Inbreeding in Captive Reptile Populations

cinnamon royals

DISCLAIMER: Some of the images depicted in this article are provoking great discussion and argument, for the fact that none of them have been PROVEN to be directly caused by inbreeding. This is true, they have not been proven. However even with seemingly unrelated individuals breeding to produce these defective young, they still appear far more commonly in morph lines of animals than are represented in other more outcrossed and healthy genetic stock of other species that remain truer to their wild, unaltered form, unspoilt by human selective breeding. It also strikes me as odd that there could be so many incubation issues leading to serious deformities in animals that are bred in huge numbers; one would think the breeders would have the art of incubation down to a fine art. Food for thought. Of course it is easier to blame incubation issues instead of actually thinking that maybe breeding such closed genetic stock might have detrimental effects over time. In any case, the pictures are included as an illustration of what CAN happen due to close line breeding of various morphs, as well as deliberate or accidental inbreeding over time. Special thanks to Thomas Burton for allowing me to use his images, and I also wanted to mention that he has shared his own findings with breeding certain mutations in royal pythons to prevent people repeating breeding mistakes that may lead to animal suffering, which is highly commendable. More information on his findings can be found here:

cinnamon royal


Captive breeding of reptiles and amphibians is a widespread activity amongst the herpetoculture hobby. It is often attempted when new owners become more proficient at caring for their reptile pets and seek to broaden their knowledge and experience with these animals thus learning about their reproductive biology. More experienced hobbyists often breed their animals as a commercial venture or indeed as a conservation effort to minimise animals being taken from the wild for the pet trade or to maintain viable captive populations of threatened species. Some commercial enterprises and indeed private keepers undertake breeding projects in order to produce large numbers of desirable species, as well as new and desirable morphs of certain species that can command high prices and therefore return an impressive profit. Captive breeding of the reptiles and amphibians one keeps is often seen as a natural progression in the hobby from having a few pets to becoming a fully-fledged ‘keeper’. As with any animal production enterprise it is important to consider the outcomes and responsibilities involved in breeding of our charges, ensuring we do so in a way that minimises suffering and maintains high standards of welfare for both the animals we breed from and ultimately any offspring we produce for the remainder of their lives.

When it comes to captive breeding of reptiles in particular, there are many concerns evident within the hobby regarding irresponsible breeding and just as many misconceptions about how the practice should be carried out in the first place. One specific concern is the issue of inbreeding in captive reptiles and the detrimental effects this is having on captive populations as a whole, animal welfare at an individual level, the ethics of captive breeding and in the current climate of animal rights opposition, the public perceptions of the hobby in general. In the following discussion I will try to address the main concerns relating to inbreeding in captive reptile and amphibian populations. This discussion assumes a basic knowledge of genetics and gene function.

So what is inbreeding and why is it important?

Inbreeding can be defined as the mating of closely related individuals or those having very similar genetic constitutions. The consequences of inbreeding over time are that the offspring produced become more and more uniform in genetic similarity, and therefore the fitness of these offspring is often adversely affected. Fitness in biological terms relates to the ability of an animal to survive and reproduce thus spreading its genetic material to the next generation. This means that in the wild state those individuals that are genetically inferior and incur a disadvantage in terms of successful foraging, predator avoidance or mate acquisition for example are less likely to live and breed so ultimately their genetic contribution to the population as a whole is minimised. Survival of the fittest ensures that the wild population of any given species is maximally suited and in tune with its environment. This fitness advantage is generally achieved through the maintenance of genetic diversity, rather than uniformity, throughout the population. Genetic diversity is the biological principle that allows adaptation and evolution at a very basic level. Natural selection has ensured that any new genetic adaptations that arise through random combinations of genetic material (genes) at each mating can contribute to those genes perpetuation through the population if they are beneficial to fitness, or indeed to the elimination of such mutations if they are detrimental to fitness of the individual expressing them.

But surely inbreeding happens in the wild?

Inbreeding in the wild state does indeed happen from time to time through chance for the most part, as nature has developed many strategies and biological behaviours designed to minimise the occurrence of closely related individuals breeding together. In certain species for example the ranging behaviours of male and female offspring differs greatly meaning that by the time these individuals reach sexual maturity they have a very small chance of selecting one of their offspring or even distant relatives as a mate. Similarly there is significant evidence at least in birds and mammals that individuals recognise closely related individuals and that this affects mate choice. There has not been as much evidence of kin recognition in ‘lower’ vertebrates such as reptiles and amphibians but this is an area that warrants further study. Even if inbreeding happens occasionally, on a population level of hundreds or even thousands of individuals in a geographical range the impact of this chance occurrence on fitness is minimal. Natural selection means that if any disadvantageous traits result from such a mating pattern these are unlikely to be perpetuated through the population as a whole. So while technically inbreeding can and does occur in the wild state from time to time, the implications of these few matings are minimal. This is because the healthy and advantageous genetic diversity of the population that allows it to adapt to its environment is maintained by natural behaviours of the population as a whole.

