Climate change affects the early-life history of a freshwater turtle in a severely drying region

Freshwater turtles are one of the most threatened vertebrate groups. Climate change is a major threat to these species, with impacts affecting all life-history stages. There is currently a limited understanding of how changes in climate may alter the environmental triggers for hatching and emergence from the nests of freshwater turtle hatchlings. This precludes making predictions about how climate change may impact freshwater turtle recruitment success. The southwestern snake-necked turtle (Chelodina oblonga) is endemic to south-western Australia, a global biodiversity hotspot that has undergone severe climatic drying. Recruitment failure is thought to be occurring in many populations of the species. However, there is little understanding as to how environmental change may be influencing recruitment. This study aimed to: (1) determine the incubation duration and hatching and hatchling emergence success of C. oblonga, (2) determine if the species exhibits hatching or emergence synchrony and/or delayed emergence and (3) quantify the effects of temperature and rainfall on hatchling emergence. Using this information, the study assesses how climatic drying and warming may be impacting C. oblonga's early life-history. Between 2018 and 2020 nest sites were monitored around a large urban wetland with weekly assessments of egg and hatchling status. Incubation duration and hatching and hatchling emergence success were calculated, and generalized linear models were built to determine how temperature and/or rainfall predicted emergence. Hatchlings either emerged shortly after hatching or overwintered in the nest, and both hatching and emergence were asynchronous. Both emergence periods were positively associated with temperature and rainfall. This study reveals that incubation duration, hatching success, hatchling emergence and survival are all likely to be impacted by recent and projected climate change, and especially drying. Warming and drying are predicted for many temperate regions globally, and it is therefore important that their impacts on the early life history of freshwater turtles be better understood.     

Swimming performance of hatchling green turtles is affected by incubation temperature

In an experiment repeated for two separate years, incubation temperature was found to affect the body size and swimming performance of hatchling green turtles (Chelonia mydas). In the first year, hatchlings from eggs incubated at 26°C were larger in size than hatchlings from 28 and 30°C, whilst in the second year hatchlings from 25.5°C were similar in size to hatchings from 30°C. Clutch of origin influenced the size of hatchlings at all incubation temperatures even when differences in egg size were taken into account. In laboratory measurements of swimming performance, in seawater at 28°C, hatchlings from eggs incubated at 25.5 and 26°C had a lower stroke rate frequency and lower force output than hatchlings from 28 and 30°C. These differences appeared to be caused by the muscles of hatchlings from cooler temperatures fatiguing at a faster rate. Clutch of origin did not influence swimming performance. This finding that hatchling males incubated at lower temperature had reduced swimming ability may affect their survival whilst running the gauntlet of predators in shallow near-shore waters, prior to reaching the relative safety of the open sea.     

The effect of the thermal environment on the ability of hatchling Galapagos land iguanas to avoid predation during dispersal

Summary During the month of February 1979, several hundred hatchling land iguanas (Conolophus pallidus) were observed emerging from their natal burrows in a 2 ha communal nesting area on Isla Santa Fe, Galapagos Islands. During this emergence, as many as nine Galapagos hawks were observed to patrol the nesting area and attack hatchling iguanas.The hypothesis that the ability of hatchling land iguanas to escape predation could be influenced by the interaction of the physiological state of the lizards and the thermal environment was analyzed using (1) empirical data on the effect of body temperature (T _b) on locomotory ability of iguanas and (2) biophysical modeling of the T _b's of hatchlings under natural conditions. This hypothesis was tested by assessing the success of natural hawk attacks on lizards exposed to different thermal environments.During those periods when predicted T _b's of hatchlings were always <32°C, (at which temperatures land iguanas were shown to have less than maximal ability to sprint rapidly) hawks were successful in 67% of the observed attacks. However, when T _b's of hatchlings were always 32° C, hawks were successful on only 19% of observed attacks. During periods when hatchling T _b's could be <32° C or 32–40° C (depending upon which microhabitat the hatchling occupied before the attack), the hawks were successful in 46% of the observed attacks.These data indicate that the physical environment, as mediated through the physiological state of the lizards and to correlated locomotary abilities, significantly affects the ability of hatchling land iguanas to escape predation.     

