Bioinvasions of the medfly Ceratitis capitata: Source estimation using DNAsequences at multiple intron loci

The Mediterranean fruit fly, Ceratitis capitata, is a devastating agricultu ral pest that threatens to become established in vulnerable areas such as C alifornia and Florida. Considerable controversy surrounds the status of Cal ifornian medfly infestations: Do they represent repeated introductions or t he persistence of a resident population! Attempts to resolve this question using traditional population genetic markers and statistical methods are pr oblematic because the most likely source populations in Latin America were themselves only recently colonized and are genetically very similar. Here, significant population structure among several New World medfly populations is demonstrated through the analysis of DNA sequence variation at four int ron loci. Surprisingly, in these newly founded populations, estimates of po pulation structure increase when measures of subdivision take into account the relatedness of alleles as well as their frequency. A nonequilibrium, li kelihood-based statistical test that utilizes multilocus genotypes suggests that the sole medfly captured in California during 1996 was introduced fro m Latin America and was less likely to be a remnant of an ancestral Califor nian population. Many bioinvasions are hierarchical in nature, consisting o f several sequential or overlapping invasion events, the totality of which can be termed a metainvasion. Phylogenetic data from multilocus DNA sequenc es will be Vital to understanding the evolutionary and ecological processes that underlie metainvasions and to resolving their constituent levels.