“Best of Health” – July 2018 – Breeds as genetic pools
In March, I wrote a brief review of my Christmas reading: Managing breeds for a secure future by Sponenberg, Martin and Beranger. I discussed what a “breed” is and some of the challenges we face in ensuring breeds are sustainable. This month, I want to share some of the other important concepts covered in the book such as how to define the characteristics of an individual breed.
Which dogs should be included in a breed?
This is an interesting and challenging question for many breeders and the various discussions about Colour Not Recognised (CNR) registrations is a topical example. Sponenberg suggests that a combination of phenotype, history and genetic analysis is the best way to ensure the right animals are correctly included as members of a breed. It is unwise and unsafe to make decisions based on just one of these factors.
Breed experts can usually evaluate an individual dog’s phenotype and determine if it is a typical representative of its breed. This is a useful way to bring working examples into a narrow show gene pool, for example. The subjectivity of this evaluation can be reduced by developing a matrix of characteristics based on Breed Standard criteria, against which a dog can be assessed. The history of a candidate dog should also be considered; the more that is known about its ancestors, the easier it will be to classify it or reject it. This does, of course, depend on the availability of suitable records and it’s not unknown for breeders to have introduced some “new blood” into what was otherwise a purebred dog! These days, the availability of DNA profiling techniques provides a further way to identify the origins of an individual dog. The work of Elaine Ostrander and her colleagues in classifying dogs into clades, where their common ancestors can be traced, is a useful addition to our collective knowledge in this area. We also need to be aware that just because a particular dog may exhibit recessively inherited traits (e.g. coat colour, pattern, type) doesn’t mean that it is the result of fraudulent outcrossing. If a recessive mutation has existed in a breed from its early days, it is entirely predictable that the recessive phenotype will “pop up” eventually, even if this does come as an unwelcome surprise to current-day breed purists. Political agendas to exclude these animals from the “breed” are, at best, misguided and fly in the face of inherent breed genetics.
Dog breeds are typically defined based on a combination of history, genetics and politics. Breeds within a group are interesting examples of how and where decisions have been made to split “breeds”. For example, the Dachshunds are one breed with (in the UK) 6 varieties. Many of the small terriers share similarities, as do the various retrievers and, to an outsider, the boundaries between some breeds might appear to be rather arbitrary.
3 tiers in the gene pool
Understanding how a breed is organised as a “genetic pool” is important if we are interested in their management and conservation. For most pedigree dogs with closed stud books, there is a 3-level structure to the gene pool. Firstly, there is what Sponenberg calls an “elite” tier; this is a relatively small proportion of the total breed. Most readers will recognise this as the show population which contains the most prized dogs. Generally, this is a closed group as far as introduction of new genetic material is concerned. Breeders produce replacements (the next generation) with no introductions from the other tiers. Next up is what is known as the “multiplier tier” made up of dogs of more average quality, but still recognisable and typical members of the breed. This tier is larger than the elite tier and, typically, breeders here use males from the elite tier to breed with their bitches and to “upgrade” their puppies. So, genes flow from the elite tier into the multiplier tier. Finally, there is a “commercial” tier which tends to be larger than the other 2 where the motivation of breeders is to make money from dogs as a product, rather than any interest in the quality or sustainability of the breed. The commercial tier usually buys in males from the multiplier tier to add to their pool of stud dogs. Overall, there is a flow of genetic material from the elite tier down through the multiplier tier and then into the commercial tier. There is little or no flow back to the elite tier and, over time, the dogs in this population become less genetically diverse. A more “open” system would see stud dogs from the elite tier used on bitches in both the other tiers. More importantly, in an open model, suitable quality bitches would be brought into the elite tier from the lower tiers and would provide for more genetic diversity across the entire breed.
I have written previously about the potential benefits of breeding from puppies in “pet homes” and in an open system, clever breeders in the elite tier would be open to buying-in dogs or bitches from the lower tiers.
Bloodlines and sub-groups within a breed
Bloodlines and varieties within a breed may be useful additional sources of genetic diversity. Bloodlines are usually linked to a particular breeder or kennel and may be historically distinct or exhibit a distinct type within an overall breed. The risk, of course, is that certain bloodlines become “flavour of the month”, maybe as a result of show success and this can lead to the genetically unhelpful strategy of breeders flocking to use a so-called Popular Sire. The genetic diversity of a breed then becomes swamped by a particular bloodline and little or nothing of other bloodlines may survive.
In some breeds, varieties exist, separated only by a single gene difference (e.g. the 3 coats in Dachshunds). Often they share the same foundation history but have been separated for the (arbitrary) purposes of showing. In the case of Dachshunds, the KC’s decision to allow “recessive coated” puppies to be registered as per their coat is entirely logical and addresses the anomaly of having to register them as per their parents’ coat type. Decisions to subdivide breeds into varieties does inevitably mean the gene pool will be narrower and breed conservation will be more challenging than if all varieties were considered to be one breed.
Managing bloodlines and varieties is important but can be complicated by politics and economics. Breeders may be more motivated by income from stud fees and puppy sales, rather than the overall good of the breed. Owners of stud dogs that are used solely within the elite gene pool need to be aware of the risks of the Popular Sire effect but, equally, they can have a positive impact by upgrading a variety of bitches in the multiplier (pet/hobby breeder) tier.
There is a clear role for breed clubs and councils to ensure all breeders and potential breeders are aware of the state of their breed. That oversight should extend across all 3 tiers and they should not simply be obsessed with what is happening within the show community.
- Posted in: Best of Health - Our Dogs