Reproductive Isolation and Phylogenetic Divergence in Neurospora: Comparing Methods of Species Recognition in a Model Eukaryote

Abstract

We critically examined methods for recognizing species in the model filamentous fungal genus Neurospora by comparing traditional biological species recognition (BSR) with more comprehensive applications of both BSR and phylogenetic species recognition (PSR). Comprehensive BSR was applied to a set of 73 individuals by performing extensive crossing experiments and delineating biological species based on patterns of reproductive success. Within what were originally considered two species, N. crassa and N. intermedia, we recognized four reproductively isolated biological species. In a concurrent study (Dettman et al. 2003), we used genealogical concordance of four independent nuclear loci to recognize phylogenetic species in Neurospora. Overall, the groups of individuals identified as species were similar whether recognized by reproductive success or by phylogenetic criteria, and increased genetic distance between parents was associated with decreased reproductive success of crosses, suggesting that PSR using genealogical concordance can be used to reliably recognize species in organisms that are not candidates for BSR. In one case, two phylogenetic species were recognized as a single biological species, indicating that significant phylogenetic divergence preceded the development of reproductive isolation. However, multiple biological species were never recognized as a single phylogenetic species. Each of the putative N. crassa x N. intermedia hybrids included in this study was confidently assigned to a single species, using both PSR and BSR. As such, no evidence for a history of hybridization in nature among Neurospora species was observed. By performing reciprocal mating tests, we found that mating type, parental role, and species identity of parental individuals could all influence the reproductive success of matings. We also observed sympatry-associated sexual dysfunction in interspecific crosses, which was consistent with the existence of reinforcement mechanisms.

Paracoccidioides brasiliensis: phylogenetic and ecological aspects

“…This reinforcement is very important because speciation involves not only divergence, but also maintenance, mainly when the derived species coexist [81]. Dettman et al [87] showed how these barriers to inter-species interbreeding may be different between allopatric and sympatric species of Neurospora; they observed a higher reproductive success for allopatric heterospecific pairings than for sympatric ones.…”

Asymmetric Postmating Isolation: Darwin's Corollary to Haldane's Rule

“…generally differ in sterility in a small, and occasionally in a high degree,'' citing Kölreuter and Gärtner, the same plant hybridizers whose hundreds of intra-and interspecific crosses inspired Mendel in 1865 (translated in Bateson 1901). Asymmetry was subsequently found in essentially all systems subject to systematic hybridization experiments, including many invertebrates (e.g., Muller 1942;Oliver 1978;Harrison 1983;Coyne and Orr 1989a;Gallant and Fairbairn 1997;Presgraves and Orr 1998;Navajas et al 2000;Willett and Burton 2001;Presgraves 2002), vertebrates (e.g., Thornton 1955;Rakocinski 1984;Bolnick and Near 2005), and fungi (e.g., Dettman et al 2003). A recent analysis of reciprocal species crosses within 14 diverse angiosperm genera found significant isolation asymmetry in 35-45% of all species pairings, evaluated at three different postmating stages of reproductive isolation (Tiffin et al 2001).…”

Endophytic Cryphonectriaceae on native Myrtales: Possible origin of Chrysoporthe canker on plantation-grown Eucalyptus

“…The partition homogeneity test of the combined regions conducted in PAUP resulted in a P-value of 0.01, thus lower than the conventionally accepted value of 0.05 required to combine data. However, several studies have accepted P-values greater than 0.001 (Cunningham 1997;Dettman et al 2003) and a decision was made to do so in this case. The parsimony analysis of the combined dataset resulted in the retention of 91 most parsimonious trees (TL = 316, CI = 0.854, RI = 0.968, RC = 0.827, HI = 0.146).…”