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evolution and development of the skull modules and networks modular development and evolution when and how during development and evolution? • increase in brain size • decrease in facial size human candidate genes • FOXP2 [forkhead box P2] (Lai et al. 01) – some alleles associated with speech and language disorder – humans have specific allele, different from great apes – human allele also in Neanderthals (Krause et al. 07) • MYH [myosin heavy chain expression] (Stedman et al. 04) – less expressed in humans (MYH16 inactivation) compared to great apes • ASPM [abnormal spindle-like microcephaly-assoc.] (Mekel Bobrov et al. 05) MCPH1 [microcephalin] (Evans et al. 05) – some alleles involved in primary microcephaly – some alleles show signs of recent selective sweeps in humans, but they are not related to brain size skull: development, evolution, function ear ossicles Meckel s cartilage desmocranium: intramembranous (desmal) neurocranium chondrocranium: enchondral (cartilaginous) splanchnocranium human neonate skull (CT reconstruction) developmental modules or developmental network? skull development and evolution branchial (pharyngeal) arch transformation Reichert's theory eye stapes nasal bones maxilla squamosum mandibula incus malleus proc. styl. hyoid larynx MC: Meckel's cartilage PQ: palatoquadratum TR: trabeculae Reichert's theory synapsid (mammal-like reptile) angular mammal Liem et al. 04 branchial arches and circulation Liem et al. 04 branchial arches and circulation internal (dorsal) carotid Liem et al. 04 external (ventral) carotid frog human carotid pathways ce/ci: carotis ext./int. s: a. stapedia p: a. promontorii pa: a. pharyngea ascendens most lemuriforms Geissmann, 03 cheirogaleids loriforms tarsiers anthropoids Gray s Anatomy branchial arches and human anatomy arch" skeletal elements" arteries" cranial nerves" maxilla, mandible, incus, mastication" malleus" stapes, styloid process, " facial expression" body and lesser horns of hyoid" -" V trigeminus" -" VII facialis" 3" body and greater horns of hyoid " stylopharyngeus" int. carotis" IX glossopharyngeus" 4-6" laryngeal cartilages" palatine, pharyngeal, laryngeal, trapezius, sternomastoid" 4: aorta, " subclavia" 5,6: -" X vagus + acc.cran." XI acc.spin." 1" 2" muscles" gene expression patterns during early head development Kuratani 04 Santagati & Rijli, 03 genetics of craniofacial development congenital malformations Franceschetti (Treacher-Collins) syndrome Apert/Crouzon (1st branchial arch) syndrome skull evo-devo and human craniofacial malformations FGFR-2 gene mutations lead to congenital malformations of head and limbs: „1st+2nd branchial arch disorders“ • e.g. Apert syndrome (acrocephalo-syndactyly) – – – – craniosynostoses underdevelopment of maxilla low position of ears syndactyly • e.g. Franceschetti (Treacher Collins) syndrome – underdevelopment of mandible, zygomatic bones and external/middle ears developmental reorganization during evolution • heterotopy: spatial reorganization – deposition vs. resorption – size, shape, arrangement of dep. and res. fields • heterochrony: temporal reorganization – sequence of growth events (onset - duration - offset) – local rates of growth and development speciation and development heterochrony, heterotopy, allometry definitions • ontogeny: structural (form) change from conception to death • form: size and shape • growth: change in size • development: change in shape • allometry: size-related change (or variation) in shape speciation through ontogenetic reorganization • heterotopy: spatial reorganization of ontogeny, change in directions of growth and development – e.g. migration patterns of NCC – e.g. nr. and arrangement of dental cusps – e.g. spatial arrangement of depository and resorptive bone growth fields • heterochrony: temporal reorganization of ontogeny, change in rates of growth and development – e.g. proliferation rates of NCC – e.g. onset, duration, and offset of dental cusp formation – e.g. local rates of bone resorption and deposition heterochrony example: humans and chimps cranial size human chimp dental age neurocranial size splanchnocranial size dental age birth adult dental age birth adult heterochrony example: humans and chimps cranial shape: splanchno/neuro size chimp human dental age birth adult log (cranial shape) adult ontogenetic allometry birth log (cranial size) heterochrony: paedomorphosis adult descendant similar in shape to juvenile ancestor phenotype juvenile ancestor developmental time adult descendant heterochrony: peramorphosis juvenile descendant similar in shape to adult ancestor phenotype adult ancestor developmental time juvenile descendant heterochrony: pattern and process • different heterochronic processes can result in similar heterochronic patterns • example: paedomorphy of the human head can result from – delayed facial growth – decelerated facial growth – early cessation of facial growth – advanced brain growth – accelerated brain growth – long duration of brain growth – … or a combination of these processes è all result in small-faced, large-brained heads