Search results for "Heterochrony"
showing 9 items of 19 documents
The role of post-natal ontogeny in the evolution of phenotypic diversity in Podarcis lizards
2011
Understanding the role of the developmental pathways in shaping phenotypic diversity allows appreciating in full the processes influencing and constraining morphological change. Podarcis lizards demonstrate extraordinary morphological variability that likely originated in short evolutionary time. Using geometric morphometrics and a broad suite of statistical tests, we explored the role of developmental mechanisms such as growth rate change, ontogenetic divergence ⁄ convergence ⁄ parallelism as well as morphological expression of heterochronic processes in mediating the formation of their phenotypic diversity during the post-natal ontogeny. We identified hypermorphosis – the prolongation of …
Vascular Senescence: A Potential Bridge Between Physiological Aging and Neurogenic Decline
2021
The adult mammalian brain contains distinct neurogenic niches harboring populations of neural stem cells (NSCs) with the capacity to sustain the generation of specific subtypes of neurons during the lifetime. However, their ability to produce new progeny declines with age. The microenvironment of these specialized niches provides multiple cellular and molecular signals that condition NSC behavior and potential. Among the different niche components, vasculature has gained increasing interest over the years due to its undeniable role in NSC regulation and its therapeutic potential for neurogenesis enhancement. NSCs are uniquely positioned to receive both locally secreted factors and adhesion-…
Combining ontogenetic and evolutionary scales of morphological disparity: a study of early Jurassic ammonites
2007
SUMMARY Two major research themes in Evolutionary Developmental Biology and in Paleobiology, respectively, have each become central for the analysis and interpretation of morphological changes in evolution: the study of ontogeny/ phylogeny connections, mainly within the widespread and controversial framework of heterochrony; and the study of morphological disparity, the morphological signal of biodiversity, describing secular changes in morphospace occupation during the history of any given clade. Although enriching in their respective fields, these two themes have remained rather isolated to date, despite the potential value of integrating them as some recent studies begin to suggest. Here…
Hétérochronies du développement chez des foraminifères crétacés: Exemples et réflexions
1989
Resume Differentes modifications de l'ontogenese (neotenie, acceleration, hypermorphose), associees a des innovations, sont illustrees chez des foraminiferes planctoniques et benthiques de l'Aptien-Albien du Bassin de Paris.
Skull osteology ofParvilacerta parva, a small-sized lacertid lizard from Asia Minor
2002
The skull of the poorly known Asia Minor lacertid lizard Parvilacerta parva is described. In comparison to other palaearctic lacertids, Parvilacerta parva displays several peculiar traits such as a large braincase, a short parietal table, closed post-temporal openings, reduced ossification, or a large lacrimal. Many features are related to the small size of Parvilacerta parva and are of apparently heterochronic nature, as they can also be found in certain ontogenetic stages of other lacertid species. Small size and heterochrony even seem to be factors involved in the less-developed sexual dimorphism of Parvilacerta parva. The described morphology is interpreted to be related to a life histo…
Paramblypterus duvernoyi(Actinopterygii): skull morphology and intra-specific variation, and its implications for the systematics of paramblypterid f…
1999
ABSTRACT More than 300 specimens of Paramblypterus duvernoyi from four lakes of the Lower Permian of Germany are examined to determine intra-specific variation of this species and to revise the diagnosis of the genus Paramblypterus. For the first time, a three-dimensional model of the skull and the snout of Paramblypterus is reconstructed. A partial tooth bearing premaxilla, which forms the anterior most part of the gape, is described; in contrast, the absence of a premaxilla had until now been considered a synapomorphy of the genus Paramblypterus. Information obtained from the study of P. duvernoyi has required a new revision of Paramblypterus gelberti. A comparison between the two species…
The complex nature of progenetic species — examples from Mesozoic ammonites
1991
Several examples of progenetic species among Mesozoic ammonites are investigated. The ammonites are Middle Jurassic kosmoceratids, Upper Jurassic oppeliids, and Upper Cretaceous scaphites. As assessed through outgroup comparison, the progenetic species in each of these examples is characterized by small size at maturity and the presence of morphological features typical of those of the juveniles of more primitive species. However, in none of these examples is the progenetic species a duplicate form of the juvenile stage of more primitive species. There are at least three kinds of features of progenetic species that differ from those of the juveniles of more primitive species: (1) symplesiom…
Genetic basis of speed of development in Senecio vulgaris L var. vulgaris, S. vulgaris ssp. denticulatus (O.F. Muell.) P.D. Sell, and Senecio vernali…
1996
The genetic basis of differences in speed of development from germination to first bud formation was investigated in Senecio vulgaris var. vulgaris and S. vulgaris ssp. denticulatus, and also in S. vernalis sampled from Israel and Germany. In the case of S. vulgaris, F2 segregation analysis and the recovery of very late and very early lines from extreme F2 phenotypes showed that differences can be explained by a single major gene model, whereas segregation data from F2 and backcross progenies in S. vernalis are not incompatible with a digenic model of inheritance. Senecio vernalis from Israel and S. vulgaris var. vulgaris reached the different developmental stages in a substantially shorter…