RAUK - Archived Forum - Inbreeding depression

All,

I have wondered to what extent our native reptiles and amphibians are suffering from inbreeding depression.

With continued habitat loss and increasingly isolated populations, what are peoples views on the relative merits of captive breeding of out-bred animals, for release, and the translocation of adults from thriving populations into inbred populations to help combat the effect?

The only article I am aware of concerns a small population of Vipera berus, that appeared to benefit from the introduction of novel genes via the translocation of adult males to the inbred population from a larger population.

The article is currently viewable at:

 http://www.helsinki.fi/ml/ekol/egru/pdf/Madsenetal1999.pdf

I am seeking permission from the copyright holder to reproduce the article in full for the Adder section of the RAUK e-forum.

Inbreeding û an overlooked aspect of herpetofauna decline.

For many years I have suspected that isolated populations are suffering from inbreeding depression.

Not only the remnant populations of the glamorous species, such as Sand Lizards and Natterjack Toads, but also increasingly, isolated populations of our more common species.

Observers are reporting that well known populations of the Adder (Vipera berus), are declining at an alarming rate.

The Madsen study¹ in my mind raises a number of important issues for the continued conservation efforts of reptiles and amphibians in the UK.

Firstly, the expected signs of inbreeding associated with domesticated pets are of little consequence. We would not expect polymorphic snakes to survive predation and be extent in the wild. Observation of the Smooth Snake may well show they inhabit small areas today, but clearly individuals do roam if habitat is available, or else they would not have populated the United Kingdom. Madsen points to the true signs of inbreeding depression in wild populations as reduced fertility and survivor-ability of offspring. Difficult factors to measure practically in the field, we may fall back on a study of the genetic variability of the population.

We must all be aware that with changes in farming practice, increased conurbation and general fragmentation of habitat, populations of reptiles and amphibians are very likely to become isolated. It is well established that our native herpetofauna cannot cross the vast tracts of agricultural fields that now form much of our environment. A simple study of changes of land use in ones local area will quickly reveal that many remaining habitats have been isolated for 40 û 100 years. The negative affects of out-breeding depression are surely not a factor, it would seem unlikely that populations of the more common species have adapted to microclimatic differences in this short period.

It is my view that genetic conservation is overlooked at our peril. We may endeavour to save the isolated habitats that remain, but it is of little use if the animals contained within become less and less viable.

I would ask all involved to consider that it is ôpossibleö that a major-factor promoting decline of our native herpetofauna is lack of genetic variability. There are dangers; movement of animals to small populations may carry the risk of promoting disease, invasive plants and the converse effects of out breeding depression. Perhaps the solution lies in the captive breeding of genetically varied stock, perhaps more simply a few isolated areas may be studied and adults from larger populations trans-located and the affects noted.

1) Restoration of an inbred adder population 

 Thomas Madsen, Richard Shine, Mats Olsson, HÕken Wittzell

Inbreeding depression is usually defined as: a loss of fitness (vitality), characterised by difficulty in conception, increased spontaneous abortion, pre-natal and peri-natal deaths

Inbreeding: is mating between either a close relative, or mating of individuals with at least one common ancestor.

My view on the "visible" signs of inbreeding depression and  the relevance to wild animals is this, if in captivity we breed closely related animals for selective reasons and by choice, for instance to enhance a pair of recessive genes to produce a desired colour ômorphö, the animals are inbred, however the animals may not shown signs of inbreeding depression. There is an increase in the probability that deleterious recessive alleles will come together. Generation over generation the probability increases alarmingly.

In short, inbreeding depression is a danger with selective breeding, but not necessarily the result in the short term.

Considering wild animals, they are not selectively bred to produce colour polymorphism, it is simply that the mating between animals with common ancestors in the population increases the deleterious recessive alleles, leading to a general loss of vitality.

In short, Colour polymorphism maybe a result of inbreeding, it is not however a symptom or sign of inbreeding depression,

 i.e. the population may be normal for colour type, though the gene pairs controlling the phenotype of the population are reduced.

