Founder effects persist despite adaptive differentiation: a field experiment with lizards

Area of Science:

• Evolutionary Biology
• Ecology
• Population Genetics

Background:

• The relative roles of random processes (like founder effects) and natural selection in driving evolutionary divergence remain debated.
• Understanding these factors is crucial for predicting how populations adapt and speciate.

Purpose of the Study:

• To experimentally determine the independent and combined contributions of founder effects and natural selection to evolutionary divergence.
• To investigate the genetic and morphological changes in newly founded populations of brown anole lizards.

Main Methods:

• Established replicate brown anole (Anolis sagrei) populations on seven small Bahamian islands from a single, large-island source population.
• Randomly sampled founding pairs to control for initial genetic variation.
• Monitored genetic and morphological traits over time, correlating changes with environmental pressures (island vegetation width).

Main Results:

• Founder events led to significant genetic and morphological differences among the newly established island populations.
• Despite these initial differences, all populations adapted in a consistent direction (shorter hindlimbs) due to selection pressures from narrower vegetation.
• Both founder effects and natural selection played a joint role in shaping the observed trait values.

Conclusions:

• Founder effects can rapidly generate significant genetic and morphological variation, initiating divergence.
• Natural selection acts on this variation, driving adaptation in response to environmental conditions.
• Evolutionary divergence is a complex process resulting from the interplay between random genetic drift and deterministic natural selection.