A Search for the Origins of Animals and Fungi: Comparing and Combining Molecular Data

Abstract

Green plants, animals, and fungi have long held our interest as complex, largely multicellular eukaryotes of indeterminate origin. Considerable progress has now been made toward understanding the evolutionary relationships among these taxa as well as identifying their closest protistan relatives. An exclusive animal-fungal clade (the Opisthokonta) is now widely accepted based on an insertion in the protein synthesis elongation factor 1alpha (EF-1alpha) and molecular phylogenies of ribosomal RNAs and the conservative proteins actin, alpha-tubulin, beta-tubulin, and EF-1alpha. Protein data also suggest that the cellular (dictyostelid) and acellular (myxogastrid) slime molds are a close outgroup to the animal-fungal clade. Subsequent sequencing and phylogenetic analysis of EF-1alpha sequences very strongly support a monophyletic slime mold clade (the Mycetozoa or Eumycetozoa), which also includes the lesser-known protostelid slime molds. Monophyly of the opisthokont and mycetozoan clades, exclusive of green plants, is suggested by individual analyses of EF-1alpha and actin and given strong support by concatenated protein data. Neither the monophyly of the slime molds nor their close relationship to animals and fungi are consistently supported by ribosomal RNA data. Thus, it appears unlikely that any single molecule will accurately reconstruct all higher-order taxonomy.