Large-scale mutation in the evolution of a gene complex for cryptic coloration

Area of Science:

• Evolutionary biology
• Genetics
• Molecular evolution

Background:

• Understanding the genetic basis of adaptation in wild populations is crucial.
• The roles of recombination suppression and novel mutations in shaping adaptive traits remain debated.
• Structural mutations and their impact on adaptation are increasingly recognized.

Purpose of the Study:

• To investigate the genetic architecture underlying cryptic color morphs in *Timema chumash* stick insects.
• To determine the mechanisms (recombination suppression vs. large-scale mutation) driving the evolution of these morphs.
• To assess the relative contributions of balancing selection and introgression in maintaining these adaptive variations.

Main Methods:

• Analysis of linked genetic loci associated with color variation.
• Comparative genomics to identify regions of suppressed recombination and large-scale mutations.
• Population genetic analyses to infer the roles of selection and gene flow.

Main Results:

• Multiple linked loci, not a single supergene, underlie color morphs in *Timema chumash*.
• A megabase-scale deletion ("supermutation") was identified in green morphs across seven *Timema* species.
• Balancing selection appears to be a stronger force than introgression in maintaining these mutations.

Conclusions:

• Large-scale mutations, such as deletions, can effectively package gene complexes, facilitating adaptation.
• Both suppressed recombination (supergenes) and large mutations contribute to the formation of discrete adaptive units like morphs.
• This study highlights diverse evolutionary pathways for generating and maintaining biodiversity.