So if inbreeding happens in the wild, why is it a concern in captivity?

Comparing the wild state to captive populations of reptiles is scientifically invalid as it is not comparing like with like for a multitude of reasons. Inbreeding in captive populations is a huge concern for the responsible breeder of any animal including food animal production systems, pedigree dog breeding and equally in breeding captive reptiles. The basic and most important concept underlying my argument that comparing wild reptiles to captive populations is flawed is that captive populations are breeding under a system of artificial selection, which places far different pressures on the population than natural selection in the wild. Selection theory is perhaps beyond the scope of this article but at a basic level artificial selection relates to selection of genetic material to breed from based on human decisions, whereas natural selection is a process occurring in nature which seeks to maximise evolutionary advantage and adaptation of a species to its environment over time. Captive environments are incredibly different from wild environments. When we place a reptile in a captive environment we remove many of the selection pressures at play for its wild counterpart, namely providing it with optimal environmental conditions, safeguarding it from predators and providing medical care or special consideration for illness or disability. Artificial selection of reptiles in captive environments also eliminates natural systems for mate choice. In short, the animals we produce over many generations of captive breeding are most likely poorly suited for survival in the wild state. This effect is magnified in situations where generations of inbreeding, intentional or otherwise, have resulted in poor genetic diversity within a population.

Genetic diversity in captive populations of most reptile species commonly bred in the hobby is far less than that found in the wild for the simple reason that in most species the numbers in captivity are far less than the wild population. Therefore there is not as much scope for new genetic material to be encountered. Add to this fact that geographical and economic constraints affect what animals come into contact with each other, and also how far siblings and closely related individuals are distributed between keepers and future breeding projects. There is also the important fact that captive populations of some species may have derived from only a very small number of wild individuals, and that in a certain locality or country there may only be a few distinct bloodlines from which to begin a breeding project in the first place. All of these factors and more discussed later contribute to a far higher inbreeding coefficient in captive populations as opposed to wild, meaning that the probability of genetic material within that population being more uniform and closely related is higher than in a population subject to natural selection. Therefore we commonly see signs of inbreeding depression in captive populations, which can range from extremely subtle and almost invisible to distressingly and visibly severe.

Inbreeding depression can be defined as depression of performance related to inbreeding. Performance in this context can be described as simply as maintaining biological function and health, or could be measured in terms of growth rate, longevity, reproductive health and output, behavioural indicators of stress and welfare or susceptibility to disease. In comparing these indicators of health in a highly inbred population to a population with greater genetic diversity, countless scientific studies throughout the history of animal production have demonstrated that continuous inbreeding of a population decreases performance and vitality of the individuals in that population.

Farmers and dog breeders often breed closely related animals, why is it a problem?

In most animal production systems inbreeding depression is a recognised outcome of repeated close matings and therefore deliberate inbreeding is avoided as a whole except in certain circumstances. Inbreeding has had a place in the domestication of animals and the derivation of all the various animal breeds in food animals, animal athletes such as racehorses and our domestic pets. When a genetic mutation resulting in a desirable characteristic arises in a group of animals, one way to perpetuate that characteristic is to try to ‘fix’ the genetics responsible by mating the animal with a desirable trait back to a closely related individual, often a sibling or parent. As an occasional practice there are risks but they tend to be low unless lethal or severely maladaptive gene expression is magnified by doing so. Very often in a breeding programme this practice will result in establishment of a line of animals all with similar genetic expression and all carrying the same desirable traits. To use food animal production as an example, generations of artificial selection has resulted in sheep, pig and cattle breeds that all have very specific and predictable characteristics in terms of litter size, mothering ability, weight gain and carcass quality amongst others. Ultimately these are economically measurable traits that result in increased profitability for the farmer and cheaper food for the consumer.

Much of this agricultural ‘progress’ resulting in highly productive breeds came from inbreeding, or more accurately line-breeding where all the animals within the breeding population were of similar ancestry but not necessarily as closely related as sibling to sibling, or parent to offspring matings. In effect line breeding is a milder form of inbreeding, but still relies on breeding genetically similar animals together in order that the offspring have predictable and reproducible traits. In the example of food animals above, we see that the objective of these breeding practices is purely for human benefit. The opposite of inbreeding is called outcrossing where new genetic material is bred into certain lines, often to prevent or alleviate the effects on performance related to inbreeding depression. So simplistically, if for example if a farmer has a litter of piglets that reach astonishing weight gains on very low feed rations and have a lower maintenance cost from weaning to slaughter, this litter may well feature heavily in the selection of future breeding stock. He may hold back several young females and breed them back to their father or vice versa with young boars and their mother in order to test the reproducibility of this fantastic weight gain ratio. Through artificial selection, line breeding and occasional inbreeding this farmer may have developed a pig herd over many years which are far more profitable than those on many of his rival farms. Now, say for example the farmer starts to experience problems with growing numbers of female pigs (sows) having difficulty giving birth to these large piglets, or litter size in general decreasing over several years of breeding his established line. He then may find a boar from another breed or bloodline that is known to produce smaller piglets at birth or greater litter size in order to outcross some different genetic material into his line. He has experienced inbreeding depression and needs to try to inject more diversity into his bloodlines in order to keep it as profitable as he would like.

