evolution and development of the skull
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evolution and development of the skull
modules and networks
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modular development and evolution
when and how during development and evolution? • increase in brain size • decrease in facial size
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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
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skull: development, evolution, function
human neonate skull (CT reconstruction)
neurocranium desmocranium: intramembranous (desmal)
splanchnocranium chondrocranium: enchondral (cartilaginous)
Meckel’s cartilage
ear ossicles
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developmental modules or developmental network?
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skull development and evolution branchial (pharyngeal) arch transformation
Reichert's theory
eye
stapes
incus
malleus
proc. styl.
hyoid
mandibula
maxilla
squa- mosum
MC: Meckel's cartilage PQ: palatoquadratum TR: trabeculae
nasal bones
larynx
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synapsid (mammal-like reptile)
mammal
Liem et al. 04
angular
Reichert's theory
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branchial arches and circulation
Liem et al. 04
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branchial arches and circulation Li
em e
t al.
04
frog human
external (ventral) carotid
internal (dorsal) carotid
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carotid pathways
most lemuriforms
cheirogaleids loriforms
tarsiers anthropoids
Geissmann, 03 Gray’s Anatomy
ce/ci: carotis ext./int. s: a. stapedia p: a. promontorii pa: a. pharyngea ascendens
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branchial arches and human anatomy
arch" skeletal elements" muscles" arteries" cranial nerves"
1" maxilla, mandible, incus, malleus"
mastication" -" V trigeminus"
2" stapes, styloid process, "body and lesser horns of hyoid"
facial expression" -" 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."
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gene expression patterns during early head development
Kuratani 04
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genetics of craniofacial development
San
taga
ti &
Rijl
i, 03
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congenital malformations
Franceschetti (Treacher-Collins) syndrome Apert/Crouzon (1st branchial arch) syndrome
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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
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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
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speciation and development
heterochrony, heterotopy, allometry
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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
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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
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heterochrony example: humans and chimps
cranial size
dental age
birth adult
neurocranial size
dental age
human
chimp
birth adult
splanchnocranial size
dental age
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heterochrony example: humans and chimps
cranial shape: splanchno/neuro size
dental age birth adult
log (cranial size)
human
chimp
log (cranial shape)
ontogenetic allometry
birth
adult
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heterochrony: paedomorphosis
phenotype
developmental time
adult descendant similar in shape to juvenile ancestor
adult descendant juvenile ancestor
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heterochrony: peramorphosis
phenotype
juvenile descendant adult ancestor
juvenile descendant similar in shape to adult ancestor
developmental time
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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