![]() Over many subsequent environmental alternations, selection may sweep the allele to fixation. In order for a bet hedging allele to spread, it must persist in the typical environment through genetic drift long enough for alternative environments, in which the bet hedger has an advantage over genotypes adapted to the previous environment, to occur. Therefore, bet hedging alleles tend to be favored in more variable environments. While a bet hedging trait may not be optimal for any one environment, this is outweighed by the benefits of higher fitness across a variety of environments. Adaptations that allow organisms to survive in fluctuating environmental conditions provide an evolutionary advantage. ![]() This makes it appropriate for circumstances where a single genotype may have variable fitness depending on environmental circumstances.īet hedging is understood to be a mode of response to environmental change. Even rare occurrences of zero fitness for a genotype result in it having an expected geometric mean of zero. The geometric mean is highly sensitive to small values. Particularly in highly variable environments where bet hedging is likely to evolve, long-term fitness is best measured using the geometric mean, which is multiplicative instead of additive like the arithmetic mean. To determine if a bet hedging allele is favored, the long-term fitness of each allele must be compared. Unlike conservative and diversified bet hedging strategies, adaptive coin flipping isn't concerned with minimizing the variation in fitness between years. For example, an organism may produce clutches of different egg sizes from year to year, increasing variation in offspring success between clutches. Organisms using this form of bet hedging make these predictions and select strategies annually. Adaptive coin flipping Īn individual using this type of bet hedging chooses what strategy to use based on a prediction of what the environment will be like. ![]() 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. This could be demonstrated by a clutch of eggs of different sizes, each optimal for one potential environment of the 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. 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. 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. 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. In conservative bet hedging, individuals lower their expected fitness in exchange for a lower variance in fitness. There are three categories (strategies) of bet-hedging: "conservative" bet-hedging, "diversified" bet-hedging, and "adaptive coin flipping." 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. 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. 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. ![]() For example, an annual plant's fitness is maximized for that year if all of its seeds germinate. Biological bet hedging was originally proposed to explain the observation of a seed bank, or a reservoir of ungerminated seeds in the soil. Producing a range of egg sizes can both ensure that some offspring survive stressful conditions, and that many offspring are produced in good conditions.īiological bet hedging occurs when organisms suffer decreased fitness in their typical conditions in exchange for increased fitness in stressful conditions. However, larger eggs may help offspring survive stressful conditions. Fitness may be maximized by producing many, small eggs and thus many offspring. Variance in egg size is an example of bet-hedging.
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