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 un-toothed, broad and narrow and never overlapping. Flowers are long racemes longer than leaves. Main species and found in ‘non-extreme 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.