Abstract
Apis mellifera scutellata was introduced to Brazil in 1956 and Africanized honeybee populations have now spread from Argentina to the southwestern United States. Temperate climatic restrictions seem to be a natural limit to Africanized honeybee expansion around parallels 35° to 40° SL. We used allozyme loci (Mdh-1 and Hk-1) and mtDNA haplotypes to characterize honeybee populations in southern Brazil and Uruguay and define a possible transition area between Africanized and European bees. Samples of 194 bee colonies were collected from ten localities between 30°-35° SL and 52°-59° WL. The mtDNA restriction patterns of these colonies were obtained through digestion of the mitochondrial genome by Eco RI, or by digestion by Bgl II and Xba I of the cytochrome B locus and the COI-COII intergenic region, respectively. The distribution limit of African bee colonies, i.e., those populations with only the African mtDNA haplotype and with a high proportion of African genes as shown by allozyme analysis, is located in northern Uruguay, with a hybridization zone located farther south in Uruguay. A gradual cline from north to south was observed, confirmed by mtDNA, racial admixture, and genetic distance analyses. No evidence of either gametic disequilibrium between nuclear markers or cytonuclear disequilibrium among the nuclear and mtDNA genotypes was detected, suggesting that the hybridization process has been completed.
Highlights
A sub-Saharan subspecies, Apis mellifera scutellata, was introduced to Brazil in Rio Claro, São Paulo state, in the mid-1950s to improve honey production in neotropical conditions (Kerr, 1967)
Our results showed a high proportion of bee colonies with the African mtDNA haplotype, a finding similar to that described by Burgett et al (1995)
Colonies from southern Brazil and northern Uruguay had only the African type. Colonies with both African and European patterns were observed in localities farther south, sustaining the hypothesis that this area represents a zone of hybridization between Africanized and European bees (Kerr et al, 1982; Burgett et al, 1995)
Summary
A sub-Saharan subspecies, Apis mellifera scutellata, was introduced to Brazil in Rio Claro, São Paulo state, in the mid-1950s to improve honey production in neotropical conditions (Kerr, 1967). Populations of Africanized honeybees, expressing scutellata-like reproductive, foraging, and defensive behavior, spread rapidly from that area to as far south as mid-Argentina and to southern Texas due to their high adaptability to tropical ecological conditions. During this expansion, they hybridized with European bees Mellifera, and A.m. iberica) that had been in the region since the XVIII century These Africanized bees arrived in the United States in 1990 and presently occupy part of the states of Texas, Arizona, New Mexico, and California (Rowell et al, 1993; Sanford, 1995). Nuclear and mitochondrial DNA polymorphisms (Hall, 1986, 1990; Smith and Brown, 1988; Hall and Muralidharan, 1989; Oldroyd et al, 1992; Sheppard et al, 1991a,b; Clarke et al, 2001), and, more recently, microsatellites (Estoup et al, 1993, 1994, Franck et al, 1998) have proven to be very useful molecular markers for honeybee population genetics
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