Hybridization in the flickers (Colaptes) of North America. Bulletin of the AMNH ; v. 129, article 4

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New York : [American Museum of Natural History]
"Information is presented concerning the relationships, ecology, and behavior of North American flickers, Colaptes auratus, including the subspecies groups auratus, cafer, chrysoïdes, chrysocaulosus, and mexicanoïdes. 2. The situation of hybridization between the auratus and cafer groups of Colaptes auratus is analyzed, with the use of color and mensural characters. The hybrid zone, including the area in which 95 per cent or more of the flickers are hybrids, is a broad band of variable width extending from British Columbia eastward to Alberta and southward and eastward from there to Texas. 3. Evidence is presented for the occurrence of introgression in populations of auratus and cafer. Diminishing effects of hybridization are detectable in populations of auratus to the Atlantic Ocean, and cafer to the Pacific Ocean and Mexico. 4. Color characters used in the study were found to be somewhat correlated in hybrids but not to an extent invalidating their use as separate characters. No evidence for assortative mating was found in a study of the mating patterns of a limited number of hybrid pairs. 5. Localized hybridization occurs between the cafer and chrysoïdes groups. Considerable introgression has occurred, although the hybrids are found largely in hybrid swarms, more or less geographically isolated from parental populations. Some hybrid swarms have undergone partial stabilization. Evidence is offered that indicates that genes from eastern auratus populations, introgressing into the western cafer populations, are able to enter the chrysoïdes population as a result of the hybridization between cafer and chrysoïdes. 6. An attempt is made to trace the history of the hybrid situations in North American flickers. The hypothesis is developed that chrysoïdes originated in Baja California as an isolated cafer population. Hybridization between auratus and cafer has apparently occurred over a long period. Hybridization between cafer and chrysoïdes is thought to be of more recent occurrence. 7. Introgression was probably of major importance for the survival of some animal species in the Pleistocene and is probably a factor in their present success under conditions of constant human modification of the environment. 8. Selection, isolating mechanisms, and reinforcement are discussed in terms of the advantages of gene exchange between populations. Criteria are discussed for determination of the taxonomic status of hybridizing populations, including (a) hybridization along a broad area of contact between populations with strongly developed and those with poorly developed, or nondeveloped, isolating mechanisms; (b) hybridization along narrow contacts, involving populations exhibiting strongly and weakly developed isolating mechanisms; and (c) both ordinary and stabilized hybrid swarms, geographically isolated from their parental populations. 9. The North American flickers are considered to be conspecific. Five subspecies groups of the species Colaptes auratus are recognized. These are auratus, cafer, chrysoïdes, mexicanoïdes, and chrysocaulosus"--P. 421.
p. 309-428 : ill., maps ; 27 cm.
Includes bibliographical references (p. 422-428).