Morphological divergence among Spanish Common Crossbill populations and adaptations to different pine species

Abstract

Crossbills (Loxia spp.) provide a classical avian model of ecological specialization on food resources. Previous studies have suggested that morphometric, genetic and vocal diversification among Common Crossbill Loxia curvirostra populations is better explained by ecological distance (use of different conifers) than by geographical distance, indicating that populations have diverged adaptatively. We tested for adaptive divergence in Iberian crossbills using bill and body size measurements of 6082 crossbills from 27 sites, each consisting of a dominant or single pine (Pinus) of four possible species. Crossbills using different pines differed significantly in body size and bill size and shape. There was no correlation between geographical and morphological distance among sampling sites, consistent with the hypothesis that the morphological divergence of Iberian crossbills is shaped by their ecological differences (foraging on alternative conifers) rather than geographical distance. However, for unknown reasons, Common Crossbills foraging on Pinus sylvestris in Iberia have on average much smaller bills than Parrot Crossbills Loxia pytyopsittacus feeding on the same pine species in northern Europe. The extent to which crossbills specialize on Iberian P. sylvestris remains to be established. Specialization on conifers with overlapping geographical distributions may be facilitated by matching habitat choice of crossbills as a function of their local intake rates.

Habitat‐linked genetic variation supports microgeographic adaptive divergence in an island‐endemic bird species

“…Variations in bill morphology related to habitat gradients have been observed in several bird species and have been attributed to differences in local foraging substrates (Alonso et al, 2020; Badyaev et al, 2008; Benkman, 1993, 2003). Both bill depth and length have been shown to respond rapidly to selection due to food resource availability (Grant & Grant, 1993, 2002).…”

“…differences in local foraging substrates(Alonso et al, 2020; Badyaev F I G U R E 3 Results of GEA and GWA of 123 island scrub-jays. (a) Ordination plot of RDA showing the habitat-linked (pine vs. oak) genetic divergence.…”

Ecological niche divergence or ecological niche partitioning in a widespread Neotropical bird lineage

“…These populations have niches within the broader Progne subis niche reminiscent of other extant species occupying subsets of the broader Progne niche elsewhere ( e.g., P. murphyi and P. sinaloae ), further supporting the notion of niche partitioning and niche specialization across a geographic mosaic, as opposed to significant ecological niche evolution leading to large ecological shifts. Diversification via niche partitioning of a broader ancestral state may be more common than is realized in continental taxa, given the propensity of groups like Zosterops to undergo taxon cycles in montane regions (Ricklefs & Cox, 1972; Melo, Warren & Jones, 2011; Pearson & Turner, 2017; Engler et al, 2021), and the propensity for related populations to partition and specialize on different food sources across space and time (Benkman et al, 2009; Cenzer, 2016; Alonso et al, 2020).…”

Morphology of migration: Associations between wing, and bill morphology and migration in kingbirds (Tyrannus)

“…For example, specific bill shapes could accommodate spatiotemporal changes in the competitive landscape (Navalón et al , 2019) or provide increased stability for prey capture in perch-gleaning or hover-gleaning foraging techniques (Fitzpatrick, 1985; Fitzpatrick et al , 2004; Botero-Delgadillo, 2011; Botero-Delgadillo & Bayly, 2012). The diversity of habitats that migratory taxa encounter during their annual cycle may shape phenotypes in more complex ways than previously thought, and techniques that incorporate more advanced characterizations of morphological variation may expose novel insight into how movement life history strategies shape phenotypes (e.g., Pol et al , 2009; Mallarino et al , 2011; Navalón et al , 2019; Alonso et al , 2020; Medina et al , 2020).…”