Chapter 15.3

Evolution in Action

Case Study: Caribbean Anole Lizards

• Often, scientists compare groups of organisms and look for patterns to group them better

• For example: Anole lizards in the Caribbean islands have different body types based on their environments– Anole lizards that live mostly in trees have stocky

bodies and long legs– Anole lizards that live on slender twigs usually have

thin bodies, short legs and tails and large toe pads

Anole Lizards

• There are two hypotheses that could explain these similarities:– An ancestral anole species adapted for twigs lived on one

island and migrated to other islandsOR

– Each twig-dwelling species evolved independently on each island from distinct anole ancestors

• Both hypotheses were tested through DNA testing and the DNA evidence supported the second hypothesis

• This process is known as convergent evolution

Divergent Evolution

• The model of the anole lizards can ALSO explain how the lizards adapted to different habitats

• Long-legged trunk-dwellers can run faster and the short-legged twig-dwellers, but these could climb better

• Both kinds of species on each island were closely related, but had become adapted to their own habitat: divergent evolution

Adaptive Radiation

• Sometimes, divergent evolution will happen to a new species in a new habitat until the population fills the space

• This is called adaptive radiation• The anole lizards may have migrated to a new

island and quickly evolved into several new populations/species in order to fill the new habitat

• The fossil record indicates that adaptive radiation happened several times on the geologic time scale

Artificial Selection

• Darwin’s first chapter in On the origin of species… was about artifical selection

• This is the process of choosing individuals in a population based on certain characteristics

• Breeders of dogs and cats, farmers, etc do this a lot in order to get the best qualities into one “product”

• With dogs: if we look into the genetics of dogs, we can see that all dogs descend from wolves in East Asia, where the first domestic dogs were selected from

Coevolution

• Evolution is an ongoing process and is happening all the time

• Each species has forces of natural selection acting upon it

• If two or more species evolve adaptations to each other’s influence (predator/prey for example), this is called coevolution

• Flowering plants/insects, antibiotics/bacterial resistance, etc