Development and life history 2 PDF

Development and life history 2 BI2CV1 Comparative Vertebrate Biology Dr Manabu Sakamoto [email protected] Embryonic development Later stages of embryonic development differ by vertebrate groups and species. Some develop into a larva. Others...

Development and life history 2 BI2CV1 Comparative Vertebrate Biology Dr Manabu Sakamoto [email protected] Embryonic development Later stages of embryonic development differ by vertebrate groups and species. Some develop into a larva. Others develop into a fetus. All major features are developed by the fetal stage. Metamorphosis Metamorphosis is the radical and abrupt postembryonic changes to become an adult. Widespread in animals including vertebrates. Distinct stages including larval and adult. Metamorphosis controlled by thyroid hormones. Evolution of metamorphosis in vertebrates Metamorphosis may be ancestral to vertebrates. Non-vertebrate chordates (tunicates2 and lancelets3) undergo metamorphosis. Thyroid hormone induced metamorphosis in lancelets. Non-jawed vertebrates (lampreys4) undergo metamorphosis. Ontogeny Development of an organism into an adult. Ontogeny is an ongoing process throughout an individual’s lifetime. Ontogeny and phylogeny Does ontogeny recapitulate phylogeny? Ernst Haeckel argued that embryonic development goes through the evolutionary sequence of the ancestors, thus ontogeny recapitulates (repeats) phylogeny. Known as the biogenetic law. Von Baer’s law Karl Ernst Von Baer argued that development proceeds from the general to the specific. Von Baer’s law of the general to the specific. Vertebrate body plan (bauplan) The vertebrate body plan is observed across vertebrates during the phylotypic stage of embryonic development. Morphological diversity of embryos converges towards this conserved body plan, then diverges again: The “hourglass model”. Martinez-Morales 2016. Brief Funct Genomics 15: 315-32 Evolutionary developmental biology Modern evolutionary developmental biology seems to be more in alignment with von Baer’s Law. Heterochrony Heterochrony Heterochrony is an ontogenetic shift in the timing of adult features appearing in descendant species. Paedomorphosis When adults resemble the juveniles of ancestors. Humans Progenesis Neoteny Progenesis Early cessation of somatic development. Growth stops at an early age. Sexual maturity is attained at an early age. Paedomorphic adults. Neoteny Features grow at a slower rate. Sexual maturity overtakes somatic maturity. Paedomorphic adults. Peramorphosis Development of new adult morphologies by extension of ancestral ontogenetic sequence. Adding more steps to growth.