| Summary: | The genus Callopora is typical of a very large number of encrusting neocheilostomate genera and can be used to demonstrate the range of autozooid morphology seen in the group. Morphometric analyses of zooid length (ZL), zooid width (ZW), ovicell length (OL) and ovicell width (OW) were conducted in order to study morphological variation in different populations of Callopora dumerilii, Callopora lineata and CaUopora rylandi and to partition the morphological variation within and between sites and colonies for each species using a nested analysis of variance and a principal component analysis approach. In addition, the genetic structure in populations of these three Callopora species using the mitochondrial DNA COI gene was examined to test hypotheses concerning levels of population differentiation and intrapopulation variation. The relationships of mtDNA lineages within and between species was also investigated to clarify the phylogenetic relationships of the three species and to search for possible phylogenetic subdivisions within species. The morphological characters zooid length and zooid width were significantly different between different sites for Callopora lineata and Callopora dumerilii, but not for Callopora rylandi. However, major differences for these two morphological variables appeared in all three species in between colony within site comparisons. When comparing the ovicell length variable between different sites, noteworthy differences appeared only for Callopora rylandi, whereas considerable differences appeared in all three sites for between colonies within site comparisons. On the other hand, non-significant differences appeared for all three species when comparing ovicell width between different sites whereas highly significant differences appeared for between colony within site comparisons. The results of principal component analysis together with the results from nested ANOVA revealed that for factor 1, which defines aspects of the overall size of the zooid, there were significant differences between sites, as well as between colonies within sites for Callopora rylandi. For Callopora dumerilii and Callopora lineata, it appeared that there were no significant differences between different sites whereas there were notable differences between different colonies within sites. For factor 2, which defines aspects of the shape of the organism, there were significant differences between sites as well as between colonies within sites for both Callopora rylandi and Callopora dumerilii, while for Callopora lineata it emerged that there were no significant differences between sites, but there were important differences between colonies within sites. Analysis of the mitochondrial DNA population structure in these three species based on either haplotype frequencies or sequence divergence showed a large percentage of genetic variation within populations and a much smaller percentage of genetic variation among populations. However, for haplotype frequencies the among populations P values were significant for all species whereas when sequence divergence was taken into account only the P value for Callopora rylandi was significant. Overall nucleotide diversity was similar for Callopora dumerilii and Callopora lineata and higher than that of Callopora rylandi, whereas overall haplotype diversity was similar in all three species. Tajima's D and Fu's Fs test statistic appeared more negative in Callopora rylandi than the other species suggesting greater purifying selection or a recent population expansion. Comparisons based on dn/ds ratio suggested purifying selection as well. Reconstruction of phylogenetic relationships showed three major lineages which are mixed in all three species. Tests of neutrality in these lineages, which do not correspond to species, also suggested the existence of purifying selection.
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