Speciation Biology 10 at GI Biology 11

Speciation  The development of a new species  Usually the result of reproductive isolation How does this occur? Two populations of the same species are separated somehow Separation may be by: Geography (geographical isolation) Time (temporal isolation) Behaviour (behavioural isolation) Habitat (ecological isolation)

 Separation leads to reproductive isolation i.e. the members of the separate groups can no longer mate with members of the wider population  The now separate populations evolve in their own environments and in time  Their gene pools will change independently of each other  With enough changes, interbreeding will no longer be possible  A NEW species is formed!

Modeling speciation in fruit flies

Reproductive isolation  Physical barriers to reproduction result in ALLOPATRIC speciation Each environment is different allowing for different adaptations to become common

Three similar birds… on three different continents! (An example of geographical isolation)

Separation of beetle populations by a river

What about these two species? The giant panda and the red panda live in the same habitat. How did they speciate from a common ancestor?

 Barriers to reproduction other than physical (e.g. ecological, temporal, behavioural) lead to SYMPATRIC speciation

 BIOLOGICAL DISTANCE – is a measure of the differences that exist between gene pools.  The greater (longer) the biological distance, the greater the difference between two species.

DIVERGENT EVOLUTION  Diversification from simple to complex forms e.g. complexity of shell leading to lighter, but stronger, shells.

Divergent Evolution/Adaptive radiation  Evidence for this is seen in fossil records  The number of similarities between populations of species decrease over time and hundreds or thousands of generations  Species from a common ancestor may grow to be completely dissimilar.  Happens because each species is subjected to different selection pressures

ADAPTIVE RADIATION: a special kind of divergent evolution These organisms have similar but different beaks. These are homologous structures.

Adaptive radiation beginning?

EXAMPLES OF CONVERGENT EVOLUTION

Convergent Evolution  Species from different evolutionary branches come to resemble one another  Usually occurs between species in similar environments and therefore subjected to similar selection pressures.  Results in body structures or even whole organisms that look similar  Similarity as a result of convergence is called analogy and such structures are called analogous structures

The two processes may work together:

How quickly does evolution occur?  Gradualism  the theory that new species arise from many small changes building up over time

Gradually we see new species…

The Role of Extinction  Extinction of a species means that the species was no longer ‘fit’ for survival. It reproduces less than others, or not at all and its genes are not seen in future generations. Few environmental changes  few extinctions. Large environmental changes (e.g. earthquake, climate change)  many extinctions.

EXTINCTIONS OVER TIME

Theory of Punctuated Equilibrium  If there are huge environmental changes, many niches are left open via extinction and some traits are highly “favoured” (passed on more)  Speciation may occur more quickly  Theory developed by Stephen Jay Gould and Niles Eldridge in 1972

Which do you think is more likely?