Exclusive predation of sea turtle hatchlings by juvenile blacktip reef sharks Carcharhinus melanopterus at a turtle nesting site in Malaysia

This study reports the discovery of the exclusive predation of sea turtle hatchlings by several juvenile blacktip reef sharks (Carcharhinus melanopterus) in Chagar Hutang bay on Redang Island, Malaysia, in the South China Sea. Three dead specimens of C. melanopterus were retrieved from ghost nets, and the entire digestive tracts of these sharks solely contained the partially digested bodies of sea turtle hatchlings, with no evidence of the remains of any other prey. Thus, juvenile C. melanopterus may opportunistically feed primarily on turtle hatchlings during times when hatchling abundance is high.     

Oxidative stress and antioxidant capacity of a terrestrially hibernating hatchling turtle

Hatchlings of the painted turtle, Chrysemys picta, hibernate terrestrially and can survive subfreezing temperatures by supercooling or by tolerating the freezing of their tissues. Whether supercooled or frozen, an ischemic hypoxia develops because tissue perfusion is limited by low temperature and/or freezing. Oxidative stress can occur if hatchlings lack sufficient antioxidant defenses to minimize or prevent damage by reactive oxygen species. We examined the antioxidant capacity and indices of oxidative damage in hatchling C. picta following survivable, 48 h bouts of supercooling (−6°C), freezing (−2.5°C), or hypoxia (4°C). Samples of plasma, brain, and liver were collected after a 24 h period of recovery (4°C) and assayed for Trolox-equivalent antioxidant capacity (TEAC), thiobarbituric acid reactive substances (TBARS), and carbonyl proteins. Antioxidant capacity did not vary among treatments in any of the tissues studied. We found a significant increase in TBARS in plasma, but not in the brain or liver, of frozen/thawed hatchlings as compared to untreated controls. No changes were found in the concentration of TBARS or carbonyl proteins in supercooled or hypoxia-exposed hatchlings. Our results suggest that hatchling C. picta have a well-developed antioxidant defense system that minimizes oxidative damage during hibernation.     

The Good,the Bad,and the Ugly: Agonistic Behaviour in Juvenile Crocodilians

We examined agonistic behaviour in seven species of hatchling and juvenile crocodilians held in small groups (N = 4) under similar laboratory conditions. Agonistic interactions occurred in all seven species, typically involved two individuals, were short in duration (5–15 seconds), and occurred between 1600–2200 h in open water. The nature and extent of agonistic interactions, the behaviours displayed, and the level of conspecific tolerance varied among species. Discrete postures, non-contact and contact movements are described. Three of these were species-specific: push downs by C. johnstoni; inflated tail sweeping by C. novaeguineae; and, side head striking combined with tail wagging by C. porosus. The two long-snouted species (C. johnstoni and G. gangeticus) avoided contact involving the head and often raised the head up out of the way during agonistic interactions. Several behaviours not associated with aggression are also described, including snout rubbing, raising the head up high while at rest, and the use of vocalizations. The two most aggressive species (C. porosus, C. novaeguineae) appeared to form dominance hierarchies, whereas the less aggressive species did not. Interspecific differences in agonistic behaviour may reflect evolutionary divergence associated with morphology, ecology, general life history and responses to interspecific conflict in areas where multiple species have co-existed. Understanding species-specific traits in agonistic behaviour and social tolerance has implications for the controlled raising of different species of hatchlings for conservation, management or production purposes.     

Compass Orientation During Dispersal of Freshwater Hatchling Snapping Turtles (Chelydra serpentina) and Blanding's Turtles (Emydoidea blandingii)

Freshwater turtle hatchlings primarily use visual cues for orientation while dispersing from nests; however, hatchlings rapidly develop a relationship between a sun or geomagnetic compass and a dispersal target that allows them to maintain an established direction of movement when target habitats are not visible. We examined dispersal patterns of hatchling snapping turtles (Chelydra serpentina) and Blanding's turtles (Emydoidea blandingii) dispersing in large arenas in a mowed field and in dense corn. The dispersal of three categories of hatchlings were examined: (1) naïve individuals (no previous dispersal experience), (2) arena‐experienced (limited dispersal experience in arenas in natural habitat), and (3) natural‐experienced hatchling Blanding's turtles (captured after extensive experience dispersing W in natural habitats toward wetlands). Experienced hatchlings were assigned to treatments consisting of having a magnet or a non‐magnetic aluminum sham or nothing glued to their anterior carapace before release in the corn arena. Dispersal patterns of naïve hatchlings of both species were strongly directional in the field arena with visible target horizons and primarily random in the corn arena where typical target horizons were blocked. When released in corn, dispersal patterns were similar for arena‐experienced hatchlings with magnets or shams attached and differed from their prior dispersal headings in the field arena as naïve hatchlings. Natural‐experienced hatchling Blanding's turtles with and without magnets were able to accurately maintain their prior headings to the WNW while dispersing in the field or corn arenas (i.e., the presence of a magnet did not disrupt their ability to maintain their prior heading). Based on the assumption that no other type of compass exists in hatchlings, we conclude that they were not using a geomagnetic compass, but by default were using sun compass orientation to maintain dispersal headings in dense corn where no typical target habitats were visible.     

