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Heterochronic shifts explain variations in a sequentially developing repeated pattern: Palatal ridges of muroid rodents

Abstract : Metazoans are largely made of repeated parts, and metazoan evolution is marked by changes in the number of these parts, called meristic changes. Understanding the mechanisms associated with development and evolution of these repeated parts is a thus a critical issue to (evolutionary) developmental biology. Palatal rugae are sensory ridges regularly arranged on the hard palate of mammals. In a previous study, we had shown that mouse rugae develop sequentially following mesio-distal growth of the palate, and that activation-inhibition mechanisms very likely control spacing and timing of this sequential addition. In the present study, we characterized trends in rugae number evolution among muroid rodents, showing that most species display 8 ± 1 rugae, changes by one being very frequent in the phylogeny. We then compared development of three muroid species: mouse (9 rugae), rat (8) and golden hamster (7). We showed that palatal growth rate, spacing and addition rate in mouse/rat were remarkably similar (with respect to the embryo size difference), and that increase to 9 rugae in mouse is achieved by postponing the end of the addition process (hypermorphosis). Such a heterochronic shift may be typical of ±1 variations observed among muroid rodents. In contrast, decrease to 7 rugae in golden hamster is attributed to early growth termination (progenesis) of the palate, which correlates with the severe shortening of gestation in this species. Our results provide an experimental support to the intuitive view that terminal heterochronies are especially relevant to meristic evolution of traits that rely on a sequential addition process.
Keywords : RAT
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Sophie Pantalacci, Marie Semon, Arnaud Martin, Pascale Chevret, Vincent Laudet. Heterochronic shifts explain variations in a sequentially developing repeated pattern: Palatal ridges of muroid rodents. 16. Annual Conference of the International Society of-Development-Biologists, Sep 2009, Edinburgh, United Kingdom. ⟨10.1016/j.mod.2009.06.653⟩. ⟨hal-02753427⟩



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