Character evolution in heterotrophic euglenids

Abstract

This article attempts to describe the key morphological innovations associated with the evolutionary transitions between bacteriotrophy, eukaryotrophy, phototrophy, and osmotrophy in euglenids. Attention was focused on heterotrophic euglenids in an effort to establish a robust phylogenetic hypothesis for the group as a whole. We present a cladistic analysis of a large morphological data set from the following taxa: Petalomonas, Entosiphon, Lentomonas, Ploeotia, Dinema, Distigma, Rhabdomonas, Menoidium, Peranema, Urceolus, Eutreptia, and Euglena. The majority of the 37 characters and 97 states recognized were associated with the pellicle, the feeding apparatus, and the flagellar apparatus. In addition to having pellicle strips, Petalomonas cantuscygni possessed mitochondrial inclusions that were strikingly similar to the kinetoplasts found in kinetoplastids. Dinema sulcatum held a pivotal position in the phylogenetic tree and possessed many characters that bridged bacteriotrophic taxa with eukaryotrophic taxa. Distigmids and rhabdomonads formed a clade of osmotrophs that descended from eukaryotrophic ancestors, while Urceolus cyclostomus possessed a feeding apparatus, a putative photoreception apparatus and cytoskeletal features that clearly linked the phototrophs to eukaryotrophic ancestors. Evolutionary implications that emerged from these results were discussed.