Effects of Incubation Temperature on Crocodiles and the Evolution of Reptilian Oviparity

Crocodylus porosus is a mound-nesting crocodilian in which incubationtemperature influences the rate of embryonic development, theprobability that embryos will survive to hatching, post-hatchinggrowth rates and the probability of hatchlings surviving to2 yr of age. Similar responses have been described in Alligatormississippiensis (Joanen et al., 1987) and C. niloticus (Hutton,1987), and they reflect a suite of "non-sexual" effects of incubationtemperature. Temperature-dependent sex determination allocatessex on the basis of these "non-sexual" effects. In C. porosus,it results in maleness being assigned to embryos with high probabilitiesof surviving and good potential for post-hatching growth. Withinthe limits of survival, effects of the moisture environmenton embryological development rate and hatchling fitness seemminor relative to those of the temperature environment. Reptilian orders have either obligate oviparity (chelonians,crocodilians and rhynchocephalians) or facultative oviparity(squamates), depending on the extent of embryonic developmentwithin the oviducts. The distinction is equally one betweenembryos which are buffered from thermal effects within a female'sbody (facultative oviparity) and those that are not (obligateoviparity). Facultative oviparity and internal thermal bufferingmay be the primitive condition within the Class Reptilia, andthe "shell-less" eggs of extant squamates may reflect the originalamniote egg. Obligate oviparity, which also exists in birds,appears to have been a specialized development, and is a blindend in the evolution of viviparity among vertebrates. The significanceof thermal buffering being lost in obligate oviparous reptilesremains unclear.     

EXPERIMENTAL EVIDENCE FOR THE EVOLUTIONARY SIGNIFICANCE OF TEMPERATURE-DEPENDENT SEX DETERMINATION

The evolutionary significance of sex-determining mechanisms, particularly temperature-dependent sex determination (TSD) in reptiles, has remained unresolved despite extensive theoretical work. To investigate the evolutionary significance of this unusual sex-determining mechanism, I incubated eggs of the common snapping turtle (Chelydra serpentina) at a male-producing temperature (26°C), a female-producing temperature (30°C), and an intermediate temperature that produced both sexes about equally (28°C). Laboratory experiments indicated that two performance variables, but no morphological measurements, were significantly influenced by incubation temperature (P ≤ 0.05): hatchlings from cooler incubation treatments swam faster than turtles from warmer incubation treatments, and hatchlings from 28°C exhibited a greater propensity to run than did individuals from 26°C and 30°C. In the field, hatchlings from the all-male and all-female producing temperatures had significantly higher first-year survivorship than did consexuals from the incubation temperature that produced both sexes (G = 6.622, P = 0.03). Significant directional selection was detected on propensity of hatchlings to run (β′ = –0.758, P = 0.05): turtles that tended to remain immobile had a higher probability of first-year survivorship than did individuals that moved readily. Thus, the effects of the gender × incubation temperature interaction on survivorship of hatchling turtles observed in the field experiment may have been mediated by temperature-dependent antipredator behavior. These results provide a possible functional explanation for the evolutionary significance of TSD in turtles that is consistent with predictions of theoretical models.     

