cold temperature incubation. We released individually marked hatchlings into the wild in 2014 and 2015, and monitored their survival over 10months. In 2014 and 2015, hot-incubated hatchlings had higher annual mortality (99%, 97%) than cold-incubated (11%, 58%) or wild-born hatchlings (78%, 22%). To determine future trajectories of velvet gecko populations under climate warming, we ran population viability analyses in Vortex and varied annual rates of hatchling mortality within the range 78- 96%. Hatchling mortality strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was >86%, populations had a higher probability of extinction (PE: range 0.52- 1.0) with mean times to extinction of 18-44years. Whether future changes in hatchling survival translate into reduced population viability will depend on the ability of females to modify their nest-site choices. Over the period 1992-2015, females used the same communal nests annually, suggesting that there may be little plasticity in maternal nest-site selection. The impacts of climate change may therefore be especially severe on communal nesting species, particularly if such species occupy thermally challenging environments.

A new species of Velvet Gecko (Oedura: Diplodactylidae) from the limestone ranges of the southern Kimberley, Western Australia.

We describe a new species of large Oedura from the Oscar Range on the southern edge of the Kimberley Craton in north-western Australia. Oedura murrumanu sp. nov. can be distinguished from all congeners by the combination of large size (snout-vent length to 103 mm), moderately long and slightly swollen tail, tiny scales on the dorsum, fringe of laterally expanded lamellae on each digit, and 6-7 paired distal subdigital lamellae on the fourth toe. The new species is the first endemic vertebrate known from the limestone ranges of the southern Kimberley; however, this area remains poorly surveyed and further research (particularly wet season surveys and genetic analyses) is required to better characterise regional biodiversity values.

Proliferative Thyroid Lesions in Three Diplodactylid Geckos:Nephrurus amyae,Nephrurus levis, andOedura marmorata

Over a 5-mo period, three diplodactylid geckos housed at the National Aquarium were diagnosed with proliferative thyroid lesions: a rough knob-tail gecko (Nephrurus amyae), a smooth knob-tail gecko (Nephrurus levis), and a marbled velvet gecko (Oedura marmorata). Clinical signs included an intraoral mass or ventral throat swelling (or both), oral bleeding, and weight loss. Both of the knob-tail geckos died. The histologic diagnosis for the rough knob-tail gecko was thyroid carcinoma with metastases to the liver and lungs, and thyroid carcinoma with no metastases was reported in the smooth knob-tail gecko. A thyroidectomy was performed on the marbled velvet gecko with a histologic diagnosis of adenomatous hyperplasia. Postoperative weight loss and bradycardia resolved following oral supplementation with levothyroxine. The animal is in normal health 10 mo post-surgery. Five other diplodactylid geckos in the collection remain unaffected, giving a 38% prevalence of proliferative thyroid lesions (3/8). The etiology remains undetermined. This is the first report of a cluster of proliferative thyroid lesions in geckos.

Generalization of predator recognition: Velvet geckos display anti-predator behaviours in response to chemicals from non-dangerous elapid snakes

Abstract Many prey species detect chemical cues from predators and modify their behaviours in ways that reduce their risk of predation. Theory predicts that prey should modify their anti-predator responses according to the degree of threat posed by the predator. That is, prey should show the strongest responses to chemicals of highly dangerous prey, but should ignore or respond weakly to chemicals from non-dangerous predators. However, if anti-predator behaviours are not costly, and predators are rarely encountered, prey may exhibit generalised antipredator behaviours to dangerous and non-dangerous predators. In Australia, most elapid snakes eat lizards, and are therefore potentially dangerous to lizard prey. Recently, we found that the nocturnal velvet gecko Oedura lesueurii responds to chemicals from dangerous and non-dangerous elapid snakes, suggesting that it displays generalised anti-predator behaviours to chemicals from elapid snakes. To explore the generality of this result, we videotaped the behaviour of velvet geckos in the presence of chemical cues from two small elapid snakes that rarely consume geckos: the nocturnal golden-crowned snake Cacophis squamulosus and the diurnal marsh snake Hemiaspis signata. We also videotaped geckos in trials involving unscented cards (controls) and cologne-scented cards (pungency controls). In trials involving Cacophis and Hemiaspis chemicals, 50% and 63% of geckos spent long time periods (> 3 min) freezing whilst pressed flat against the substrate, respectively. Over half the geckos tested exhibited anti-predator behaviours (tail waving, tail vibration, running) in response to Cacophis (67%) or Hemiaspis (63%) chemicals. These behaviours were not observed in control or pungency control trials. Our results support the idea that the velvet gecko displays generalised anti-predator responses to chemical cues from elapid snakes. Generalised responses to predator chemicals may be common in prey species that co-occur with multiple, ecologically similar, dangerous predators.

