About
It is important to remember that species do not exist as independent entities but rather as a component of a larger living system (an ecosystem), so I approach my research from a framework that incorporates the interaction of abiotic and biotic factors, because any conservation efforts that do not consider all of the moving parts of an ecosystem will be unsuccessful in preserving the existence of a species into the long-term future. I am trying to gain as complete of an understanding into the diversity of fauna and flora on New Caledonia, how the composition of communities has changed over evolutionary time, time and spatial variations in abiotic factors, species interactions, historic species distributions, climate and geology, and past/ongoing threats.
My previous work identified considerable individual variation in the sex ratios of gargoyle gecko offspring, with some geckos producing highly male-skewed litters, others producing female-skewed litters, and some with more balanced sex ratios. My hypothesis is that the extreme variation in sex ratios is the result of an interaction between genotype and incubation temperature, with certain incubation temperatures capable of overriding the chromosomal sex-determining signals such that sex-reversed individuals are produced some of the time. Such a genetic x environmental sex determining system with sex-reversed individuals could explain why certain animals produce all male or all female litters. I am testing this hypothesis by randomly assigning the eggs from 20 pairs of gargoyle geckos to four different incubation temperature treatments across the range of viable incubation temperatures (67.1 F, 71.6F, 76.1 F, and 80.6 F). We will not have the results from this study for another year or so, but our hope is that this experiment provides evidence to reject or confirm the role of incubation temperature in sex determination. If we find a definitive link between incubation temperature and sex ratios then we will have further studies to determine the thermosensitive period, pivotal temperature points, and genetic variation in thermosensitivity. We are also interested in investigating the role of hormones and the aromatase gene in sex determination.
For more information see: An Introduction to Environmental Sex Determination
We have ongoing studies that are exploring the inheritance of gargoyle gecko color and pattern morphs. Methods of analysis include absorption spectroscopy to quantify color values such as hue and lightness, image processing programs to analyze pigment and pattern distributions, and histology to describe the structure of chromatophores and pigment-containing molecules.
Gargoyle Gecko Color Development
Our research facility supports New Caledonia Gecko conservation efforts in three main ways: (1) by maintaining ex-situ assurance populations and a captive breeding program breeding, (2) pioneering research that is directly transferable to supporting New Caledonia conservation programs, and (3) through raising awareness and providing educational information to the general public.
The natural populations of Giant Geckos are declining due to habitat loss and degradation associated with mining activities, agriculture, logging, invasive species, and fires. As the habitats of New Caledonia Giant Geckos become increasingly altered and degraded by human activities the risk of extinction increases, and the need for sustainable ex-situ populations becomes increasingly critical in securing the long-term survival of these species.
We have established a diverse captive population of Rhacodactylus auriculatus with an effective population size of 51.7 (28 females and 24 males) that can be sustainably maintained for generations without experiencing the effects of inbreeding depression. This breeding population of geckos was established from an original founding population with an effective population size of 300 individuals (151 females and 149 males), and with an average Pedigree-Based Inbreeding Coefficient equal to F=0.007 the probability of two individuals sharing identical alleles by descent is approximately 0.7%. The degree of relatedness for this ex-situ breeding population is far below the recommendations for a maximum IBD of F=0.125. Additionally, we have several unrelated wild lineages of Yate and Mount Koghis localities (F1, F2, and F3 generation). Ultimately the goal of maintaining this assurance population is to reduce the risk of extinction and to preserve options for future conservation strategies. This population could be used to restore the genetic viability of wild populations experiencing a bottleneck or signs of infertility, supplement natural population numbers, or to reintroduce geckos to their historic range.
While we have mainly focused on R. auriculatus we are also breeding and maintaining the following species in smaller numbers: Bavayia cyclura, Correlophus ciliatus (Ile des Pines), Correlophus sarasinorum, Mniarogekko chahoua (Grande Terre and Ile des Pins localities), and Rhacodactylus leachianus (Grande Terre, Ile des Pins, and Ilot Moro localities).
It is important to remember that individuals managed in artificial conditions experience different selection pressures from those in natural conditions of their natural habitat, but that reptiles when compared to mammals have a lower relative risk for artificial adaption during consecutive generations in captivity. In an attempt to reduce the rate of artificial adaptation I have maintained all geckos in semi-natural conditions where individuals are subject to near natural environments (climate, living environment, shelter, nutrition, water). At some point in the future with enough funds and space I would like to construct large multi-species enclosures that more closely mimic the selective pressures that they experience in the wild including competition for access to resources, sexual selection, and predation.
Our captive gecko populations provide an opportunity to conduct conservation research projects to gain insight into the ecology of New Caledonian gecko species. Specific research efforts that support conservation include recognizing specific life stages that are at higher risk of exploitation or human-related mortality, life stages that would provide a greater benefit for reintroduction, factors influencing developmental success and survival rates, optimal population age and sex distributions, life history information, species interactions, species-typical behavior, and nutritional requirements.
Furthermore, maintaining these geckos in captivity allows for educational demonstrations which gives people a chance to learn about and observe them in captivity, which has been an effective method for increasing awareness to the threats that New Caledonia geckos experience in the wild and the need for their conservation. I have been able to engage both the general public and fellow scientists in conservation efforts by bringing live specimens to research presentations. Furthermore, I have provided the scientific and herpetoculturist communities with free information that empowers informed decision making and improves husbandry standards.
Introduction to the New Caledonian Giant Geckos
Meet the Gecko that Can Clone Itself [Parthenogenesis]
Gargoyle Gecko Hatch Weight Calculator
Free articles are available at Herpetological Information
This project characterized the reproductive behavior and development of the gargoyle geckos, including the breeding season, reproductive output, incubation length, differential parental investment, influence of maternal body condition on offspring fitness, clutch size and weight, hatchling size and growth rate. See the links below for more information.
Analysis of the mineral content revealed that New Caledonia geckos lay a unique type of eggshell with an unusually high calcium content. This type of eggshell is unlike the two types of gecko eggs described in literature, with the eggshell of New Caledonia giant geckos resembling the appearance of soft and flexible parchment-shelled eggs that are seen in other tropical gecko species but with the calcium content closer to what is seen in hard rigid-shelled eggs of desert gecko species. Further studies will be investigating the factors that influence variation in the mineral content of gargoyle gecko eggshells. Currently I am exploring the role of maternal body condition, breeding experience, fertile versus non-fertile eggs, and freshly laid versus freshly hatched eggshells.
In this study I explored the geographical variation in R. leachianus morphology and identified the ecological factors that influence colors, pattern, and body size.