Effects of incubation temperature on the energetics of embryonic development and hatchling morphology in the Brisbane river turtle Emydura signata

Incubation temperature and the amount of water taken up by eggs from the substrate during incubation affects hatchling size and morphology in many oviparous reptiles. The Brisbane river turtle Emydura signata lays hard-shelled eggs and hatchling mass was unaffected by the amount of water gained or lost during incubation. Constant temperature incubation of eggs at 24 °C, 26 °C, 28 °C and 31 °C had no effect on hatchling mass, yolk-free hatchling mass, residual yolk mass, carapace length, carapace width, plastron length or plastron width. However, hatchlings incubated at 26 °C and 28 °C had wider heads than hatchlings incubated at 24 °C and 31 °C. Incubation period varied inversely with incubation temperature, while the rate of increase in oxygen consumption during the first part of incubation and the peak rate of oxygen consumption varied directly with incubation temperature. The total amount of oxygen consumed during development and hatchling production cost was significantly greater at 24 °C than at 26 °C, 28 °C and 31 °C. Hatchling mass and dimensions and total embryonic energy expenditure was directly proportional to initial egg mass. Accepted: 18 March 1998     

Embryonic development rate and hatchling phenotypes in the Chinese three-keeled pond turtle (Chinemys reevesii): The influence of fluctuating temperature versus constant temperature

Although the effects of constant temperatures on hatchling traits have been extensively studied in reptiles, the effects of fluctuating temperatures remain poorly understood. Eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) were incubated at a constant temperatures (28 °C) and two fluctuating temperatures (28±3 °C and 28±6 °C) to test for the influence of thermal environment on incubation duration, hatchling traits, and post-hatching growth. Incubation duration was shorter at constant temperature than at fluctuating temperatures. The sex ratio of hatchlings varied among temperature treatments, with more females from 28±6 °C than from 28 °C. The size and mass were greater for hatchlings from a constant temperature than from fluctuating ones, but this difference in body size disappeared when the hatchlings were 3 months old. In addition, the swimming ability, survival, and growth of hatchlings from fluctuating temperatures did not differ from those of hatchlings from constant temperature, when they were kept at an artificial environment without food scarcity or predation. Therefore, the thermal environments with various temperature fluctuations used in this study do not significantly affect fitness-related hatchling traits in this species.     

Age‐dependent,negative heterozygosity–fitness correlations and local effects in an endangered Caribbean reptile,Iguana delicatissima

Inbreeding depression can have alarming impacts on threatened species with small population sizes. Assessing inbreeding has therefore become an important focus of conservation research. In this study, heterozygosity–fitness correlations (HFCs) were measured by genotyping 7 loci in 83 adult and 184 hatchling Lesser Antillean Iguanas, Iguana delicatissima, at a communal nesting site in Dominica to assess the role of inbreeding depression on hatchling fitness and recruitment to the adult population in this endangered species. We found insignificant correlations between multilocus heterozygosity and multiple fitness proxies in hatchlings and adults. Further, multilocus heterozygosity did not differ significantly between hatchlings and adults, which suggests that the survivorship of homozygous hatchlings does not differ markedly from that of their heterozygous counterparts. However, genotypes at two individual loci were correlated with hatching date, a finding consistent with the linkage between specific marker loci and segregating deleterious recessive alleles. These results provide only modest evidence that inbreeding depression influences the population dynamics of I. delicatissima on Dominica.     

Response of diapausing eggs hatching to changes in temperature and the presence of fish kairomones

It has been hypothesized that the production of diapausing eggs in Daphnia can be induced by fish kairomones. A population of Daphnia could survive severe predation using this predator avoidance strategy. However, in changing environments, diapausing eggs experience various temperature conditions, and hatchlings at emergence may be exposed to the same predation risks as their mothers. Therefore, staying in diapause or an immediate response upon hatching to available environmental information could be important for hatchling survival. For this study, we investigated the impact of water temperature (10, 15, 20, and 25°C) in the presence and absence of fish kairomones (Lepomis macrochirus) on the hatching success of resting eggs (D. galeata). Results show that no diapausing eggs hatched at the lowest temperature (10°C), and the highest hatch percentage occurred at 15°C. Although higher water temperatures reduced hatching success, diapausing eggs hatched more quickly. The number of hatchlings was significantly higher after exposure to fish kairomones, and this was more noticeable at higher temperatures (20 and 25°C). The present results suggest that the diapausing eggs were produced as a predator avoidance strategy in Daphnia; however, the presence of fish works as a positive signal to increase hatchlings when the diapausing stage is terminated.     

