THIS IS THE TRANSCRIPT OF A TALK GIVEN AS PART OF THE NATIONAL
BEEKEEPERS ASSN OF NZ SEMINAR IN HASTINGS, JULY 1992.
ITS ONE OF THE MOST UNDERSTANDABLE TALKS I'VE HEARD ABOUT THE
DIFFICULTIES OF BEE BREEDING (I'M NOT A GENETICIST!), GIVEN BY
A PRACTICAL, COMMERCIAL QUEEN BREEDER/PRODUCER...
PRESENTED BY DAVID YANKE
IMPROVING OUR BEE STOCKS: WHY IT IS SO DIFFICULT TO DO IT
NATURALLY
The ground I hope to cover with this talk is that mountainous,
probably impassable stuff which stands between us and the ever-
elusive super- bee. As elusive, was a concise way in which to
put together this talk so please bear with me.
The mechanics of heredity are the same whether it be bees or
buffalo. In organisms that reproduce sexually, their progeny are
not exact duplicates of their parents, but instead usually vary
in many traits. This variation is the spice of life. It is what
allows a species to adapt and evolve, and it is this natural
variation, which plant and animals breeders exploit in the
domestication of that species. Before we go on, we should have
a quick basic look at the mechanics of heredity, so that some of
the concepts later on, are easier to understand.
First some basic genetics: DNA is the carrier of the genetic
message which is coded into its molecular structure.
Genes are the actual base units of inheritance, in structure they
are a length of DNA, and they are responsible for a given
physical trait. Variations of the same gene are called alleles.
Every sexually reproducing species inherits 2 alleles, one from
each parent. These pairs of alleles we inherit, interact with
varying degrees of dominance of one allele over the other. There
may be several different alleles for any given gene.
Chromosomes are cellular bodies found in the nucleus of cells
which carry the genes.
So talking in human terms, we all have in each and every one of
our cells the complete genetic blueprint of our being held in two
complete sets of genes - one set from our mother, and one from
our father. These 2 sets of genes are carried on a given number
of chromosomes characteristic of each species - humans have 40,
potatoes 48, and honey bees 32. This number is known as the
diploid number of chromosomes. The sex cells have half this
number and are said to be haploid. Honey bee drones, because
they develop, amazingly, from unfertilised eggs have the haploid
number of chromosomes which is 16.
Something very important happens in the formation of our sex
cells, be they eggs or sperm. Early on in this process known as
meiosis, the chromosomes pairs stretch out and are lying close to
each other. While they are in this intimate state they exchange
sections of their DNA, with each section consisting of one or
more genes. This process is known as crossing over. Crossing
over is responsible for most of the variation we see in progeny.
Back to this very important word variation, and back to what I
am supposed to be talking about and that is Bee stock
improvement.
The mechanics of inheritance, and the unique reproductive biology
of the honey bee promote genetic diversity. So when we apply
selection pressure to a bee population in an effort to make the
stock more useful, we are bucking the system. We are trying to
modify the frequencies of the genes within that population -
increasing the frequency of the genes responsible for desirable
traits, but in doing so we affect other gene frequencies as well,
and there can be great peril in that. So the trick is to be able
to effectively apply selection pressure to a breeding population
over many generations, gently modifying gene frequencies, but
maintaining sufficient genetic diversity to be able to avoid the
many pitfalls and perils along the way. These are what I see to
be the main barriers to bee stock improvement.
1. MATING BEHAVIOUR
When the virgin queen is about 6 days old, and the weather
conditions are fine, with light winds and temperatures of at
least 20 degrees C, she flies out a considerable distance from
her hive to mate. Research has shown the average distance
between apiary and mating place is 2km. She has been shown to
fly out as far as 5km. Mating flights last between 5 and 30
minutes. She will make between 1 and 3 flights. The number of
flights she makes depends on the concentration of spermatozoa in
her spermatheca. Once it reaches a certain concentration she
will not fly again. To achieve this concentration she must mate
with several drones - at least 7, maybe many more.
