Vertebrate evolution/diversification Flashcards
evolution
forces of natural selection operation on genetically controlled variation among individuals could result in changes within lineages over time
conditions for evolution
variation
differential reproduction
heredity
mechanisms of change
(all of them change proportions of genes) mutation random (genetic drift) migration (gene flow) selection (context dependent)
mutation
due to recombination and results in dif phenotypes
random/genetic drift
killed off for random reason
ex: founder effect (genes of founders have high frequency)
migration (gene flow)
new genes introduced from the migration of an individual with a new phenotype into population
selection
positive or negative and relies upon the context
purifying selection
negative
eliminates variation producing either stabilizing or disruptive selection
directional selection
positive
increases phenotypic and or genetic variation
fitness
the effect of a phenotype on an organisms ability to produce and raise viable offspring
is context dependent
heterochrony
developmental change in the timing of events leading to changes in size of and shape
best explanation for dif sizes/shapes in similar population
reasons for heterochrony
change in initiation
change in duration of growth
change in rate of growth
splanchnocranium
phylogenetically oldest part of the skull
many derived bones
important ones: incus malleus and stapes
gill arches, palatoquadrate, meckles cartilage, hyoid cartilage
chondrocranium
phylogenetically second oldes part of skull
supporst the brain
includes otic capsule, optic capsule, olfactory capsule
dermatocranium
phylogenetically youngest part of the skull
frontal, temporal, tympanic, occipital parietal etc.
what is splanchnocranium made out of/what does it do?
part of endoskeleton
supports the gills
allows ear ossicles to develop (only in mammals)
chondrocranium is…
cartilaginous trough beneath brain
comes from fusion of cartilage capsules around nasal and otic organs
dermatocranium originated from..
enlarged head scales which gradually sunk into the head
originated in skin
as chordates evolved their dermal bones…
reduced
fused
were eliminated