It may be concluded from this, that there are no visible signs in the phenotype of a population that is suffering from inbreeding depression. The animals may appear normal for colour type, but are infact suffering from a loss of vitality - so in answer to one of your questions, waiting for the visible signs will be too late, they will not appear, as there are no visible signs of inbreeding depression. A population can only be said to be free of inbreeding depression if it has good genetic diversity.

If my estimates are right, that many small wild populations have now been isolated for 100 or more years in the UK, the process is advanced and it is likely that ôharmfulö alleles have been reinforced, promoting their decline towards extinction.

In the past these deleterious effects of inbreeding in wild populations were offset by immigration of adult animals carrying novel genes.

It is generally regarded that the species indigenous to the UK were all highly mobile, at least historically, or it is unlikely they would have populated the UK after the last ice period. I fear that the lack of mobility of the Smooth Snake as seen today, maybe a symptom of inbreeding depression, not a reason to dismiss it. I also accept that it maybe due to habitat limitation, I find it difficult to accept it is simply their normal behaviour.

On the subject of smooth snakes, though the adults have a very small home range, I think it's the juveniles that will be colonizing new areas. Obviously in isolated habitats, there's nowhere new for them to go to.

If their behaviour is a result of inbreeding depression, then animals from mainland Europe, where they are more common, will exhibit different behaviour. Does anyone here have any experience with continental smooth snakes?

I'm always struck by the fact that the Romney Marsh marsh frogs are all descended from only a dozen individuals- they're still thriving and spreading after 30 years.

The Romney Marsh Marsh frogs are a good example of how a population can grow and flourish when it is not faced with habitat limitation. Assuming the founders came from a large population, so were unrelated and 6 were males and 6 were females, the first generation of offspring only had a 1 in 6 chance of mating with a sibling, most second generation mating would be between unrelated animals.  As the frogs are populating new habitats without much competition, the number of adult breeding frogs has rapidly grown and the population will be genetically diverse.

Inbreeding depression comes about in the opposite case when the number of breeding adults is severely limited by habitat constraints. The small population soon becomes closely related and genetic diversity is lost.

(The Marsh Frog was introduced in 1935)

Quote: Originally posted by Gemma Fairchild on 08 March 2003

---

(The Marsh Frog was introduced in 1935)

---

Yes, I thought 70 and typed 30!

Its getting late - just a word on smooth snake movement - I will respond to other aspects later regarding adder etc.

Dave Bird and I work in the same area with the same species, more or less.

On one site where Dave is working he captures different smooth snakes on most occassions. i.e. very few recaptures. On two of my sites I regularly catch the same snakes over and over again. Some now for two decades or more. This does not necessarily mean that they are sedentary. Two males regularly forage 400m to wet heath from their 'tin' and return to digest their meal - and then repeat the process - they also retire under their tins when moulting. One male has now used the same tin for nine years.

There is also a definite male bias with regard sex ratio in most of the populations that I have studied. Interestingly, about 30% of a population is made up of immature snakes>30cm. compared to Adder populations that I am currently studying which exhibit just 10% immatures of the total population. 

I have my doubts about translocations - mainly because receptor sites are rarely monitored - lack of funds? or just not considered within a budget?

Currently just starting DNA Micochondrial work to establish relationships between adder populations. Adders exhibit a 100% fidelity to their site and are sensitive to changes, even subtle ones, in their habitat. A classic example comes from the work of a colleague, Wolfgang Volkl. One hibernations site in the German highlands was destroyed, not by people, but by one nights foraging by wild boar!

Tony Phelps - Reptile Research & Imagery

Tony, thanks for taking the time to post info here and in other threads on this website.

Martin

I think that we have made a start with the DNA sample recently collected throughout the UK for the work of Rhys Jones at University of Cardiff. It is still a good idea to gather as much sample as possible for all species with the idea of forming a 'bank' I've got a freezer full of shed skin, dead lizards, snakes etc. All in 75% ethanol. So, keep all you find - it will be useful reference for future work.

