Convergent origins of ambrosia fungi

The genus Ambrosiella appears to be nonmonophyletic based on evidence from cladistic analysis of characters derived from nuclear encoded small subunit (18S) rDNA sequences. The conclusion also is supported by differential sensitivity to cycloheximide. Six species of Ambrosiella (A. brunnea, A. sulcati, A. gnathotrichi, A. sulfurea, A. macrospora, and A. ips) are closely related to species of Ophiostoma (Ophiostomatales) and show cycloheximide tolerance. Three other species (A. xylebori, A. ferruginea, and A. hartigii) are related to Ceratocystis (Microascales) and are intolerant of cycloheximide. The difficulty in determining monophyletic groupings based on morphological characters among the asexual Ambrosiella species parallels that of their close sexual relatives Ophiostoma or Ceratocystis that also had been considered closely related in the past. This finding emphasizes the role of strong selection pressure for insect dispersal features, not only for sexual states, but for conidial and yeast forms as well.