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

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Abstract
As a first attempt to investigate evolutionary patterns of spore size in Agarics, 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 congeneric species (a three-fold difference in cap diameter was used to discriminate big and small mushrooms). It is argued that larger spore size does not consistently confer higher fitness in fungi, owing to aerodynamic constraints. Surprisingly, the cap–spore correlation was strongly lineage-specific. Thus, spore volume correlated significantly with cap diameter in five of 16 large genera (four positive and one negative correlation). Positive cap–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 genera investigated are discussed.

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