Biology 1st Edition by Jerome Krueger, Kendra Hill, Robert Noyd

Exercise 21

Wood-decay fungi grow as filaments, or threads, within wood. When threads of one fungus encounter a compatible thread, they reproduce sexually by merging their bodies into a single thread. However, in some cases fungal threads encounter an incompatible fungus and initiate a killing reaction by secreting dark-colored chemicals into the wood. These protective chemicals sharply define the interaction zone between two incompatible fungi and result in zone lines in the wood ( Fig. ). Zone lines represent which type of reproductive barrier in these fungal species? Does this killing reaction promote or inhibit the generation of genetic variation? Does it promote or inhibit speciation?
Figure Zone lines.