The evolutionary history and genomics of European blackcap migration

Abstract

Seasonal migration is a taxonomically widespread behaviour that integrates across many traits. The European blackcap exhibits enormous variation in migration and is renowned for research on its evolution and genetic basis. We assembled a reference genome for blackcaps and obtained whole genome resequencing data from individuals across its breeding range. Analyses of population structure and demography suggested divergence began ~30,000 ya, with evidence for one admixture event between migrant and resident continent birds ~5000 ya. The propensity to migrate, orientation and distance of migration all map to a small number of genomic regions that do not overlap with results from other species, suggesting that there are multiple ways to generate variation in migration. Strongly associated single nucleotide polymorphisms (SNPs) were located in regulatory regions of candidate genes that may serve as major regulators of the migratory syndrome. Evidence for selection on shared variation was documented, providing a mechanism by which rapid changes may evolve.

Seasonal migration as a life history trait facilitating adaptation to climate change

“…This supports the hypothesis that variation in the occurrence of seasonal migration represents an adaptive response to temporal variation in climate and its influence on resource availability and osmotic and/or thermal stress. Moreover, the close correspondence of our empirical climate niche model with observed patterns of spatial variation seasonal migration in BC imply that this variation is shaped by natural selection (e.g., Arcese et al, 2002; Peters et al, 2017; Reid et al, 2018; Delmore et al, 2020).…”

“…Song sparrows also vary predictably in traits widely recognized as adaptations to climatic variation in seasonality and primary production (Saether et al, 2016) including migratory, territorial, dispersal, and breeding behaviors, and demographic traits linked to fecundity, parental effort, and longevity (Arcese, 1989;Arcese et al, 2002;Germain & Arcese, 2014;Tarwater & Arcese, 2017;Reid & Arcese, 2020). Because many such traits have an additive genetic basis (e.g., Schluter & Smith, 1986;Wolak & Reid, 2016;Reid & Arcese, 2020), it is plausible that spatial variation in natural selection has contributed to heritable variation in migratory phenotype, as extensively described in European blackcaps (Sylvia atricapilla; e.g., Berthold, 1991;Berthold & Pulido, 1994;Delmore et al, 2020). If so, the pace of adaptation to climate warming in song sparrows might first be measured as the rate by which residency has become established in local populations known to have been migrants historically, and secondarily by estimating the rate of change in allele frequencies at functional loci (Rellstab et al, 2016;Capblancq et al, 2020).…”

Individual variability and versatility in an eco-evolutionary model of avian migration

“…Additional work is needed to investigate this idea, including direct observations of mated pairs and their offspring in the divide. We also note that genetic differentiation across this divide is low [18,[48][49][50]. However, the genetic work on this system has largely focused on allopatric populations distant from the divide [18,20,50,51].…”

Ecological and geographical marginality in rear edge populations of Palaearctic forest birds

“…We acknowledge that this classification can offer a simplified view of the actual differentiation of species and that further studies could alter some aspects of the taxonomical proposal in Clements et al, (2019). For example, while the specific differentiation of Cyanistes (Illera et al, 2011) and the subspecific division of Fringilla (Svensson, 2015) has been recently tested, it seems that the African population of Sylvia atricapilla may differ from European population (Delmore et al, 2020). However, despite the uncertainties, our results do not support that endemic birds fail to adjust the predictions of the centre–periphery hypothesis.…”