Population genetic studies in bees (APIDAE, Hymenoptera). I. Genetic load

Three populations of Apis mellifera each predominantly of a different subspecies (mellifera, ligustica and adansonii) and 7 species of stingless bees (Meliponinae, Apidae) were manipulated for applying the MORTON, CROW & MULLER's methodology in order to estimate the lethal equivalents (B) of each population. A total of 249 queens were used, 27 being meliponids and 222 Apis mellifera. The populations of Apis have a B that does not differ significantly when they are compared to each other (1.29, 1.36, 1.32) and the balanced average equals 1.33. When the x-alleles are not considered, this balanced value is 0.262. The figures for B in the seven species of stingless bees ranged between 0.104 and 0.159 with balanced average of 0.132. The main reason for this smaller load in meliponids may rest in their effective population numbers, which are smaller than those of Apis. The average mortality for diploid females (0.141) and for haploid males (0.163) allows the estimation of the total elimination (sigma E = 0.073). Since for haplo-diploid systems the total mutation rate is sigma mu = 2 sigma E divided by 3 the figure 0.048 is obtained. Since about 15% of the genes in Apis mellifera are sex limited, this value of sigma mu should be added of 0.0072 (that is 0.15 X 0.048) and then, the total mutation rate becomes 0.055. Using a quite different method, the one by MORTON, CROW & MULLER, the figure 0.076 was obtained. If a mutation rate of 10(-5) is assumed, the number of genes in Apis mellifera that can make a contribution to the genetic load would vary between 5,500 and 7,600.