The functional biology of scleractinian corals is strongly affected by skeletal structure yet the mechanisms determining morphology within this taxon are poorly understood. To gain insight into these mechanisms, patterns of skeletal variation were investigated by quantifying the variability
of 11 skeletal structures (traits) in Montastraea franksi. Different clones and clone-mates were used to gain insight into putative genetic and non-genetic effects, respectively. Principal component analysis of 11 traits generated 4 PCs which were significantly different among clones,
thereby suggesting that intraspecific genetic variation had a substantial effect on morphology. Coefficients of variation (CV) for eight linear traits were used to compare the degree of variation among traits. All CVs within groups of clone-mates were relatively high (means >0.07) and ranged
from 0.071 for calyx diameter to 0.322 for calyx depth. CVs were not significantly different among clones, but they were significantly different among traits with calyx depth and the length and width of spines being more variable than other traits. Thus, the degree of variation of skeletal
structures appeared not to vary among clones, but differed among traits. These results indicate that corallite structure is determined by both genetic and non-genetic (environmental) factors and suggest that the degree of variability in skeletal structures is conserved intraclonally but that
the absolute range over which it operates is genetically variable. As the morphology of coral colonies can be affected by corallite features such as their size and spacing, it is possible that further studies of corallite structure may be useful in understanding the mechanisms controlling
colony morphology in M. franksi and possibly other scleractinians. The present results provide a method to select corallite structures for study based on their degree of variabilty, and suggest that the most useful will be either highly variable (calyx depth, spine length, spine width)
or relatively invariable (calyx and corallite diameter) structures.
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