So what are the costs of inbreeding?

Unfortunately the costs are generally directly related to animal welfare. In the case of food animal production, some of the greatest animal welfare concerns of modern agriculture are derived directly from artificial selection for human benefit. Vulnerability to production diseases such as mastitis, milk fever and lameness in dairy cattle is greatly increased when the main factor pushing breeding decisions is maximum milk yield. In pig production, the farmer above may cull many weak and malformed piglets per year as it is not viable or profitable to try to nurture them without affecting profit. Culling all of these ‘defective’ piglets is a welfare issue but is accepted as the price of increased production or performance. Similarly many of his animals may suffer from disease outbreaks as their genetic resistance to pathogens is adversely affected not only by the conditions they are kept in but also by their finely tuned genetic constitution and lack of genetic diversity relating to disease resistance. If a pathogen enters an intensive production unit in which all animals are genetically similar and that pathogen is well equipped to cause infection, it may spread easily throughout the entire unit from animal to animal killing most or all of the animals within. This may not be the case where genetically diverse animals with more vigour and vitality due to outcrossing and careful breeding to ensure disease resistance were bred.

The effects of inbreeding over too many matings and crosses are generally deleterious or negative either in terms of performance, as defined earlier, or in terms of overall animal welfare, health and longevity. Professional and conscientious breeders of any species recognise this risk, and try to keep sibling to sibling or parent to offspring matings to a minimum. They will also make conscious efforts to outcross new genetic material into their line without negating the desirable traits they attempted to fix. Perhaps more visible than food animal costs of inbreeding or line breeding over time are the massive array of genetic health problems affecting pedigree dogs due to generations of close matings required to establish certain breeds from a small genetic pool of similar ancestors. Sadly the selection pressure for pedigree dog breeding is not longevity, vitality and health but purely aesthetic for what physical traits tend to be desirable and win in the show ring. Many dog breeds have become so deformed and biologically maladapted through artificial selection and close breeding practices including inbreeding and line breeding that without veterinary intervention they would quickly die out, the British Bulldog being a sad case in point. This breed almost inevitably requires Caesarian section surgery to give birth due to large puppy size, head shape and the narrow pelvic canal of the bitch in relation to the pups.

What does all this have to do with inbreeding in reptiles?

The reason I have used the above examples to briefly explain the concepts, logic, benefits and costs of inbreeding in general in food animals and domestic pets is that the majority of scientific study to date on inbreeding and artificial selection effects is in these fields. My own undergraduate degree was at an agricultural college studying animal science so I studied food animal production in great detail. Much of the knowledge of genetics and breeding is derived from studies and trials related to the food animal sector. Unfortunately, such scientific studies on the effects of various practices in captive breeding of reptiles are absent or in their infancy by comparison to the wealth of information in other species. However, the same basic biological principles apply whether you are breeding snails, guppies, lizards, snakes or high performance cattle and horses. Good breeders know the circumstances under which inbreeding may be deemed acceptable, and take great care to determine the degree of genetic diversity in the populations of animals they are working with. There is a great deal of care and design that goes into selection of animals for improvement of particular bloodlines, and thankfully nowadays much of this artificial selection is considered not only in terms of human benefit but at the same time with due attention to the welfare implications in the animals concerned.

Unfortunately in the reptile community as a whole, this background knowledge of animal breeding concepts and best practice is frequently lacking in pet owners with very little knowledge due to inexperience keeping animals and very often subject to various myths and misunderstandings even from the so called experts in reptile breeding. All too often we hear and read opinions that inbreeding doesn’t affect reptiles, that it is fine to mate sibling to sibling/offspring to parent just once, or that a breeder has mated several generations of offspring to parents without any visible ill effects. The crucial word in this latter claim is ‘visible’. I hope in this article to dispel some of these myths and misconceptions, as well as provide facts rather than opinion on why inbreeding in captive reptile populations is doing a tremendous damage to animal welfare and the hobby in general, the consequences of which we may not be able to see for some time to come.

So what are the consequences of inbreeding over time?

The consequences of inbreeding are often seen as positive to those deliberately breeding closely related reptiles in that new and attractive colour morphs or patterns can be produced. The production of new varieties and strains in captive reptile breeding has seen a massive rise in the value of individual animals, with rarity often determining extraordinary market price. One of the standard methods of producing such rarities is the use of line breeding or inbreeding once genetic aberrations appear in a population of animals. The reptile community has become more of an industry in recent years and a worrying trend of dismissing any criticism of inbreeding has emerged, with many wrongly assuming there are few if any negative consequences. The justification for this practice is, as in agricultural practice, based on human benefit rather than animal welfare and so it is important for the community and leaders in the industry to recognise and discuss the issue.

