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

Species living in high mountain areas are currently threatened by climate change and human land use changes. High-elevation birds frequently inhabit island-like suitable patches around mountain peaks, and in such conditions the capability to exchange individuals among patches is crucial to maintain gene flow. However, we lack information regarding the dispersal ability of most of these species and the possible influence of landscape features on dispersal. In this study, we used population genomics and landscape resistance modelling to investigate dispersal in a high-elevation specialist migratory bird, the water pipit Anthus spinoletta. We aimed to assess the levels of gene flow in this species within a wide area of the European Alps, and to assess the effects of environmental characteristics on gene flow, by testing the isolation by distance (IBD) hypothesis against the isolation by resistance (IBR) hypothesis. We found clear support for IBR, indicating that water pipits preferentially disperse across suitable breeding habitat (i.e., high-elevation grassland). IBR was stronger in the part of the study area with less extended suitable habitat. Landscape resistance was slightly better described by habitat suitability models than landscape connectivity models. Despite the observed IBR, gene flow within the study area was high, probably also because of the still wide and relatively continuous breeding range. The forecasted reduction of range of this species may lead to stronger effects of IBR on gene flow. Other high-elevation specialist birds may show similar IBR patterns, but with possibly stronger effects on gene flow because of their more reduced and patchy habitats.

A molecular phylogeny of the Sylvia cantillans complex: cryptic species within the Mediterranean basin.

The subalpine warbler Sylvia cantillans is formally considered a polytypic species, with four subspecies, European S. c. cantillans, albistriata, moltonii (recently resumed name: subalpina) and North African S. c.inornata. They are very similar in external morphology but clearly differ in their vocalizations. We evaluated their uncertain taxonomic status reconstructing the phylogenetic and phylogeographic relationships among populations sampled across major biogeographical areas in the European species' range, using nucleotide sequences of the mitochondrial cytochrome b gene (mtDNA cyt b). A variety of phylogenetic analyses concordantly led to identify four major groups, only partially corresponding to the three European nominal subspecies. Phylogenetic trees showed a monophyletic group including all moltonii individuals, well diverged from all other taxa. Populations taxonomically assigned to cantillans were polyphyletic being split into two distinct clades (western and southern cantillans), with monophyletic albistriata closely related to southern cantillans. Individuals of moltonii and southern cantillans sampled in sites of sympatry in central Italy were assigned to their respective groups, with perfect concordance between phenotypic and genetic identifications. All findings indicate that moltonii should be ranked as a distinct species. Former subspecies cantillans is polyphyletic, but additional data are needed to define the taxonomic status of its two clades. Albistriata is phylogenetically related to southern cantillans and should be provisionally kept as a subspecies of S. cantillans. The cantillans complex thus provides an interesting case-study illustrating geographical structuring across small geographical ranges, and it exemplifies speciation through differentiation in allopatry leading to reproductive isolation after a secondary contact.