Reconciling actual and inferred population histories in the house finch (Carpodacus mexicanus) by AFLP analysis

The house finch (Carpodacus mexicanus) is a native songbird of western North America that was introduced to the eastern United States and Hawaiian Islands in historic times. As such, it provides an unusually good opportunity to test the ability of molecular markers to recover recent details of a known population history. To investigate this prospect, genetic variation in 172 individuals from 16 populations in the western and eastern United States, southeastern Canada, Hawaiian Islands, and Mexico, as well as genetic variation in the closely related purple finch (Carpodacus purpureus) and Cassin's finch (Carpodacus cassinii) was studied by a semi-automated fluorescence-labeled amplified fragment length polymorphism (AFLP) marker system. A total of 363 markers were generated, of which 258 (71.2%) were polymorphic among species, 166 (61.4%) polymorphic among house finch subspecies, and 157 (60.2%) polymorphic among populations within the frontalis subspecies complex. Heterozygosities and interpopulation divergences revealed by the analysis appeared relatively low at all taxonomic levels, but there are few similar studies in avian populations with which to compare results. Whereas the known population history predicts that both eastern and Hawaiian finches should have been derived from within western populations, tree analysis using both populations and individuals as units suggests weak monophyly of eastern populations and indicates that Hawaiian populations are not clearly derived from California populations. However, the genetic distinctiveness of native and recently founded populations was disclosed by analyses of molecular variance as well as by a model-based assignment approach in which 98%, 94%, and 99% individuals from western, Hawaiian, and eastern regions, respectively, were assigned correctly to their populations without using prior information on population of origin, suggesting that these recent introductions have resulted in detectable differentiation without substantial loss of AFLP diversity. Our results indicate that AFLPs are a useful tool for population genetic and evolutionary studies of birds, particularly as a prelude to finding molecular markers linked to traits subjected to recent adaptive evolution.