Hi Jon,
Well explained!
Recent research has now identified 11 -19 CSD alleles for the honeybee, therefore the genetic permitations i.e. genetic diversity you could have even in a small number of colonies is huge.
Hi Jon,
Well explained!
Recent research has now identified 11 -19 CSD alleles for the honeybee, therefore the genetic permitations i.e. genetic diversity you could have even in a small number of colonies is huge.
Once upon a time there was a magic bowl of fruit. It had 6 plums, 6 apples, 6 pears and 6 oranges. A hungry family ate half of the fruit each day - totally at random. This being a magic bowl of fruit, every remaining item duplicated itself overnight.
After the first night, how many types of fruit had you lost - any?! Half of them? I can't be bothered working out the probabilities, but in many cases all would survive into the subsequent year (no, day) despite the high overall attrition rate.
The system is self-balancing. If a fruit gets slightly more abundant than is its due, it is more likely to be picked and its frequency will fall back again. Although random events will eliminate single types of fruit from time to time, in general an equilibrium is reached.
If these bowls of fruit were bee colonies (the example above is just to indicate statistical processes, not mimic units of bee populations) then the bowls which remain diverse reproduce themselves better, whereas those which, by chance, become less diverse are less vigorous and less likely to survive or to reach a size to swarm.
Hi
I found these interesting papers among many which qualify the csd factor. It would seem that the occurence of diploid males in a closed, and reducing population has quite a lethal effect, despite the csd factor. The observant experienced beekeeper has notice that most colonies today have varying and in some cases truly significant pepper-potting, resultig from inbreeding and diploid drone elimination.
Best Regards
Eric
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Population structure, mating system, and sex-determining allele diversity of the parasitoid wasp Habrobracon hebetor
M F Antolin1, P J Ode2, G E Heimpel3, R B O'Hara4 and M R Strand5
1. 1Department of Biology, Colorado State University, Fort Collins, CO 80523, USA
2. 2Department of Entomology, North Dakota State University, Fargo, ND 58105, USA
3. 3Department of Entomology, University of Minnesota, St Paul, MN 55108, USA
4. 4Department of Ecology and Systematics, University of Helsinki, Helsinki, Finland
5. 5Department of Entomology, University of Georgia, Athens, GA 30602, USA
Correspondence: MF Antolin, Department of Biology, Colorado State University, Fort Collins, CO 80523-1878, USA. E-mail: antolin@lamar.colostate.edu
Received 10 April 2003.
Top of page
Abstract
Besides haplo-diploid sex determination, where females develop from fertilized diploid eggs and males from unfertilized haploid eggs, some Hymenoptera have a secondary system called complementary sex determination (CSD). This depends on genotypes of a 'sex locus' with numerous sex-determining alleles. Diploid heterozygotes develop as females, but diploid homozygotes become sterile or nonviable diploid males. Thus, when females share sex-determining alleles with their mates and produce low fitness diploid males, CSD creates a genetic load. The parasitoid wasp Habrobracon hebetor has CSD and displays mating behaviours that lessen CSD load, including mating at aggregations of males and inbreeding avoidance by females. To examine the influence of population structure and the mating system on CSD load, we conducted genetic analyses of an H. hebetor population in Wisconsin. Given the frequency of diploid males, we estimated that the population harboured 10–16 sex-determining alleles. Overall, marker allele frequencies did not differ between subpopulations, but frequencies changed dramatically between years. This reduced estimates of effective size of subpopulations to only Ne 20–50, which probably reflected annual fluctuations of abundance of H. hebetor. We also determined that the mating system is effectively monogamous. Models relating sex-determining allele diversity and the mating system to female productivity showed that inbreeding avoidance always decreased CSD loads, but multiple mating only reduced loads in populations with fewer than five sex-determining alleles. Populations with Ne less than 100 should have fewer sex-determining alleles than we found, but high diversity could be maintained by a combination of frequency-dependent selection and gene flow between populations.
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Proceedings of the National Academy of Sciences of the United States of America
Signatures of selection among sex-determining alleles of the honey bee
1. Martin Hasselmann * and
2. Martin Beye *
+ Author Affiliations
1. Institut für Zoologie, Biozentrum, Martin-Luther-Universität Halle/Wittenberg, Weinberg Weg 22, 06120 Halle, Germany
1. Edited by May R. Berenbaum, University of Illinois at Urbana–Champaign, Urbana, IL, and approved February 9, 2004 (received for review November 4, 2003)
The fact that allelic composition governs sexual fate has long been of interest to biologists (16), not only because of its differences from sex chromosomal-based sex-determining systems (1, 17, 18) but also because of its major impact on population genetics (9, 10). The sex-determining alleles provide an excellent example for the maintenance of genetic variation by natural selection under a well characterized mode of selection, in which homozygotes have zero fitness. In addition to the general biological aspects, the occurrence of diploid males in the economically important honey bee has considerable consequences for applied bee management and for bee selection programs (6, 19). The fact that allelic composition governs sexual fate has long been of interest to biologists (16), not only because of its differences from sex chromosomal-based sex-determining systems (1, 17, 18) but also because of its major impact on population genetics (9, 10). The sex-determining alleles provide an excellent example for the maintenance of genetic variation by natural selection under a well characterized mode of selection, in which homozygotes have zero fitness. In addition to the general biological aspects, the occurrence of diploid males in the economically important honey bee has considerable consequences for applied bee management and for bee selection programs (6, 19).
