Habitat-associated Genomic Variation in a Wall Lizard from an Oceanic Island.

Area of Science:

• Evolutionary Biology
• Genomics
• Island Ecology

Background:

• The lizard Teira dugesii on Madeira Island shows morphological variation between coastal beach and inland habitats.
• Understanding the genetic basis of adaptation in island populations is crucial for evolutionary studies.
• Previous hypotheses suggested ancient allopatric divergence as a driver for similar patterns in other Atlantic islands.

Purpose of the Study:

• To investigate the genomic underpinnings of morphological divergence in Teira dugesii populations.
• To test the hypothesis of divergent selection versus ancient allopatric divergence in shaping adaptation to contrasting habitats.
• To identify specific genetic markers associated with beach and inland ecotypes.

Main Methods:

• Genotyping-by-sequencing was employed to obtain 16,378 single nucleotide polymorphisms (SNPs) from 94 Teira dugesii individuals.
• Statistical outlier analyses (pcadapt, OutFLANK) and Redundancy Analysis (RDA) were used to detect SNPs under selection.
• Contingency analyses of allele frequencies and comparisons with a reference wall lizard genome were performed.

Main Results:

• A total of 168 outlier SNPs were identified, with 17 strongly associated with beach versus inland habitats.
• Fifteen of these habitat-associated SNPs mapped to a specific region on chromosome 3 of the reference genome.
• Six other outlier SNPs were linked to site elevation, with four located on chromosome 5.

Conclusions:

• Divergent natural selection between contrasting beach and inland environments is the primary driver of morphological divergence in Teira dugesii.
• This selection pressure effectively overcomes gene flow between adjacent populations.
• The study supports the role of contemporary selection in shaping adaptation in island lizard populations.