Effects of climate change on an egg-laying reptile
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NO FULL TEXT AVAILABLE. This thesis contains 3rd party copyright material. ----- Climate warming poses a threat to lizard populations. Thus information on the thermal sensitivity of eggs and neonates is crucial for identifying vulnerable taxa. In particular, information is currently lacking about how air temperatures influence nest temperatures, and how elevated nest temperatures predicted to occur under climate warming affect hatchling phenotypes. I used a combination of field data and incubation experiments to investigate whether higher nest temperatures are likely to affect the phenotype and survival of hatchling velvet geckos, Amalosia lesueurii. I found a strong linear correlation between air temperature and temperatures inside communal nest sites. To investigate how incubation temperature affects the morphology, behaviour, thermal tolerance limits, and locomotor performance of hatchling geckos, I incubated eggs inside programmable incubators that mimicked current thermal regimes experienced inside natural nests (‘cold’) and future nest temperatures (‘hot’) that might be experienced in 2050 if climate warming continues. After I completed laboratory experiments, I individually marked hatchlings and returned them to the field sites and estimated their long-term survival by sampling study sites once per month over two years. Hatchlings from hot-temperature incubation were smaller and lighter, and had a lower critical thermal maximum and a higher critical thermal minimum, and had lower locomotor performance than hatchlings from cold-temperature incubation. Hot-incubated hatchlings emerged 27 days earlier than cold incubated hatchlings. In the field hot-incubated hatchlings experienced more thermally stressful conditions, and had lower survival rates in the wild than cold-incubated hatchlings. Population viability analyses showed that hatchling mortality rates strongly influenced the probability of extinction and the mean time to extinction. When hatchling mortality was > 86% (similar to that of hot-incubated hatchlings in the field), velvet gecko populations had a higher probability of extinction with mean times to extinction of 18-44 years. Incubation temperature also affected the spatial learning ability of geckos in a task designed to simulate an attack from a predator. In the lab, hot-incubated lizards were slower learners than cold-incubated lizards. Learning scores were positively correlated with hatchling survival rates, indicating that cognitive abilities likely affect fitness in lizards. Potentially, poor learning ability, in concert with and impaired locomotor performance may increase a hatchlings’ vulnerability to predation. In summary, I demonstrated that in the absence of maternal plasticity in nesting behavior, increases in communal nest temperatures may negatively affect the persistence of a widespread oviparous lizard. My study underscores the importance of studying the effects of temperature on all life stages in order to better understand how organisms may respond to climatic changes. Communally nesting species, by virtue of putting all their eggs in one basket, may be particularly sensitive to summer heatwaves that are predicted to increase in frequency and duration in future. A greater understanding of the interactions between temperature and life history traits of individual species can help identify vulnerable species, and in concert with population viability analyses can be used to forecast the future likelihood of extinction. As a group, lizards appear to be particularly sensitive to climate warming, and many Australian species are currently threatened by land clearing and habitat fragmentation. Whether lizards can adapt to rapid environmental change remains to be seen. Future monitoring of lizard populations is crucial for providing early warnings that can allow scientists and conservation managers to intervene before populations go extinct.
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