Extensive hybridization between two Andean warbler species with shallow divergence in mtDNA

Abstract

Studying processes acting on differentiated populations upon secondary contact, such as hybridization, is important to comprehensively understand how species are formed and maintained over time. However, avian speciation studies in the tropical Andes have largely focused on the role of topographic and ecological barriers promoting divergence in allopatry, seldom examining hybridization and introgression. We describe a hybrid zone involving 2 closely related Andean warblers (Parulidae), the Golden-fronted Redstart (Myioborus ornatus), and the Spectacled Redstart (Myioborus melanocephalus). Geographic ranges of these species abut near the Colombia-Ecuador border and many specimens from the region exhibit intermediate phenotypes, but a formal description of phenotypic variation in the contact zone was heretofore lacking. We collected specimens across a transect encompassing the area where ranges abut and areas where only “pure” parental phenotypes of M. ornatus chrysops and M. melanocephalus ruficoronatus occur. We described variation in plumage traits including patterns of head and ventral coloration and tail markings based on 321 specimens. To describe genetic variation in the contact zone and over a broader phylogeographic context, we used sequences of the mitochondrial ND2 gene for 219 individuals across the transect and the entire range of both species, including all subspecies, from Venezuela to Bolivia. We documented a hybrid zone ~200 km wide based on head coloration, where intermediate plumage phenotypes are most common and “pure” forms do not overlap geographically, consistent with extensive hybridization. Across the range of the M. ornatus–M. melanocephalus complex, mitochondrial genetic structure was shallow, with genetic breaks only coinciding clearly with one topographic feature. Such a low genetic structure is striking given the high diversity in plumage phenotypes and the current taxonomy of the group. Our phenotypic data suggest that barriers to hybridization are not strong, and allow us to postulate hypotheses to be tested using forthcoming genomic data.

Cycad phylogeny predicts host plant use of Eumaeus butterflies

“…Incomplete reproductive isolation between E. minyas and E. godartii is consistent with the short branch lengths subtending these species in the most recent whole‐genome phylogeny (Robbins et al, 2021 ). Indeed, the Cauca valley is known to be a hybrid zone between other species of butterflies, such as Heliconius (Arias et al, 2008 ), and vertebrates such as the Andean warbler (Céspedes‐Arias et al, 2021 ).…”

Geogenomics of montane palms points to Miocene–Pliocene Andean segmentation related to strike‐slip tectonics

“…Thus, in the case of the westcentral groups, genetic grouping pattern did not relate to geographical distance, as individuals of both groups were sampled sometimes in close proximity. Morphological displacement with gene flow has been recently assessed in an Andean bird complex also in southern Colombia (Céspedes‐Arias et al, 2021) but was in that case explained as a result of hybridization between different valid species and not of morphological differentiation within a complex.…”

Cycad phylogeny predicts host plant use ofEumaeusbutterflies

“…Incomplete reproductive isolation between E. minyas and E. godartii is consistent with the short branch lengths subtending these species in the most recent whole-genome phylogeny (Robbins et al, 2021). Indeed, the Cauca valley is known to be a hybrid zone between other species of butterflies, such as Heliconius (Arias et al, 2008) and vertebrates, such as the Andean warbler (Céspedes-Arias et al, 2021).…”