Virtually no improvements have been made in terms of animal welfare through inbreeding of captive reptile populations as far as I am aware. By contrast, many examples of compromised welfare can be seen as a direct result including both visible and non-visible effects. Visible effects include kinked spines and other skeletal malformations, reduced or defective growth rates, neurological problems as seen in Spider Royal Pythons, and even offspring hatching with severe physical deformities such as a lack of eyes or internal organs exposed outside the body. Invisible effects on the other hand are more difficult to quantify and often only come to the fore later in an animal’s life, by which time it may have already passed on its defective genetic material to many more generations. These effects include genetic defects not conducive to survival for a natural lifespan, or animals not surviving far past hatching or birth if at all, decreased disease resistance, a failure to thrive or internal deformities not apparent on first glance. The countless neonates produced by large scale breeders of reptiles which fail to hatch or are dead at birth are often dismissed as casualties of breeding large numbers of animals. Some survive, some do not. I would hazard a guess that far higher rates of neonatal death or deformity occurs in units where closely related animals are being bred than in those where heterosis is achieved or the breeder makes concerted efforts to outsource unrelated bloodlines on a regular basis and pays close attention to detail where pedigree or ancestry of the animals in their care are concerned. Perhaps this is an area that warrants further scientific research.

Bearded Dragon neonate with no eyes, several littermates affected

Bearded Dragon neonate with no eyes, several littermates affected

Persistent inbreeding over time, particularly when deliberate, is extremely difficult to justify ethically when all the scientific research and evidence points to the fact that it leads to a decline in health and welfare of the animals concerned over time. As a breeder, one has to firstly accept this as fact and then ask themselves whether they have a greater concern for the health of the animals in their care, or for making a profit at the expense of animal welfare.

Closed captive populations

Apart from deliberate inbreeding in order to ‘fix’ certain traits or enhance certain physical characteristics in a bloodline that pleases the breeder or ultimately makes more money in the commercial market, a substantial level of inbreeding occurs accidentally in captive reptiles. The reason for this is that most captive populations are relatively closed with a low level of new genetic material entering from outside sources. In a relatively small geographical area, many of the individual animals kept by enthusiasts of that particular species or morph may be descended from the same small number of individuals historically. It may have been that only a small number were imported as the founder colony of the entire captive population in that city or country, or it may be that a few breeders produced large numbers of offspring from a few pairs, thus saturating the local market with genetically similar animals. Unwittingly several years later when all of these animals mature and their owners seek out suitable mates it may mean that they are unwittingly selecting siblings or closely related individuals even if they seek new stock from reliable sources far away. Geographical and economic limitations of importing new genetic material and unrelated stock in certain species may mean it is impossible to source unrelated specimens at the right time or without considerable effort and expense. The net result of these trends over time is that closed captive populations of many commonly kept reptiles are becoming more and more inbred despite the efforts of even the most conscientious and responsible breeders. More worrying from a conservation point of view is that in endangered species where the aim of captive breeding is to protect the species from extinction in the wild these same factors can often influence the genetic variance of the captive population. The outcome is the production of animals that are genetically inferior with a substantial fitness disadvantage compared with their endangered wild counterparts. Any hope of reintroduction after a species becomes extinct in the wild is diminished if the captive breeding of that species over time has resulted in animals that are ill equipped to survive in the wild or less disease resistant.

As an example of saturation of local markets, consider the successful Bearded Dragon or Yemen Chameleon breeder, both species which have become enormously popular in recent years. These are lizards with a huge reproductive potential laying large clutches of eggs, possibly several times per year. They are also considered good ‘beginner’ lizards, the former perhaps more appropriately than the latter. Using a simple example of a breeder who has several females breeding and sells their offspring to a handful of shops in the local area or even within a 30-40 mile radius, it is easy to see that the sheer number of surviving animals that may be direct siblings when picked at random in that small geographical area two years later would be enormous. Because these animals may have been bought from the local pet store by relatively inexperienced keepers, the basics of breeder responsibility or even biology may be lacking by the time a year or two later the beginner keeper has developed confidence enough to attempt to breed from their pet. They may seek a mate for their pet from a local pet store or online classifieds and generally will not travel too far to make their purchase. Unwittingly a sibling pair is bred from and the cycle perpetuates. Several years on the majority of bearded dragons or chameleons in one small geographical area may in fact be derived directly from the same single adult pair. The magnitude of sibling to sibling or offspring to parent matings that happened along the way may span several generations. If you scale this up to a national level it is easy to imagine that genetic diversity and hence vigour can be lost accidentally, with the result that we are churning out pretty poor specimens for the pet trade, many of which succumb to our failings in captive care far sooner than if they were a little more robust like earlier generations. It is no coincidence whatsoever that certain popular species in the reptile trade are developing more and more inexplicable as well as obvious health problems when the attention to detail in selecting for genetic diversity and overall health and vigour has sharply declined and that species has become greatly overbred by amateur, short sighted, irresponsible or inexperienced hobbyists.

