Abstracts (first author)
A completely unknown lifecycle in mushrooms: cyclical inbreeding and haplo-diploidy
Mycena galericulata (Basidiomycota, Agaricales) occurs in two forms, a clampless with two-spored basidia and a clamped with four-spored basidia. It is generally accepted that the two-spored form is haploid asexual (apomictic), and the four-spored form sexual (dikaryotic and heterothallic). In order to study the interrelationship between both forms, we performed mating tests and phylogenetic and genetic analyses of a sample of both forms. Surprisingly, our results are inconsistent with any currently known life-cycle. While the four-spored form is heterothallic indeed, we show that the two-spored form is diploid, and produces diploid spores via intra-tetrad selfing. However, the absence of genetic differentiation between both forms, and the high degree of heterozygosity in the two-spored form, indicate that the two-spored form frequently arises from the four-spored. We hypothesise that the two-spored form can again give rise to four-spored forms. Consistent with this, we discovered that a small percentage of fruiting bodies has both two-spored and four-spored basidia.
Allorecognition stabilizes multicellularity
The cells of a multicellular individual face the social dilemma of potentially increasing their personal fitness by increased reproduction at the cost of fitness of the multicellular individual. Organisms capable of somatic fusion are most sensitive to this somatic parasitism, since parasitic mutant cells can infect other individuals. Allorecognition, found in many multicellular organisms, limits the spread of somatic parasites. However, previous models have not satisfactorily demonstrated that this long-term benefit is sufficient to offset immediate disadvantages of reduced fusion experienced by new, initially rare, allorecognition types. Using a cellular automaton approach, we model the joint evolution of allorecognition and somatic parasitism in a multicellular organism resembling an asexual ascomycete fungus. Individuals can fuse with neighboring individuals, but only if they have the same allotype. Fusion with a parasite decreases the total reproductive output of the individual, but the parasite compensates for this individual fitness reduction by a disproportional share of the offspring. Our study shows that the mere threat of parasitism can select for high allorecognition diversity, which on its turn provides efficient protection against invasion of somatic parasites. Moderate population viscosity combined with weak global dispersal provided the best conditions for the joint evolution of allorecognition and stable multicellularity.