Implications for Evolutionary Trends From the Pairing Frequencies Among Golden-Winged and Blue-Winged Warblers and Their Hybrids

Abstract

Extensive range loss for the Golden-winged Warbler (Vermivora chrysoptera) has occurred in areas of intrusion by the Bluewinged Warbler (V. cyanoptera) potentially related to their close genetic relationship. We compiled data on social pairing from nine studies for 2,679 resident Vermivora to assess evolutionary divergence. Hybridization between pure phenotypes occurred with 1.2% of resident males for sympatric populations. Pairing success rates for Golden-winged Warblers was 83% and for Blue-winged Warblers was 77%. Pairing success for the hybrid Brewster's Warbler was significantly lower from both species at 54%, showing sexual selection against hybrids. Backcross frequencies for Golden-winged Warblers at 4.9% was significantly

Extensive historical and contemporary hybridization suggests premating isolation in Vermivora warblers is not strong: A reply to Confer et al.

“…Fieldwork on these birds is challenging, but a number of research teams have monitored pairs and examined nesting success under natural conditions. Confer et al (2020) aggregate these field data from multiple studies to present an analysis of social pairing patterns in Vermivora, with the stated goal of providing greater insights into the extent of reproductive isolation in areas of breeding sympatry.…”

“…We structure our critique in three parts and conclude with a more nuanced and comprehensive interpretation of hybridization and reproductive isolation in Vermivora warblers. Confer et al (2020) focus on "primary hybridization," which they describe as the mating of "genetically pure" V. chrysoptera and V. cyanoptera. In this system, several classes of hybrids have plumage characteristics distinct from both parental types and have traditionally been named (e.g., "Brewster's warbler" is a hybrid phenotype long associated with typical first-generation [F 1 ] hybrids).…”

“…In our reply, we show that this finding is not supported by other lines of evidence, and significant drawbacks of their study design preclude such strong conclusions. In our critique, we show that (a) coarsescale plumage classifications cannot be used to accurately estimate hybrid ancestry in Vermivora; (b) extra-pair paternity is very high in Vermivora and is likely facilitating hybridization, yet was not considered by Confer et al (2020), and we suggest this will have a substantial influence on the interpretation of reproductive isolation in the system; and…”

“…Recent genetic data from Vermivora also suggest hybrid ancestry cannot be accurately predicted from plumage traits alone, and several of these traits change with age (Baiz et al 2020). Ancestry analysis from Baiz et al (2020) found that none of the six "Brewster's" warblers analyzed were F 1 hybrids, refuting the assumptions of Confer et al (2020) that "Brewster's" warblers are the direct products of "primary hybridization." Moreover, all of the "pure" parental phenotypes sequenced by Toews et al (2016) showed extensive genomic homogeneity, suggesting high rates of historical introgression and little evidence that genomically "pure" V. chrysoptera and V. cyanoptera actually exist.…”

“…(Ecology and Evolution, 10, 2020). Confer et al (2020) aggregate data from multiple studies of social pairing between Vermivora chrysoptera and V. cyanoptera, two wood…”