Today, I would like to discuss two papers on hybridization in woodpeckers. The first paper provides the description of a cross between two species in Paraguay. The second study concerns a genomic analysis of hybrid zones between three Sphyrapicus species.
Andrés Oscar Contreras Chialchia and Paul Smith provide a detailed description of a hybrid between Cream-backed Woodpecker (Campephilus leucopogon) and Crimson-crested Woodpecker (C. melanoleucus), two species that co-occur along the banks of the Paraná River in Paraguay. Because one picture says more than a thousand words: here is the hybrid specimen alongside the parental species. You can clearly recognize traits of both species. For example, the black-and-white spot on the cheek and the creamy back of the Cream-backed Woodpecker and the striped belly of the Crimson-crested Woodpecker.
Sapsucker Hybrid Zones
Three species of Sphyrapicus woodpeckers – Red-breasted Sapsucker (S. ruber), Red-naped Sapsucker (S. nuchalis) and Yellow-bellied Sapsucker (S. varius) – interbreed in several hybrid zones. Red-breasted and Red-naped Sapsucker are more closely related to each other compared to the third species. This situation provides an excellent setting to study the build-up of reproductive isolation and genetic differentiation over time.
Christine Grossen and her colleagues examined over 30 000 genetic markers (Single Nucleotide Polymorphisms or SNPs) along hybrid zones in the Coast Mountains and Rocky Montains. The genomic analyses showed that the tree species are clearly distinct with a small number of hybrids in each hybrid zone. This indicates that there is moderately strong reproductive isolation between them.
There were no large regions of differentiation in the genome (so-called ‘genomic islands of differentiation’). However, the authors uncovered 19 small regions of differentiation, some of which were shared between species. One of those regions contained a candidate locus associated with plumage, which could contribute to reproductive isolation.
The authors conclude that ‘[o]ur comparative analysis of species pairs of different age and their hybrid zones showed that moderately strong reproductive isolation can occur with little genomic differentiation, but that reproductive isolation is incomplete even with much greater genomic differentiation, implying there are long periods of time when hybridization is possible if diverging populations are in geographic contact.’
Chialchia, A. O. C. & Smith, P. (2014). A notable hybrid woodpecker (Campephilus leucopogon x C. melanoleucus)(Aves: Picidae) from Paraguay. ORNITOLOGIA NEOTROPICAL 25, 459-464.
Grossen, C., Seneviratne, S. S., Croll, D. & Irwin, D. E. (2016). Strong reproductive isolation and narrow genomic tracts of differentiation among three woodpecker species in secondary contact. Molecular ecology 25, 4247-4266.
Both papers have been added to the Piciformes page.