The variance of incubation temperatures does not affect the phenotype of hatchlings in a colubrid snake, Xenochrophis piscator

It has been documented in some reptiles that fluctuating incubation temperatures influence hatchling traits differently than constant temperatures even when the means are the same between treatments; yet whether the observed effects result from the thermal variance, temperature extremes or both is largely unknown. We incubated eggs of the checkered keelback snake Xenochrophis piscator under one fluctuating (Ft) and three constant (24, 27 and 30 °C) temperatures to examine whether the variance of incubation temperatures plays an important role in influencing the phenotype of hatchlings. The thermal conditions under which eggs were incubated affected a number of hatchling traits (wet mass, SVL, tail length, carcass dry mass, fatbody dry mass and residual yolk dry mass) but not hatching success and the sex ratio of hatchlings. Body sizes were larger in hatchlings from incubation temperatures of 24 and 27 °C compared with the other two treatments. Hatchlings from the four treatments could be divided into two groups: one included hatchlings from the 24 and 27 °C treatments, and the other included hatchlings from the 30 °C and Ft treatments. In the Ft treatment, the thermal variance was not a significant predictor of all examined hatchling traits, and incubation length was not correlated with the thermal variance when holding the thermal mean constant. The results of this study show that the mean rather than the variance of incubation temperatures affects the phenotype of hatchlings.     

Do temperature fluctuations during incubation always play an important role in shaping the phenotype of hatchling reptiles?

Fluctuating temperatures (FTs) influence hatchling phenotypes differently from constant temperatures (CTs) in some reptiles, but not in others. This inconsistency raises a question of whether thermal fluctuations during incubation always play an important role in shaping the phenotype of hatchlings. To answer this question, we incubated eggs of Naja atra under one CT (28 °C, CT), two temperature-shift [cold first (CF) and hot first (HF) in which eggs were first incubated at 24 or 32 °C and then at the other, each for 20 days, and finally at 28 °C until hatching], and one FT thermal regimes. Female hatchlings were larger in snout–vent length but smaller in tail length, head size than male hatchlings from the same-sized egg; female hatchlings had more ventral scales than did male hatchlings. The FT and HF treatments resulted in shorter incubation lengths. Tail length was greatest in the CT treatment and smallest in the FT treatment, with the CF and HF treatments in between; head width was greater in the CT treatment than in the other three treatments. Other examined hatchling traits did not differ among treatments. The observed morphological modifications cannot be attributed to the effect of thermal fluctuations but to the effect of temperatures close to the upper and lower viable limits for the species. Our results therefore support the hypothesis that hatchling phenotype is not altered by thermal fluctuation in species with no phenotypic response to incubation temperature within some thresholds.     

Molecular assessment of the genetic integrity,distinctiveness and phylogeographic context of the Saltwater crocodile (<Emphasis Type="Italic">Crocodylus porosus</Emphasis>) on Palau

The saltwater crocodile (Crocodylus porosus) is the largest and most broadly distributed crocodilian species, and thus is of special conservation and economic interest. Similar to other parts of its range throughout the Indo-Pacific, C. porosus distributed in the Republic of Palau have experienced a severe population decline over the past century primarily due to commercial hunting and eradication campaigns. In addition, several thousand crocodiles of undocumented species and origin were imported into Palau during the 1930’s for commercial farming purposes, potentially polluting the gene pool of the endemic saltwater crocodiles. Analysis of 39 individuals collected throughout the Republic of Palau revealed a single mitochondrial DNA control region haplotype shared by populations sampled in Sulawesi, Borneo and Australia. The mtDNA results, in combination with microsatellite genotypic data at six loci, detected no evidence for inter-specific hybridization between endemic Palauan C. porosus and potentially introduced Crocodylus species. There was no evidence for a genetic bottleneck in the Palauan population, however an excess of rare alleles was identified, indirectly suggesting a recent history of admixture potentially linked to introductions of non-native C. porosus. Following from these findings, Palauan C. porosus should be included in the single ESU previously established for all saltwater crocodiles given the recovery of a fixed, but geographically widespread haplotype. Although Palauan C. porosus exhibited significant genetic differentiation relative to all other sampled populations, it’s delineation as a distinct management unit is precluded at the present time by evidence that the genetic integrity of the population may have been compromised by the introduction of non-native saltwater crocodiles.     

