Conidiogenesis: Its Evolutionary Aspects in the Context of a Philosophy of Opportunity (Lectics)

Abstract

Inspired by the discovery of the anatomical symplesiomorphies distinguishing monocots and dicots in the Plantae, mycologists searched for equivalent phylogenetically revelatory developmental patterns in the morphology of conidial fungi. Ultimately, they found them in the Hughes system of patterns of conidiogenesis. In this chapter, the pathways within evolution that allow such distinctive, stable, ‘fundamental’ patterns of developmental characters to persist in diverse habitats are given context within an overall philosophy of evolutionary opportunity—itself substituent to a comprehensive philosophy of opportunity, i.e. lectics. The exigencies that cause normally highly stable functions such as conidiogenesis to change patterns are examined. Examples are given of fungi such as Coccidioides spp. that have evolved completely novel forms of conidiogenesis in one habitat, while in other habitats they have maintained the stable type of conidiogenesis characteristic of their overall taxonomic order. The dramatic lability shown by Hyphomycetes that are selected under novel environmental conditions is contrasted with the impressive consistency of structures seen under ‘normal’ conditions. A radical example is given in Neocosmospora cyanescens comb. nov., a ‘Fusarium solani complex’ haplotype isolate that, after 33 years in human tissue, apparently became completely transformed into a slow-growing, hyperpigmented chlamydosporic mass making a few rudimentary phialides.