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[QUOTE]Eric.
I'm not sure I understand what you mean when you say 'despite the csd factor'
It's not so much in a 'closed and reducing' population as in one which has already been seriously reduced.
You don't get closed populations of honeybees unless you are on an island maybe 5-10 miles off shore or at an oasis in the middle of a desert.
No one disputes that diploid drones are a drain on a colony but it has been demonstrated that the issue only becomes a serious problem when the 16-20 or so CSD alleles drop to 5 or 6 in a closed population.
This is statistically highly unlikely. (see fruit bowl above)
Dorian Pritchard also quoted some Japanese research which stated that the csd alleles reach an equilibrium in a population and tend to be equally represented - so if you have 20 alleles each will make of around 5% of the total number of csd alleles.
I thought this unlikely and questioned him on it after his lecture but he assured me that the issue was clear.
What makes you think this must be due to inbreeding?The observant experienced beekeeper has notice that most colonies today have varying and in some cases truly significant pepper-potting, resultig from inbreeding and diploid drone elimination.
There are other factors which cause pepperpot brood:
varroa damage to brood + hygienic behaviour
chalk brood damage + hygienic behaviour
Incomplete mating
Queen damage especially to antennae
AFB
EFB
etc etc.
In my own colonies I have seen sporadic pepperpot brood but this often cures itself over time which would not happen if it were caused by inbreeding, ie a queen storing semen with a restricted number of csd alleles some of which match her own pair.
Last edited by Jon; 09-09-2010 at 11:12 PM.
Hi Jon,
I have also noticed pepperpot but it was from an old queen who should have been replaced.
You also missed out another factor i.e. the beekeeper. I have heard it quoted that the main problem with beekeeping today stands behind the hive.
Hi Jimbo/Jon
I read both your replies with astonishment and begin to wonder how much science you guys have between you - one of you seems to be a greengrocer obsessed with bowls of fruit - and worse both of you seem to be in denial of the phenomenon of inbreeding - which is now quite widespread in Scotland's honey bee colonies. Read the prose in the previous reply! I spoke about the key word in beekeeping being "experienced" Any comments?
Read the appended - you both might learn something!
The post only permits 10000 characters- Access the original paper youselves - for further enlightenment!
Regards
Eric
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Genetic sex determination and extinction
Philip W. Hedrick, Ju¨ rgen Gadau and Robert E. Page Jr
School of Life Sciences, Arizona State University, Tempe, AZ 85287, USA
Genetic factors can affect the probability of extinction
either by increasing the effect of detrimental variants or
by decreasing the potential for future adaptive
responses. In a recent paper, Zayed and Packer demonstrate
that low variation at a specific locus, the
complementary sex determination (csd) locus in Hymenoptera
(ants, bees and wasps), can result in a sharply
increased probability of extinction. Their findings illustrate
situations in which there is a feedback process
between decreased genetic variation at the csd locus
owing to genetic drift and decreased population growth,
resulting in an extreme type of extinction vortex for
these ecologically important organisms.
Genetics and extinction
Several factors can contribute to the extinction of
endangered species, including habitat loss and alteration,
interactions with non-native species, and hunting or
killing by humans. Although these extrinsic ecological
factors can be dominant in influencing population or
species persistence, the general genetic effects of detrimental
genetic variants causing inbreeding depression or
genetic load and the loss of adaptive genetic variation that
is essential for future adaptation are also often significant
[1,2]. The overall importance of the influence of genetics
and evolutionary processes on the extinction of endangered
species is generally accepted, particularly in small
populations, but has been questioned by some
nongeneticists [3].
Low genetic variation at specific loci of adaptive
significance, such as the self-incompatibility (SI) genes
in higher plants and the major histocompatibility complex
(MHC) loci in vertebrates, has been implicated or
suggested to imperil endangered species [4,5]. The sex
determination locus csd (Box 1) in Hymenoptera (ants,
bees and wasps) has also been suggested as another
genetic system that can severely affect the persistence of
populations [6]. When this locus is heterozygous, normal
diploid females are produced. However, when it is
homozygous, inviable or sterile diploid males are produced,
reducing the number of females in the population
and decreasing the population growth rate. Now, detailed
simulations by Zayed and Packer provide a convincing
quantitative demonstration that lowered csd genetic
variation can result in a much higher probability of
extinction in solitary Hymenoptera[7].
Loss of sex determination variation and the extinction
effect
To examine the effect of the loss of csd variation
on extinction risk, Zayed and Packer developed an
individual-based simulation computer program, analogous
to VORTEX (http://www.vortex9.org/pm2000.html),
for a single population of haplodiploid organisms. They
determined the probability of extinction of the population
over time for a range of population growth rates and
carrying capacities, using initial demographic parameters
that mimicked those of solitary haplodiploid populations,
with and without the presence of the csd locus.
