Morphological variation in the coral genus Platygyra: environmental influences and taxonomic implications

Abstract

Scleractinian corals are notoriously variable and the high degrees of morphological variation displayed by some species, particularly in response to environmental influences, confound our understanding of species boundaries. In order to fully understand the ranges of variation and the influence of habitat on colonies within the genus Platygyra, levels of intra-and interspecific morphological variation were quantified and colony morphology was examined relative to environmental gradients. Measurements of 9 skeletal characters of colonies of Platygyra were analysed by multivariate analysis of variance and canonical discriminant analysis to examine morphological species boundaries. While the taxonomic literature suggests the existence of 5 morphological species of Platygyra, results from this study suggest there may be 7 present on the Great Barrier Reef, Australia. A comparison of skeletal characters of 2 species, F? daedalea and F? pini, across 4 different habitats indicates that the environment does not influence skeletal characteristics in these species. Similarly, a detailed survey of distribution patterns of Platygyra spp. indicates that all species occur sympatrically across 6 reef habitats and that colony morphology does not change predictably along environmental gradients. The absence of any association between morphology and habitat in Platygyra suggests environment has little influence on morphology in these species. Numerical techniques are likely to be useful for defining species boundaries in highly variable groups of corals and similarly for understanding ranges of intraspecific morphological variation.

Assessing hidden species diversity in the coral Pocillopora damicornis from Eastern Australia

“…Miller 1994;Shaish et al 2007;Todd 2008). In some taxa, transplant experiments have demonstrated that colony morphology can largely vary with habitat changes (e.g.…”

Genotype × environment interactions in transplanted clones of the massive corals Favia speciosa and Diploastrea heliopora

“…Knowlton et al 1992, 1997, Weil 1993, Van Veghel & Bak 1993, Knowlton & Jackson 1994, Lasker et al 1996, whereas other 'morphological species' are being found to have only small genetic or reproductive differences (e.g. Miller 1994, Szmant et al 1997.…”

“…Analogous to plants, this variation can be due to genetic differentiation (Willis & Ayre 1985, Ayre & Willis 1988, phenotypic plasticity (Foster 1977, Miller 1994, Bruno & Edmunds 1997, Muko et al 2000 or both in synthesis (Foster 1979, Amaral 1994. As the majority of coral systematics is based upon morphological traits (Brakel 1977, Veron 2000, any plasticity of taxonomically important characters has far-reaching consequences.…”

Diel `tuning' of coral metabolism: physiological responses to light cues

“…While most of these changes take longer than a day, some, such as polyp expansion and contraction, occur within minutes (Levy et al, 2003). Changes in the density of the zooxanthellae and reshuffling of their species occur within days, whereas changes in growth form of the coral colony may take several months to years (Graus and Macintyre, 1982;Miller, 1994;Todd et al, 2004), and genetic selection takes thousands of years (Falkowski et al, 1990).…”