belong to the protist group Mesomycetozoa (Adl et al
2005), recently established to accommodate a group
of fish and shellfish parasites, human and anuran
pathogens as well as the ectocommensal Amoebidium
parasiticum (Mendoza et al 2002). The group, initially
known by the acronym DRIPs, first was recognized by
Ragan et al (1996) based on 18S sequence data that
placed the group near the animal-fungal divergence.
Amoebidiales and Eccrinales have convergent adapta-
tions for life in the guts of arthropods. Our current
understanding of these organisms is limited, but they
warrant additional study and expanded taxon sam-
pling because the group could provide answers to
animal-fungal origins and divergence.
Chytridiomycota and early diverging Fungi.— Our
analysis placed Chytridiomycetes on the basal-most
branches of the fungal tree, consistent with idea that
the common ancestor of the Fungi had a flagellated
life stage (Cavalier-Smith 2001). The phylogeny based
on combined rDNA recovers three groups of Chy-
tridiomycetes: the Blastocladiales, the ‘‘core Chytri-
diomycota’’ and Olpidium. These results suggest that
the Chytridiomycota is paraphyletic, a result consis-
tent with other phylogenetic studies (James et al
2006b, Forget et al 2002). The placement of
Basidiobolus has been problematic because some
earlier phylogenetic studies consistently grouped
Basidiobolus with Chytridiomycetes (Nagahama et al
1995, James et al 2000). Despite morphological
similarities to other Entomophthorales this grouping
was interesting because Basidiobolus spp. possess
a nucleus-associated organelle similar to a centriole,
as found only in flagellated fungi (McKerracher and
Heath 1985). In our study Basidiobolus spp. grouped
in a novel position, separate from the majority of
chytrids and Entomophthorales. Specifically they
branched early among the Zygomycota with the
chytrid Olpidium brassicae, although without statistical
support. Previous studies using 18S (James et al 2000)
and RPB1 (Tanabe et al 2005) suggested a relation-
ship between the Blastocladiales and Entomophtho-
rales. In this study however the Blastocladiales forms
a lineage of Fungi separate from other Zygomycota
and Chytridiomycota.
We purposefully did not include Microsporidia in
these analyses, despite the hypothesis that they have
diverged from among the Zygomycota (Keeling
2003), because of their notoriously rapid evolution
and sensitivity to LBA artifacts in ribosomal RNA
phylogenies (Keeling and Fast 2005). Further sam-
pling of slow-evolving genes of diverse Zygomycota
eventually might allow a definitive placement of these
enigmatic organisms. It also is possible that other yet
undiscovered or unrecognized extant taxa also will be
placed within the early diverging fungi. Clearly our
phylogenetic understanding of the Zygomycota is
enlightened by analyses of combined rDNA sequence
data, but further studies with broader taxon and gene
sampling are warranted as the next significant step
toward resolving the natural relationships of the
nonzoosporic basal fungi.
ACKOWLEDGMENTS
MMW gratefully acknowledges the National Science Foun-
dation (NSF) for awards that have supported a decade
of studies on the Harpellales (DEB-9521811, -0108110,
-0344722). In addition MMW, TYJ and MJC have been
grateful participants on two NSF-financed projects: Assem-
bling the Fungal Tree of Life (DEB-0228657) and Research
Coordination Network: a phylogeny for kingdom Fungi to
M. Blackwell, J.W. Spatafora and J.W. Taylor (DEB-0090301)
that helped provide some data generation and analytical
training in the lab of Rytas Vilgalys at Duke University. TYJ
and KO thank AFTOL for aiding publication of the
Zygomycota page on the Tree of Life Website. The
University of Georgia permitted reproduction of various
SEM images from KO’s (1979) book that Don Fraser used to
prepare the Zygomycetes plate (F
IG
. 2). Robert W. Licht-
wardt helped assemble the Harpellales plate (F
IG
. 3) and
proofread a final manuscript draft. Paula Clarke also proof
read the manuscript, and Sara Pittman helped collect
reference materials.
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