Evolutionary dynamics of hybridization and introgression following the recent colonization of Glossy Ibis (Aves: Plegadis falcinellus) into the New World

Abstract

Geographic range shifts can cause secondary contact and hybridization between closely related species, revealing mechanisms of species formation and integrity. These dynamics typically play out in restricted geographic regions, but highly vagile species may experience major distributional changes resulting in broad areas of contact. The Glossy Ibis (Plegadis falcinellus) is a dispersive waterbird of the Old World and Australia that colonized eastern North America in the early 19th century and came into contact with the native White‐faced Ibis (P. chihi). Putative hybrids between the two species have been observed across North America. To examine the population genomic consequences of this natural invasion, we sequenced 4,616 ultraconserved elements from 66 individuals sampled across the distributions of falcinellus, chihi, and the Puna Ibis (P. ridgwayi) of South America. We found genomic differentiation among the three species. Loci with high sequence divergence were often shared across all pairwise species comparisons, were associated with regions of high nucleotide diversity, and were concentrated on the Z chromosome. We detected signals of genetic admixture between chihi and falcinellus in individuals both near and far from their core area of sympatry. Genomic cline analyses revealed evidence of greater introgression into falcinellus from chihi, but we found little evidence for selection against hybrids. We also found signals of admixture between ridgwayi and South American populations of chihi. Our results indicate vagile species can experience pervasive introgression upon secondary contact, although we suggest these dynamics may be more ephemeral than the stable hybrid zones often observed in less dispersive organisms.

The Spatial Signature of Introgression After a Biological Invasion With Hybridization

“…A well-documented pattern is the expected asymmetric introgression between local and invasive organisms, with small levels of introgression into the local organisms and considerable introgression in the invasive organisms (Currat et al, 2008;Excoffier et al, 2014;Quilodrán et al, 2019). There are many examples following this pattern in both plant and animal kingdoms (e.g., Duminil et al, 2006;Darling et al, 2014;Oswald et al, 2019). This pattern is influenced by three main factors.…”

Locus-specific introgression in young hybrid swarms: drift dominates selection

“…For comparison, many studies of hybridization that have used bgc have not found significant β estimates. For example, a recent study of ibis hybridization using diagnostic markers found no significant negative β SNPs, in spite of the ibis hybrid zone probably only being 60 or so years old (Oswald et al 2019). In contrast, a study of recent sole (Solea aegyptiaca x S. senegalensis) hybridization found 52% of all loci exhibited an extreme β value, with 26% of all loci exhibiting a negative β estimate (Souissi et al 2018).…”

Plegadis ridgwayi (J.A. Allen, 1876) (Aves, Threskiornithidae): range extension and a new country record for Ecuador

“…The dynamics of the recent previous records from the northern coast of Peru (Chávez-Villavicencio 2007;Angulo-Pratolongo et al 2010;Parra and Callán 2011;Rivas et al 2013), in addition to the sightings in Ecuador (Ahlman 2015;herein), suggest that P. ridgwayi may be expanding its geographic distribution beyond its historical area of occupancy (Chávez-Villavicencio 2007;Schulenberg et al 2010). Oswald et al (2019) proposed that the expansion of the geographic distribution of P. ridgwayi along the Peruvian coast during the last century is likely a result of the nomadic nature of this species in addition to anthropogenic modifications of the landscape, namely the application of large-scale irrigation practices and the increase of open habitats. Elphick (2010) and Toral et al (2012) have also shown that flooded crops, such as rice fields, provide alternative habitats for a number of waterbirds, including the genus Plegadis.…”