Turner, Elizabeth; Taylor*, John W. Evolutionary genetics of a reproductive isolation barrier separating Neurospora crassa and N. intermedia. In: International Meeting on "Population and Evolutionary Biology of Fungal Symbionts", Ascona, Switzerland, 2007. AB-36. Click here to download the presentation on pdf format.

Reproductive isolation barriers between different mated pairs of Neurospora crassa and N. intermedia range from mild (reduced numbers of viable progeny) to severe (failure to develop fruitbodies). For the N. crassa clade NcC, which is endemic in southern India, the severity of reproductive isolation from N. intermedia is biogeographically structured: crosses to sympatric N. intermedia show more severe barriers. This pattern is consistent with reinforcement, the evolution of stronger reproductive isolation barriers by natural selection against hybridization. However, the reinforced barrier appears to be a postmating barrier—the abortion of hybrid fruit bodies—so the pattern diverges from “classical” reinforcement where premating isolation is reinforced. The potential fitness advantage of the reinforced postmating barrier was demonstrated in experiments showing that early abortion dramatically increases overall fecundity of NcC females that have additional opportunities to mate with conspecific males. QTL analysis using a mapping population derived from a cross between N. crassa strains of the NcA and NcC clades identified eleven loci significantly associated with the development of hybrid fruitbodies fertilized by N. intermedia sympatric to NcC. For ten of these loci, the NcC allele negatively affects fruitbody development. This genetic architecture is consistent with evolution by positive natural selection.

Keywords: hybridization, reinforcement, fungi

*Institution: University of California, Berkeley

Email: jtaylor@nature.berkeley.edu