[2D1] Sympatric Speciation and Evolution of Social Parasitism ? Recent Evidence

Symposium

Kazuki TSUJI (University of the Ryukyus)

• PLENARY TALK: The evolution of social parasitism by workers: Emery�fs rule in Cape honeybees?
  Peter Neumann (Martin-Luther-Universitat Halle-Wittenberg, Institut fur Zoologie)

  Social parasites are widespread in social insects and tend to be close phylogenetic relatives of their hosts (= Emery�fs rule). Cape honeybee workers, Apis mellifera capensis, are facultative social parasites of honeybee colonies. They can fully activate their ovaries under queenright conditions to produce clonal female offspring and may develop a queenlike pheromonal bouquet. Recently, an exceptionally virulent strain of A. m. capensis workers has invaded the neighbouring subspecies A. m. scutellata resulting in the �gCapensis calamity�h with losses of several 100,000 colonies per year. Throughout South Africa infested A. m. scutellata colonies are parasitized by a single clonal worker line, indicating that it was established by a sole worker and that only the most virulent clone survived after severe intra- and intercolonial selection. Since the parasitic workers reproduce parthenogenetically, gene flow from the host to the parasite is not possible. Although gene flow from parasite to host can occur, hybridisations seem to be rare, resulting in sympatric reproductive isolation between conspecific host and parasite. These constraints on gene flow may result in sympatric speciation of a queenless social parasitic honeybee, thus providing a new mechanism for Emery�fs rule.

• Direct observation of altruists-cheater evolutionary dynamics in the parthenogenetic ant, Pristomyrmex pungens.
  Kazuki Tsuji (University of the Ryukyus)

  Direct observation of micro-evolutionary change is usually difficult for many ecologically interesting traits of organisms in the wild, such as social behavior. Here I show a pilot case in which two genetically and morphologically distinct lineages, altruists and socially parasitic cheaters, are coexisting in some field populations of the ant, Pristomyrmex pungens. In this species morphologically defined workers reproduce parthenogenetically instead of queens. All altruists (that are the common type called small workers) work and reproduce, while the rare socially parasitic lineage called �glarge-workers�h which hardly takes part in colonial tasks such as nursing and foraging except reproduction. My colleagues and I measured multilevel selection operating in the field and showed the short-term evolutionary changes follow the prediction of kin and group selection models. I discuss that the origin of those cheaters, that are also parthenogenetic, is clearly a mutant occurred in the past in the altruist-host populations, Emery�fs rule holding true.

• Sympatric speciation in the host-parasite relationship in eusocial insects - a phylogenetic evaluation of Emery's rule -
  Eisuke�@Hasegawa (Department of Ecology & Systematics, Graduate School of Agriculture, Hokkaido University.)
  

  In 1909, C. Emery pointed out the possibility of sympatric speciation of a parasite species from a host population in eusocial insects, as brood-rearing techniques make it hard for parasites to parasitize phylogenetically distant species. This so-called Emery's rule has not been examined for a long time due to difficulties in phylogenetic reconstruction among closely related taxa. However, recent progress in molecular phylogeny now allows us to examine and challenge this rule in the evolution of social parasitism. In this talk I will review several articles on host-parasite relationships in ants, and discuss the evolution of social parasitism in ants with special reference to the relationship between mode of social parasitism (inquilinism, facultative social parasitism and slavery) and Emery's rule.






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