Reproducing, Strain Selection and The Importance of Genetic
Variation
The importance of genetic variation is widely recognised among
scientists and trained animal breeders; but most beekeepers belong to
neither group. Yet all beekeepers are, after a fashion, animal breeders,
and the breeding choices they make affect both their own future stock,
that belonging to close neighbours, and any wild bees nearby. As a
community we jointly shape the honeybee population, and the future of
the species is to a large degree in our hands. Both individuals and
local associations can make choices that will drastically affect the
future of the bees, both in their own areas and, as a global community,
worldwide.
With this in mind I paste below three short pieces for consideration,
which will hopefully supply grounds for discussions aimed at improving
our understanding of the mechanisms that will be in play. This will help
us form understand the impacts particular strategies are likely to have.
The first comes from a website about pony breeding, and makes general
points about the consequences of narrow breeding for particular traits.
The second is from Chicago Zoological Society, and makes a good
introduction to the perils of loss of genetic variation. So the first is
largely about the breeding of domestic animals, while the second is
about the same issues in the wild setting. Since bees (uniquely)
straddle this divide, it seems to me to be a good idea to think about
both together. The third is an extract from the Wiki article: Genetic
Diversity
1) The Importance of Genetic Variety by Dionis MacNair
The loss of genetic variety can have a significant impact upon our
native breeds. Nature does not provide parity of sex without good reason
and when the ratio of male to female goes below one to thirty all
genetic variation is lost in five generations. In ponies that is within
about 40 years.
Why should this matter? In-breeding fixes type but reduces adaptability.
Circumstances always change, so the ability to react to and adapt to
that change is vital for survival.
Mutations within species frequently occur and most of them are
insignificant. However some of them can be very beneficial and this is
how evolution advances; for example Eclipse was bred from relatively
moderate parents but his tracing ability was phenomenal. It was a skill
he was able to pass on to his progeny, but his own sire never again
sired anything like as good.
Some mutations are potentially catastrophic if there is little genetic
variety. A further complication is that recessive mutations can be
carried for five generations before reappearing.
The fact that a breed is numerous can be of no help in this situation.
As an example from a different species, Holstein cows are very numerous
but also have very little genetic variety, and now suffer very badly
from lameness. However worse than the lameness, which in itself is a
significant welfare issue, more and more frequently they are also
suffering from fertility problems, not good news in a dairy cow!
http://www.nationalponysociety.org.u...itforthefuture
2) Population Genetics, from Chicago Zoological Society’s
Population Genetics Program
Since its inception in 1985, the Chicago Zoological Society’s
Population Genetics Program has played a pivotal role in promoting
species health and survival. Under the leadership of Dr. Robert Lacy, a
software--called VORTEX--has been used to facilitate virtually all
cooperatively-managed zoo breeding programs around the world.
Population Genetics was created to address an often-ignored threat to
the survival of endangered species: the loss of genetic diversity due to
inbreeding. As populations dwindle or are separated by habitat
devastation, the pool of available mates shrinks, and so does the pool
of genetic variations available to future generations.
Population Genetics takes a long-term view of species survival. Its goal
is not just to ensure that threatened species reproduce, but also that
they pass on the genetic variations necessary to ensure the adaptability
of the species.
The program has been an international trailblazer, giving wildlife
conservationists around the globe a detailed understanding of the
effects of inbreeding and offering data gathered from computer models
for use in preserving the widest possible genetic diversity.
Taking the Guesswork Out of Breeding
Program scientists are currently working to address the challenges posed
by incomplete or indeterminate pedigrees. There are many animals for
whom detailed genetic histories are not available, forcing conservation
scientists to make breeding decisions with little or no guidance.
Population Genetics is taking the guesswork out of such breeding
decisions by developing the next generation of population management
software. This software has the built-in capability to do probabilistic
analyses (averaging across alternative possibilities), which results in
better breeding decisions.
Ensuring Genetic Diversity
Breeding decisions ultimately can impact whether a threatened species
survives or becomes extinct. The best decisions are those that preserve
the greatest genetic diversity in a species. Greater genetic diversity
allows threatened species to better adapt to challenges like climate
change and the shrinking of habitats. For species that no longer have
the natural habitat or population necessary to promote genetic
diversity, advances made by the Population Genetics program offer their
best hope against eventual extinction.
http://www.brookfieldzoo.org/czs/Ani...ation-Genetics
[3] Wiki: Genetic Diversity
Finally the wiki article Genetic Diversity makes clearer the technical
distinctions between 'diversity' and 'variation' (not terribly important
for our purposes) and supplies more detail, including:
Survival and adaptation
Genetic diversity plays a very important role in survival and
adaptability of a species because when a species’s environment
changes, slight gene variations are necessary for it to adapt and
survive. A species that has a large degree of genetic diversity among
its population will have more variations from which to choose the most
fit alleles. Species that have very little genetic variation are at a
great risk. With very little gene variation within the species, healthy
reproduction becomes increasingly difficult, and offspring often deal
with similar problems to those of inbreeding.[4]
Agricultural relevance
When humans initially started farming, they used selective breeding to
pass on desirable traits of the crops while omitting the undesirable
ones. Selective breeding leads to monocultures: entire farms of nearly
genetically identical plants. Little to no genetic diversity makes crops
extremely susceptible to widespread disease. Bacteria morph and change
constantly. When a disease causing bacterium changes to attack a
specific genetic variation, it can easily wipe out vast quantities of
the species. If the genetic variation that the bacterium is best at
attacking happens to be that which humans have selectively bred to use
for harvest, the entire crop will be wiped out.[5]
http://en.wikipedia.org/wiki/Genetic_diversity
Best to All,
Mike
