Download evolution and development of the skull

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