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Article Excerpt
Nearly 10% of all non-marine avian species occasionally or regularly hybridize (Grant and Grant 1992, Allendorf et al. 2001, McCarthy 2006). It is often possible to use Mendelian genetics to identify the inheritance of plumage characters and to classify individuals as either first, second, or later generation hybrids (e.g., Parkes 1951, Graves 1993). However, due to presumed backcrossing and mating of hybrids with parents, many hybrid zones contain a wide variety of phenotypic characters (Gill and Murray 1972, Parsons et al. 1993, Vallender et al. 2007b). Studies of wood-warbler hybrid zones (Rohwer 1994, Vallender et al. 2007b) have found instances of cryptic hybridization where plumage analyses may lead to erroneous conclusions regarding the parentage of hybrids.
Parental diagnosis is even more difficult when hybrid individuals result from rare crosses involving unknown parents. There have been at least 69 suspected hybrid crosses within the North American wood-warblers involving 62 species (McCarthy 2006). The taxonomic distribution of suspected hybridization in the Parulidae led to the description of a pattern now termed "Parkes' Paradox" (Gill 1998): the possibility that wood-warblers in different genera are more prone to occasional hybridization than are congeneric wood-warblers (Parkes 1978). We now suspect 48 congeneric crosses and 21 hybrids involving parents of different wood-warbler genera (McCarthy 2006). Most of these crosses are known from only single hybrid individuals, but several pairs of congeners commonly interbreed, e.g., Townsend X Hermit warblers (Dendroica townsendii X D. occidentalis), and Golden-winged X Blue-winged warblers (Vermivora chrysoptera X V. pinus), and have been doing so for up to 100 years (Gill 1980, Morrison and Hardy 1983). Most hybrids appear to be fertile and show little, if any, reproductive costs associated with mixed genomes (Rohwer and Wood 1998, Vallender et al. 2007a), perhaps due to their close phylogenetic relatedness (Lovette and Bermingham 1999, 2002; Griffith et al. 2002; Vallender et al. 2007b). Much less is known about the context of rare hybrid crosses in the Parulidae, or the fitness of the resulting hybrid offspring.
Our objective is to report an unusual hybridization event involving captive wood-warblers housed within the Montrral Biodome (Canada). This cross between a female Yellow-rumped Warbler (Dendroica coronata) and a male Black-and-white Warbler (Mniotilta varia) involved parents from deeply divergent lineages within the Parulidae (Lovette and Bermingham 1999, Lovette and Hochachka 2006), which have diverged in reproductive behaviors related to both courtship and nest site selection (Kricher 1995, Hunt and Flaspohler 1998). One hybrid offspring survived to maturity in captivity and we described that hybrid's phenotype, including its full sequence of molts and its song. We also use this individual to validate a DNA sequenced-based method to identify both maternal and paternal ancestry of Parulidae hybrids that should be generally useful in investigations of hybrid birds.
METHODS
Hybridization Context.--The Montreal Biodome is a museum exhibiting live indoor representations of ecosystems in the Americas, among which is a 1,500 [m.sup.2] representation of the mixed deciduous forest in the Laurentians, an ecoregion north of Montreal, Quebec, Canada (45[degrees] 31' N, 73[degrees] 34' W). Captive individuals of seven Parulidae species were in the Laurentian exhibit during the 2000 breeding season: Black-throated Blue Warbler (Dendroica caerulescens, 2 males), Yellow-rumped Warbler (1 female), Black-throated Green Warbler (D. virens, 1 female), Common Yellowthroat (Geothlypis trichas, 1 male and 1 female), Ovenbird (Seiurus aurocapilla, 1 male), Northern Waterthrush (S. noveboracensis, 1 male and 1 unknown gender), and Black-and-white Warbler (1 male).
A recently fledged warbler was found within the enclosure on 1 July 2000. Later that day, a female Yellow-rumped Warbler was observed repeatedly feeding the fledgling. A male Black-and-white Warbler was observed feeding the fledgling on 4 July 2000. We were able to confirm the presence of three fledglings, all presumed to be the result of a hybridization event between the male Black-and-white and...
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