CONVERGENT ORIGINS OF AMBROSIA FUNGI

The genus Ambrosiella appears to be nonmonophyletic based on evidence from cladistic analysis of characters derived from nuclear encoded sma ll subunit (18S) rDNA sequences. The conclusion also is supported by d ifferential sensitivity to cycloheximide. Six species of Ambrosiella ( A. brunnea, A. sulcati, A. gnathotrichi, A. sulfurea, A. macrospora, a nd A. ips) are closely related to species of Ophiostoma (Ophiostomatal es) and show cycloheximide tolerance. Three other species (A. xylebori , A. ferruginea, and A. hartigii) are related to Ceratocystis (Microas cales) and are intolerant of cycloheximide. The difficulty in determin ing monophyletic groupings based on morphological characters among the asexual Ambrosiella species parallels that of their close sexual rela tives Ophiostoma or Ceratocystis that also had been considered closely related in the past. This finding emphasizes the role of strong selec tion pressure for insect dispersal features, not only for sexual state s, but for conidial and yeast forms as well.