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Lecture 12

BIOLOGY 1M03 Lecture Notes - Lecture 12: Pharyngeal Jaw, Adaptive Radiation, Cichlid

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Ben Evans

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Biology 1M03 Lecture 12
Biological Innovations as a Trigger
Are situations where there's some new characteristic that evolves during evolution
The evolution of many key innovations allow ancestors to rapidly diversify, live in new areas,
exploit new food sources
The evolution of many other key innovations allow ancestors to rapidly diversify, live in new areas,
exploit new food sources, and move in new ways
Cichlid Fish
Underwent multiple adaptive radiations
Adaptions for feeding, variation in social behaviour, size, and morphology
Have a functionally decoupled set of jaws
o The oral jaw and the pharyngeal jaw
o Frees up jaws to specialize in food collection and processing
They evolved this unique morphological innovation and then diversified into many other species
that have separated in ecological niches
Ecological Opportunity
Can trigger adaptive radiation as well
o Are unoccupied ecological niches that species can exploit
o Meaning the availability of new types of resources
E.g. In the Caribbean islands, species or Anolis vary in leg length and tail length
o Some species are ground dwelling, others live in distinct regions of shrubs or trees
o These ecotypes evolved independently and repeatedly on the large island of the Caribbean
o The same adaptive radiation of Anolis has occurred on different islands, starting from
different types of colonists
Ecological opportunity also influences adaptive radiation of Darwin's finches, variation in bill shape
corresponds with trait utility
The "background rate" of extinction refers to the level of extinction during periods when mass
extinctions are not occurring
Mass extinctions are periods with extreme levels of biodiversity loss
Background extinctions typically occur when normal environment change, emerging diseases, or
competition reduces certain populations to zero
Mass extinctions result from extraordinary, sudden, and temporary changes in the environment;
they cause extinction randomly with respect to individuals' fitness under normal conditions
Differential Survival
o Some evolutionary lineages were better able than others to withstand the environment
change brought on by the meteorite impact
o Among vertebrates, the dinosaurs, pterosaurs, and large marine reptiles went extinct, but
mammals, crocodilians, amphibians, and turtles survived
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