A Test of Phylogenetic Versus Biological Species Concepts in the Fungus Neurospora

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

9981987 Taylor Working with colleague Dr. David Jacobson at University of California-Berkeley, Dr. John Taylor aims to challenge the existing Biological and Morphological Species Concepts in the filamentous fungus Neurospora (Ascomycetes) by using concordance of multiple gene genealogies to diagnose phylogenetic species. In parallel, they will refine the current Biological Species Concept (BSC) via experimental matings among Neurospora species. Recent studies in Taylor's laboratory of gene genealogy concordance to diagnose fungal species have uncovered genetically isolated species within morphologically defined species, just as has been the case with experimental matings. In one case, fungi placed in a single species due to mating behavior sort into at least four genetically distinguishable phylogenetic species. Therefore, the phylogenetic species concept (PSC) diagnoses genetically isolated species in nature, as should the BSC, but it can be applied to all fungi, whether or not they exhibit sexual reproduction (many do not), as can the Morphological Species Concept. The choice of Neurospora, an organism used widely as a model in developmental and evolutionary biology, is based on four major reasons. 1) The 13 known species exhibit the range of reproductive behavior seen throughout fungi, including outbreeding (heterothallic), selfing (homothallic), and mixtures of the two. 2) The outbreeding species have been diagnosed as biological species from the start, and over 4,600 individuals are available from the NSF-funded Fungal Genetics Stock Center, each of them having been assigned to species by mating tests. 3) Mating tests to assign individuals to biological species are not always clear cut, and more than one set of "testers" has been required to accommodate variation found in N. crassa and N. intermedia. This variation suggests that the BSC for Neurospora may be lumping genetically isolated groups (or lineages). 4) Preliminary molecular phylogenetic studies indicate that gene flow may be occurring among some biological species in the genus, further questioning the applicability of the mating-test based BSC. Using the abundant DNA sequence information for fungi in GenBank and the Neurospora Genome Project, the researchers will PCR amplify gene regions, check for useful variation, and construct at least five gene genealogies, tracking the five major chromosomes. Phylogenetic trees can then be constructed for each of the genes individually and then combined; simultaneous analysis of all five regions reveals basal branches common to all five single gene trees due to lineage sorting following genetic isolation, while conflict among terminal branches (with resulting polytomies in the consensus tree) reveals recombination among individuals in genetically isolated species. The interface between the shared branches and the conflicting branches represents the species boundary, the zone of lineage separation.