Evolutionary rescue and the limits of adaptation

Area of Science:

• Evolutionary biology
• Population genetics

Background:

• Natural selection aids populations facing severe stress.
• Ecological and genetic constraints can limit the effectiveness of natural selection.
• The concept of evolutionary rescue highlights adaptation under environmental stress.

Purpose of the Study:

• To explore the constraints on natural selection and evolutionary rescue.
• To emphasize the importance of absolute fitness in adaptation.
• To investigate the role of population size and genetic variation in evolutionary rescue.

Main Methods:

• The study discusses theoretical principles of natural selection and adaptation.
• It analyzes the concepts of cost of natural selection and genostasis.
• The role of absolute fitness versus relative fitness is examined.

Main Results:

• Evolutionary rescue is constrained by the cost of natural selection and genostasis (lack of genetic variation).
• Absolute fitness, not just relative fitness, is critical for sustained population growth under stress.
• Population size influences the number of individuals exposed to selection, impacting rescue potential.

Conclusions:

• Permanent adaptation requires broad genetic variation in absolute fitness.
• Gradually deteriorating environments may allow prior adaptation to sublethal stresses.
• Neither standing genetic variation in small populations nor mutation supply in large populations is consistently sufficient for evolutionary rescue.