Genetic characterization of Bombyx mori (Lepidoptera: Bombycidae) breeding and hybrid lines with different geographic origins.

The domesticated silkworm Bombyx mori L. comprises a large number of geographical breeds and hybrid lines. Knowing the genetic structure of those may provide information to improve the conservation of commercial lines by estimating inbreeding over generations and the consequences of excessive use of those lineages. Here, we analyzed the genetic diversity of seven breeds and eight hybrid lines from Eastern Europe and Asia using highly polymorphic microsatellites markers to determine its genetical impact on their use in global breeding programs. No consistent pattern of deviation from Hardy-Weinberg equilibrium was found for most breed and hybrids; and the absence of a linkage disequilibrium also suggests that the strains are in equilibrium. A principal coordinate analysis revealed a clear separation of two silkworm breeds from the rest: one (IBV) originated from India and the other one (RG90) from Romania/Japan. The tendency of the other breeds from different geographic origins to cluster together in a general mix might be due to similar selection pressures (climate and anthropogenic factors) in different geographic locations. Phylogenetic analyses grouped the different silkworm breeds but not the hybrids according to their geographic origin and confirmed the pattern found in the principal coordinate analysis.

Climate rather than geography separates two European honeybee subspecies.

Both climatic and geographical factors play an important role for the biogeographical distribution of species. The Carpathian mountain ridge has been suggested as a natural geographical divide between the two honeybee subspecies Apis mellifera carnica and A. m. macedonica. We sampled one worker from one colony each at 138 traditional apiaries located across the Carpathians spanning from the Hungarian plains to the Danube delta. All samples were sequenced at the mitochondrial tRNA(Leu)-cox2 intergenic region and genotyped at twelve microsatellite loci. The Carpathians had only limited impact on the biogeography because both subspecies were abundant on either side of the mountain ridge. In contrast, subspecies differentiation strongly correlated with the various temperature zones in Romania. A. m. carnica is more abundant in regions with the mean average temperature below 9 °C, whereas A. m. macedonica honeybees are more frequent in regions with mean temperatures above 9 °C. This range selection may have impact on the future biogeography in the light of anticipated global climatic changes.

Intraspecific support for the polygyny-vs.-polyandry hypothesis in the bulldog ant Myrmecia brevinoda.

The number of queens per colony and the number of matings per queen are the most important determinants of the genetic structure of ant colonies, and understanding their interrelationship is essential to the study of social evolution. The polygyny-vs.-polyandry hypothesis argues that polygyny and polyandry should be negatively associated because both can result in increased intracolonial genetic variability and have costs. However, evidence for this long-debated hypothesis has been lacking at the intraspecific level. Here, we investigated the colony genetic structure in the Australian bulldog ant Myrmecia brevinoda. The numbers of queens per colony varied from 1 to 6. Nestmate queens within polygynous colonies were on average related (r(qq) = 0.171 ± 0.019), but the overall relatedness between queens and their mates was indistinguishable from zero (r(qm) = 0.037 ± 0.030). Queens were inferred to mate with 1-10 males. A lack of genetic isolation by distance among nests indicated the prevalence of independent colony foundation. In accordance with the polygyny-vs.-polyandry hypothesis, the number of queens per colony was significantly negatively associated with the estimated number of matings (Spearman rank correlation R = -0.490, P = 0.028). This study thus provides the rare intraspecific evidence for the polygyny-vs.-polyandry hypothesis. We suggest that the high costs of multiple matings and the strong effect of multiple mating on intracolonial genetic diversity may be essential to the negative association between polygyny and polyandry and that any attempt to empirically test this hypothesis should place emphasis upon these two key underlying aspects.