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See detailFacultative paedomorphosis and the pattern of intra- and interspecific variation in cranial skeleton: lessons from European newts (Ichthyosaura alpestris and Lissotriton vulgaris)
Ivanović, Ana; Cvijanović, Milena; Denoël, Mathieu ULg et al

in Zoomorphology (2014), 133(1), 99-109

Paedomorphosis, the presence of ancestral larval and juvenile traits that occur at the descendent adult stage, is an evolutionary phenomenon that shaped morphological evolution in many vertebrate lineages ... [more ▼]

Paedomorphosis, the presence of ancestral larval and juvenile traits that occur at the descendent adult stage, is an evolutionary phenomenon that shaped morphological evolution in many vertebrate lineages, including tailed amphibians. Among salamandrid species, paedomorphic and metamorphic phenotypes can be observed within single populations (facultative paedomorphosis). Despite wide interest in facultative paedomorphosis and polymorphism produced by heterochronic changes (heterochronic polymorphism), the studies that investigate intraspecific morphological variation in facultative paedomorphic species are largely missing. By quantifying the cranium size and development (bone development and remodeling), we investigated the variation at multiple levels (i.e., between sexes, populations and species) of two facultatively paedomorphic European newt species: the alpine and the smooth newt. The pattern of variation between paedomorphs (individuals keeping larval traits at the adult stage) and metamorphs (metamorphosed adult individuals) varied between species and among populations within a single species. The patterns of variation in size and skull formation appear to be more uniform in the alpine than in the smooth newt, indicating that developmental constraints differed between species (more pronounced in alpine than in smooth newt). Our study shows that the cranial skeleton provides detailed insight in the pattern of variation and divergence in heterochronic polymorphism within and between species and open new questions related to heterochronic polymorphism and evolution of cranial skeleton. [less ▲]

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See detailDiversification of the pectoral fin shape in damselfishes (Perciformes, Pomacentridae) of the Eastern Pacific
Aguilar-Medrano, Rosalia; Frederich, Bruno ULg; Balart, Eduardo F. et al

in Zoomorphology (2013)

Fin shape strongly influences performance of locomotion across all swimming styles. In this study, we focused on the diversity of the pectoral fin morphology in damselfishes of the Eastern Pacific ... [more ▼]

Fin shape strongly influences performance of locomotion across all swimming styles. In this study, we focused on the diversity of the pectoral fin morphology in damselfishes of the Eastern Pacific. Underwater observations and a review of literature allowed the characterization of ten behavioral groups. Territorial and non-territorial species were discriminated easily with traditional morphometrics. Five ecomorphological groups were recognized by geometric morphometric analyses. Geometric data segregated the outgroup from the damselfishes and allowed the distinction of mean morphologies from extreme ones within territorial and non-territorial species. Additionally, geometric morphometric data split Abudefduf into two groups: (1) A. troschelii is similar to C. atrilobata and (2) A. concolor and A. declivifrons are close to Stegastes. Solitary territorial species (e.g., Stegastes) show rounded and high fins whereas non-territorial species living in groups (e.g., Chromis) present long and curved pectoral fins. In the range of morphological variation, the morphologies of Microspathodon (elongate with highly curved hydrodynamic trailing edge) and Azurina (long, slender and angular) represent the extreme morphologies within territorial and non-territorial species, respectively. Our study revealed a strong relationship between the pectoral fin shape and the behavioral diversification in damselfishes. [less ▲]

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See detailFunctional morphology of Tethya species (Porifera): 2. Three-dimensional morphometrics on spicules and skeleton superstructures of T-minuta
Nickel, M.; Bullinger, Eric ULg; Beckmann, F.

in Zoomorphology (2006), 125(4), 225-239

The biomechanics of body contraction in Porifera is almost unknown, although sponge contraction has been observed already in ancient times. Some members of the genus Tethya represent the most contractile ... [more ▼]

The biomechanics of body contraction in Porifera is almost unknown, although sponge contraction has been observed already in ancient times. Some members of the genus Tethya represent the most contractile poriferan species. All of them show a highly ordered skeleton layout. Based on three main spicule types, functional units are assembled, termed skeleton superstructures here. Using synchrotron radiation based x-ray microtomography and quantitative image analysis with specially developed particle and structure recognition algorithms allowed us to perform spatial allocation and 3D-morphometric characterizations of single spicules and skeleton superstructures in T. minuta. We found and analyzed three skeleton superstructures in the investigated specimen: (1) 85 megasclere bundles, (2) a megaster sphere, composed by 16,646 oxyasters and (3) a pinacoderm-tylaster layer composed by micrasters. All three skeleton superstructures represent composite materials of siliceous spicules and extracellular matrix. From structure recognition we developed an abstracted mathematical model of the bundles and the sphere. In addition, we analyzed the megaster network interrelation topology and found a baso-apical linear symmetry axis for the megaster density inside the sphere. Based on our results, we propose a hypothetical biomechanical contraction model for T. minuta and T. wilhelma, in which the skeleton superstructures restrain physical stress generated by contraction in the tissue. While skeletal structures within the genus Tethya have been explained using R. Buckminster Fullers principle of tensegrity by other authors, we prefer material science based biomechanical approaches, to understand skeletal superstructures by referring to their composite material properties. [less ▲]