Two chameleons from same litter, kept in exact same conditions, one failed to thrive; a possible invisible inbreeding effect

Two chameleons from same litter, kept in exact same conditions, one failed to thrive; a possible invisible inbreeding effect

Deliberate inbreeding

Having discussed accidental inbreeding and inbreeding depression as a natural and at times somewhat unavoidable consequence of closed captive populations, it is now time to consider deliberate and unapologetic inbreeding of captive reptiles in order to produce animals as commodities for commercial gain. I may not hold a popular view here and certainly won’t endear myself to many large scale breeders but if my oath as a veterinary surgeon is to act always in the interest of the animal than I consider it vital that we get the hobby talking about the serious welfare implications the reptile industry imposes on the animals in our care. There are many supporters and advocates of deliberate inbreeding that are extremely vocal about their practices, and offer misleading justification for the practice in order to defend it. The fact as outlined previously is that inbreeding for commercial gain directly compromises individual animal welfare over time, whether that is visible immediately in physical deformity or years down the line when far more subtle signs of health and disease resistance become apparent. One of the often cited defences is referencing a particular bloodline or breeder that has bred animals closely for many generations without any problems. I would always argue that such a breeder has been very lucky, but just because they haven’t had a visible or quantifiable problem as yet doesn’t mean there isn’t a genetic time bomb lurking just below the surface of the animals in question. Such an absence of evidence is not proof that there is no risk; it just means an unfavourable outcome for that activity has not happened yet. Similarly, what a certain breeder advertises and what is kept hidden from public knowledge and perception are often two very different things. Many large scale breeders become accustomed to a level of losses, deformities or deaths amongst the animals they produce. Certainly many will recognise these as a direct result of their breeding practices, but if their venture is commercially successful and produces animals that are visibly, outwardly healthy and that earn a profit, then there is very little advantage in advertising the fact that many more animals were produced that didn’t survive or had to be culled due to health issues in their bloodline. This is the hidden cost to animal welfare that is often swept under the rug, and the average consumer buying a Royal Python morph for example does not factor in these losses of life that were part of producing their new pet.


The morph craze

The rise of colour morphs in certain species, most notably in Royal Pythons and Leopard Geckoes in recent years has seen a massive increase in the level of inbreeding within the reptile hobby that is not only now expected but also glorified and defended with extraordinary vigour. My introduction to the reptile community in my early teenage years was surrounded by keepers who were fascinated by the natural biology and behaviour of the myriad of reptile and amphibian species from different regions of the world. Generally enclosures and husbandry techniques attempted to emulate the wild habitat and the use of naturalistic vivaria with living plants was widespread. Selective breeding for unusual traits or ‘domestication’ of species was not so widespread. The hobby has changed considerably since then, and the more worrying trend is that it has become more of an industry for many where animals are kept and produced in minimal welfare standards in order to maximise profit. I’ve mentioned elsewhere the health implications and welfare concerns inherent in mass production of reptiles in large scale facilities, and the culture that extends to the small scale keeper as a result in terms of housing, husbandry and value of the individuals kept.

Crested gecko hatchling with no limbs

Crested gecko hatchling with no limbs

The boom in popularity of reptiles as pets in recent years has led to a stunning variety of morphs or man-made artificially selected forms that vary significantly from the wild-type of that particular species. These morphs have arisen through careful selection for desirable traits, and are often exemplified or propagated by inbreeding. Without inbreeding it would not be possible to produce many of the common morphs we see today, some of which have superceded the original wild type form in certain species to the point it has itself become a rarity in the trade. The two biggest species I mention above in terms of morphs created, the Leopard Gecko and Royal Python, are also the best examples to use when describing the specific problems that manifest when inbreeding is lauded as a positive practice and the negative consequences of the practice ignored or worse still falsely justified. For fear of writing a book instead of an article I will not go into tremendous detail on all the genetic problems associated with morphs in these species but I would encourage all readers to investigate for themselves the genetic dysfunctions inherent in the following few examples:

Enigma Leopard Geckoes with neurological or vestibular (balance) disease

Cryptosporidium susceptibility in many Leopard Gecko strains (thought to have some genetic component for parasite resistance)

Spider Royal pythons with mild to severe neurological issues aka ‘wobbles’

Lethal gene combinations in many Royal morph pairings

Spinal kinking, duckbills, bug eyes and other physical malformations in Royal Pythons

It is simply undeniable that a great proportion if not all of these health issues of the animals being produced are at least partly if not fully attributable to degrees of inbreeding associated with their production. Breeders and hobbyists alike can argue all they want on the merits and justifications of doing so, but the bottom line is that to continue breeding these defective lines of animals without substantial and considered efforts to improve the lines by outcrossing is tantamount to animal abuse and is only justified for financial gain.


