Science and sensibility

This post is part of a story that grew beyond control and so was serialised, if you haven't read the first part then you should do that before embarking on this post

When we left her our queen she was lying asleep under the ground waiting for the spring, as you can imagine at this stage her story gets a little monotonous so spare a thought now for the workers of the nest. With their honey stores depleted by the hibernating queens and the smorgas board of flowering plants that was the summer coming to an end they were left with no food to survive the winter. Soon after the new queens flew out from the nest for the last time the original queen died and the colony disbanded, the remnants perhaps attacked by parasitic wasps, leaving surviving workers to fend for themselves. Their instincts to collect nectar may have kept them going for a while but sooner or later a Dunedin frost would have taken them all. It’s a pretty bleak picture, but before you start reaching for your copy of Karl Marx’s Quotable Quotes to decry the position of workers within bee society consider that the workers may actually have benefited in an evolutionary sense from “farming” reproductive males and queens during the summer.

The nest can be seen like the population of some science fiction planet sending forth its best and brightest to populate a new world while theirs dies. But in their case the journey to a more habitable place is through time, not space. Faced with the prospect of a winter that the nest could never survive it produces a few queens that can act as vessels carrying the worker’s genes into another season. In fact, the nest spends all summer preparing for the coming catastrophe, amassing enough honey to give their few hopes of survival every likelihood of mating and making it through winter to build new nests next summer when the whole story will be told again. Indeed a quirk in the genetics of the hymenoptera (the group of insects that includes ants, bees and wasps) mean that workers in a colony stand to ‘gain’ more from their sisters’ (the new queens) success in forming a new colony than from their own daughters doing the same thing.

The quirk referred to in the above paragraph deals is in the details of sex determination in hymenopterans and some other insects. Mammal's and bird's body cells all have two complete, matcing sets of chromosomes including two sex determining chromosomes, these cells are said to be "diploid." When diploid organisms create gametes (sperms or eggs) each one gets only 1 set of chromosomes with one sex determining chromosome and are said to be 'haploid'. When the two haploid gametes are fused they produce diploid offspring with sex determined by the pressence or lack of the Y chromosome. Things are a little different for the bumble bee, sex is not dertemined by the presence or lack of one chromosome but by the presence or lack of an entire set of chromosomes; males are haploid and females diploid. As we saw earlier the queen stores her mate’s sperms through the winter, only using them as they are needed. Each of the queen’s eggs and each of her mate’s sperms carry one set of the bee’s chromosomes. When the queen chooses to fertilise one of her eggs the two haploid genomes fuse generating the familiar diploid offspring which are therefore female, either workers or queens. The trick comes when a queen chooses to lay an unfertilised egg. The egg will still develop, producing a haploid bumble bee that got all of its genes from its mother (and consequently didn’t have a father) and as I said haploid bees are males.

One of the interesting outcomes of this system of sex determination is that females are more closely related to their sisters than to their mother or their own potential offspring. Since males are haploid and sperms are haploid all sperms will carry all of the males genes, and since queens only mate once all of the male’s genes will be in all of the queens offspring. Putting it another way, all of the female offspring will inherit the same set of genes from their father as well as half of their mother’s genes. When it’s all added up sister bees on average share 75% of their genes with each other while they only share 50% of their genes with any potential daughters (which would carry a males genes as well as theirs). Because of this scenario it can become and evolutionary sensible strategy for most female bee’s to give up their own ability to reproduce and throw their lot in to help their mother produce sisters, including queens more closely related to them than the daughters they have forgone. This behaviour has been called reproduction by proxy and has evolved 11 times within the hymenoptera (which includes the wasps, ants and bees) and only twice outside of that group.

You’ll recall when we left on that little digression the star of our story was lying under some soil sleeping the winter away. Last week the spring sun shone on her little patch of soil, producing enough heat in her hibernaculum to convince her that her long wait had finished and spring had finally sprung. It is believed that her emergence was timed to coincide with the willow tree’s first flowers, which are an important food source. If the newly emerged queen was to fulfil her purpose she would need to create a new nest from which to generate another generation of males and queens. First though she would need to eat; nectar to provide her with the energy for the search for a nest site and pollen to provide enough protein to aid the final development of her ovaries. Sadly our leading lady didn’t even get that far, emerging from her overwintering spot still a little drowsy from her long sleep and lack of sugar she made a fatal mistake: she flew into the open back door of a student flat.

Unable to find any nectar she decided to leave but couldn’t find her way out and instead tried to no avail to fly through a window. Finally, sapped of energy from her frantic attempts of, and lacking nectar to replace it her body temperature plummeted and she died. With her died the prospect of a new nest, hundreds of workers to pollinate thousands of plants and a new batch of reproductives to carry her genes into another season.

As sad as the loss may be life proverbially goes on. All around me even now other queens are eating, flying and generally scoping out the place in search of a nest. I hope you won’t think it too disrespectful of me to finish a series of posts that started as a eulogy by adding one more post completing a decription of a bumble bee's life cycle and so detailing the potentail that was lost with our star's death. Again I'll add a link to the next post here when it is up.

The final part of this series is now online, click here to finish the story