How to be fecund : be fruitful and multiply
Sometimes when you read about the human population explosion you may think our own species’ fecundity must be enormous. However, even assuming an average life span of 65 years and an average number of children of four in a person’s life, our reproductive rate would not at all be high. Rodents are doing much better and have no trouble at all outperforming us.
Take a golden hamster, for instance. It may only live for two years, but reaching sexual maturity at three months of age, having a gestation period of 16 days and being able to produce a litter of 7 or 8 pups (even ten as my daughters would be able to tell you) , it could have a hundred babies in a life time, for if it can have several pregnancies in a year.
Birds, for example the common barnyard chicken, are not doing badly either. A hen (if not so unfortunate as to land prematurely on somebody’s plate) can live for 20 years and, if she is a good egg-layer, will produce 300 eggs per annum. This gives 3,000 potential chicks in ten years (and us something to think about when we bite into a poulet roast or enjoy an omelette). But truly amazing figures come from some invertebrates and fishes.
A queen termite, for example, can live up to at least 30 years, possibly more, and in this time her sole job is to produce eggs, between 10,000 and 20,000 a day, day in day out. In her lifetime she would have laid millions of eggs. The grotesque looking oceanic sunfish Mola mola is more productive still and credited with ovaries containing 200 million eggs. Topping even that are the tapeworms, well not all of them, but those residing in the guts of swine, cow (or human), etc. They can stay in these comfortable surroundings of plenty for many years.
A single beef tapeworm sheds approximately half a million eggs a day (or 200 million in a year) and by the end of its life would have reached a staggering 2 – 4,000,000,000 egg tally. Humans and tapeworms represent two extreme reproductive strategies: you can either limit the offspring to a few, well looked after young and be what is termed a “k-strategist”, or you can release enormous numbers of tiny eggs with hardly any yolk and be an “r-strategist”, hoping that at least two of them will make it to a mature adult.
Both strategies (as well as their intermediate forms) can be successful and are widely represented in the animal world. Howeer, what amazes me most is that the tapeworm does everything by him/herself – it is a hermaphrodite which practices self-fertilization and that precludes sexual mixing, but means that only one single individual out of the 4 billion eggs needs to make it to sexual maturity to make sure the species doesn’t go extinct.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2016.
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