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See detailMorphological comparison of the buccal apparatus in two bivalve commensal Teleostei : Encheliophis dubius and Onuxodon fowleri (Carapidae, Ophidiiformes)
Parmentier, Eric ULg; Castro-Aguirre, J. L.; Vandewalle, Pierre ULg

in Zoomorphology (2000), 120

Onuxodon fowleri and Encheliophis dubius are two Carapidae species that live in bivalve hosts and, their diet is made of the same type of prey. The aim of this study is to compare their cephalic ... [more ▼]

Onuxodon fowleri and Encheliophis dubius are two Carapidae species that live in bivalve hosts and, their diet is made of the same type of prey. The aim of this study is to compare their cephalic morphology to see whether 1) the head anatomy of both species is related to the constraints of their way of life, and 2) there are difference between these species and commensal carapids that shelter in other invertebrates. The components of their skeletons and muscles are similar, but differ in size and are arranged differently. In O. fowleri, the buccal cavity is smaller than in E. dubius, the jaws (bearing very large anterior teeth) are larger, the quadrato-mandibular joint lies further to the rear, the fibres of muscle bundles A3a, A2a and A2b are more vertical and insert higher on the neurocranium. The buccal system of O. fowleri appears better suited for ingesting food by biting and grasping. That of E. dubius seems better adapted to a feeding mechanism where sucking would have a more important role. The E. dubius head morphology is more similar to the cephalic anatomy of non-bivalve commensal species than to O. fowleri features. Diet constraints may have greater influence than the different host constraints on the head construction. A simulated backward rotation of the posterior part of the E. dubius suspensorium around the posterior joint between the hyomandibular and the neurocranium brings the jaws and the cheeks to coincide with those of O. fowleri. This model could be indicative of how structure modifications and their influences on annex pieces could in part have a role in the biodiversity. [less ▲]

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See detailSkeleton resorption in echinoderms : regression of pedicellarial stalks in Sphaerechinus granularis (Echinoidea)
Bureau, Fabrice ULg; Dubois, Philippe; Ghyoot, M. et al

in Zoomorphology (1991), 110

When a globiferous pedicellaria of Sphaerechinus granularis injects its venom, the head autotomizes whereas the stalk remains on the test and enters a regression process with concomitant resorption of its ... [more ▼]

When a globiferous pedicellaria of Sphaerechinus granularis injects its venom, the head autotomizes whereas the stalk remains on the test and enters a regression process with concomitant resorption of its supporting ossicle (i.e. the rod). Scanning electron microscope investigations of the morphological changes undergone by the stereom of resorbing rods show that: (1) resorption proceeds both axially and laterally, and leads to a reduction of approximately 80% of the original length of the rod, (2) secondary growth of new stereom processes occurs concomitantly with resorption but never ensures even a partial regeneration of the rod, and (3) resorption and secondary growth stop before the rod is totally destroyed leaving a static stump that remains in place up to 190 days. Particular resorption figures result from either the axial or the lateral resorption of the rod shaft. These consist chiefly of terraced conical cupules, dense cylinders and concentric lamellae whose walls or edges are typically made of closely piled and/or aligned subprismatic crystallites. Whatever their location along the rod, these crystallites always organize strictly parallel to the rod axis. Whether the crystallites are mosaic blocks composing larger monocrystalline units or discrete monocrystals themselves is for the moment unclear. A growth model, which accounts for the observed resorption figures, is proposed for the shaft of pedicellarial rods. According to this model, the early growth of the shaft would produce elongated, interconnected trabeculae (initial trabeculae) made of densely piled and perfectly aligned crystallites. Thickening and coalescence of adjoining trabeculae would progressively occur by adjunction around the initial trabeculae of successive and concentric layers of similarly arranged crystallites. Coalescent trabeculae would then be cemented together in a perforate stereom layer by the final deposition of larger crystallite layers surrounding the whole shaft periphery. Growth of secondary stereom processes occurs both in the resorbing rod (here the newly formed processes are resorbed soon after they have been produced) and in rods where resorption has stopped. These are always irregular processes that localize near or on the actual sites of resorption. It is suggested these processes result from an uncontrolled activation of the skeleton-forming cells in areas where the concentration of calcium ions increases as a consequence of calcite resorption [less ▲]

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