Natural selection in populations subject to a migration load

Area of Science:

• Evolutionary Biology
• Population Genetics

Background:

• Migration-selection balance typically constrains population divergence.
• Immigration's impact on recipient population fitness and selection is less studied.
• Migration can reduce local adaptation, causing a 'migration load' and persistent selection.

Purpose of the Study:

• To investigate how migration rates influence maladaptation and natural selection within populations.
• To test theoretical predictions using data from Timema cristinae walking-stick insects.
• To examine if increased maladaptation due to immigration leads to larger selection differentials.

Main Methods:

• Developed a two-island migration-selection balance model.
• Collected color morph frequency data from 25 natural Timema cristinae populations.
• Analyzed the relationship between immigration rates, maladaptation (frequency of non-cryptic morphs), and selection differentials.

Main Results:

• Confirmed that higher immigration rates correlate with increased population maladaptation.
• Demonstrated that elevated maladaptation leads to larger selection differentials.
• Provided evidence that immigration increases fitness variance, consistent with Fisher's Theorem.
• Observed that recurrent migration may obscure selection effects.

Conclusions:

• Immigration can increase maladaptation and drive stronger natural selection within populations.
• The study supports theoretical models linking migration, selection, and fitness.
• Recurrent migration may complicate the detection of selection in natural populations.