The ghost of connections past: A role for mainland vicariance in the isolation of an insular population of the red‐billed chough (Aves: Corvidae)

Abstract

Aim Oceanic islands have often been colonized by small groups of individuals dispersing from the nearest mainland, giving rise to insular populations characterized by locally adapted phenotypes and low genetic diversity. Alternatively, due to past geo‐climatic changes, the present‐day distribution of the species may not correspond to that found at the time of the original colonization so that the current mainland distribution may not include the original source area, leading to erroneous assumptions regarding colonization history. Here, we use patterns of genetic variation to evaluate alternative colonization scenarios of an insular passerine in the Canary Islands. Location La Palma (Canary Islands), Northern Africa and the Iberian Peninsula. Taxon Red‐billed chough (Pyrrhocorax pyrrhocorax). Methods We use phylogeographical and coalescent analyses of mitochondrial DNA sequences and 10 microsatellite loci, together with Bayesian demographic modelling, to determine whether choughs on the island of La Palma originate from (a) present‐day populations in Iberia, (b) present‐day populations in the mountains of inland Morocco or (c) former populations in coastal Morocco, where suitable habitat existed in the past. Results Both the mitochondrial and nuclear datasets indicate that the chough population on La Palma is genetically well differentiated from those in Iberia and Morocco, and that La Palma choughs are more closely related to choughs in Iberia than to those in Morocco. Genetic diversity in La Palma is lower than that of mainland populations, but shows no evidence of past bottlenecks. The best supported demographic model to explain the origin of La Palma choughs that is congruent with both genetic datasets includes a ‘ghost’ population closely related to Iberia, from which the insular population diverged within the last 30,000 years. Main conclusions Our results are most consistent with the existence of a former connection between La Palma and Iberia along the North African coast, when suitable habitat was found there. Subsequent desertification of these coastal areas led to local extinctions that restricted gene flow between Iberia and the islands, promoting genetic differentiation. Our results provide a counterintuitive solution to a biogeographical enigma, and could help resolve the colonization history of other systems with similarly complex climatic pasts.

Genetic diversity, differentiation and historical origin of the isolated population of rooks Corvus frugilegus in Iberia

“…Many corvids are widely distributed throughout temperate and boreal zones of Europe, Siberia and north Africa, and they represent excellent study systems for phylogeographic studies on western Palearctic birds (Haring et al 2007, de Knijff 2014, Poelstra et al 2014, Vijay et al 2016, Knief et al 2019, Kryukov 2019, Morinha et al 2020). Several genetic studies suggest that Pleistocene glacial cycles have played a major role in diversification and speciation, and a variety of geographical patterns of population structure indicates that the genetic basis of speciation is highly species‐specific and context‐dependent (Haring et al 2007, Kryukov 2019).…”

“…Populations in these former glacial refugia in the south have often survived to the present, and some have subsequently evolved as isolated lineages (Fok et al 2002, Kryukov et al 2004, Haring et al 2007, 2012, Zhang et al 2012). Alternatively, currently isolated populations in southern regions may have originated as a consequence of recent population fragmentation caused by environmental changes not related with glaciations, with or without subsequent gene flow, which have often led to range contraction and demographic declines in isolated populations of many species in Europe and North Africa (Agudo et al 2011, Wenzel et al 2012, Graciá et al 2015, Morinha et al 2020). In addition, disjunct distributions and population isolation in southern regions may occur through pre‐Pleistocene processes, recent colonization from main distribution nuclei in northern latitudes or southern distribution, and through re‐colonization of former glacial refugia (Klicka and Zink 1997, Sanmartín 2003, Zink et al 2004, Gómez and Lunt 2007).…”

Convergent evolution on oceanic islands: comparative genomics reveals species-specific processes in birds

“…We sampled mainland populations of the common chaffinch (Fringillidae: Fringilla coelebs) and the redbilled chough (Corvidae: Pyrrhocorax pyrrhocorax) in the Iberian Peninsula at Segovia and Los Monegros, respectively (see (60,61). The insular populations from both species were sampled in La Palma, the most north-western island of the Canary Islands archipelago (Fig.…”

Convergent evolution on oceanic islands: comparative genomics reveals species-specific processes in birds

“…We sampled mainland populations of the common chaffinch (Fringillidae: Fringilla coelebs) and the redbilled chough (Corvidae: Pyrrhocorax pyrrhocorax) in the Iberian Peninsula at Segovia and Los Monegros, respectively (see , Morinha et al 2020. The insular populations from both species were sampled in La Palma, the most north-western island of the Canary Islands archipelago (Fig.…”

“…We selected four passerine species that have mainland populations and have also colonized oceanic islands; two species from mainland Europe that have colonized the island of La Palma in the Canary Islands, Atlantic Ocean, the common chaffinch (Fringilla coelebs/canariensis) and the red-billed chough (Pyrrhocorax pyrrhocorax), and two species from North America that have colonized Guadalupe Island on the Pacific Ocean, the house finch (Haemorhous mexicanus) and the dark-eyed junco (Junco hyemalis/insularis). The red-billed chough and the house finch have diverged from mainland populations within the last 100,000 years, whereas the common chaffinch and the junco have been separated from their mainland relatives for over 500,000 years (Aleixandre et al, 2013;Morinha et al, 2020;. Given that all four species have colonized oceanic islands and have been subjected to potentially similar selective pressures, we first analyzed if the differences phenotype between insular and mainland counterparts affected the same traits across species.…”