Program Book - 27th Fungal Genetics Conference

CONCURRENT SESSION ABSTRACTSThursday, March 14 3:00 PM–6:00 PMChapelFungi and Evolutionary TheoryCo-chairs: Hanna Johannesson and Duur AanenReaching the wind: the fluid mechanics of spore discharge, and potential for dispersal mechanisms to shape the evolution of sporocarp and sporemorphologies. Anne Pringle 1 , Michael Brenner 2 , Joerg Fritz 2 , Marcus Roper 3 , Agnese Seminara 2 . 1) Organismic & Evolutionary Biology, Harvard University,Cambridge, MA; 2) School of Engineering and Applied Sciences, Harvard University, Cambridge, MA; 3) Department of Mathematics, University ofCalifornia, Los Angeles, CA.Fungi play critical roles in human agriculture and Earth’s biogeochemistry, but mechanisms of fungal dispersal are poorly understood. Thinking hasfocused on the passive spread of spores by air and water, and neglected the biomechanics used by fungi to actively move spores to new habitats. In thistalk we focus on terrestrial ascomycetes, a group including plant and animal pathogens, mycorrhizal fungi, and lichens. We build theory to catalog andexplain the morphological features used by ascomycetes to shoot spores and facilitate the crossing of the boundary layer, a sheath of nearly still airsurrounding sporocarps. Crossing the boundary layer is critically important to the fitness of a spore: a spore that cannot escape will fall back on the parentfungus, where probabilities of germination and survival are low. But after crossing the boundary layer, a spore must also travel in wind, and by explicitlymodeling discharge and dispersal we identify a previously unsuspected trade-off constraining the sizes of spores. Large spores cross boundary layers moreeffectively, while small spores are more easily carried by wind. Spore dispersal shapes the epidemiology of disease, and will mediate range shifts inresponse to global change; understanding how and how quickly fungi move across landscapes will enable both management and conservation.Neurospora tetrasperma mating-type chromosomes: Testing hypotheses on the effects of degeneration and introgression on performance. Jennifer L.Anderson, Yu Sun, Pádraic Corcoran, Hanna Johannesson. Department of Evolutionary Biology, Uppsala University, Uppsala, Sweden.Following hybridization between species, parts of one species’ genome can be incorporated into the genome of the other. This transfer of geneticmaterial, introgressive hybridization, is a well-known driver of speciation, diversification, and adaptive evolution. Introgression has occurred repeatedly inthe fungus Neurospora tetrasperma and has resulted in the presence of large regions of DNA (< 4 Mbp tracts) from other species of Neurospora on themating-type (mat) chromosomes of N. tetrasperma. The mat chromosomes of N. tetrasperma also contain large regions of suppressed recombination thatare associated with the accumulation of mutations and possibly a reduction in biological fitness. It has been proposed that introgressions of DNA fromother taxa, with freely recombining mat chromosomes, onto the mat chromosomes of N. tetrasperma could counteract the deleterious effects of mutationaccumulation and “reinvigorate” fitness. Alternatively, interspecific introgression into N. tetrasperma mat chromosomes could be either neutral ordeleterious to fitness, but are maintained due to lack of recombination between mat chromosomes. To test these hypotheses we have quantifiedphysiological performance (linear growth rate, LGR) in homokaryons from eight strains of N. tetrasperma with mat chromosomes that differ inintrogression history (e.g. introgressions from different species) and degree of degeneration. Differences in LGR between mating types and chromosometypes (introgressed or degenerate) will inform our understanding how hybridization and chromosomal structure and content effect physiologicalperformance and possibly fitness.Nuclear arms races: sexual selection for masculine mushrooms. Bart Nieuwenhuis, Duur Aanen. Laboratory of Genetics, Wageningen University,Wageningen, Netherlands.When many gametes compete to fertilize a limited number of compatible gametes, sexual selection will favor those traits that increase competitiveadvantage during mating. In animals and plants, sperm and pollen competition have yielded many interesting adaptations for improved mating success. Infungi, similar processes have not been directly shown yet. We test the hypothesis that sexual selection can increase competitive fitness during mating,using experimental evolution in the mushroom fungus Schizophyllum commune. Mating in S. commune occurs by donation of nuclei to a mycelium. Thesefertilizing ‘male’ nuclei migrate through the receiving ‘female’ mycelium. In our setup, an evolving population of nuclei was serially mated with a nonevolvingfemale mycelium for 20 sexual generations. Four of the 12 tested strains had significantly increased competitive fitness and one had decreasedfitness. The main characteristic that explained fitness change was the relative success in colonization of the female mycelium. In most cases, no trade-offswere found with other fitness components. Our results show that sexual selection can act in mushroom fungi and that sexual selection can lead toincreased competitive ability during mating.Genome-wide mutation dynamic within a long-lived individual of Armillaria. James B. Anderson. Deptartment of Biology,, Univ Toronto, Mississauga,Ontario, Canada.Mutation is the ultimate source of all genetic variation in populations and yet the events themselves remain unobservable and buried in the past. Longlivedindividuals of Armillaria gallica, a common opportunistic fungal pathogen of tree roots in temperate forests of the northern hemisphere, provide aspatial context for the mutational dynamic. Each individual of A. gallica arises in a single mating event between two haploid gametes and the resultingdiploid genotype then grows vegetatively to occupy a discrete spatial territory including many adjacent tree root systems. In effect, this leaves a spatialrecord of growth over time within which mutations can be pinpointed. To identify mutations, the entire genomes of three spatially separated samples ofone individual of A. gallica approximately 200 by 60 m in size were sequenced and compared. In this comparison, mutations and chromosomal regions ofloss of heterozygosity (LOH) were identified and then assayed in another 22 isolates from the same individual.by conventional PCR and Sanger sequencing.The genotype network of all 10 mutations and two LOH events in the 90 MB genome assembly was without internal conflict. Further, the spatialdistribution of genotypes was non-random and appeared to reflect the vegetative expansion leading to the present-day individual. I will discuss theimplications of the whole-genome data in estimating mutation rates and cellular generation times.27th Fungal Genetics Conference | 49