Keeping reptiles is a rewarding experience, one that develops a bond with these animals. Consequently, we find ourselves asking questions and raising issues rooted in morality and ethics. One such question has been surfacing lately regarding the continued breeding of some of the most popular species such as crested geckos (Correlophus ciliatus), gargoyle geckos (Rhacodactylus auriculatus), and especially leopard geckos (Eublepharis macularius). The argument is that these animals have limited genetic variability and that wild caught animals are not being brought into captive populations anymore to add new genetic vigor. The argument is one of concern for the future offspring being produced and comes from an emotional response to what is perceived as an issue. However, this question can be addressed with many scientifically established concepts. These concepts include ‘effective population’, ‘inbreeding coefficient’, and ‘founder effect’. Many of these concepts assume that the population is a closed population or that there are no emigration or immigration events and therefore no genes leaving the population and no genes being introduced into the population.
An effective population is the least number of individuals able to retain an appropriate amount of genetic variability of the larger population. Knowing this number is vital to establishing a captive population that reflects the entire wild population. With many of the gecko species we keep in captivity, we know nothing about the size of the wild population. Many of the species we keep are in difficult to access areas of the world due to geography or in the case of leopard geckos (Eublepharis macularius), their native range is too dangerous for scientific research. Another factor to take into consideration is the actual range of the species to determine the wild population. As genetic research improves so does our understanding of species delineation and therefore some of these animals we assign to one species could be members of another. A good example of this is the crested geckos’ closest relative Correlophus belepensis. This animal was only described in 2012 and is from a small island measuring only 26.8 square miles!! C. belepensis looks very similar to C. ciliates; the most distinguishing characteristic is a group of white tubercles on the dorsal aspect of the pelvis girdle. Before 2012 these animals would have easily been grouped in with C. ciliates and the wild population would have been misrepresented.
The inbreeding coefficient is a formula used to determine the homozygosity and relatedness of any individual within a closed population to another individual in that same population. This value varies among populations and can be a useful tool when determining inbreeding depression in captivity. A factor many do not take into consideration is how detrimental inbreeding can be to certain species. In the previous case of C. belepensis, the species has evolved on a small island that began with little genetic diversity and through time became a genetically distinct species. The harmful genes, which would have caused the population to go extinct, were selected against and the animals retained the beneficial genes, allowing them to survive to the present day. Inbreeding was the only option and it did not hinder the ability of that population to persist.
A closed population is a group of individuals whose genetic flow is cut off from outside genetic variability. This can be observed in a population relegated to an island in the ocean or within a small body of water. Geographic barriers, such as a large river or high mountain range can cause this phenomenon as well. Similarly, animals brought into captivity are examples of a closed population based on the assumption that no animals are brought from wild populations and introduced to the captive population.
Animals have been brought into captivity for decades beginning in the late 1970’s. Regarding leopard geckos, E. macularius, only a few hundred animals were brought into the country in the late 70’s. As time passed, we began to see thousands coming into the country and by the mid 1990’s orders were coming into the United States numbering 1,000+ for each importer. Trappers in Pakistan stated that they could easily fill orders of 10,000. This can give a glimpse into what the wild population is like, furthermore this set up the captive populations up with an exceeding amount of genetic diversity. These numbers are only for the United States; this does not take into account how many animals were incorporated into European collections during this time frame. Pakistan closed its exportation of reptiles in 1994 and the last WC leopard geckos were brought into the United States in 1997. The base population for leopard geckos can be estimated to be in the tens of thousands within the United States. Even if animals from the wild were not being brought into captivity at present this beginning population would be sufficient to allow for enough genetic diversity to avoid problems with captive breeding populations. However, animals are still brought into captivity from wild caught stock. Many of these are available in Europe and then make their way into U.S. collections. Leopard geckos aren’t the only species still being brought into the country: many times the author has observed gargoyle geckos from wild caught origins being offered for sale.
We observe that the captive populations are not closed systems after all and therefore do not succumb to the pressures of an effective population nor do they exhibit the effects of inbreeding. There are a few examples within the hobby such as working with line bred, polygenetic traits that could pose issues due to extreme inbreeding. Experienced, mindful individuals who understand the repercussions of this type of breeding to achieve the desired results, should use caution when breeding for these traits due to the extreme inbreeding that occurs and the potential defects that could arise. At one time bug eyes were a problem among the captive leopard gecko population, but this has not been observed for many years. The gene’s absence is due to people selecting against these genes by not allowing those animals to breed and pass them on to subsequent generations.
In conclusion, we now have the understanding and tools to determine what should and should not be bred in captivity from a moral standpoint. Some could argue that certain genes should not be bred, but given the information presented the argument to stop breeding entire species within the hobby is purely opinion based and has no supportive data to back the claim. We can and should continue to breed these magnificent animals for many reasons and paramount to those is to better understand the world around us. Our responsibility to the hobby and the animals we work with is to select against deleterious genes by means of culling those individuals and to keep detailed records of our endeavors. By keeping these two things in mind we will be contributing to the scientific community, the herpetocultural community, and we will better ourselves.
- Primack, Richard. 2006; Essentials of Conservation Biology, Fourth Edition. pp249-253
- Personal communication with former importer, 1992-1999