Abstract
Oceanic archipelagos are excellent systems for studying speciation, yet inference of evolutionary process requires that the colonization history of island organisms be known with accuracy. Here, we used phylogenomics and patterns of genetic diversity to infer the sequence and timing of colonization of Macaronesia by mainland common chaffinches (Fringilla coelebs), and assessed whether colonization of the different archipelagos has resulted in a species-level radiation. To reconstruct the evolutionary history of the complex we generated a molecular phylogeny based on genome-wide SNP loci obtained from genotyping-by-sequencing, we ran ancestral range biogeographic analyses, and assessed fine-scale genetic structure between and within archipelagos using admixture analysis. To test for a species-level radiation, we applied a probabilistic tree-based species delimitation method (mPTP) and an integrative taxonomy approach including phenotypic differences. Results revealed a circuitous colonization pathway in Macaronesia, from the mainland to the Azores, followed by Madeira, and finally the Canary Islands. The Azores showed surprisingly high genetic diversity, similar to that found on the mainland, and the other archipelagos showed the expected sequential loss of genetic diversity. Species delimitation methods supported the existence of several species within the complex. We conclude that the common chaffinch underwent a rapid radiation across Macaronesia that was driven by the sequential colonization of the different archipelagos, resulting in phenotypically and genetically distinct, independent evolutionary lineages. We recommend a taxonomic revision of the complex that takes into account its genetic and phenotypic diversity.
Highlights
Oceanic archipelagos are excellent model systems to study evolution and have been crucial in advancing our understanding of species diversification and ecosystem assembly processes (Emerson, 2002; Losos and Ricklefs, 2009; Warren et al, 2015; Patino et al, 2017; Whittaker et al, 2017)(Leroy et al, 2021)
This leads to species radiations in which phenotypic diversification could be driven either by adaptation to vacant ecological niches and available resources in the different islands (Schluter, 2000; Grant and Grant, 2008; Blanco et al, 2014), or by ge netic drift and sexual selection in geographic isolation (Rundell and Price, 2009), both types of processes can be at work within a single radiation (Gillespie et al, 2020)
We concur with previous studies on this system (Marshall and Baker, 1999; Suarez et al, 2009; Rodrigues et al, 2014; Illera et al, 2016; Perktaset al., 2017; Clement, 2018), on the need for a taxonomic revi sion of this group, and based on their and our results, we propose that the common chaffinch be divided into five different species, corre sponding to Eurasia (Fringilla coelebs), North Africa (Fringilla spodiog enys/africana), Azores (Fringilla moreletti), Madeira (Fringilla maderensis) and the Canary Islands (Fringilla canariensis)
Summary
Oceanic archipelagos are excellent model systems to study evolution and have been crucial in advancing our understanding of species diversification and ecosystem assembly processes (Emerson, 2002; Losos and Ricklefs, 2009; Warren et al, 2015; Patino et al, 2017; Whittaker et al, 2017)(Leroy et al, 2021). Delmore et al, 2020) This leads to species radiations in which phenotypic diversification could be driven either by adaptation to vacant ecological niches and available resources in the different islands (Schluter, 2000; Grant and Grant, 2008; Blanco et al, 2014), or by ge netic drift and sexual selection in geographic isolation (Rundell and Price, 2009), both types of processes can be at work within a single radiation (Gillespie et al, 2020).
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