Dispelling the Myths

Many excuses or justifications are given when the practice of inbreeding is raised. All can be rebuttalled easily, applying the following logic.

Crossing siblings, parents, and heterozygotes carry different levels of risk

This may be true in isolation for single matings but if one considers the effect of many breeders ‘allowing’ close matings over many years and in geographically limited areas the inbreeding coefficient for the whole population rises sharply. By ‘allowing’ close matings in your collection to ‘enhance’ the appearance of whatever strain or morph you are producing, you are having a detrimental impact on the overall genetic health of that population as a whole in the future.

Single matings aren’t harmful, only repeated crossings of related animals

Again one breeder ‘allowing’ a single mating between two siblings or parent to offspring may not carry a huge risk when viewed as an isolated event, but considering the bloodline involved may be highly inbred already if traced back far enough, and considering the likelihood of future closely related crossings being carried out with the offspring produced, each single mating dismissed as an isolated low risk event has the potential to impact the genetic integrity of the animals in future. Breeders should not be so short-sighted as to think their actions in their current generation of apparently healthy animals has no impact on the future health of the next generations.

Wild occurrence

As discussed earlier wild populations are maximally suited to their environment, otherwise they would not survive. Comparing artificially selected animals bred for appearance and other arbitrary human values, aesthetic or economic, with wild populations where an occasional inbreeding event has no great impact on the population is an invalid argument.

Low incidence in certain species or bloodlines

I have seen many times in discussions on inbreeding the person defending the practice citing an example they know where they or a colleague has ‘bred seven generations of Jaguar Carpet pythons using sibling and parent matings with no problems’ for example. This is not proof that inbreeding is not harmful. This is an example where someone has not seen any of the visible effects of inbreeding over time in their line of animals. They may be lucky so far that nothing visible has been identified. Genetics relies on chance mutations and gene combinations. Many times highly inbred animals can be produced and don’t display any negative effects. But arguing that because this is true that inbreeding in general is without risk is foolish. Applying a similar logic someone might say car crashes do not happen or are very low risk because they have been driving for 20 plus years and have never had a crash. It is simply an illogical defence and no excuse to make light of the often serious consequences of inbreeding.

Primitive Vs advanced vertebrates?

Another opinion that is often given to defend current breeding practices and standards in the reptile industry is that inbreeding does not seem to affect lower vertebrates such as fish, amphibians and reptiles compared with mammals for instance. This is not proven fact. The fact is that much of the research carried out on inbreeding to date in the scientific literature relates only to mammal species and birds. The reason for this is that agricultural and animal science research has primarily focused to date on agricultural species. As discussed earlier vast data and research exists on genetic variation and inbreeding effects in terms of the domestication of species, and animal production for human benefit. Unfortunately, herpetoculture is still in it’s infancy by comparison to agriculture which has been around for thousands of years. Fecundity of captive reptiles, as in their ability to reproduce large numbers of offspring, is lower in many species than others. And we have also been breeding many of the species we keep in captivity for a few generations in relatively small numbers so to date may not have seen the effects of inbreeding depression in most. With the huge rise in inbreeding in the past 10-20 years we have also seen a variety of health problems becoming more apparent, some very subtle and relating to disease resistance and reproductive success which may be directly related to genetic issues.

Defective young are culled so good breeders only sell or breed healthy animals

There are two serious problems with this sort of statement. Firstly, there is an ethical dilemma with producing large numbers of defective offspring only to cull them immediately or once realised that they are excess to requirements. Not to mention that methods of culling are often questionable in humane terms or in efficacy. Secondly, if you have even 10% of a clutch of eggs hatching physically deformed neonates then arguably none of the rest of the related clutch should be deemed as reproductively viable animals. Invariably they are all carrying the potential to display this trait in future generations. Therefore saying the unhealthy ones are culled and a breeder is responsible because they only sell the physically perfect specimens ignores the fact that the breeder is selling from a bloodline that carries invisible genes and problems. If a new owner buys from this bloodline and decides to breed later they are likely unaware of the full genetic potential of their animal, to produce desirable and undesirable offspring in the same clutch or litter. Subsequent generations may have an even higher instance of congenital deformities. This sort of problem in the industry is the hidden cost of the morph craze and deliberate inbreeding. Many thousands of animals fail to hatch, fail to thrive or are so badly deformed that they are killed immediately after birth or hatching. Do we as hobbyists want this as the reality and standard of how we operate, especially in light of all the opponents that criticise us on animal welfare grounds? Most people don’t take into account when they buy their high end royal python morph for example the sheer number of defective and unthrifty babies that were produced and culled in order to produce our pet. Is that a standard practice we should consider or knowingly contribute to? I would argue that these are the things we should consider when buying into a culture of deliberate inbreeding. But most people are unaware because the breeders are not advertising their genetic mutant offspring for all to see and marvel over. And some people just don’t want to know at what cost their animal is produced, which is a great pity.



