Abstract:
Mutualism between microbes and insects is common and alignment of the reproductive
interests of microbial symbionts with this lifestyle typically involves clonal reproduction
and vertical transmission by insect partners. Here the Amylostereum funguseSirex woodwasp
mutualism was used to consider whether their prolonged association and predominance
of asexuality have affected the mating system of the fungal partner. Nucleotide
information for the pheromone receptor gene rab1, as well as the translation elongation
factor 1a gene and ribosomal RNA internal transcribed spacer region were utilized. The
identification of rab1 alleles in Amylostereum chailletii and Amylostereum areolatum populations
revealed that this gene is more polymorphic than the other two regions, although
the diversity of all three regions was lower than what has been observed in free-living
Agaricomycetes. Our data suggest that suppressed recombination might be implicated in
the diversification of rab1, while no evidence of balancing selection was detected. We
also detected positive selection at only two codons, suggesting that purifying selection is
important for the evolution of rab1. The symbiotic relationship with their insect partners
has therefore influenced the diversity of this gene and influenced the manner in which selection
drives and maintains this diversity in A. areolatum and A. chailletii.
