Evolution of Nassauvia Comm. ex Juss. (Asteraceae; Nassauvieae): new insights from old data

Mark Alan Hershkovitz

The present work collated and reanalyzed DNA sequences for species of Nassauvia Comm. ex Juss. (including erstwhile Triptilion Ruiz & Pav.) (Asteraceae, Nassauvieae) reported in several previously published phylogenetic analyses. These sequences included: (i) the nuclear ribosomal DNA internal transcribed spacer region (ITS) and (ii) 5’ external transcribed spacer (ETS), and (iii) the plastome (cpDNA) rpl32-trnL(UAG) intergenic spacer (rpl32-trnL), (iv) trnL(UAA) intron plus trnL(UAA)-trnF(GAA) intergenic spacer (trnL-trnF), and (v) ndhF. Several low-quality and substantially erroneous sequences were found and discarded, and noisy flanking regions characterizing most sequences were trimmed. A few sequences are aberrant taxonomically, and some contained spurious but analytically innocuous deletions. Following filtering/cleaning of bad data, the consequent analysis (1) reconciled discordant topologies published previously; (2) confirms earlier findings that erstwhile Triptilion is nested within Nassauvia, hence is included here within Nassauvia; (3) demonstrates that species formerly classified in Triptilion are polyphyletic within Nassauvia, hence are classified here in two separate Nassauvia sections; (4) demonstrates that phylogenetic relations suggested by nuclear and cpDNA sequences for species formerly classified in Triptilion may be incongruent; (5) demonstrates and analyzes possible nuclear/cpDNA tree incongruence at the intersectional level; (6) confirms polyphyly of sequences with relation to the sectional classification; (7) reports sequence polymorphism and polyphyly at the infraspecific levels; (8) reports possible intersectional hybridization; (9) otherwise analyzes the historical cause of the infraspecifically polyphyletic sequences in general; and (10) reevaluates Nassauvia taxonomy in light of the present results. But besides merely deferring to causas proximas of gene tree incongruencies with each other and with morphology-based taxonomy (viz. hybridization and lineage sorting), the present work emphasizes the causa ultima, viz. the ontological distinction between genes and organisms. In particular, while genes and organisms are physically hierarchically linked and mutually interdependent, they otherwise can “drift” evolutionarily as long as the conditions for their quasi-independent existence and capacity for systemic reproduction are maintained. In this way, the genome lineage may be highly polyphyletic, while the morphological/behavioral ontogenetic phenotype of the organismal lineage remains monophyletic. Thus, some, apparent incongruencies may be red herrings.