Semelparity – Why some animals don’t survive mating season

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Semelparity is a reproductive strategy whereby certain species of animals (sometimes both sexes, sometimes only males) only survive one mating episode and die shortly after mating. This serves as a strategy to maximize reproductive fitness – even at the cost of the current generation. Semelparity has evolved multiple times in independent environments. It is much less common among mammals though, as the females are required to care for their children. Some examples are:  – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

  1. Pacific Salmon
  2. Antechinus (sometimes called Marsupial mice. They look kind of cute and are related to kangaroos).
  3. Some insects like the Gipsy Moth. They don’t really die because of mating, it’s just that many insects starve because they don’t have a digestive system as adults. But technically, that still counts.

When it’s mating time, antechinus get flooded with testosterone and cortisol. They have extremely large testes in comparison to their body size and essentially try to mate with everything that moves. At the end of the mating season, they essentially die from exhaustion and organ failure. The National Geographic has an interesting piece about antechinus.

Salmon also die in the first two weeks after mating from an overdose of corticosteroids (mostly cortisol) produced by their adrenal glands. After mating they usually die, leaving more of the available resources to their offspring. The interesting catch is this: if you artificially remove a salmon’s adrenal gland after mating, it will survive and live happily ever after.

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Edit: related post: Phenoptosis – Are We Programmed to Die?

2 Comments

  1. “After mating they usually die, leaving more of the available resources to their offspring.”

    Stumbled across this while writing my own blog post. What do you exactly mean by “available resources”? The dead bodies of the fish? Or maybe resources, at large ?

  2. I was more thinking about resources at large. To be sure, it is always a bit difficult to speculate of individuals or even entire species – when really the level at which evolutionary pressure occurs is the gene (or a complex of genes).
    Happy to get in touch if you like. I would also be curious to read your piece once it’s done!
    You might also find my somewhat related post on Phenoptosis, or the planned death of an individual interesting: (followtheargument.org/phenoptosis-programmed-death-and-why-sepsis-may-be-a-way-to-protect-your-species). That one talks a bit about individuals dying in the context of the entire species.

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