The virgin does not fly haphazardly about hoping by sheer chance
to encounter the drones she hopes to mate with. The virgin
flies directly to drone congregation areas. These areas are
as the name suggests places where drones congregate. Exactly why
drone congregation areas originate where they do is not fully
understood but the same areas are used year after year. The
drones within any congregation area come from many different
colonies, and probably several different apiaries. Drones have a
flight range of up to 6km with flights of 5km common. Thus
drones can range over an area of roughly 78 square km. It has
been shown using genetically marked drones that virgins very
rarely mate with related drones. Even from my scarcely detailed
description, we can see that the mating behaviour of the honey
bee is very complex and for it to have evolved it must be a
significant factor in colony survival. It appears that the
benefit it brings, results from the reduced chances of
inbreeding.
Bringing this back to stock improvement, the effect of this
mating behaviour is that if we allow virgins to mate naturally,
we have no control over which drones the virgin mates with. Even
with isolated mating yards, control is not absolute. What other
plant or animal breeder has to make an attempt at genetic
improvement with only control over 1/2 of the genetic equation?
To compound this, is multiple matings. With each virgin mating
with 7 or more drones, it means that the population of each
colony is made up of 7 or more sub-families.
2. SEX ALLELES
Honey bee drones develop from unfertilised eggs, with the result
that the drone carries only one set of genes, and as we said
before is said to be haploid in chromosome number. Honey bees
also determine sex in a more conventional fashion which results
in the formation of diploid drones. I said it was more
conventional only because it results in diploid males, but it is
still unique. In most sexually reproducing organisms, sex
determination is governed by a sex chromosome. Bees have to be
different though, and instead of sex chromosomes, sex is
determined by a single gene. This gene has many variants or
alleles, maybe as many as 18, but you should feel lucky if you
can maintain 10 or or so in a breeding population. It works
like this, if 2 different alleles come together at fertilisation,
a female results- either a worker or a Queen. If 2 of the same
allele come together then a diploid male will result. We never
see diploid drones in the hive because when the diploid drone
larvae are only a few hours old, they are cannibalised by the
workers, but what we do see is a hole in the slab of newly capped
worker brood and as the % of diploid drones produced increases so
does the spottyness of the brood. So, as number of sex alleles
decreases, the more likely it is that 2 of the same allele will
come together, and therefore the % of diploid drones increases.
There is an obvious impact on productivity when the meddling of
some well-intention bee breeder reduces the number of sex alleles
in the population of bees he is trying to improve, down to lets
say 7. Then even if the queens he raises are of high
physiological quality and of high genetic potential, then those
queens are handicapped in that 15% of the eggs she lays result in
non-viable brood. Faced with that handicap those queens would
struggle to be competitive with any old mongrel queen.
The mechanics of heredity and the mating behaviour of the honey
bee are geared to genetic diversity, so the mechanism of sex
determination in honey bees using sex alleles is allied to this
end in that it penalises any narrowing of this natural diversity.
The other side of the same coin is the effect of -
3. INBREEDING DEPRESSION
We have all heard of hybrid vigour. It results when 2 unrelated
members of a species are crossed. The vigour of the progeny
exceeds that of either of the parents. This extraordinary vigour
is also known as heterosis- a mostly unexplained lifeforce. The
crossing of unrelated parents, results at a gene level in many
more of the pairs of genes carrying 2 different alleles. When a
pair of genes consists of to different alleles that gene is said
to be heterozygous. This increase in heterozygosity is
responsible for triggering heterosis. The opposite state is
when an allelic pair carries 2 of the same allele, and it is said
to be homozygous. The opposite of heterosis occurs as the degree
of inbreeding passes down through a critical level - it is called
inbreeding depression and is triggered when the % of homozygous
genes increases to a certain level. It results in an
unexpected loss of vigour-- sluggish build-up, loss of disease
resistance, decreased production, and higher winter loss. This
can be all in spite of selections over generations for the best
gene combinations by again a well meaning bee breeder. Fact is
it is not in spite of, but because of the actions of the bee
breeder. A couple generations back he probably thought that he
was really getting somewhere, but his downfall was that he was
ruthlessly applying selection pressure to too small a population.
