Growth, Differentiation and Sexuality

unit (an individual colony) is advantageous in
competitive environments. In a confrontation
between the cord-forming wood decomposers
H. fasciculare and Steccherinum fimbriatum, one
species eventually replaced the other. Which
species eventually dominated over the other was
strongly influenced by inoculum size (Dowson
et al. 1988). In confrontations between a competitor
and colonies from the same isolate, but of
different sizes, larger colonies had a higher success
rate than smaller ones (Holmer and Stenlid 1993).
These data from basidiomycete species suggest
that, in ascomycete species, too, the capacity of
conidial germlings or colonies of like genotype to
undergo anastomosis to generate a larger colony
may provide a competitive advantage.
VII. Conclusion
Anastomosis captured the imagination of early
mycologists, and numerous studies describing
the morphology of hyphal fusion in ascomycete
and basidiomycete species have been published.
However, work describing mutant phenotypes
or the molecular function of genes and proteins
required for anastomosis in filamentous fungi has
largely been ignored. Advances in cell biology
techniques and live cell imaging of the hyphal
fusion process will hopefully lead to an increased
awareness and interest in this important aspect of
filamentous fungal biology. In addition, advances
in molecular and genetic tractability of a variety of
filamentous fungi, and the availability of genome
sequences will lead to in-depth comparative
analyses that will, hopefully, begin to reveal the
rich tapestry of inter- and intrahyphal communication
that accompanies both developmental
and morphogenetic processes. Many questions
regarding the mechanism and function of hyphal
anastomosis remain unanswered. What are the
diffusible chemotropic molecules responsible
for causing fusion-competent hyphae to grow
toward each other, and how do they regulate
Spitzenkörper behavior? Is the signal transduction
machinery involved in regulating hyphal homing
and fusion between conidial germlings the same
or different to that involved in homing and fusion
between hyphae in the colony interior? How
similar or different are the signaling and fusion
machineries involved in vegetative stages vis-à-vis
those involved in sexual stages of the life cycle?
Anastomosis in Filamentous Fungi 135
Finally, what selective advantage maintains the
capacity of germlings and hyphae to undergo
anastomosis, and under what conditions?
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