The Process of Speciation The formation of new biological species, usually by the division of a single species into two or more genetically distinct one. Species: Group of organisms that are able to reproduce with one another and produce viable offspring

Three Isolating Mechanisms: Isolate species forming subspecies and perhaps causing speciation. Geographic Isolation Behavioral Isolation Temporal Isolation

1. Geographic Isolation Two populations separated by a geographic barrier; river, lake, canyon, mountain range.

Example: 10,000 years ago the Colorado River separated two squirrel populations. Kaibab Squirrel Abert Squirrel

Kaibab Squirrel Abert Squirrel This resulted in a subspecies, but did not result in speciation because the two can still mate if brought together

2. Behavioral Isolation Two populations are capable of interbreeding but do not interbreed because they have different ‘courtship rituals’ or other lifestyle habits that differ.

Example: Eastern and Western Meadowlark Eastern and Western Meadowlark populations overlap in the middle of the US

Example: Eastern and Western Meadowlark Male birds sing a mating song that females like, East and West have different songs. Females only respond to their subspecies song.

Liger Tigon

3. Temporal Isolation Populations reproduce at different times, which prevents them from mating January 1 2 3 4 5 6 7 8 9 10 11 12 13

Example: Northern Leopard Frog & North American Bullfrog Mates in: Mates in: April July

Conclusion: Geographic, Behavioral and Temporal Isolation are all believed to lead to speciation.

However: No examples ever observed in animals A couple examples that may demonstrate speciation exist in plants and some insects.

Genetic Drift random change in allele frequency that occurs in small populations

The results of genetic crosses can usually be predicted using the laws of probability. *Example: Punnett Squares However, In small populations,, these predictions are not always accurate.

Two phenomena that result in small populations and cause genetic drift Founder Effect Bottleneck Effect

Founder effect allele frequencies change due to migration of a small subgroup of a population

Founder Effect: : Fruit Flies on Hawaiian islands

2. Bottleneck effect major change in allele frequencies when population decreases dramatically due to catastrophe

(Catastrophy)

Bottleneck Effect: Northern Elephant Seal Population Hunted to near extinction Population decreased to 20 individuals in 1800’s, those 20 repopulated so today’s population is ~30,000 No genetic variation in 24 genes

Follow Up Questions? Explain how Lyell’s theory on principles of geology and geographic isolation are related to each other. When Darwin visited the Galapagos Islands he noticed that the Finches on the Island Looked very different from those on the mainland of South America. Explain why using the idea of founders effect. The elephant seal population is in a ‘genetic crisis’ what do you think this means, and why could the population still be endangered even though their numbers are over 30,000.

1. Explain how Lyell’s theory on principles of geology and geographic isolation are related to each other. Geographic isolation relies on Lyell’s theory that the earth is continually changing. If this is not true, then mountains, lakes, deserts, rivers, or any geographic barriers would not form over time causing populations to be separated.

2. When Darwin visited the Galapagos Islands he noticed that the Finches on the Island Looked very different from those on the mainland of South America. Explain why using the idea of founders effect. The finches on the islands only have the genetic variety of the founding population. This may not include all of the variation from the mainland finch population. Also, different environmental pressures on the island vs the mainland would effect the survival of variations differently.

Genetic crisis: not enough variation to maintain healthy population. 3. The elephant seal population is in a ‘genetic crisis’ what do you think this means, and why could the population still be “endangered” even though their numbers are over 30,000. The elephant seal population dropped to only 20 individuals eliminating much of the population’s variation. Genetic crisis: not enough variation to maintain healthy population. If a disease was to strike the E.Seal pop. Their may not be enough variability between seals to allow some to survive

END