Genomic signatures of drift and selection driven by predation and human pressure in an insular lizard

Marta Bassitta,Cori Ramon,Richard P Brown,José A Castro,Ana Pérez-Cembranos,Valentín Pérez-Mellado,Antònia Picornell

doi:10.1038/s41598-021-85591-x

Abstract

Genomic divergence was studied in 10 small insular populations of the endangered Balearic Islands lizard (Podarcis lilfordi) using double digest restriction-site associated DNA sequencing. The objectives were to establish levels of divergence among populations, investigate the impact of population size on genetic variability and to evaluate the role of different environmental factors on local adaptation. Analyses of 72,846 SNPs supported a highly differentiated genetic structure, being the populations with the lowest population size (Porros, Foradada and Esclatasang islets) the most divergent, indicative of greater genetic drift. Outlier tests identified ~ 2% of loci as candidates for selection. Genomic divergence-Enviroment Association analyses were performed using redundancy analyses based on SNPs putatively under selection, detecting predation and human pressure as the environmental variables with the greatest explanatory power. Geographical distributions of populations and environmental factors appear to be fundamental drivers of divergence. These results support the combined role of genetic drift and divergent selection in shaping the genetic structure of these endemic island lizard populations.

Highlights

Genomic divergence was studied in 10 small insular populations of the endangered Balearic Islands lizard (Podarcis lilfordi) using double digest restriction-site associated DNA sequencing
Patterns of divergence based on FST distance analysis were highly congruent with previous results, with the populations of the islands of Menorca showing a clear differentiation with respect to the populations of the islands of Mallorca together with Cabrera populations (Supplementary Figure 1)
The RADseq methodology has been applied in other studies of squamate, increasing understanding of the processes related to genetic divergence and the identification of genomic regions of interest

Summary

Introduction

Genomic divergence was studied in 10 small insular populations of the endangered Balearic Islands lizard (Podarcis lilfordi) using double digest restriction-site associated DNA sequencing. Geographical distributions of populations and environmental factors appear to be fundamental drivers of divergence These results support the combined role of genetic drift and divergent selection in shaping the genetic structure of these endemic island lizard populations. The Balearic lizard, Podarcis lilfordi, as an insular endemism inhabiting a large group of coastal islands and islets of Mallorca and Menorca (Balearic Islands, Spain), provides a suitable system for studying selection and genetic drift as mechanisms of evolution. Small populations managed to survive on the coastal islands and islets situated around Menorca and Mallorca, as well as the uninhabited Cabrera archipelago (Fig. 1) The sizes of these populations varies considerably, ranging from fewer than 100 individuals, to over 100,000 individuals[18]. Despite subsequent glacial events causing sea-level fluctuations[22], no evidence of historical gene flow or Scientific Reports | (2021) 11:6136

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