Transcript Patterns of Evolution

Evolution
Patterns of evolution
Four types
• Convergent evolution: independent
evolution of similar adaptive features in
originally different species because they
have adapted to the same environment
(e.g. dolphin, ichthyosaur and sharks).
Features can be homologous (descended
by inheritance from a common ancestor)
e.g pentadactyl limbs
or features can be analogous: similar in
function and often in superficial structure
but different evolutionary origin e.g. the
wings of a bird and an insect.
• Divergent evolution: (this is what happens
under allopatric speciation). Start with
same parent group then get isolation from
the parent group and new species.
• Adaptive radiation: this is a form of
divergent evolution. It is the emergence
from a common ancestor into many
different forms to occupy different niches.
The best example is Darwin’s finches.
• Co-evolution: the genetic change in one species
in response to a genetic change in another
species. Best examples are between plants and
herbivores.
• Key feature is that there are traits in both
species that are not present in related species.
The changes have evolved in response to each
other.
Adaptive radiation in NZ
E.G.1 – Hebe’s
More than 80 species in NZ and none occur all
over. Most are restricted by their adaptations to
very specific parts of the country, mainly in rocky
sites. The original plant was probably a large
shrub with normal leaves set in alternate pattern.
Flowers were racemes and blue, red, white or
purple (there is only one type of native bee so
environment did not change this feature).
The three main groups of hebe:
1) large leafed: most like the ancestral type,
ranging in size but with leaves that are untoothed, broad and narrow and never
overlapping. Flowers are long racemes longer
than leaves. Main species and found in ‘nonextreme areas like coast, forest and scrub. E.g.
H.elliptica, H.salicifolia.
2)medium leafed: show xenomorphic features
(adaptations to dry, arid, cold conditions). Have
toothed and fleshy leaves, which can be flat or
concave and short. Flowers are spikes or
racemes.
found in subalpine to alpine regions mainly
near rocks. E.g.H.hulkeana,H.subalpina.
3)small leaved: has adaptations to
withstand cold, snow and harsh growing
conditions. Leaves are reduced to scales
and are overlapping and tough. Roots are
branching and plant is small. Flowers are
few and small near tips. E.g. H.epacridea,
H.tetragona. If planted in good conditions
revert to being large leafed.
• E.G.2 –Molluscs
• Soft bodied animals with three main parts:
a muscular foot, the visceral mass and
mantle (which secretes a shell). All have
some form of shell
• Great website for NZ examples:
http://sci.waikato.ac.nz/evolution/NZevidence.shtml
Rates of evolutionary change
• 2 models:
• Gradualism (traditional):- evolution
proceeds slowly but continuously.
• Punctuated:- long periods of stasis
interrupted by short periods of rapid
speciation.