Data from: Females drive asymmetrical introgression from rare to common species in Darwin's tree finches

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The consequences of hybridization for biodiversity depend on the specific ecological and evolutionary context in which it occurs. Understanding patterns of gene flow among hybridizing species is crucial for determining the evolutionary trajectories of species assemblages. The recently discovered hybridization between two species of Darwin's tree finches (Camarhynchus parvulus and C. pauper) on Floreana Island, Galápagos, presents an exciting opportunity to investigate the mechanisms causing hybridization and its potential evolutionary consequences under conditions of recent habitat disturbance and the introduction of invasive pathogens. In this study, we combine morphological and genetic analysis with pairing observations to explore the extent, direction and drivers of hybridization and to test if hybridization patterns are a result of asymmetrical pairing preference driven by females of the rarer species (C. pauper). We found asymmetrical introgression from the critically endangered, larger-bodied C. pauper to the common, smaller-bodied C. parvulus, which was associated with a lack of selection against heterospecific males by C. pauper females. Examination of pairing data showed that C. parvulus females paired assortatively while C. pauper females showed no such pattern. This study shows how sex-specific drivers can determine the direction of gene flow in hybridizing species. Furthermore, our results suggest the existence of a hybrid swarm comprised of C. parvulus and hybrid birds. We discuss the influence of interspecific abundance differences and susceptibility to the invasive parasite Philornis downsi on the observed hybridisation and recommend that the conservation of this iconic species group should be managed jointly rather than species-specific.

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Peters et al. GenotypeDataAllele size data for tree finches on Floreana Island, Galapagos "Ring#" refers to the identifier inscribed on an aluminum band around a bird's tarsus. ‘Cluster’ refers to population assignment based on analyses of microsatellite loci using the program STRUCTURE (C. parvulus, Hybrid, C. pauper). Remaining information refers to allele size (maximum height at peak of allele) at each of nine microsatellite loci (Gf01, Gf03, Gf04, Gf05, Gf06, Gf07, Gf11, Gf12, Gf13)Peters et al. MorphologyDataMorphological measurements of tree finches sampled on Floreana Island, Galápagos in 2004, 2005, 2006, 2008, 2010, 2012, 2013 and 2014. Techniques for measuring morphological variables are described in the associated manuscript. ‘Putative population’ refers to assignment based on morphology for exploratory analyses (see associated manuscript and supplementary material). ‘Cluster’ and ‘Membership Coefficient’ refers to population assignment based on analyses of microsatellite loci (using the program STRUCTURE).Peters et al. PairingDataAssortative pairing, genetic and morphological data for male and female tree finches sampled on Floreana Island, Galapagos, 2005, 2010, 2012, 2014 and 2014. Techniques for measuring morphological features are described in the associated manuscript. ‘Cluster’, ‘Cluster_2’ and ‘Membership Coefficient’ refers to population assignment based on analyses of microsatellite loci (using the program STRUCTURE).