The Tyrant-flycatchers are the largest family of birds, containing more than 400 species. They occur throughout North and South America. Despite the large amount of species, hybridization has only been recorded in a few genera.
Pied-crested Tit-tyrant (A. reguloides) and Black-crested Tit-tyrant (A. nigrocristatus) interbreed in central Peru. Phenotypic traits and genetic markers showed steep clines acroos the hybrid zone, indicating strong selection against hybrids. Detailed analyses suggest that Black-crested Tit-tyrant is more resistant to high-altitude hypoxic stress. This specialization might, in combination with competitive exclusion, isolate the species despite interbreeding (Dubay & Witt, 2014).
The Neotropical Flycatchers Elaenia display a complicated pattern of nuclear and mitochondrial polyphyly. This can be attributed to the interplay of three factors: (i) faulty taxonomy, (ii) late Pleistocene hybridization, and (iii) incomplete lineage sorting (Rheindt, Christidis & Norman, 2009). Further analyses uncovered two putative hybridization events: one between yellow-bellied elaenia (E. flavogaster) and members of a subgroup with three species: small-billed elaenia (E. parvirostris), brownish elaenia (E. pelzelni) and large elaenia (E. spectabilis), and one between white-crested elaenia (E. albiceps) and small elaenia (E. pallantangae). The latter case is supported by recent reports of hybrids between these species in Ecuador and Bolivia (Tang et al. 2018).
Allozyme analyses of the Pacific-slope Flycatcher (E. difficilis) complex revealed moderately high levels of genes flow among mainland populations (Johnson & Marten, 1988). It also led to the elevation of Cordilleran Flycatcher (E. occidentalis) to species status. This decision is questioned by Rush et al. (2009), following a genetic analyses of a hybrid zone between these species.
Willow Flycatcher (E. traillii) and Alder Flycatcher (E. alnorum) live sympatrically, but do not seem to interbreed. Two genetic studies failed to detect hybridization (Seutin & Simon, 1988; Winker, 1994).
Intergeneric hybrids between Willow Flycatcher (E. traillii) and Eastern Wood Pewee (Contopus virens) have also been recorded (Short Jr & Burleigh, 1965).
The Dusky-capped Flycatcher (M. tuberculifer) is taxonomically challenging and comprises up to 13 recognized subspecies. Paraphyly in mtDNA of certain subspecies can be attributed to hybridization and/or recent divergence (Joseph & Wilke, 2004).
The Suiriri Flycatcher (S. suiriri) is represented by three distinct forms that occur in parapatry (suiriri, affinis and bahiae). At several locations, affinis hybridizes with suiriri. The intermediate size and increased plumage variability of bahiae resembles affinis x suiriri hybrids, and that bahiae might be of hybrid origin (Hayes, 2001).
A population of Peruvian Tyrannulet (Zimmerius viridiflavus) has been described a mosaic, because it vocally and biometrically resembles conspecifics from other populations, but also shares plumage characteristics with another species Golden-faced Tyrannulet (Z. chrysops). Genetic analyses revealed low levels of gene flow from the northern into the mosaic population (Rheindt et al., 2014).
Dubay, S. G. & Witt, C. C. (2014). Differential high-altitude adaptation and restricted gene flow across a mid-elevation hybrid zone in Andean tit-tyrant flycatchers. Molecular Ecology 23, 3551-3565.
Hayes, F. E. (2001). Geographic variation, hybridization, and the leapfrog pattern of evolution in the Suiriri Flycatcher (Suiriri suiriri) complex. Auk 118, 457-471.
Johnson, N. K. & Marten, J. A. (1988). Evolutionary Genetics of Flycatchers .2. Differentiation in the Empidonax-Difficilis Complex. Auk 105, 177-191.
Joseph, L. & Wilke, T. (2004). When DNA throws a spanner in the taxonomic works: testing for monophyly in the Dusky-capped Flycatcher, Myiarchus tuberculifer, and its South American subspecies, M-t. atriceps. Emu 104, 197-204.
Rheindt, F. E., Christidis, L. & Norman, J. A. (2009). Genetic introgression, incomplete lineage sorting and faulty taxonomy create multiple cases of polyphyly in a montane clade of tyrant-flycatchers (Elaenia, Tyrannidae). Zoologica Scripta 38, 143-153.
Rheindt, F. E., Fujita, M. K., Wilton, P. R. & Edwards, S. V. (2014). Introgression and Phenotypic Assimilation in Zimmerius Flycatchers (Tyrannidae): Population Genetic and Phylogenetic Inferences from Genome-Wide SNPs. Systematic Biology 63, 134-152.
Rush, A. C., Cannings, R. J. & Irwin, D. E. (2009). Analysis of multilocus DNA reveals hybridization in a contact zone between Empidonax flycatchers. Journal of Avian Biology 40, 614-624.
Seutin, G. & Simon, J. P. (1988). Genetic-Variation in Sympatric Willow Flycatchers (Empidonax-Traillii) and Alder Flycatchers (Empidonax-Alnorum). Auk 105, 235-243.
Short Jr, L. & Burleigh, T. (1965). An intergeneric hybrid flycatcher (Contopus X Empidonax) from Idaho. Proc. Biol. Soc. Washington 78, 33-37.
Tang, Q., Edwards, S.V. & Rheindt, F.E. (2018) Rapid diversification and hybridization have shaped the dynamic history of the genus Elaenia. Molecular Phylogenetics and Evolution.
Winker, K. (1994). Divergence in the Mitochondrial-DNA of Empidonax-Traillii and E-Alnorum, with Notes on Hybridization. Auk 111, 710-713.