He may not have thought so - because he was selecting his
breeders from perhaps hundreds of colonies. Unfortunately, it is
not the size of the test population but instead the number of
breeders used, which determines how quickly you get into trouble
with both inbreeding depression and sex alleles.
4. QUANTITATIVE TRAITS
The characteristics we are trying to improve in honey bees are
complex physical and behavioural traits each involving many
genes, and each contributing only small effect. This type of
trait is called a Quantitative trait. Compounding their
complexity, is the fact that with honey bees, these are not the
characteristics of a single breeding individual but, instead the
characteristics of an entire colony with many sub-families.
When trying to improve these traits, it has to be understood that
once selections cease any improvement which has been achieved is
lost very quickly as gene frequencies return to pre-selection
balances. To get anywhere in the first place, you have to do
things right with great attention to detail. Your selections
have to be done with great care, environmental variation
minimised, and you must have absolute control over matings.
Besides this you have to keep the number of characteristics you
are trying top improve to a minimum - one or two. On an
encouraging note, the important economic traits such as honey
production and winter hardiness, even though they are hugely
complex, and controlled by a depressing number of genes, do show
good response to selections. So, if we do things right, we will
get somewhere. One of those things we have to do right is ---
5. MINIMISING ENVIRONMENTAL VARIATION
Even if we have a breeding program structure which will allow us
to apply selection pressure successfully over many generations,
we still go nowhere unless our evaluations can reliably identify
the genetically superior individuals in the test population.
With honey bees, we are evaluating colony performance in the
field so it is hard to control the level of environmental
influence which is very considerable, but we can do a lot to
minimise environmental variation by doing such things as:
carefully equalising colonies before evaluations begin;
minimising drift; not carrying out evaluations between apiaries;
and because a queens physiological quality can have a major
effect on some aspects of colony performance we should, to the
best of our ability, ensure that the queens undergoing evaluation
are physiologically uniform. Even if we take heed of this, and
put into our evaluations the care and effort required, it is all
for naught, if the genetic superiority we identified with our
evaluations is not heritable. Heterosis is not heritable, and
leads us on to --
6. RACIAL HYBRIDS
We have 2 races of honey bee in New Zealand, and unfortunately
one of them is the Dark European honey bee, but that is besides
the point. Even though most of our bee breeding effort goes into
maintaining our commercial bee stocks as Italian type, the
reality is that most of our colonies are to varying degrees
racial hybrids. Racial hybrids can be great, and through hybrid-
vigour can be very productive, but they are of no breeding value,
and provide only red-herrings to someone carrying out colony
evaluations. To get anywhere, we have to breed true to race --
what ever that race is. The Dark European honey bee drones,
like the All Blacks in the rucks recently, must be very
aggressive in the drone congregation areas, because they appear
to have a mating advantage of almost Africanised-bee like
proportions. So the only way to keep our test population true to
race, without colour becoming the major selection criteria, and
having the fear of what those dark drones are doing to our yellow
virgins drive us blindly into the jaws of sex alleles and
inbreeding depression, - is to have absolute control over the
mating using Insrumental Inseminations.
7. RIGHT PLACE - WRONG RACE
I left this to last because I wanted to give a bit of a stir, and
because it only a barrier if we choose the wrong option. Italian
type bees, although they have good production potential, can be a
very costly bee to overwinter. Carniolans are at least as gentle
and as productive, and are beyond doubt a more cost effective bee
to overwinter besides other little things like tending to rob and
drift less than Italians. What I am trying to say is that we
have to keep an open mind. It may be a lot cheaper to import a
silk purse, then to try and make one out of a sows ear. Taking
advantage of different races and breeding work done overseas by
importing genetic material could save time and money and be a
dramatic shortcut to better bees.
Times have changed, importations of genetic material can be done
safely, whether they be semen or breeder queens. It is a dream
of mine to see a participant-funded breeding program maintaining
and improving, in parallel, both Italian-type and Carniolan bees.
I know there are many areas in N.Z. where the Carniolan would
become the preferred bee, and as those of us who already export
queens and packages know ther would be a big demand for them in
our markets overseas.
BEATING THE BARRIERS
It is possible to beat the barriers and breed better bees.
