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  1. #1
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    Default Confused about the genetics of bee reproduction

    I remain confused about the genetics mechanisms of bee reproduction.

    From what I have read there seems to be male bees (drones) that mate with a virgin queen (female) bee. The female (queen) then lays fertile eggs. Some eggs develop into female bees (nurse bees--->worker bees) which I have read are from fertilized eggs but they themselves remain sterile. Then to confuse things I see posts about workers (sterile female bees) laying eggs but I am not certain what type of bee these eggs develop into. Then there are male bees (drones) that are fertile but somewhere I read that they are from unfertilized queen eggs...this seems quite odd to me.

    So...if the workers are sterile what is the purpose of their laying eggs at all...if they are sterile then one would expect their eggs would never hatch (and I take it they don't mate with drones). Next if the Queen is mated and stores drone sperm does she actually make a decision as to whether her eggs will be covered by the stored sperm to produce workers or not covered by stored sperm to produce drones. What genetically determines workers to always be sterile?

    Does bee reproductive genetics have any similarity to the mammalian version? If so if the Queen eggs that produce drones aren't fertilized where does the male determining gene come from? If drones are essentially genetic clones of the queen how can they be male and fertile?

    What determines if a female egg/sperm combination from a queen will be a sterile worker or a fertile queen? I realize that when the hive is working at producing a queen that the environment in which the egg develops is managed differently by the bees but the DNA chromosome coding would be there when the egg is laid. Does the manner in which the egg/larva is managed affect gene expression after the egg has been deposited in the cell.

    In mammals the Y chromosome determines if the offspring will be male and that chromosome comes from the male (sperm). If drones are unfertilized eggs..how are they becoming male..and fertile male at that..with no male chromosome input and only the female set of chromosomes?

    Is there a site that explains this? Perhaps I haven't chosen appropriate search terms as I am not finding this information.

    If egg development conditions can affect gene expression in bees then manipulation of the developmental environment would open up a huge area of genetic manipulation.

    Am I the only one that finds this both interesting and confusing?

  2. #2
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    Default Re: Confused about the genetics of bee reproduction

    Bees are member of the Hymenoptera, or insects with membrane wings, and are colonial. In each colony there will be one fertile Queen, laying all the eggs for all the members of the colony.

    Diploid (fertilized) eggs produce female offspring, haploid (unfertilized eggs) produce male offspring, and the Queen can lay either type at will.

    In bees, the difference between a queen and a worker is that the queen is fed only royal jelly, a substance produced by special glands on the bees, and worker are only fed royal jelly for a few days, then "bee bread" (fremented or raw pollen) and other substances. The rich diet of royal jelly causes the development of complete ovaries and secondary sexual equipment so the queen can mate, store sperm from numerous drones, and lay large numbers of eggs. Worker bees have rudimentary ovaries and cannot mate.

    When there is no queen in a colony, and hence no open brood, the pheremones that suppress ovary development are reduced or missing, and ovary development in worker bees can procede far enough for them to lay a few unfertiziled eggs, and very rarely a diploid egg. As a result, a hive without a queen for a long period can develop laying workers, producing numerous drones but no worker brood. Since the laying workers also produce small amounts of queen mandibular pheremone, the hive "thinks" it has a queen and will destroy an introduced one as if they had a functional queen.

    Very rarely, a diploid egg will be laid by a laying worker, and the bees will raise a normal queen from it.

    Hope this helps.

    Peter

  3. #3
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    Default Re: Confused about the genetics of bee reproduction

    OK, I'll *try* to "sum it up" somewhat succinctly here, to capture in a few paragraphs what could fill a couple of books, if fully explained....

    1: Chromosome count:
    • Drones have "haploid" genomes, meaning they only have 1/2 the chromosome count of a worker/queen bee (i.e. for a mammalian comparison, they have only the haploid chromosome set, resultant of meiosis, from the unfertilized egg). This, rather than an "X chromosome" is what determines gender in honey bees.
    • Workers have "diploid" genomes. The egg must be fertilized prior to laying in order to develop into a female (worker, OR queen) bee.
    • Queens also have "diploid" genomes, same as workers.


    2: Fertility:
    • Drones are male-reproductive, they produce sperm &, during a single mating, transfer all of their sperm to a single "virgin" queen, then die, similarly to a worker dying after stinging a human.
    • Workers have no developed "semen storage" organ, as queens do, and thus cannot be "fertilized" by drones. Therefore, any eggs laid by a worker must necessarily be haploid (unfertilized), resulting in their growing into drones, assuming they're allowed to mature.
    • Queens have fully developed reproductive organs, both for producing large quantities of eggs, and for storing drone semen for a period of years. Queen bees can selectively lay fertilized (worker or queen) eggs, or unfertilized (drone) eggs, determined, as you suspected, by the queen at time of laying.


