Current landscape attributes and landscape stability in breeding grounds explain genetic differentiation in a long‐distance migratory bird

Abstract

Numerous studies have highlighted a major role of isolation by both geographic distance and current landscape resistance in controlling bird population genetic differentiation. However, the importance of past landscape features or landscape temporal stability in shaping population genetic structure remains undervalued, particularly in birds. We assessed the role of isolation by landscape resistance – derived from current landscape attributes and measures of landscape stability –, in comparison to geographic isolation, as drivers of genetic differentiation of the Iberian bluethroat (Luscinia svecica azuricollis), a migratory bird whose populations breed in fragmented and dynamic landscapes affected by land use change. First, we characterized bluethroat genetic structure using microsatellite genotypes and evaluated genetic distances. Then, we built species distribution models using as a predictor a time series (two decades) of values of the Normalized Difference Vegetation Index as proxies of recent past landscape stability and current landscape features to ultimately generate landscape resistance values through different functions. Finally, we used maximum‐likelihood population effects models to evaluate the relationships between genetic distances and both geographic and landscape resistance distances. We found a genetic structure of four clusters in the Iberian bluethroats populations, as well as a high level of genetic differentiation. Genetic structure was better associated with landscape resistance, rather than with geographic distance. The highest values of habitat suitability corresponded to areas where vegetation remained mostly stable during the two decades prior to bird surveys, with low annual precipitation and spring temperature, being the relationship between gene flow and presence of intervenient habitat among populations linear or quasi‐linear. Our results suggest that conservation policies and land management practices that promote the maintenance of semi‐open pasture‐shrub mosaics (e.g. through extensive livestock grazing) can strongly benefit Iberian bluethroat populations, improving gene flow and population connectivity.

Landscape characteristics influence regional dispersal in a high‐elevation specialist migratory bird, the water pipit Anthus spinoletta

“…García et al (2021) found evidence of IBR in a long‐distance migrant passerine bird, the bluethroat Luscinia svecica , when investigating more scattered populations over a wider area than in our study. The authors suggested that the known high philopatry of the investigated populations was probably involved in determining the observed restriction in gene flow (García et al, 2021). In fact, despite their high movement capability, dispersal of migratory birds can be restricted by high philopatry (e.g., Ceresa et al, 2016; Hansson et al, 2002), probably due to risks and costs connected to dispersal (e.g., increased mortality, physiological costs; Plissner & Gowaty, 1996; Waser et al, 1994).…”

“…More generally, birds are underrepresented in landscape genetic studies, possibly due to a preconceived assumption of lack of landscape effects on dispersal in this taxon (Kozakiewicz et al, 2018). García et al (2021) found evidence of IBR in a long-distance migrant passerine bird, the bluethroat Luscinia svecica, when investigating more scattered populations over a wider area than in our study. The authors suggested that the known high philopatry of the investigated populations was probably involved in determining the observed restriction in gene flow (García et al, 2021).…”

Morphological differentiation in a migratory bird across geographic gradients in mountains of southern Europe

“…This dataset was used to evaluate: (i) genetic differentiation on the basis of F ST values, as a measure of pairwise genetic distance; and, (ii) genetic structure by means of Rgeneland 4.0.4 (Guillot et al, 2005), a package that applies a Bayesian clustering method to infer a number of clusters (K) of individuals. The achieved four clusters (Figure 1) were already considered in a previous study (García et al, 2020) dealing with the genetic differentiation of the Iberian bluethroat. Further methodological information can also be found in Alda et al (2013).…”

“…The phenotypic (Arizaga et al, 2006;García et al, 2017;Hogner et al, 2013) and genotypic (Johnsen et al, 2006(Johnsen et al, , 2007 variation of this species constitutes a complex subspecific mosaic associated to differences in geographic morphs and life history, where the Iberian breeding bluethroat L. s. azuricollis is considered among the most ancestral forms (Johnsen et al, 2006). This subspecies is distributed across strong geographical and environmental gradients in northwestern Iberian mountains, where it shows a moderate degree of genetic differentiation (Alda et al, 2013;García et al, 2020). Iberian bluethroats breed along an altitudinal gradient ranging from 750 to 2400 m a.s.l., under considerably different climatic conditions (i.e.…”

“…azuricollis is considered among the most ancestral forms (Johnsen et al, 2006). This subspecies is distributed across strong geographical and environmental gradients in northwestern Iberian mountains, where it shows a moderate degree of genetic differentiation (Alda et al, 2013; García et al, 2020). Iberian bluethroats breed along an altitudinal gradient ranging from 750 to 2400 m a.s.l., under considerably different climatic conditions (i.e.…”