In addition to experimental studies, computational models provide valuable information about colony development in scleractinian corals. Using our simulation model, we show how environmental factors such as nutrient distribution and light availability affect growth patterns of coral colonies. To compare the simulated coral growth forms with those of real coral colonies, we quantitatively compared our modelling results with coral colonies of the morphologically variable Caribbean coral genus Madracis. Madracis species encompass a relatively large morphological variation in colony morphology and hence represent a suitable genus to compare, for the first time, simulated and real coral growth forms in three dimensions using a quantitative approach. This quantitative analysis of three-dimensional growth forms is based on a number of morphometric parameters (such as branch thickness, branch spacing, etc.). Our results show that simulated coral morphologies share several morphological features with real coral colonies (M. mirabilis, M. decactis, M. formosa and M. carmabi ). A significant correlation was found between branch thickness and branch spacing for both real and simulated growth forms. Our present model is able to partly capture the morphological variation in closely related and morphologically variable coral species of the genus Madracis.Keywords: corals; morphogenesis; morphology; simulation; CT scan; Madracis INTRODUCTIONScleractinian corals exhibit great inter-and intraspecific variation in coral colony morphology (e.g. Veron 1995;Bruno & Edmunds 1997). Intra-specific variation often arises from plasticity in a colony's growth process in response to variable environmental conditions, such as flow speed, availability of light and availability of dissolved inorganic carbon (Muko et al. 2000;Todd et al. 2004;Todd 2008). Because genetic and environmental factors determine a colony's three-dimensional structure, the relative importance of either factor is often difficult to determine. Experimental studies whereby corals are grown under different environmental conditions are often limited by the slow growth rates of corals and difficulties with controlling environmental parameters of the system. Therefore, plastic responses to environmental changes are studied in relatively few (about 17) coral species (Todd 2008).To determine the degree of phenotypic plasticity among colonies of the same species under variable environmental conditions, various morphometric traits are measured to quantitatively assess whether changes in coral colony growth and form correlate with varying environmental factors (e.g. Bruno & Edmunds 1997). Morphological variation in corals exists on different scales, from differences in corallite structure within a single colony (Foster 1979) to variation among colonies in a single species. The present study aims to describe variability at the colony morphology level in species of the Caribbean coral genus Madracis. The Madracis species are characterized by the encrusting (M. pharensis), nodular (M...

Hammel, J.U., Filatov, M.V., Herzen, J, Beckmann, F., Kaandorp, J.A. and Nickel M. 2011. The non‐hierarchical, non‐uniformly branching topology of a leuconoid sponge aquiferous system revealed by 3D reconstruction and morphometrics using corrosion casting and X‐ray microtomography. —Acta Zoologica (Stockholm) 00:1–12. As sessile filter feeders, sponges rely on a highly efficient fluid transport system. Their physiology depends on efficient water exchange, which is performed by the aquiferous system. This prominent poriferan anatomical character represents a dense network of incurrent and excurrent canals on which we lack detailed 3D models. To overcome this, we investigated the complex leucon‐type architecture in the demosponge Tethya wilhelma using corrosion casting, microtomography, and 3D reconstructions. Our integrative qualitative and quantitative approach allowed us to create, for the first time, high‐resolution 3D representations of entire canal systems which were used for detailed geometric and morphometric measurements. Canal diameters lack distinct size classes, and bifurcations are non‐uniformly ramified. A relatively high number of bifurcations show previously unknown and atypical cross‐sectional area ratios. Scaling properties and topological patterns of the canals indicate a more complex overall architecture than previously assumed. As a consequence, it might be more convenient to group canals into functional units rather than hierarchical clusters. Our data qualify the leucon canal system architecture of T. wilhelma as a highly efficient fluid transport system adapted toward minimal flow resistance. Our results and approach are relevant for a better understanding of sponge biology and cultivation techniques.

A major challenge in coral biology is to find the most adequate and phylogenetically informative characters that allow for distinction of closely related coral species. Therefore, data on corallite morphology and genetic data are often combined to increase phylogenetic resolution. In this study, we address the question to which degree genetic data and quantitative information on overall coral colony morphologies identify similar groupings within closely related morphospecies of the Caribbean coral genus Madracis. Such comparison of phylogenies based on colony morphology and genetic data will also provide insight into the degree to which genotype and phenotype overlap. We have measured morphological features of three closely related Caribbean coral species of the genus Madracis (M. formosa, M. decactis and M. carmabi). Morphological differences were then compared with phylogenies of the same species based on two nuclear DNA markers, i.e. ATPSα and SRP54. Our analysis showed that phylogenetic trees based on (macroscopical) morphological properties and phylogenetic trees based on DNA markers ATPSα and SRP54 are partially similar indicating that morphological characteristics at the colony level provide another axis, in addition to commonly used features such as corallite morphology and ecological information, to delineate genetically different coral species. We discuss this new method that allows systematic quantitative comparison between morphological characteristics of entire colonies and genetic data.

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