In conclusion the issue of inbreeding in captive reptiles is one that generates a lot of interest, much argument and a great deal of mistruths being touted as fact in order to defend current practices. If one respects even the basic tenets of animal husbandry and breeding then accepting that inbreeding is detrimental to animal health and welfare over time is the only responsible option. Consistently justifying the practice as harmless and propagating mistruths to those looking for advice as a way of defending the practice is misguided at best and dangerous at worst. As the reptile hobby has grown into a multi-million dollar industry, sadly production has become more and more intensive to the point animals are now very much a commodity in line with intensive agriculture. Big commercial breeders are idolised and respected in the industry, however some are more responsible than others. Their opinion and expertise especially when it comes to breeding is respected and their methods trickle down to the small scale breeder over time. If that advice advocates deliberate inbreeding as standard practice and neglects to inform of the significant risks and costs in terms of animal welfare then I think we need to be fearful of where the industry is heading. When discussing the issue of inbreeding it is vital to consider whether it is being done for commercial gain or for the benefit of the animals. It is invariably the former, and if you are supporting that side of the industry then you must ask yourself which is more important for you as a reptile keeper, human profit and enjoyment or animal welfare?


Leopard geckos DON’T require UV Lighting. A soldier in Iraq told me so.

Random stranger on the internet:

Idk if you have ever been to Iraq sir. But I have in the united states amry. Leopard geckos do not require uvb. They stay I dark crevices under rocks or In holes. When. We did night runs is when they came out. If you do not belive me you can ask Mr Ron tremper herpetologist who essential wrote the book on them.

Me (Tired of defending best practice):

I have not been to Iraq. I have spoken to herpetologists who’ve been to Pakistan and Afghanistan and have seen them moving about at dawn and dusk when the sun is in the sky, albeit at low levels. Ron Tremper has perfected the art of providing perfect nutrition to leopard geckos without providing them with UVB lighting because that is his livelihood for many years. Therefore I agree with you in theory, leopard geckos do not NEED UVB. However, most beginners or even moderately experienced keepers are not Ron Tremper. And I see case after case of MBD in leopard geckos in captivity that DO have MBD which could have been prevented by providing UVB lighting. They also benefit in other ways from it, and experience it in the wild despite what you think. Not seeing one exposed to it during your time in Iraq is not evidence it doesn’t happen. It just means you didn’t observe it buddy. I’ve never seen a train wreck but I believe they happen in real life. Crepuscular (not strictly nocturnal) species like leopard geckos have been shown to be far more efficient at utilising low levels and exposures than diurnal lizards. Ultimately, if you’re arguing or advocating against providing UV light to leopard geckos you are denying them of something they do obtain in the wild because you prefer to do things a cheaper, more convenient way for you the keeper, which can be misinterpreted by more inexperienced keepers and end up causing serious welfare and health problems. Your call.

PS: I’ve just seen you’re a big gecko breeder. What a surprising viewpoint. Point 1 may interest you as well as point number 4.

Can you see my heart beating? A snake with a very big problem!

Snake transport box

I received an unusual phone call recently from the owner of an 18 month old False Water Cobra (Hydrodynastes gigas), a South American rear-fanged, mildly venomous species of snake ( The owner had noticed shortly after acquiring the snake that it had what was described as a wound on it’s underside through which you could see it’s insides! Naturally, I was quite worried so asked for the snake to be brought in for examination, and in the meantime they emailed me some photos and reassurance that the snake was acting perfectly normally, eating and defaecating fine and didn’t seem in any way bothered by the strange ‘wound’.

False Water Cobra Hospital Vivarium on AdmissionFalse Water Cobra Hospital Vivarium on Admission 1

Having examined the animal, it appeared that she had a defect in the body wall on her ventral surface or belly with a large hole visible in the ventral muscles. Bizarrely, this defect was at the level of the heart about a third of her length down her body. The only tissue separating her visibly beating heart from the outside world was a thin membranous layer of body cavity lining and some connective tissue which was quite transparent. I have seen some similar lesions in reptiles at the umbilicus or site where the blood vessels carry nutrients into the growing embryo from the egg or from maternal tissues in the case of live bearing species. Sometimes when these animals hatch or are born the hole in the body wall fails to close completely and an umbilical hernia or body wall defect is left behind. However, I have never seen or even heard of such a defect high up on the body overlying the heart! I concluded that this must be a congenital problem that the snake was born with, perhaps a fluke genetic mutation or a developmental insult during incubation of the egg which disrupted the normal growth of the embryo resulting in a physical abnormality at birth. Having spoken to a few reptile enthusiasts in the UK who keep this species of snake, it turns out there have been a few reported with the exact same defect in the exact same place, so it looks likely this is a genetic problem, most likely caused by inbreeding in certain lines due to relatively low genetic diversity in the UK population.

