Modularity and complete natural homeoses in cervical vertebrae of extant and extinct penguins (Aves: Sphenisciformes).

17 pagesInternational audienceThe cervical system of extant penguins (Aves: Sphenisciformes) is organised into morphological modules, each with its biomechanical function. Indeed, for these marine pelagic birds to acquire hydrodynamic morphology, the folding of the neck is essential. Despite a common general structure, the cervical vertebrae exhibit morphological differences depending on their positioning. These characteristics are identified as apparent cases of complete natural homeotic transformations—therefore, the composition of some modules varies. Two types of complete cervical homeoses are identified between species, but the second type can also occur within some species when the post hatching development is considered. The fossil material analysed here makes it apparent that the two modular configurations characterising the anterior part of the neck—a consequence of the first homeosis—existed 36 My and 25 My ago, for one, and circa 10 My ago, for the other. These comparisons also reveal a clear differentiation in vertebral features between the fossil species of the Oligocene–Miocene ages and the more recent and extant penguins. Ultimately, these observations make the proposal of a hypothesis in relation to the ontogenetic influence of Hox genes, and their regulators, based on the changes observed in the cervical segment of Sphenisciformes

Morphology, ontogenesis and mechanics of cervical vertebrae in four species of penguins (Aves: Spheniscidae).

16 pagesInternational audiencePenguins (Aves: Spheniscidae) are pelagic, flightless seabirds, restricted to the southern hemisphere (Antarctic and sub-Antarctic areas, New Zealand, Australia, and nearby islands, as well as parts of South America and South Africa). They spend much of their life at sea, but return to islands and coasts to breed. Penguins are terrestrial as juveniles and aquatic as adults. To improve hydrodynamics, penguins tuck in their necks while swimming. They thus attain an ‘‘ichthyosaur'' or ‘‘cetacean'' body shape: characterised by telescoped cervicals. This mechanism is also used on land, associated with the posture of these birds. Our study of neck structure and cervical vertebrae morphology (morphological description, biometry and contour analysis) of the King Penguin (Aptenodytes patagonicus), Gentoo Penguin (Pygoscelis papua), Macaroni Penguin (Eudyptes chrysolophus) and Humboldt Penguin (Sphensicus humboldti) shows a highly specialised fitting in adults, which develops during ontogenesis. The growth of penguins proceeds by stages and there are key stages with regard to the design of the neck. Despite a common main structure, some characteristics vary between species. Distribution of cervical vertebrae can be defined by six modules. There are differences in modularity between species and also within species between different ontogenetical phases

Evolutionary concepts meet the neck of penguins (Aves: Sphenisciformes), towards a "survival strategy" for evo-devo.

12 pagesInternational audienceEvolutionary developmental biology (or evo-devo) is the scientific connectivity that allowed a more comprehensive and practical completeness in the contemporary conceptualisation of evolution. The links between genetics, developmental mechanics and evolution led to a better understanding of evolutionary mechanisms. An analysis of evolutionary concepts such as homology, homeoses, constraints, novelties, modularity, and selection is given through the recurring example of the variations identified in the modular repartition of the cervical vertebrae in extant and fossil penguins. The inclusion of this study about penguins in the evolutionary system also involves a reflection on the current state and the future of evo-devo. Three principles of assessment and method, applicable to many natural and conceptual scales, are introduced to define a "survival strategy" for evo-devo. The above-mentioned principles are intended to strengthen and continue the connectivity induced de facto. These current and future investigation challenges are discussed and connected to three main naturalist names related directly to the conceptualisation of evolution: Charles Darwin, Étienne Geoffroy Saint-Hilaire, and Lamarck