THE POTTIACEAE S. STR. AS AN EVOLUTIONARY LAZARUS TAXON

Abstract

  Genomic studies have shown that evolution can be based on clusters of genes that may be silenced and reactivated much later. Thus, apparent phylogenetic homoplasy may sometimes represent a one-time developmental response to selection, involving many genes or gene clusters and one or more regulators, and as such may be called homoiology. Evidence for such exaptions (pre-adaptions) in many organisms is cited. Distinctive features of the Pottiaceae (Bryopsida), the complex gametophytic morphology characterized by the pleisiomorphic Timmiella and the twisted peristome of 32 filamentous, spiculose teeth distal to a basal membrane are suggested to be likewise homoiologous. The characteristic peristome may have reappeared in the family four to seven times. Inasmuch as exaptions may skip across cladistic events tracked by non-coding or neutral gene traits, this paper re-evaluates past evolutionary schema in light of an apparent, theoretically acceptable exception to Dollo's Law that complex traits are never re-evolved. An evolutionary diagram based in part on inferred process is offered in place of the usual cladogram based on inferred events of genetic isolation.