Results of 23 years of selections in Germany with Carniolan's can
demonstrate this. The progress was slow but it was progressive,
and it was done without the aid of knowledge and technique gained
from recent research into closed population bee breeding. The
results can be a lot more impressive - the Western Australian
Department of Ag. bee breeding program which ran from the mid-
80's up until this year realised a 10% increase in honey
production per year.
There is a similar program up and running in N.Z.. It is totally
self-funded by its participants, and it has a legal structure of
a limited liability company, and goes by the name of
N.Z.B.G.I.G.. There are 25 participants and each is an equal
shareholder in the company. For their investment, they receive
improved breeding stock.
The program works like this. The aim of the program is to
improve an Italian-type bee in a closed population, maintaining
25 lines - one for each participant. Matings are absolutely
controlled using I.I.. The semen is collected in equal volumes
from each line, then pooled together and homogenised.
The structure of the program may seem simple enough, but it has
all the necessary ingredients to beat the barriers to better
bees. The foundation stock was contributed from all over the
country to maximise genetic diversity, and once the population is
closed off, maintaining 25 lines with mother daughter
replacements each generation means that the program can run for
more than 25 generations without the introduction of any stock
from outside the program and still maintain sufficient diversity
to avoid any ill-effects from either sex alleles or inbreeding
depression.
The use of pooled and homogenised semen has been a most
important breakthrough in bee breeding. It maximises genetic
diversity and selection pressure. The semen dose each queen
receives represents all 25 lines being maintained in the program.
Also because the semen, although amazingly diverse, is
homogeneous - each queen receives an equal genetic dose.
Therefore, any genetic variation uncovered by the evaluations, is
maternal in origin. Giving the selections more punch, and
meaning an increased rate of improvement. Also I.I. makes
maintaining racial purity a piece of cake, you just don't collect
semen from darkish drones. The selections are carried out in two
parts, looking at winter hardiness and honey production. The
first part is done by the participants, and is more broadly
based. Each participant receives the daughters of one line in
mid--Feb. each year. They are introduced into equalised units and
equalised again in April. The queens are evaluated for their
overwintering ability using the criteria of colony weight loss
between May and Sept.. They are also scored on brood viability,
temperment, hygenic behaviour, and colour. In late Sept., the
participants send the 2 best Queens, based on those evaluations,
up to me where they are introduce into hives in one large
dispersed apiary. They are equalised and in Dec. they are
evaluated for honey production potential using short-term colony
weight gain. An initial and a final weight are taken 10 days
apart. The queen which performed best for each line is chosen
and they become the breeders for the next generation. 10
daughters are reared from each breeder and these are inseminated
with pooled semen. It is these daughters which form the test
population for next seasons evaluations.
It is a lot of work and it is made possible only because it is
a co-operative effort, but that is what it takes to beat the
barriers and breed better bees.
7. RIGHT PLACE WRONG RACE
. I left this to last because it is only a barrier if we choose
the wrong option. Italian type bees, although they have good
production potential, are a very costly bee to overwinter.
Carniolans are at least as gentle and as productive, and beyond
doubt a more cost effective bee to overwinter. What I am trying
to say is that we have to keep an open mind. It may be a lot
cheaper to import a silk purse, then to try and make one out of a
sows ear. Taking advantage of breeding work done overseas by
importing genetic material could save time and money and be a
dramatic shortcut to better bees.
Times have changed, importations can be done safely whether they
be semen or breeder queens. It is a dream of mine to see a self-
funded centralised breeding program maintaining and improving
both Italian-type and Carniolan's. I know there are many areas
in N.Z. where the carniolan would become the preferred bee, and
as those of us who already export queens and packages know there
would be big demand for them in our markets overseas. I think
I'll stop there.
You may contact the author of this paper directly by post at:
MR DWJ YANKE
DAYKEL APIARIES
PARANUI RD3,
KAITAIA
NEW ZEALAND
or I will convey any messages to him if directed to me:
Nick Wallingford
Voice 64 7 544 0920 ext 6848 Home 64 7 578 1422
Fax 64 7 544 2386
Internet [log in to unmask]
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