Speciation

Speciation is the process of origin of a new species. For example, N. intermedia occur on burned substrates in tropical and subtropical areas in the Eastern and Western Hemispheres. A type found almost exclusively on nonburned substrates (for example, ontjom, a food item made by inoculating pressed soya or peanut cakes with Neurospora, or on corn cobs) in the Eastern Hemisphere is yellow rather than pinkish-orange. The yellow "ecotype" is distinct also in its conidia (size and nuclear number), habitat and ecology. Although the two types can be coerced to mate in laboratory conditions, yet there is no evidence that because of the geographical isolation the two types are members of an interbreeding population. The phylogenetic trees constructed based on variation in the nontranscribed spacer suggested that the yellow isolates are a separate lineage, distinct from a larger N. crassa/intermedia clade (Figure 13.6). No definite phylogeny was apparent other than N. discreta was divergent from all other species. Rather, the yellow type is on the threshold of evolving into a distinct species. Though gene homology is identified more precisely than homology based on morphological characters, nevertheless caution is necessary in drawing inferences from molecular studies or phylogenetic trees constructed based on single locus.

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