The evolution of spore size in Agarics: do big mushrooms have big spores?

As a first attempt to investigate evolutionary patterns of spore size in Ag arics, I tested whether this trait was correlated to the size of the fruit- body (basidiocarp). Based on phylogenetically independent contrasts, it was shown that big mushroom species had on average 9% longer. 9% wider and 33% more voluminous spores (all with P < 0.05, one-tailed tests) than small co ngeneric species (a three-fold difference in cap diameter was used to discr iminate big and small mushrooms). It is argued that larger spore size does not consistently confer higher fitness in fungi, owing to aerodynamic const raints. Surprisingly, the cap-spore correlation was strongly lineage-specif ic. Thus, spore volume correlated significantly with cap diameter in five o f 16 large genera (four positive and one negative correlation). Positive ca p-spore correlations are interpreted in terms of developmental constraints, mediated by hyphal swelling during cap expansion. The possible mechanisms which can account for the breakdown of this constraint in the majority of g enera investigated are discussed.