Complexity, adaptations and variations in the secondary insemination system of female Dermanyssina mites (Acari: Anactinothrichida: Gamasida): the case of Afrocypholaelaps africana.

Gamasine mites, mainly of the taxon Dermanyssina, possess a secondarily evolved insemination system (sperm access system), of which there are two, generally recognized, structurally different types, the laelapid- and the phytoseiid-type. The ultrastructure of the female sperm access system in Afrocypholaelaps africana is described. It consists of paired insemination pores, opening between the bases of legs three and four, and paired cuticle-lined tubules that converge into a large, sack-like spermatheca, remarkably cuticle-lined as well. The entire spermatheca and part of the tubules are embedded in a peculiar syncytial tissue where numerous sperm cells are present. The general organization of this insemination system is of the laelapid-type. However, it presents striking structural differences, compared with the systems described in Varroa destructor and Hattena cometis, the other gamasine mites having a laelapid-type system studied ultrastructurally until now. The functional morphology, complexity and variations of the sperm access system in Dermanyssina are discussed and correlated with the evolutionary biology of the group.

Invasion success of the bumblebee, Bombus terrestris, despite a drastic genetic bottleneck.

In early 1992, the European bumblebee, Bombus terrestris, was first seen in Tasmania and currently has spread to most of the island. Here, we report on the genetic structure, using micro-satellites, of the invading population from samples collected in the years 1998-2000, a few years after the first sighting of the species in its new area. The data show that the Tasmanian population has a very low genetic diversity, with less than half of the allelic richness (Richness=2.89 alleles; H(exp)=0.591) and lower levels of heterozygosity as compared to populations in New Zealand (4.24 alleles; H(exp)=0.729) and Europe (5.08 alleles; H(exp)=0.826). In addition, the genetic data suggest that the invasion must have happened once, probably around late 1991, and was the result of very few, perhaps only two, individuals arriving in Tasmania. Furthermore, these founders came from the New Zealand population. Today, the population in the south of Tasmania seems to act as a source population from which individuals migrate into other parts of the state. A similar source-sink structure seems also the case for New Zealand. The data show that B. terrestris is a highly invasive species capable of establishing itself even after a dramatic genetic bottleneck. B. terrestris may be an invasive species due to the haplo-diploid sex determination system, which exposes recessive, deleterious mutations to selection. Offspring of such purged lines may then be able to tolerate high levels of inbreeding.