Part of AS Relates to US 6317

What is EVOLUTION ? Evolution is change over time - Change means heritable change in a population Time means over generations

Example: Evolution of polar bears Polar bears feed only on the Arctic Ocean ice, available since less than 5 million years ago.

Seals swim under the Arctic ice, but have to keep breathing holes open.

Q: So where did polar bears come from? A: they share a common ancestor with brown bears.

TIME Evolutionary change Species A Brown bear Species B Polar bear 1. Mutation (white fur) 2. Hunting advantage (seals can’t see white bears so well) 3. Better breeding success (more white cubs) 4. Increased % white bears in population over time 5. Reproductive isolation (polar/brown bear hybrids infertile)

anagenesis = change within a population; cladogenesis = branching to produce 2 new species. Two patterns of speciation:

Biological species concept: a species is “a population or group of populations whose members have the potential to interbreed with one another to produce viable fertile offspring, but which cannot produce viable fertile offspring with members of another species.” i.e. this species concept is based on interfertility rather than physical similarity.

By this definition, separate species must be reproductively isolated. Geographical isolation by itself ≠ reproductive isolation – it is not a feature of the organisms themselves. Gallery/ExtraPhotos.html zedonknzorse/

Habitat isolation Behavioural isolation Temporal isolation Pre-zygotic isolating mechanisms operate before fertilisation: Mechanical isolation Gametic isolation

Post-zygotic isolating mechanisms operate after fertilisation: Hybrid breakdown Reduced hybrid viability Reduced hybrid fertility

Two modes of speciation

Has speciation occurred during geographic isolation?

Species A TIME Species B Species C Sequential Evolution Species A is replaced by B, then by C

Appearance of sequential evolution in the ancestry of horses (only one species survives). 1990s Extinct horsesModern horses

Species A TIME Species B Species C Divergent Evolution Species A is replaced by two or more coexisting species.

Ancestral parrot from Australia TIME Divergent Evolution 80 mya

Ancestral parrot from Australia TIME Divergent Evolution Kaka tree 80 mya 60 mya

Ancestral parrot from Australia TIME Divergent Evolution Kaka Kakapo ground tree 80 mya 60 mya

Ancestral parrot from Australia TIME Divergent Evolution Kaka Kakapo ground tree 80 mya 60 mya 3 mya

Ancestral parrot from Australia TIME Divergent Evolution Kaka Kakapo ground tree Kea alpine 80 mya 60 mya 3 mya

Ancestral parrot from Australia TIME Kaka- North Island Kaka – South Island Divergent Evolution Kaka Kakapo ground tree Kea alpine 80 mya 0.4 mya 60 mya 3 mya

Fleming 1979

Species A TIME Radiation Species C Species D Species E Species B Many descendant species in different places

Adaptive radiation of NZ wrens

Two models for the tempo of speciation

From: Arensburger et al. (2004), J. Biogeogr. 31:

Species A TIME Convergent Evolution Species X

Species A TIME Species B Convergent Evolution Species X Species Z Species C Species Y Unrelated species look similar if they live in similar environments

Sabre-tooth tigers Marsupial Placental Simpson 1980:70

Convergence in unrelated, streamlined swimmers Shark - fish Dolphins - mammals Common features: both adapted to move in water Dorsal, pectoral fins, hydrodynamic shape Differences: tail flukes reflect different ancestry Sharks always aquatic, dolphins descended from land animals

Why does evolution keep going? Why do we not get perfection?? Because: The world is always changing, producing new challenges and opportunities.

Continental drift Fig 15.3A