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 squa- incus mosum maxilla malleus proc. styl. mandibula
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
external (ventral) carotid Liemal.04et frog human carotid pathways
ce/ci: carotis ext./int. s: a. stapedia p: a. promontorii pa: a. pharyngea ascendens
most cheirogaleids tarsiers lemuriforms loriforms anthropoids
Geissmann, 03 Gray’s Anatomy branchial arches and human anatomy
arch skeletal elements muscles arteries cranial nerves
1 maxilla, mandible, incus, mastication - V trigeminus malleus 2 stapes, styloid process, facial expression - VII facialis body and lesser horns of hyoid 3 body and greater horns stylopharyngeus int. IX glossopharyngeus of hyoid carotis
4-6 laryngeal cartilages palatine, 4: aorta, X vagus + acc.cran. pharyngeal, subclavia XI acc.spin. laryngeal, 5,6: - trapezius, sternomastoid gene expression patterns during early head development
Kuratani 04 genetics of craniofacial development SantagatiRijli,& 03 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 dental age
birth adult 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: adult descendant similar in shape paedomorphosis to juvenile ancestor
phenotype
juvenile ancestor adult descendant
developmental time heterochrony: juvenile descendant similar in shape peramorphosis to adult ancestor
phenotype
adult ancestor juvenile descendant
developmental time 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