Bet-hedging (biology)

Biological bet hedging occurs when organisms suffer decreased fitness in their typical conditions in exchange for increased fitness in stressful conditions. Biological bet hedging was originally proposed to explain the observation of a seed bank, or a reservoir of ungerminated seeds in the soil. For example, an annual plant's fitness is maximized for that year if all of its seeds germinate. However, if a drought occurs that kills germinated plants, but not ungerminated seeds, plants with seeds remaining in the seed bank will have a fitness advantage. Therefore, it can be advantageous for plants to "hedge their bets" in case of a drought by producing some seeds that germinate immediately and other seeds that lie dormant. Other examples of biological bet hedging include female multiple mating, foraging behavior in bumble bees, nutrient storage in rhizobia, and bacterial persistence in the presence of antibiotics.

There are three categories (strategies) of bet-hedging: "conservative" bet-hedging, "diversified" bet-hedging, and "adaptive coin flipping."

In conservative bet-hedging, individuals lower their expected fitness in exchange for a lower variance in fitness. The idea of this strategy is for an organism to "always play it safe" by using the same successful low-risk strategy regardless of environmental conditions. An example of this would be an organism producing clutches with a constant egg size that may not be optimal for any environmental condition, but result in the lowest overall variance.

In contrast to conservative bet-hedging, diversified bet-hedging occurs when individuals lower their expected fitness in a given year while also increasing the variance of survival between offspring. This strategy uses the idea of not "putting all of your eggs in a basket." Individuals implementing this strategy actually invest in several different strategies at once, resulting in low variation in long-term success. This could be demonstrated by a clutch of eggs of different sizes, each optimal for one potential environment of the offspring. While this means that offspring specialized for another environment are less likely to survive to adulthood, it also protects against the possibility of no offspring surviving to the next year.

An individual using this type of bet-hedging chooses what strategy to use based on a prediction of what the environment will be like. Organisms using this form of bet-hedging make these predictions and select strategies annually. For example, an organism may produce clutches of different egg sizes from year to year, increasing variation in offspring success between clutches. Unlike conservative and diversified bet-hedging strategies, adaptive coin flipping isn't concerned with minimizing the variation in fitness between years.

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