Videos

=Video 1.=
 * I've included some notes. Answer the explicit questions and add anything else you think is helpful**

Evidence of evolution
The archipelago including Madeira is 120 m off W Africa. Charles Lyle was a proponent of gradual geological change over long time periods, including the emergence of islands from the sea. This influenced Darwin strongly, and set the time scale for evolutionary change.

Ancestral species arrived 12m BP on the newly formed Islands. A relatively short time scale in the context of evolution. Darwin wrote that “species arriving in new and isolated districts will be eminently liable to modification and will often produce groups of descendants” cf Birds on the Galapagos, land snails on Madeira.

Some of the Madeira colonists //snails!// and their first descendants are preserved as fossils. They provide clear evidence of modification during the course of evolution. //how?// From the same lineage have arisen dark snails living in wooded areas and related light species living in the open.

The raw material of evolution
Natural selection needs variety. JS (Steve) Jones asks why Cepeae nemoralis are so variable. Their shell colours are known to reflect genetic differences. One approach is to look at a variety of habitats to see if there are different patterns of genetic diversity. The Pyrenees provided a particularly wide range of habitats close to each other.

What are the range of heights? habitats? the area covered by the study?

What is the most important environmental variable that changes with height? How does this affect selection? How do we know its not just a chance pattern? Temperature, each snail species responds differently to climate

How is exposure to the sun measured? How does he investigate if effects are directly related to shell colour rather than some other pleiotropic effect of the genes?

What are the implications for selection?

Natural selection by predators.

Song thrushes use anvils. How is frequency dependence important? Could the same sort of processes that act on shell colour act on molecular diversity?

Gel electrophoresis detects genetic variation through differences in the speed of migration of the products of different alleles. In the Pyrenees, snail allozymes show no correlation with altitude or climate.

Motoo Kimura pondered the amount of variation in allozymes, especially fish. He came to a radical set of conclusions. The rate of substitutions is too high to be plausible explained by selection: 1 bp/ 2 years (Mutations, especially at the codon positions 1 & 2 changes the amino acid produced). Most of these mutations must be nearly neutral in effect or the genetic load would be too high.

=Video 2.=
 * I've included some notes. Answer the explicit questions and add anything else you think is helpful**

Cheetahs in South Africa
Small populations may undergo rapid evolution. In particular they are subject to severe genetic drift. These rapid changes might include speciation. (not an issue in the cheetah example though).

At the turn of the century cheetahs were widespread in Africa. They now have a much more limited distribution. Part of the reason may also underlie the problems found in captive breeding. Many males have > 20% abnormal sperm, which is associated with infertility in related species. Visualisation of genetic variation by allozyme electrophoresis indicates wild populations are almost monomorphic in South Africa.

This is consistant with fluctuating asymmetry in collections of skulls which indicates longer term inbreeding. The susceptibility of captive populations to FIP might also be explained by low diversity. The degree of loss of variation suggests as few as 1 or 2 pregnant females as founders. When? **10 000 years ago**

(But seem my lecture notes, which suggest an alternative explanation RAN).

Differences from East Africa, which is slightly more polymorphic, suggest a further bottleneck in the foundation of South African populations.

Partula on Moorea
The rate of speciation in snails can be dated using molecular evidence and information from geologists on the age of islands. They provide evidence about possible modes of selection for reproductive isolation. When did __**Crampton**__ make his observations?

What does Prof Bryan Clarke wear on collecting trips?

P. suturalis (right and left coiling) P. taeniata P. mirabalis P. tohiveana

The allozyme information can be used to reconstruct evolutionary history by within and between species comparisons.

The whole anatomy including the position of the genital aperture is affected by right and left coiling. Within species, right and left coiled morphs have reduced success in mating.

Why should there be such a pattern?

How do **__Crampton__**'s observations corroborate this story?

How does the molecular evidence show that speciation occurred in situ on the islands.

What are the ages of Tahiti and Moorea. Tahiti:

What are the relative rates of evolution on these islands and the Society islands?

Why is it difficult to explain these rates of evolution if selection is responsible for substitutions?

//**This is a very good website about Partula on Moorea:**// [|link]