Fluctuating asymmetry is a contentious indicator of stress in populations of animals and plants. Nevertheless, it is a measure of developmental noise, typically obtained by measuring asymmetry across an individual organism's left-right axis of symmetry. These individual, signed asymmetries are symmetrically distributed around a mean of zero. Fluctuating asymmetry, however, has rarely been studied in microorganisms, and never in fungi.
Objective and Methods
We examined colony growth and random phenotypic variation of five soil microfungal species isolated from the opposing slopes of Evolution Canyon, Mount Carmel, Israel. This canyon provides an opportunity to study diverse taxa inhabiting a single microsite, under different kinds and intensities of abiotic and biotic stress. The south-facing African slope of Evolution Canyon is xeric, warm, and tropical. It is only 200 m, on average, from the north-facing European slope, which is mesic, cool, and temperate. Five fungal species inhabiting both the south-facing African slope, and the north-facing European slope of the canyon were grown under controlled laboratory conditions, where we measured the fluctuating radial asymmetry and sizes of their colonies.
Different species displayed different amounts of radial asymmetry (and colony size). Moreover, there were highly significant slope by species interactions for size, and marginally significant ones for fluctuating asymmetry. There were no universal differences (i.e., across all species) in radial asymmetry and colony size between strains from African and European slopes, but colonies of Clonostachys rosea from the African slope were more asymmetric than those from the European slope.
Conclusions and Significance
Our study suggests that fluctuating radial asymmetry has potential as an indicator of random phenotypic variation and stress in soil microfungi. Interaction of slope and species for both growth rate and asymmetry of microfungi in a common environment is evidence of genetic differences between the African and European slopes of Evolution Canyon.