Mountain Dragon (Rankinia diemensis)

Applicant: University of Tasmania

Species/Taxon: Mountain dragon (Rankinia diemensis)

Location: Clifton Beach and surrounds, as well as the areas surrounding Lake Crescent and Sorell. 

Title of research: How to incubate a dragons' egg. 

Egg laying reptiles face substantial challenges in cool climates – because they need to lay their eggs somewhere where they will develop successfully. This is one of the major factors limiting the persistence of egg laying species in cool climates. Despite this, egg laying reptiles are often found in very cold places. How do they manage to achieve this? They must​ have found a way to get their eggs through development at the low nest temperatures that they get exposed to in these areas. 

The major aim of this project is to test this. Specifically, we will use one of Tasmania’s few egg laying reptiles to test whether incubation duration at set temperatures differ between eggs from females who live at cool climates (e.g., the highlands) compared to eggs from females who live at warm climates (e.g., the coast). We then aim to explore the mechanisms (e.g., basking behaviour during gestation, nest site selection, stage at oviposition, differences in developmental rate) by which cool climate females might facilitate faster embryonic development under cool temperatures and thus persist in cool climates. 

This project will provide vital information that will enhance our understanding of how organisms cope with climatic extremes - with a specific focus on a key life history trait (incubation duration and the timing of offspring emergence). This will provide benefits in terms of the enhancement of scientific knowledge regarding adaptations to climate using an iconic member of Tasmania's local reptile fauna. The benefits of this project will not only be academic, they are also directly applicable to understanding and predicting responses to global climate change. We can combine our understanding of how the thermal environment mediates incubation duration and the timing of emergence with the latest estimates of variation in soil temperatures to generate models that tell us how emergence time is likely to vary across the species distribution. This can then be used to predict how incubation duration and emergence time will change with projected changes in the thermal environment, including using this study to identify areas that are currently unsuitable for mountain dragons but may open up as the temperatures warm. This information will be crucial not only for understanding how mountain dragon populations might change across time but also how these changes may impact other species that occur there. 

We will collect 30 pregnant females from each of two locations at the climatic extremes of the population (n = 60 in total). It is estimated that these females will lay 360 eggs (average clutch size is 6), which will be incubated at set temperatures in the laboratory. We have also included an additional 40 individuals as potential by-catch. 

We will catch females close to laying. They will be brought back into the terrestrial ecology facilities at the University of Tasmania, placed in individual terraria and monitored for laying. During this time, and after laying, we will collect data on female basking behaviour. At laying, eggs from each clutch will be placed in a 20^oC (n = 2/clutch) or a 24^oC (n = 2/clutch) incubator. Forty of the remaining eggs (20 from each population) will be sacrificed and data on stage at oviposition collected. Any remaining eggs will be placed in a third incubator that will be set at 28^oC. These incubation temperatures represent the variation of incubation temperatures experienced by mountain dragon eggs in the wild. During incubation, eggs will have their heart rate monitored twice using a special heart rate monitor. At hatching, all offspring will be measured for weight, length and sexed via hemipene inversion. 

The majority (89%) of individuals will be released at point of capture. Females will be released shortly after they have laid their clutch. Offspring will be released after they hatch (at their mother’s site of capture). A small number of eggs (n = 40) will be sacrificed upon production to generate data on stage at oviposition. 

Mountain dragons are a relatively common reptile species throughout the east coast and into the central plateau and collecting the numbers needed for this project, and returning them to point of capture, is unlikely to affect the population. Furthermore, the eggs from the females will be incubated at more predictable temperatures than they are likely to experience in the wild – thus we expect hatching success to be higher than in natural nests. This will easily offset the small number of eggs that are sacrificed as part of this project.