Evolutionary Bottlenecks

Definition

An evolutionary bottleneck is a severe reduction in the size of a population due to environmental events or disasters, which can lead to a loss of genetic diversity and the fixation of deleterious alleles. This can have significant impacts on the future evolution and survival of the species.

5 Must Know Facts For Your Next Test

1. Evolutionary bottlenecks can be caused by natural disasters, disease outbreaks, climate change, or human activities that drastically reduce a population's size.
2. During a bottleneck, rare alleles are more likely to be lost, leading to a decrease in genetic diversity and the potential for adaptation.
3. Populations that undergo severe bottlenecks are more susceptible to inbreeding depression, which can further reduce fitness and increase the risk of extinction.
4. Bottlenecks can also lead to the fixation of deleterious alleles, which can negatively impact the long-term viability of the population.
5. In some cases, evolutionary bottlenecks can also trigger rapid speciation and adaptive radiation, as the remaining individuals diversify to fill new ecological niches.

Review Questions

• Explain how an evolutionary bottleneck can impact the genetic diversity of a population.
  • During an evolutionary bottleneck, the population size is severely reduced, leading to a significant loss of genetic diversity. Rare alleles are more likely to be lost, and the remaining gene pool becomes less diverse. This reduction in genetic variation can limit the population's ability to adapt to changing environmental conditions and increase the risk of inbreeding depression, which can further erode the population's fitness and long-term viability.
• Describe the potential consequences of the fixation of deleterious alleles during an evolutionary bottleneck.
  • When a population experiences a severe reduction in size, the frequency of rare, potentially deleterious alleles can increase due to genetic drift. These harmful alleles may become fixed in the population, meaning they are present in all individuals. The fixation of deleterious alleles can have significant negative impacts on the population's fitness, making it more susceptible to disease, reducing reproductive success, and increasing the risk of extinction. This can severely compromise the long-term evolutionary potential of the species.
• Analyze how an evolutionary bottleneck can lead to rapid speciation and adaptive radiation.
  • In some cases, an evolutionary bottleneck can open up new ecological niches, allowing the remaining individuals to diversify and rapidly evolve into multiple new species. This process, known as adaptive radiation, occurs when a species exploits a variety of untapped resources and adapts to fill different ecological roles. The reduced competition and availability of resources following a bottleneck can drive this rapid diversification, as the surviving individuals are able to exploit new niches without the constraints of a larger, more diverse population. This can result in the emergence of a variety of new species, each with unique adaptations, ultimately increasing the overall biodiversity of the ecosystem.

Related terms

Genetic Drift: The random change in the frequency of gene variants in a population due to chance events, which can be amplified during population bottlenecks.

Founder Effect: The loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.

Adaptive Radiation: The rapid diversification of a species into multiple new species, often following an evolutionary bottleneck that opens up new ecological niches.