No abstract

To study the degree of interpopulational differentiation and racial admixture in Africanized honeybees, we collected worker bees from three regions of Brazil (the northeast, the state of Sao Paulo, and Porto Alegre) and from Uruguay and determined their genotypes for 10 enzyme loci. We also performed a morphometric analysis on forewing measurements of worker bees from the northeast and Porto Alegre regions of Brazil and from Paysandu, Uruguay. Comparative analysis of interpopulational heterogeneity snowed that there are significant differences, especially at the Mdh locus, among the populations from different regions. An increase in the frequency of the Mdh allele was observed from north to south, with predominance in the Uruguayan populations. A small component of interpopulational variability was detected in the populations studied. Racial admixture was calculated from information obtained for Mdh in Africa and Europe. The percentages of racial admixture differed slightly but significantly among Brazilian regions. The morphometric study based on canonical variables exhibited a similar pattern. The greater proportions of Apis mellifera adansonii alleles in the admixture may be explained by selection during the initial stage of migration of Africanized bees and by preferential mating between individuals of the same race. Differences in the proportions of A. m. adansonii alleles between regions indicate incipient populational differentiation of Africanized bees. We suggest that greater gene flow from the European races in the south of Brazil could be one of the causes of this phenomenon.

For many tree species, mating system analyses have indicated potential variations in the selfing rate and paternity correlation among fruits within individuals, among individuals within populations, among populations, and from one flowering event to another. In this study, we used eight microsatellite markers to investigate mating systems at two hierarchical levels (fruits within individuals and individuals within populations) for the insect pollinated Neotropical tree Tabebuia roseo-alba. We found that T. roseo-alba has a mixed mating system with predominantly outcrossed mating. The outcrossing rates at the population level were similar across two T. roseo-alba populations; however, the rates varied considerably among individuals within populations. The correlated paternity results at different hierarchical levels showed that there is a high probability of shared paternal parentage when comparing seeds within fruits and among fruits within plants and full-sibs occur in much higher proportion within fruits than among fruits. Significant levels of fixation index were found in both populations and biparental inbreeding is believed to be the main cause of the observed inbreeding. The number of pollen donors contributing to mating was low. Furthermore, open-pollinated seeds varied according to relatedness, including half-sibs, full-sibs, self-sibs and self-half-sibs. In both populations, the effective population size within a family (seed-tree and its offspring) was lower than expected for panmictic populations. Thus, seeds for ex situ conservation genetics, progeny tests and reforestation must be collected from a large number of seed-trees to guarantee an adequate effective population in the sample.

Here, we explore the mating pattern and genetic structure of a tropical tree species, Cariniana estrellensis, in a small population in which progeny arrays (n = 399), all adults (n = 28) and all seedlings (n = 39) were genotyped at nine highly informative microsatellite loci. From progeny arrays we were able to identify the source tree for at least 78% of pollination events. The gene immigration rates, mainly attributable to pollen, were high, varying from 23.5 to 53%. Although gene dispersal over long distance was observed, the effective gene dispersal distances within the small population were relatively short, with mean pollination distances varying from 69.9 to 146.9 m, and seed dispersal distances occurring up to a mean of 119.6 m. Mating system analyses showed that C. estrellensis is an allogamous species (t m = 0.999), with both biparental inbreeding (t m − t s = − 0.016) and selfing rates (s = 0.001) that are not significantly different from zero. Even though the population is small, the presence of private alleles in both seedlings and progeny arrays and the elevated rates of gene immigration indicate that the C. estrellensis population is not genetically isolated. However, genetic diversity expressed by allelic richness was significantly lower in postfragmentation life stages. Although there was a loss of genetic diversity, indicating susceptibility of C. estrellensis to habitat fragmentation, no evidence of inbreeding or spatial genetic structure was observed across generations. Overall, C. estrellensis showed some resilience to negative genetic effects of habitat fragmentation, but conservation strategies are needed to preserve the remaining genetic diversity of this population.