Feeding across the food web: The interaction between diet,movement and body size in estuarine crocodiles (Crocodylus porosus)

The estuarine crocodile (Crocodylus porosus) is an apex predator across freshwater, estuarine and coastal environments. The impact of a changing C. porosus population upon the ecosystem is unknown, but due to large ontogenetic changes in body mass (>1000‐fold) their impact may be wide reaching and substantial. Here we investigated the relationship between diet, movement and body size in a population of C. porosus inhabiting a tidal river in northern Australia. Subcutaneous acoustic transmitters and fixed underwater receivers were used to determine the activity space and movement patterns of 42 individuals (202–451 cm in total length). There was no size‐related spatial partitioning among different sized crocodiles. Large individuals (snout–vent length (SVL): 160 cm < SVL < 188.5 cm) did, however, exhibit a much larger activity space than other size classes. Diet and individual specialization was assessed using the composition of stable carbon (δ¹³C) and nitrogen (δ¹⁵N) isotopes in tissues with different turnover rates. There was a quadratic relationship between body size and δ¹⁵N, suggesting that medium‐sized individuals (110 cm < SVL < 160 cm) incorporated a greater proportion of high trophic prey into their diets than small (SVL < 110 cm) or large individuals (SVL > 160 cm). Tissue δ¹³C composition on the other hand was positively correlated with body size, indicating that different size classes were trophically linked to primary producers in different habitats. Individual‐level analyses showed that small crocodiles were generalist feeders while medium and large size classes specialized on particular prey items within the food webs they fed. The findings further our understanding of ontogenetic variation in C. porosus diet, and suggest that change in C. porosus population size or demographics may be influential at various levels across the local food web.     

New haplotype of the complete mitochondrial genome of <Emphasis Type="Italic">Crocodylus siamensis</Emphasis> and its species-specific DNA markers: distinguishing <Emphasis Type="Italic">C. siamensis</Emphasis> from <Emphasis Type="Italic">C. porosus</Emphasis> in Thailand

Based on molecular phylogeny of available complete mitochondrial DNA (mtDNA) genome sequences reveals that Crocodylus siamensis and C. porosus are closely related species. Yet, the sequence divergence of their mtDNA showed only a few values under conspecific level. In this study, a new haplotype (haplotype2, EF581859) of the complete mtDNA genome of Siamese crocodile (C. siamensis) was determined. The genome organization, which appeared to be highly similar to haplotype1 (DQ353946) mtDNA genome of C. siamensis, was 16,814 bp in length. However, the sequence divergence between the two genomes differed by around 7–10 and 0.7–2.1% for the haplotype1 between C. siamensis and C. porosus (AJ810453). These results were consistent with the phylogenetic relationship among the three genomes, suggesting that C. siamensis haplotype1 mtDNA genome might be the hybrid or the intraspecific variation of C. porosus. On the other hand, our specimen was found to be a true C. siamensis. Simultaneously, the seven species-specific DNA markers designed based on the distinctive site between haplotype2 mtDNA sequences of C. siamensis and haplotype1 mtDNA sequence of C. siamensis–C. porosus were successfully used to distinguish C. siamensis from C. porosus. These effective markers could be used primarily for rapid and accurate species identification in population, ecology and conservation studies.     

Factors influencing the embryonic development and hatchling size of the oceanic squid Illex coindetii following in vitro fertilization

Egg masses of oceanic squid accidently collected in the wild have been observed only from a few spawning events in aquaria, and as a consequence, the study of their embryos and hatchlings is very limited. Here, we used in vitro fertilization techniques to understand the abiotic factors that influenced egg development and hatchling performance of the ommastrephid squid Illex coindetii from the Mediterranean Sea. Egg and hatchling sizes of these ommastrephids are close to the minimum for cephalopod species, and therefore, short embryonic developmental periods were expected under a Mediterranean temperature regime. Low incubation densities and the use of antibiotics in the incubation medium resulted in relatively high survival rates to hatchling. Hatching time was inversely proportional to incubation temperature and ranged from 5 to 11 days at 21 °C and 13 °C, respectively. The addition of oviducal jelly to the eggs immediately after fertilization, followed by another addition at the beginning of organogenesis, resulted in better chorionic expansion, with an increase in egg diameter, delayed hatching and higher hatchling weight, which suggests a better use of yolk reserves. Larger hatchlings in length and weight also tended to be produced at low temperature, probably also due to better yolk absorption. As this species spawns all year round, size differences between summer and winter hatchlings may be suspected. In vitro fertilization techniques used in the laboratory proved to be useful in shedding some light on the early life of this oceanic squid. Further research is needed to elaborate on tests to predict gamete quality and to develop methods to avoid premature hatching.     

Communal nesting under climate change: fitness consequences of higher incubation temperatures for a nocturnal 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 10 months. 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 18–44 years. 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.