Wrens are small, brownish passerine birds that occur mainly in the New World. Only the Eurasian Wren (Troglodytes troglodytes) occurs in the Old World. Hybridization has been documented in four genera, namely Campylorhynchus, Cantorchilus, Troglodytes and Henicorhina.
The Rufous-naped Wren (C. rufinucha) is divided over three distinct genetic lineages, two of which interbreed in a secondary contact zone in Central America (Vazquez-Miranda, Navarro-Siguenza & Omland, 2009). This contact zone was already described by Selander (1965). Analysis of song characteristics corresponds with distribution of the three lineages (Sosa-Lopez, Mennill & Navarro-Siguenza, 2013).
In Ecuador, two hybridizing subspecies of the Gray-breasted Wood-wren (H. leucophrys) display song divergence (Dingle, Halfwerk & Slabbekoorn, 2008). The subspecies showed an asymmetric response to playback experiments; one subspecies responded more to the songs of its own subspecies, while the other responded equally strong to songs of both subspecies (Dingle et al., 2010). This asymmetry could affect assortative mating and possible gene flow. In Colombia, a similar situation revealed no evidence for hybridization (Burbidge et al., 2015; Caro et al., 2013). This might be an example of parallel evolution in phenotypic traits involving Gray-breasted Wood-wren.
Winter Wren (Troglodytes hiemalis) and the Pacific Wren (T. pacificus) diverged more than four million years ago, but still interbreed. However, first-generation hybrids have practically zero reproductive success (Mikkelsen & Irwin, 2021).
The Bay Wren (T. nigricapillus) is distributed from Costa Rica to Ecuador and comprises seven subspecies. Mitochondrial DNA confirms the morphological patterns and the recognition of two groupings, “castaneus” and “nigricapillus”. Morphological intergradation takes place between these two groups in Panama, but all intergrades possess mtDNA of the castaneus group, suggesting gene flow from west to east (Gonzalez et al., 2003).
Burbidge, T., Parson, T., Caycedo-Rosales, P. C., Cadena, C. D. & Slabbekoorn, H. (2015). Playbacks revisited: asymmetry in behavioural response across an acoustic boundary between two parapatric bird species. Behaviour 152, 1933-1951
Caro, L. M., Caycedo-Rosales, P. C., Bowie, R. C. K., Slabbekoorn, H. & Cadena, C. D. (2013). Ecological speciation along an elevational gradient in a tropical passerine bird? Journal of Evolutionary Biology 26, 357-374.
Dingle, C., Halfwerk, W. & Slabbekoorn, H. (2008). Habitat-dependent song divergence at subspecies level in the grey-breasted wood-wren. Journal of Evolutionary Biology 21, 1079-1089.
Dingle, C., Poelstra, J. W., Halfwerk, W., Brinkhuizen, D. M. & Slabbekoorn, H. (2010). Asymmetric Response Patterns to Subspecies-Specific Song Differences in Allopatry and Parapatry in the Gray-Breasted Wood-Wren. Evolution 64, 3537-3548.
Gonzalez, M. A., Eberhard, J. R., Lovette, I. J., Olson, S. L. & Bermingham, E. (2003). Mitochondrial DNA phylogeography of the Bay Wren (Troglodytidae : Thryothorus nigricapillus) complex. Condor 105, 228-238.
Mikkelsen, E. K., & Irwin, D. (2021). Ongoing production of low‐fitness hybrids limits range overlap between divergent cryptic species. Molecular Ecology, 30(16), 4090-4102.
Selander, R. K. (1965). Hybridization of Rufous-Naped Wrens in Chiapas Mexico. Auk 82, 206-&.
Sosa-Lopez, J. R., Mennill, D. J. & Navarro-Siguenza, A. G. (2013). Geographic variation and the evolution of song in Mesoamerican rufous-naped wrens Campylorhynchus rufinucha. Journal of Avian Biology 44, 27-38.
Vazquez-Miranda, H., Navarro-Siguenza, A. G. & Omland, K. E. (2009). Phylogeography of the Rufous-Naped Wren (Campylorhynchus Rufinucha): Speciation and Hybridization in Mesoamerica. Auk 126, 765-778.