For low population growth rates and carrying
capacities, the presence of the csd locus increased the
probability of extinction by over an order of magnitude
compared to comparable situations without the csd locus.
For other combinations of low population growth rates and
carrying capacities, the probability of extinction was
100%, or nearly so, in 100 generations. In addition, the
extinction rates were also over an order of magnitude
higher than those estimated from inbreeding depression
in threatened diploid organisms.
Zayed and Packer describe the increased risk resulting
from the loss of variation at the csd locus as a feedback
loop that eventually results in population extinction, a
type of extinction vortex [8] that they call a ‘diploid male
vortex’. First, the population size is initially reduced by
extrinsic factors, such as habitat loss, non-native organisms
and so on. This then results in a sequence of events in
a feedback loop: (i) loss of variation at the csd locus
through genetic drift; (ii) increased production of diploid
males; (iii) lower population growth rate because there are
fewer females; and (iv) lower population size, which
results in further loss of csd locus variation, and so on.
Following this scenario, the basis of the high extinction
rates in the simulated populations observed by Zayed and
Packer becomes clear.
Hi Eric
1. I'm the greengrocer obsessed with bowls of fruit, not Jon or Jimbo. Did you think about the implications?
2. If you add up the science expertise of the two gents you mention it amounts to quite a lot, though Jon might protest that much of his is informal. They also have oodles of commonsense.
3. No-one is denying that inbreeding is an issue in some cases. Just that it is something that shouldn't be over-hyped.
4. Nothing in the csd abstracts and exerpts you quote disagrees with what anyone is saying as far as I can see - except your 'despite the csd factor'.
5. It is a good point that beekeepers see hygienic behaviour and confuse it with diploid drone gaps. I would have thought that with your enthusiasm for ferals and their possible role in spreading Varroa resistance you might have appreciated that.
6. I had hoped that *you* might learn something from this. Are you ready yet to concede that your articles were wrong on what happens when colonies in an isolated apiary reduces in number from 10 to 5 colonies then recovers repeatedly over several seasons?
best wishes
Gavin
Hi Eric
Is there actually any evidence for that - other than pepperpot brood which has a variety of possible explanations?and worse both of you seem to be in denial of the phenomenon of inbreeding - which is now quite widespread in Scotland's honey bee colonies.
Have you measured the frequency of the aforementioned csd alleles in any populations where you think there is inbreeding?
I see the article you cut and pasted mentioned Amro Zayed.
He has published some interesting stuff relating to inbreeding and the consequences for honeybee survival.
http://zayedlab.apps01.yorku.ca/word...apidologie.pdf
It's 25 pages long but well worth reading if you are interested in haplodiploid genetics
I have argued elsewhere on the basis of this paper that you have to be careful with reducing numbers of colonies, mainly with regard to those who say we should all stop treating for varroa and let the survivor colonies regenerate. My problem with this is that no one knows if the survivors will be 5%, 1% or 0.001% and if numbers go down too much inbreeding could certainly become a problem.
However, the bbka had a press release a couple of months back claiming that UK colony numbers had doubled in 2 years so it looks like UK bee stocks are not even in decline.
Re denial, I make no claim to be a scientist but I have learned a lot by asking questions rather than trying to impose pet theories on others.
What's your background Eric? I know that Jimbo and Gavin do genetics as a day job and as such I tend to sit back and listen to what they say on the matter.
Genetics is not an easy subject for the layman with its specific language such as haploid, diploid, allele, csd locus and suchlike.
There are a lot of pet theories in beekeeping, Mike Bispham with his no-medication conspiracy theory mantra, Oscar Perone who claims that the key to beekeeping success is keeping a colony in an outsize hive, Boris whatsiname who claims that his bees never swarm due to some cockandbull manipulation, those who claim that everything wrong with bees is due to Imidicloprid in spite of a wealth of independent evidence which fails to support this.
What all these folk have in common is a tendency to get angry and browbeat anyone who happens to disagree with them.
Getting back to inbreeding, I may be mistaken but I think you may be confusing a general reduction in genetic material with the specific inbreeding problem which can be caused by a reduced number of alleles at the csd locus.
That is certainly the impression given in the scanned article in Scottish beekeeper at the start of the thread where you mention 160 alleles being lost over a number of generations.
Last edited by Jon; 09-09-2010 at 07:56 PM.
Jon, I think that Eric's confusion here was that he thought that 16 alleles of csd might exist in one colony, and that 10 colonies would therefore have 160 alleles. Patent nonsense of course. It is the entire population of bees in a region that might have 16 or 19 or 20 csd alleles. Unless I misunderstood you Eric?
Gavin
PS Grammar, syntax and various items of editorial pedantry including spelling are of course optional on a forum like this, but I've just italicised the gene name as is the convention. Hope that you like it.
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