Snake membranous hernia before surgery

The risk of leaving the snake in this condition was that during the course of her life she may snag this fragile membrane protecting her heart and eviscerate herself or worse still puncture her heart. Although this risk was small, it would be safer to carry out a surgery now than always wonder and worry if she might do some damage and seriously injure herself, when pulling off her shed skin for example. I admitted her and set her up in our reptile ward in a heated vivarium to bring her body temperature up to preferred range. Once her temperature was correct I injected her with a combination of sedative drugs into the muscle in her back. I say I injected her, but actually I restrained her with a thick pair of gloves whilst my nurse Justyna gave her the injection. She was very feisty, strong, and objected to restraint, trying to bite the gloves. Obviously considering her potential to give a painful bite and possible envenomation we took great care at this stage. Rear fanged snakes are different to other venomous species in that they have modified salivary glands and teeth at the back of their mouth, with which they chew their prey in order to inject and subdue it. Therefore it would be difficult to get a dangerous bite  from a rear fanged species unless you allowed the snake to chew on you. Front fanged species can deliver a dry or wet bite from the front of the mouth with a rapid strike and minimal contact so are far more dangerous to work with and handle. After her injection we left her back in her hospital vivarium in the correct temperature to allow her to metabolise the drugs efficiently. Ectothermic or ‘cold-blooded’ animals such as reptiles rely on external temperature to control their biological functions and metabolic rate, so it is vital when treating ill specimens and indeed when undertaking anaesthesia and surgery to maintain their body temperature in the correct range so everything runs smoothly and drug dosages work effectively. After about a 20-30 minute induction period, now nice and relaxed after her sedation we removed her and placed her into an anaesthetic gas chamber so she fell further asleep and we could position and prepare her for surgery. She was maintained under anaesthesia by using a gas mask delivering a safe gaseous drug called Sevoflurane. Normally for a prolonged surgical procedure in a snake I would intubate the animal with a solid plastic or rubber tube placed into the windpipe or trachea for better control and access to her airway should she stop breathing for instance, but in the case of venomous species I prefer not to mess around in the mouth due to the risk of accidental envenomation. A correct sized mask with her head taped inside in place and sealing the entrance provides the next best option and is safer for all involved.

Snake anaesthesia preparing for surgery


Here’s a video link showing the heart visibly beating underneath the membranous layer of the abdominal wall defect:

Once Justyna prepped her with a surgical scrub and insulating layers to maintain her body temperature lying belly up on a surgical heat mat, I was ready to begin. I carefully dissected away the thin membrane covering her heart from the scales on either side of the deficit. I had to be extremely careful as this layer of tissue was so thin and the heart was literally beating against it directly underneath. Tiny blades and scissors were required, and I cut in time between the beats to avoid cutting at the moment the heart filled to maximum capacity with blood. Myself, Justyna and the veterinary student who is seeing practice with us this week to learn more about exotic pet medicine were all holding our breaths at times. Credit to the student Conor for taking the photographs while I operated by the way. Justyna found this anaesthetic very easy to monitor throughout as we were literally watching the heart beating throughout so she could record heart rate and strength with the naked eye for a change! Often we use sensitive probes to monitor heart rate through the body wall but not needed in this case.

And here is a video during the surgery when I had carefully dissected away the thin tissue revealing the heart beating underneath before I began to suture the defect closed:

Once the tissue had been separated away from the half sized scales lining either side of the lesion I set about suturing the hole back together, bringing the soft tissue of the internal body wall and the edges of the scales together to meet in the middle and form a tight seal which would heal and protect the heart and blood vessels underneath. I was quite happy with a neat and tidy job at the end. She was given a long acting pain medication and anti-inflammatory by injection, and a reversal drug for the sedatives given earlier and placed back in a clean dry cage with paper substrate to recover. We turned up the heat temporarily to boost her metabolic rate and aid her clearance of the anaesthetic drugs, and within 20 minutes she was groggy but wandering around her cage getting her bearings again. It always surprises me how tough these animals are. Reptiles have been around for millions of years and they really are quite resilient and remarkable in what they can withstand. Many of my clients fret and worry about anaesthetic risk in particular if their pet reptile needs a surgery for example. Although the general risk is higher than in dogs and cats I find them to be remarkably sturdy anaesthetic patients for the most part, so the risk is still quite low as long as you seek out an experienced and knowledgeable reptile vet.

Snake repair after closure


In terms of aftercare, she just needs to be kept clean and dry. No antibiotics were prescribed as it was a sterile op and good hygiene practices should prevent infection from here. Being a semi-aquatic species that likes to bathe in water, I’ve specified that she is not allowed a water dish in which she could submerge as the wound could act as an entry point for water and bacteria or other contamination into the body cavity if she submerged in the coming week or so. I will keep her in overnight and send her home tomorrow. So far she is making an excellent recovery. The sutures I placed are dissolvable over time and should slough off the next time she sheds her skin or possibly after that, so I just need to recheck her in a week to make sure the wound looks good, is healing well and is free of infection. Problem solved!

Snake in recovery