Says the winter bee to the summer bee
I suppose the Nobel prize winner Bob Dylan did not think of the honey bee, when he penned the lyrics to his song “Forever Young”, but when we compare the longevities between summer and winter honey bees, it almost seems as if the long-lived winter bees stay forever young: they stay around from about October until at least March while the short-lived summer bees are lucky to reach an age of 6 weeks. The reason is not that during the summer, bees are more susceptible to disease, preyed upon more heavily or work so much harder than the winter bees, for even though winter bees spend the entire winter in the hive, they too work hard. They shiver to create heat and make sure that the cluster of bees surviving the cold season with their queen does not become colder than 15°C. But how can they possibly stay active (and alive) for so many months longer than the summer bees?
First of all, the members of a bee hive need to sense that the cold season is approaching. This may involve the increasingly difficult task of finding pollen in August to feed the brood. It follows that brood rearing becomes reduced and eventually stops until it resumes in January. With no foraging summer bees needed, they all die in the autumn and are replaced by the morphologically identical winter bees. The latter begin to store large amounts of ‘vitellogenin’, (a glycolipoprotein known to be a zinc carrier) in their fat body, the equivalent of our liver. In the winter this substance also increases in the haemolymph, the equivalent of our blood. At the same time, the so-called ‘juvenile hormone’, important during the nursing of the brood, decreases to almost undetectable levels. The amount of a neuromodulator molecule from the brain, known as octopamine, also falls when foraging is no more possible in winter.
The nutrients stored by the winter bees in the form of vitellogenin are not used by them for themselves, but are kept to be utilised when new bee brood is produced again by the queen bee in anticipation of the coming spring with its flowers and sources of protein-rich pollen. How the queen bee ‘knows’ that spring will approach when she starts to lay eggs anew in the middle of winter, the coldest and darkest season of the year, is still a mystery, but how the winter bees keep themselves and their queen warm is much better understood. In the ball-like cluster that the winter bees form, those at the periphery every now and then exchange places with bees from the warmer centre and then also to replenish their food intake. After all, to create heat by shivering, means that they are expending a lot of energy.
The ‘fuel’ the bees use to warm themselves and the hive up is sugar! It’s the main or perhaps the only reason why they collected nectar and turned it into honey during the summer: the carbohydrates keep them alive throughout the winter, so that in spring they can feed the new brood with the vitellogenin they stored in their fat body. Actually, rearing new brood already starts in late winter when pollen are not yet available and the trigger for the transition from winter to short-lived summer bees is, therefore, not at all understood. Perhaps the decrease in vitellogenin, needed to feed the new brood, causes a concomitant rise in juvenile hormone and octopamine. The fact is that all winter bees, irrespective as to when they left their pupal cases, whether that was in October and the early months in winter or as late as January, they all die within a very short time. Forever young? Well maybe not forever, but applied to humans it would be a life of 400 years! And if that’s not long enough, how about the rotifer, a tiny wheel animalcule, an extreme “Rip Van Winkle” of the animal world? Dormant in a frozen state for 24,000 years, it was revived recently by the Russian soil scientists Lyubov Shmakova and colleagues of Pushchino in Russia, and it even multiplied (it did not need a male). A multicellular organism with a gut, a nervous system, sense organs, frozen stiff, for 24,000 years: what a life – if you can call that a life at all.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2021.
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