Adaptive RadiationAdaptive Radiation To radiate To radiate means to spread outward. It refers to means to spread outward. It refers to one or a few species which diversify one or a few species which diversify ("spread out") and generate multiple ("spread out") and generate multiple

daughter species, something like thisdaughter species, something like this

Evolution & DiversityAdaptive radiation

Proliferation of a species by adaptation to a different way of life

Best example of speciation as observed by Charles Darwin on his Galapagos Island “stop-over”

The 13 species of finches that are depicted on the following slides are believed to be descended from mainland finches via the following mechanisms

Mainland migration to island #1, population increases, some individuals migrate to other islands

The islands are ecologically different from one another to promote divergent feeding habits

Thus, the finches are physically similar to one another but differ in their beak structure which came about from natural selection of variants that appeared over time

Evolution & Diversity

Factors that Cause Evolutionary Change

1.Mutations2.Genetic Drift (i.e bottleneck effect, founder effect)3.Gene flow (migration)4.Non-random mating5.Natural Selection

MutationMutation is the only source of new alleles in a species.

Mutation provides the raw material of evolution.

Mutation acting alone works too slowly to drive evolution.

Types of Mutations:

gene mutations, such as point mutations, and

chromosomal mutations, such as deletions or inversions, etc.

Genetic DriftGenetic drift is random fluctuation in allele frequency between generations. Its effects are pronounced in small populations.

A Genetic Bottleneck (Genetic Drift Continued)

Animals known to be affected by genetic bottlenecks include the northern elephant seal, cheetah, and some human populations.

A genetic bottle neck is one form of genetic drift in which a population “crashes” then rebounds.

A fairly recent hypothesis about human evolution suggests that we came very close to extinction because of a "volcanic winter" that occurred 71,000 years ago. Some scientists estimate that there may have been as few as 15,000 humans alive at one time. The volcanic winter lasted about six years. It was followed by 1,000 years of the coldest Ice Age on record. By Dr David Whitehouse BBC News Online science editor Tuesday, 8 September, 1998, 11:40 GMT 12:40 UK

Bottleneck Effect

A Genetic Bottleneck

The Founder Effect (Genetic Drift Continued)The founder effect is another form of genetic drift in which a small portion of a population migrates to a new area then expands in number.

The Founder effect accounts for the high frequency of Ellis-van Crevald syndrome in Amish characterized by short-limb dwarfism, polydactyly (additional fingers or toes), malformation of the bones of the wrist, dystrophy of the fingernails, partial hare-lip, cardiac malformation, and often prenatal eruption of the teeth; colourblindness, and other genetic recessives

In this case, the allele frequencies in the expanded population are often very different from those of the founder population.

Another Example of the “Founder Effect”

The Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists. Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to have that gene with unusually high frequency.

People who inherit this genetic disease have an abnormal dominant allele that disrupts the function of their nerve cells, slowly eroding their control over their bodies and minds and ultimately leading to death.

Gene Flow or Migration

Gene flow makes separate populations more similar genetically.

The effects of gene flow are seen in many human populations.Why?……….ease of transportation.

Gene flow in plants – wind-dispersed pollen moving between Monterey pines.

Inbreeding – One Form of Non-Random Mating

Inbreeding occurs when related individuals mate.

Inbreeding reduces the proportion of heterozygotes and increases the proportion of homozygotes in a population.

This is a bad idea when considering recessive genetic disorders.

EA mating between first cousins increases the risk of albinism 10-fold.

Albinism – a recessive genetic condition.

Inbreeding, genetic bottlenecks and founder effects all come into play in reducing genetic diversity.