The International Research Fellowship Program enables U.S. scientists and engineers to conduct nine to twenty-four months of research abroad. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad.
This award will support a sixteen-month research fellowship by Dr. Kristine L. Grayson to work with Dr. Nicola J. Nelson at Victoria University in New Zealand.
Understanding the ecological impacts of climate change is an urgent research priority. The ability of temperature to dramatically impact population dynamics is particularly apparent in species with temperature-dependent sex determination (TSD). Even small shifts in climate have the potential to alter nest temperatures and bias the sex ratio of an entire population. This research project measures the influence of climate on population structure in a reptile species with TSD, the tuatara (Sphenodon punctatus), and determines if a biased sex ratio amplifies the risk of extinction. First, they are using small island populations of tuatara across northern New Zealand to measure current population sex ratios across a natural latitudinal gradient. The variation in population structure across islands is being examined in relation to 1) past temperature regimes, 2) available thermal nesting microhabitats, and 3) female condition and fecundity. Second, they are using an experimental approach to determine the interactions and behavior altered by a male-biased sex ratio over the short-term and the impact on female morphology and condition over the long-term. Finally, they are combining their data with long-term population data from the tuatara research group to inform a projection matrix model. This model will allow them to explore theoretical questions about the links between a biased sex ratio and population processes, as well as generate realistic estimations of tuatara population viability.
Their research tests hypotheses about the influence of rising air temperatures and available thermal nesting habitats on the degree of adult sex ratio bias across natural populations. They use a species with Type Ib TSD, where warmer nests produce male offspring, to test theoretical predictions about the role of population sex ratio in linking individual interactions and the social system to the growth, decline, or extinction of a population. In addition, their population data will provide much needed information to guide the conservation of important remnant populations of tuatara, a threatened species of evolutionary, cultural, and international significance. This fellowship also includes opportunities to support local primary science education through the Spinyback Trust and work with the northern island tribes of the Mâori.
Awardee: Kristine L. Grayson This research measured the influence of climate and biases in population sex ratio on extinction risk in a New Zealand reptile species, the tuatara (Sphenodon punctatus). Tuatara are considered "living fossils" with an evolutionary history dating back 200 million years and are the only surviving species in one of the four orders of reptiles. They are extremely long-lived and slow to mature, with females only breeding every 2 – 9 years. In tuatara, as in many reptiles, the nest temperature during incubation of eggs determines the sex of offspring. For tuatara, warmer nests produce male offspring while cooler nests produce females; thus, sex ratio bias is a concern for this species under the increasing air temperatures from global climate change. Once widespread across New Zealand, natural populations of tuatara are now only found on approximately 32 outlying islands. The tuatara is a particular conservation concern due to its restricted range, susceptibility to environmental modification, unique evolutionary history, and cultural significance to the indigenous M?ori people. I completed three projects during my 16 months at Victoria University of Wellington. First, I conducted population surveys on seven islands across the latitudinal range of tuatara to test for shifts in body condition and population structure compared to surveys conducted 20 years ago. Initial results indicated most populations had balanced sex ratios and animals with high body condition, except for North Brother Island in the Cook Strait. A male-bias was first noticed in this population in the late 1990s and surveys over the last decade indicate that the female population has declined further. In collaboration with researchers in the Department of Conservation and at University of Western Australia, we conducted further studies testing the impact of increases in nest temperature and competition between the sexes on population viability and extinction risk. We also conducted a male removed experiment, showing that the male bias in the population is reducing female activity. This project has been submitted to a peer-reviewed scientific journal. Finally, I conducted an experiment in juvenile tuatara at Nga Manu Nature Reserve to quantify the impact of a male-biased sex ratio on female activity and body condition. These head-started juveniles were then translocated to mainland reintroduction sites, where my data will provide critical baseline measures of animal health and condition. Taken together, my International Research Fellowship work contributes to a new area of research that examines how the influences of population sex ratio on individual behavior tie into population dynamics. Biased population sex ratios, despite evolutionary theory that predicts they should be rare, are increasingly documented in natural populations and can be a challenge for conservation programs. This project also provided important survey data for the New Zealand Tuatara Recovery Group that will aid in conservation planning for this species. During my residence in New Zealand, I expanded relationships with North Island M?ori tribes (particularly Ng?tiwai) and trained a research student connected to a tribe from the Cook Strait (Te Atiawa). I built collaborations with faculty and graduate students at Victoria University of Wellington that will continue to be productive for many years to come.