Nesting in a thermally challenging environment: nest-site selection in a rock-dwelling gecko, Oedura lesueurii (Reptilia: Gekkonidae)

In egg-laying species, maternal oviposition choice can influence egg survival and offspring phenotypes. According to the maternal-preference offspring-performance hypothesis, females should choose oviposition sites that are optimal for offspring fitness. However, in thermally challenging environments, maternal oviposition behaviour may be constrained by the limited availability of suitable oviposition sites. We investigated nest-site selection in a nocturnal lizard [velvet gecko Oedura lesueurii (Dumeril and Bibron)] that inhabits a thermally challenging environment in south-eastern Australia. The viability of these gecko populations is critical for the persistence of an endangered snake species (Hoplocephalus bungaroides Wagler) that feeds heavily on velvet geckos. Female geckos chose nest sites nonrandomly, with 87% of nests (N = 30) being laid in deep crevices. By contrast, only 13% of clutches were laid under rocks, which were the most readily available potential nest sites. Nest success in crevices was high (100%), but no eggs hatched from nests under rocks. Temperatures in nest crevices remained relatively low and constant throughout the incubation period (mean = 22.7 degrees C, range 21.0-24.5 degrees C), whereas thermal regimes under rocks showed large diurnal fluctuations. Geckos selected crevices that were deeper, had less canopy cover, and were warmer than most available crevices; in 85% of cases, such crevices were used simultaneously by more than one female. The thermally distinctive attributes of nest sites, and their frequent communal use, suggest that nest sites are a scarce resource for female velvet geckos, and that the shading of rock outcrops through vegetation encroachment may influence nest success in this species.

Context-dependent avoidance of predatory centipedes by nocturnal geckos (Oedura lesueurii)

Most research on the anti-predator behaviour of vertebrate prey has focused on their responses to vertebrate predators. Nonetheless, invertebrates are abundant predators in terrestrial ecosystems, and some invertebrates (e.g., centipedes, spiders) attack and consume vertebrates. We used a combination of field data and laboratory experiments to determine whether a predatory centipede (Scolopendridae: Cormocephalus sp.) influences habitat selection by the nocturnal rock-dwelling velvet gecko, Oedura lesueurii. In the field, centipedes and geckos were syntopic, and sheltered beneath rocks with similar physical dimensions, thermal regimes and degree of sun exposure. Nonetheless, geckos rarely shared rocks with centipedes in the field. In laboratory trials, both geckos and centipedes selected shelters with narrow rather than wide crevices. The presence of a centipede modified habitat selection by juvenile geckos, which preferred wide crevices without centipedes to narrow crevices containing centipedes. In contrast, adult geckos continued to select narrow crevices even if these contained centipedes. When we added centipedes to narrow crevices beneath small and large rocks occupied by geckos, both juvenile and adult geckos exited the crevice (especially if it was under a small rather than large rock). Our results show that centipedes influence habitat selection by velvet geckos, and demonstrate that anti-predator behaviours of geckos are both size- and context-dependent. Ontogenetic shifts in behaviour and habitat selection by vertebrates in response to invertebrate predators may be widespread.

A new species of velvet gecko (Diplodactylidae: Oedura) from north-east Queensland, Australia

A new species of velvet gecko (Diplodactylidae: Oedura) from north-east Queensland, Australia

Population ecology of the velvet gecko, Oedura lesueurii in south eastern Australia: Implications for the persistence of an endangered snake

Abstract Ecological specialization, such as major dependence upon a single‐prey species, can render a predator taxon vulnerable to extinction. In such cases, understanding the population dynamics of that prey type is important for conserving the predator that relies upon it. In eastern Australia, the endangered broad‐headed snake Hoplocephalus bungaroides feeds largely on velvet geckos (Oedura lesueurii). We studied growth, longevity and reproduction in a population of velvet geckos in Morton National Park in south‐eastern Australia. We marked 458 individual geckos over a 3‐year period (1992–1995) and made yearly visits to field sites from 1995–2006 to recapture marked individuals. Female geckos grew larger than males, and produced their first clutch at age 4 years. Males can mature at 2 years, but male–male combat for females probably forces males to delay reproduction until age 3 years. Females lay a single clutch of two eggs in communal nests in November, and up to 22 females deposited eggs in a single nest. Egg hatching success was high (100%), and juveniles had high survival (76%) during their first 6 months of life. Velvet geckos are long‐lived, and the mean age of marked animals recaptured after 1995 was 6.1 years (males) and 8.4 years (females). Older females (7.5–9.5 years) were all gravid when last recaptured. Like other temperate‐climate gekkonids, O. lesueurii has a ‘slow’ life history, and population viability could be threatened by any factors that increase egg or adult mortality. Two such factors – the removal of ‘bush rocks’ for urban gardens, and the overgrowth of rock outcrops by vegetation – could render small gecko populations vulnerable to extinction. In turn, the reliance of predatory broad‐headed snakes on this slow‐growing lizard species may increase its vulnerability to extinction.