The estrildid finches are small passerine birds of the Old World tropics and Australasia. Hybridization occurs in several genera, but only a few cases have been studied in detail.
Sympatric red and black colour morphs of the Gouldian Finch (E. gouldiae) show postzygotic incompatibilities. An experiment comparing pure and mixed breeds found large inviability effects. Mortality was most severe for hybrid females, consistent with Haldane’s Rule (Pryke & Griffith, 2009). These morphs may be on their way to becoming separate species. Assortative mating is probably mitigated by genes controlling colour expression and genes causing hybrid dysfunction on the Z-chromosome (Pryke, 2010).
A genomic analysis of this genus (sampling 11 of the 13 species) uncovered substantial autosomal introgression between sympatric species. There were, however, some divergent genomic regions containing colour genes, which could explain the phenotypic diversity in this group of birds (Stryjewksi & Sorenson, 2017). This study found one hybrid between Great-billed Mannikin (L. grandis) and Chestnut-breasted Mannikin (L. castaneothorax).
A hybrid between Chestnut-breasted Mannikin (L. castaneothorax) and Yellow-rumped Mannikin (Lonchura flaviprymna) was reported in northern Australia (Immelmann, 1962).
Hybrids between Chestnut-breasted Mannikin (L. castaneothorax) and Scaly-breasted Munia (L. punctulata) are sterile, probably due to genetic incompatibilities during spermatogenesis (Swan & Christidis, 1987).
Two subspecies of the Zebra Finch (T. guttata guttata and T. g. castanotis) mate assortatively based morphological and vocal cues (Clayton, 1990a). Several experiments were conducted to assess the effects of cross-fostering on mate choice (Clayton, 1989; Clayton, 1990b).
Mate choice experiments with three species of Blue Waxbill revealed that males and females use different criteria. Males focus on female size, while females rely on male ornamentation. This difference in mate choice criteria could lead to hybridization (Luddem et al., 2004).
Clayton, N. S. (1989). The Effects of Cross-Fostering on Selective Song Learning in Estrildid Finches. Behaviour 109, 163-175.
Clayton, N. S. (1990a). Assortative Mating in Zebra Finch Subspecies, Taeniopygia-Guttata-Guttata and T-G-Castanotis. Philosophical Transactions of the Royal Society of London Series B-Biological Sciences 330, 351-370.
Clayton, N. S. (1990b). The Effects of Cross-Fostering on Assortative Mating between Zebra Finch Subspecies. Animal Behaviour 40, 1102-1110.
Immelmann, K. (1962) Besiedlungsgeschichte und Bastardierung von Lonchura castaneothorax und Lonchura flaviprymna in Nordaustralien. Journal of Ornithology 130(4), 344-357.
Luddem, S. T., Collins, S. A., Brooks, M. A. & Winter, M. (2004). Some males are choosier than others: Species recognition in blue waxbills. Behaviour 141, 1021-1039.
Pryke, S. R. (2010). Sex Chromosome Linkage of Mate Preference and Color Signal Maintains Assortative Mating between Interbreeding Finch Morphs. Evolution 64, 1301-1310.
Pryke, S. R. & Griffith, S. C. (2009). Postzygotic Genetic Incompatibility between Sympatric Color Morphs. Evolution 63, 793-798.
Swan, M. A. & Christidis, L. (1987). Impaired Spermatogenesis in the Finch Hybrid L-Castaneothorax by L-Punctulata – Transmission Electron-Microscopy and Genetic-Analysis. Gamete Research 17, 157-171.
Stryjewski, K.F. & Sorenson, M.D. (2017) Mosaic genome evolution in a recent and rapid avian radiation. Nature Ecology & Evolution 1, 1912-1922.