    3: Development/Gene expression:
    • Drones are raised from non-fertilized eggs, the larvae being directly fed a small amount of royal jelly directly as they develop; then maturing in a horizontally-aligned cell into a fully-fertile adult male.
    • Workers are raised from fertilized eggs, the larvae being directly fed a small amount of royal jelly directly as they develop; then maturing in a horizontally-aligned cell into a partially-fertile adult female.
    • Queens are raised from fertilized eggs, the larvae being literally floated on a "sea" of royal jelly, eating it nearly exclusively, and as much as they can consume; then maturing (still with ready access to a nearly limitless supply of royal jelly) in generally MUCH larger, vertically aligned cell into a fully-fertile adult female.



    I hope that at least *started* to clarify things for you. Please feel free to ask more questions for any specific clarifications now, having that as a "background starting point" to go on...I'll answer as best I can, & I'm sure others will chime in too

  4. #4
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    Default Re: Confused about the genetics of bee reproduction

    Does the manner in which the egg/larva is managed affect gene expression after the egg has been deposited in the cell.
    Yes, that is exactly what happens. Queens do not choose to make other queens, rather that choice is made by workers who pick a normal egg at the right stage of development and feed the larvae royal jelly which causes that bee to become a queen.

    What genetically determines workers to always be sterile?
    Nothing genetically, it is determined by how they are raised.

    If drones are essentially genetic clones of the queen how can they be male and fertile?
    The drones have only half the genes from the queen, which is enough to build an entire male bee (unlike in humans) The workers have half of the genes from the queen and the other half is from the drones that she mated with.

    None of the bees are clones of the queen. Since the queen mates with more than one drone workers aren't even all full sisters but more like half sisters. Drones have only half of the genes from their queen so they are not clones either.

    So...if the workers are sterile what is the purpose of their laying eggs at all...
    You have to look at it from the point of view of evolution which cares only about the survival of genes, not individuals or societies.

    If a hive is hopeless queenless then it is doomed as are its genetics. By raising as many drones as possible the hive at least has a chance for one of its drones to mate with a foreign queen and for its genetics to escape. Think of it drones like little lifeboats carrying a copies of a message out into the world while the ship sinks.



    Does bee reproductive genetics have any similarity to the mammalian version?
    Not a lot.

    One interesting thing to note though is that only female humans who receive enough calories are fertile. If a women goes on a highly restrictive diet she will become infertile. If she is given enough calories again she well become fertile again so their is some mammalian precedent for diet dependent fertility but bees are one of the most dramatic examples of animal development influenced by environmental factors rather than genetics.

    There systems allows gives every fertilized egg the ability to perpetuate the species without requiring every individual to maintain a costly reproductive system and since every colony can produce queens, workers and drones a single isolated colony could in theory be enough to populate an entire ecosystem with bees.

  5. #5
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    Default Re: Confused about the genetics of bee reproduction

    Thank you very much for these succinct answers Bees appear to be highly developed wee creatures. It makes me wonder if we should be looking more to what they can do when left to their resources rather than trying to bend what they do to fit our needs. I guess the answer lies in a blend of curiosity and greed

    Again thank you..this is a great forum!

  6. #6
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    Default Re: Confused about the genetics of bee reproduction

    Bees have been making hives much much longer than people have been "keeping" bees..... about 100 million years longer.

    Peter

  7. #7
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    Default Re: Confused about the genetics of bee reproduction

    I think using the term sterile is a bit misleading. Worker bees aren't sterile, they are underdeveloped and under the correct conditions the ovaries develop. If you've ever seen a laying worker hive, it's not just a couple eggs it's a ton of eggs, granted there are multiple bees laying at that point, but I've seen cells with eggs just stacked up inside there.

  8. #8
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    Default Re: Confused about the genetics of bee reproduction

    I think using the term sterile is a bit misleading.
    True, infertile would probably be more accurate.

  9. #9
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    Default Re: Confused about the genetics of bee reproduction

    >From what I have read there seems to be male bees (drones) that mate with a virgin queen (female) bee.

    Yes.

    > The female (queen) then lays fertile eggs.

    Sometimes.