Tony

Celeb,

Yes, but for some aspects tissue or blood is necessary

Tony

Tony,

When you state "Currently started DNA work to establish relationships between populations", is there scope within this to study the genetic diversity within the separate populations? 20% young recruits in an Adder population corresponds to a point of advanced decline in the Madsen et al study, is it possible that you can get bloods from those populations showing only 10% to see if they exhibit inbreeding, or are the populations large and healthy from your observations? (I do appreciate that many other factors could be responsible for low numbers of immature and that populations can naturally peak and trough)

I think it is interesting to note that Madsen et al, makes no reference to phenotypic abnormality, in a population of Adders that was shown via genetic analysis to be severely inbred and on the brink of extinction. (It appears the population was initially selected simply on the basis that long term geographic isolation was demonstrated, most of our Adder populations must now fall into this category)

I would like to see coordinated studies across the country, both of small and large populations, I feel there is a good basis to use Adders for this, as evidence now exists that declines can be reversed in this species using genetic conservation. If inbred populations are found to be the norm, it will take a huge effort from all involved to start moving animals around between populations and monitor the results.

Gemma,

Rhys Jones' work is nationwide and involves the three snake species plus some from Europe and I think his is using European Elaphe sp as an outgroup.

We have a joint proposal with regard paternity for my study area - about ten sites including two urban. You will have to read my paper, "Population dynamics and spatial distribution of Vipera berus in southern England" published later this year. But basically this highlights the known fidelity of adults over three decades and also reveals that other populations recruit via random dispersal of young (<4yrs old). Most of the populations have been remarkably stable - others in more dynamic habitat show marked fluctuation.

(e.g. habitat degeneration, fluctuating food resource)

The study is ongoing.

We have enough DNA material now to perform a detailed microsatellite analyses for all the populations. This would entail the creation of 10-15 microsatellite markers for berus to identify individual snakes and progeny throughout all populations.

If we get the funding we can confirm what it has taken me thirty years to achieve in just two years, and indeed go beyond.

This is all new for me and I lean heavily on people like Rhys, and Mats Hoggren in Sweden. And of course Wolfgang can give you much more detail.

Tony

Thanks Tony, puts my mind at rest a bit, Contact for Rhys for those able to collect samples (e.g. preserved road kills, or collected sloughs)

Rhys Jones, G10, BIOSI 1, Main Building, Cardiff University, Park Place, Cardiff CF10 4BT, 029 20875776 (Lab), JonesR9@cf.ac.uk

It would seem to be wise to at least seriously consider the possibility of captive breeding and/ or translocation of commoner species to sites that have been isolated for some time. Sites could be considered as ranging from large areas with a good matrix of links, supporting a high metapopulation - at one end of the scale - through to small sites surrounded by intense urbanisation. These may be as cut off - for population transfer potential - as islands in the sea. For the many and varied range of sites falling inbetween these two extremes, one would expect that making and enhancing habitat links where possible would be the preferred option as far as naturalness goes. One would dare to hope that the forthcoming changes to CAP subsidies (more emphasis on agri-environment works) could go some way to helping bring this about in rural areas.

In cases of isolated sites with no likely potential for linking existed, and where animals might to be introduced to boost the gene pool, one would want to be reasonably sure that the population on site was not dying out due to some other pressure such as cat predation or habitat decline (both of which may be big influences in many cases). Starting a programme of captive breeding and translocation would also imply monitoring of results to evaluate success, and assuming sites remained isolated, one would expect that there would come a time in the future when there would once more be a need for new animals to boost genetic variation of the population, so there might effectively be a need for an ongong cycle of transferes which mimics a natural flow of animals between populations within a meta population. An interesting idea - certainly very artificial (but the problem of isolation has been brought about by humans in the first place) - but it might become vital as a means of saving spicies in certain areas. The alternative could be to resign ourselves to the fact that many reptiles will tend to die out in their surviving pockets in areas with high human populations.

Print size increased to help read.Moderator37837.5463310185
Dave Cowley