The Cardinals are found in North and South America. Hybridization occurs in several genera, such as Piranga, Spiza, Cardinalis, Saltator, Cyanocompsa, Pheuticus and Passerina. The latter two have been studied in greater detail.
This genus contains seven species, of which some are known to hybridize. Early on, these hybrids were reported, for example:
- Indigo Bunting (P. cyanea) x Lazuli Bunting (P. amoena) (Brechenridge, 1930; Youngworth, 1932)
- Indigo Bunting (P. cyanea) x Painted Bunting (P. ciris) (Taylor, 1974)
- Varied Bunting (P. versicolor) x Painted Bunting (P. ciris) (Storer, 1961)
The most studied hybrid zone between Indigo Bunting and Lazuli Bunting is located on the Great Plains in Northern America (Kroodsma, 1975; Sibley & Short, 1959). Comparison of sympatric and allopatric populations revealed that birds from sympatric populations responded stronger to heterospecific plumage and song cues compared to individuals from allopatric populations (Emlen, Rising & Thompson, 1975). Playback experiments indicated that this reaction is mainly determined by syllabic cues (Baker, 1991).
In an experimental setting, it was shown that mate choice is assortative (Baker, 1996; Baker & Baker, 1990), even after an exposure of 25 days to heterospecific cues (Baker, 1994). This conclusion was confirmed in a field study over four years, birds mated according to plumage and song index. In addition, hybrids showed lower reproductive success (Baker & Boylan, 1999).
Matthew D. Carling provided a genetic perspective on this hybrid zone. Based on mtDNA, it appears that the hybrid zone is shifting westward and narrowing, which is consistent with reinforcement theory (Carling & Zuckerberg, 2011). The speciation of the Buntings is characterized by postdivergence gene flow that is mainly driven by autosomal loci (Carling, Lovette & Brumfield, 2010). Furthermore, introgression is lower in Z-linked loci and mtDNA, as predicted by Haldane’s Rule (Carling & Brumfield, 2008). Detailed analysis of the sex chromosome identified a candidate gene for speciation, VLDLR9, which is related to egg-laying capacity in chickens (Carling & Brumfield, 2009).
Rose-breasted Grosbeak (P. ludovicianus) and Black-headed Grosbeak (P. melanocephalus) hybridize on the Great Plains in Northern America (Swenk, 1936). This hybrid zone has been described across different US states, namely Nebraska (West, 1962), South Dakota (Anderson & Daugherty, 1974) and North Dakota (Kroodsma, 1974). Recent genetic analyses showed that the hybrid zone has remained stable and narrow, which indicates selection against hybrids and led the authors to classify the hybrid zone as a tension zone (Mettler & Spellman, 2009).
Anderson, B. W. & Daugherty, R. J. (1974). Characteristics and reproductive biology of Grosbeaks (Pheucticus) in the hybrid zone in South Dakota. Wilson Bulletin 86, 1-11.
Baker, M. C. (1991). Response of Male Indigo and Lazuli Buntings and Their Hybrids to Song Playback in Allopatric and Sympatric Populations. Behaviour 119, 225-242.
Baker, M. C. (1994). Does Exposure to Heterospecific Males Affect Sexual Preferences of Female Buntings (Passerina). Animal Behaviour 48, 1349-1355.
Baker, M. C. (1996). Female Buntings from hybridizing populations prefer conspecific males. Wilson Bulletin 108, 771-775.
Baker, M. C. & Baker, A. E. M. (1990). Reproductive-Behavior of Female Buntings – Isolating Mechanisms in a Hybridizing Pair of Species. Evolution 44, 332-338.
Baker, M. C. & Boylan, J. T. (1999). Singing behavior, mating associations and reproductive success in a population of hybridizing Lazuli and Indigo Buntings. Condor 101, 493-504.
Brechenridge, W. J. (1930). A Hybrid Passerina: Passerina Cynaea Passerina Amoena. Occ. Pap. Univ. Minn. Mus. Nat. Hist 3, 39-40.
Carling, M. D. & Brumfield, R. T. (2008). Haldane’s Rule in an Avian System: Using Cline Theory and Divergence Population Genetics to Test for Differential Introgression of Mitochondrial, Autosomal, and Sex-Linked Loci across the Passerina Bunting Hybrid Zone. Evolution 62, 2600-2615.
Carling, M. D. & Brumfield, R. T. (2009). Speciation in Passerina buntings: introgression patterns of sex-linked loci identify a candidate gene region for reproductive isolation. Molecular Ecology 18, 834-847.
Carling, M. D., Lovette, I. J. & Brumfield, R. T. (2010). Historical Divergence and Gene Flow: Coalescent Analyses of Mitochondrial, Autosomal and Sex-Linked Loci in Passerina Buntings. Evolution 64, 1762-1772.
Carling, M. D. & Zuckerberg, B. (2011). Spatio-temporal changes in the genetic structure of the Passerina bunting hybrid zone. Molecular Ecology 20, 1166-1175.
Emlen, S. T., Rising, J. D. & Thompson, W. L. (1975). Behavioral and Morphological Study of Sympatry in Indigo and Lazuli Buntings of Great-Plains. Wilson Bulletin 87, 145-179.
Kroodsma, R. L. (1974). Hybridization in Grosbeaks (Pheucticus) in North Dakota. The Wilson Bulletin, 230-236.
Kroodsma, R. L. (1975). Hybridization in Buntings (Passerina) in North-Dakota and Eastern Montana. Auk 92, 66-80.
Mettler, R. D. & Spellman, G. M. (2009). A hybrid zone revisited: molecular and morphological analysis of the maintenance, movement, and evolution of a Great Plains avian (Cardinalidae: Pheucticus) hybrid zone. Molecular Ecology 18, 3256-3267.
Sibley, C. G. & Short, L. L. (1959). Hybridization in the buntings (Passerina) of the Great Plains. The Auk, 443-463.
Storer, R. W. (1961). A hybrid between the Painted and Varied Buntings. The Wilson Bulletin, 209-209.
Swenk, M. H. (1936). A study of the distribution, migration and hybridism of the Rose-breasted and Rocky Mountain Black-headed grosbeaks in the Missouri Valley region. Nebraska Ornithologists’ Union.
Taylor, W. K. (1974). New Hybrid Bunting (Passerina-Cyanea X Passerina-Ciris). Auk 91, 485-487.
West, D. A. (1962). Hybridization in grosbeaks (Pheucticus) of the Great Plains. The Auk, 399-424.
Youngworth, W. (1932). Another hybrid between the Indigo and Lazuli Buntings. The Wilson Bulletin, 239-240.