    >Some eggs develop into female bees (nurse bees--->worker bees) which I have read are from fertilized eggs but they themselves remain sterile.

    They have underdeveloped ovaries which will develop over time in the absence of open worker brood pheromones.

    > Then to confuse things I see posts about workers (sterile female bees) laying eggs but I am not certain what type of bee these eggs develop into.

    They are unfertilized eggs. Unfertilized eggs have only one set of chromosomes and develop into drones.

    > Then there are male bees (drones) that are fertile but somewhere I read that they are from unfertilized queen eggs...this seems quite odd to me.

    It is how many insects and even some arachnids work. A diploid (fertilized egg with two sets of chromosomes) develops into a female and the haploid (unfertilized egg with one set of chromosomes) develops into a male. It even works this way with Varroa mites.

    >So...if the workers are sterile what is the purpose of their laying eggs at all...

    IF it servers a purpose at all, it would be a last ditch effort to pass on the genes of the colony since the colony is otherwise doomed.

    >if they are sterile then one would expect their eggs would never hatch

    They do.

    > (and I take it they don't mate with drones).

    They don't.

    > Next if the Queen is mated and stores drone sperm does she actually make a decision as to whether her eggs will be covered by the stored sperm to produce workers or not covered by stored sperm to produce drones.

    No one knows. The prevailing theory is that there is a switch in her brain that is flipped by her measuring the cell and that causes her to fertilize or not fertilize the egg.

    > What genetically determines workers to always be sterile?

    It's epigenetics that determines this. The workers have the exact same genes as the queens, but what they are fed turns on different genes which cause them to develop an entirely different anatomy from the queen. The workers have pollen baskets, the queen does not. The workers have a hypopharengeal gland, the queen does not. The workers have a barbed stinger, the queen has a smooth stinger. The queen has a QMP gland, the workers do not. The queen has other pheromone producing glands that the workers do not. The queen has fully developed ovaries and other reproductive facilities that the workers do not have.

    >Does bee reproductive genetics have any similarity to the mammalian version?

    In sex determination, no. In some things, such as the production of proteins etc. yes.

    > If so if the Queen eggs that produce drones aren't fertilized where does the male determining gene come from?

    There are several alleles and if there is only one set it acts as a matching alelle. If there are two sets, then a matching set produces a diploid drone, which the bees will remove before it develops.

    >If drones are essentially genetic clones of the queen how can they be male and fertile?

    When the queen makes a gamete (in this case an egg) one of her cells divides into two haploid gametes and each gets a random set of one of the two possible genes for each position. For a worker this is then fertilized with another set from the sperm the queen has stored. For a drone, it's just that set with nothing added. It is not a clone of the queen, that would require both sets, but a random mixture of each of the two possibilities for every trait. Not all the drones from a queen are identical. There are thousands of different possibilities for the entire mixture, but only two possibilities for any given trait.

    >What determines if a female egg/sperm combination from a queen will be a sterile worker or a fertile queen?

    They are fed different food.

    > I realize that when the hive is working at producing a queen that the environment in which the egg develops is managed differently by the bees but the DNA chromosome coding would be there when the egg is laid.

    Yes.

    > Does the manner in which the egg/larva is managed affect gene expression after the egg has been deposited in the cell.

    Yes.

    >In mammals the Y chromosome determines if the offspring will be male and that chromosome comes from the male (sperm).

    In mammals, yes. In bees, not.

    >If drones are unfertilized eggs..how are they becoming male..and fertile male at that..with no male chromosome input and only the female set of chromosomes?

    When a drone produces sperm it is a clone of themselves as there is only one possible set of genes. The ones they carry. As far as being male or female that determination is entirely different in bees than mammals. There is no Male or Female chromoxome (like the X or Y), just a matching (or single set) or nonmatching set of alleles that determine the sex of a bee.

    >Is there a site that explains this? Perhaps I haven't chosen appropriate search terms as I am not finding this information.

    http://www.beeuntoothers.com/

    there is a video at the bottom of the page.

    >If egg development conditions can affect gene expression in bees

    It does.

    >then manipulation of the developmental environment would open up a huge area of genetic manipulation.

    Perhaps.

    >Am I the only one that finds this both interesting and confusing?

    Apparently not.
    Michael Bush bushfarms.com/bees.htm "Everything works if you let it." ThePracticalBeekeeper.com 40y 200h 37yTF

  10. #10
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    Default Re: Confused about the genetics of bee reproduction

    Once again...thanks. I will check out the video.

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