1. MECHANISMS OF EVOLUTION.....AND ELEPHANTS Evolution & Homeostasis 2012

2. Evolution via natural selection Overpopulation Variation Competition Evolution in the population

3. Remember that evolution is change in a population over time, so we are looking at factors that result in changes in the gene pool.

5. Mutations Mutations are the source of all new alleles. Mutations may be beneficial or not. Mutations are the source of variation, essential for evolution via natural selection Environmental conditions change Generations Mutation causes the formation of a new recessive allele Allele frequency

7. Natural Selection Natural selection may produce phenotypic change over time. The direction of change will depend on the selection pressure.

8. Stabilizing Selection Stabilizing selection is probably the most common trend in natural populations. Stabilizing selection reduces variation by selecting against the extremes at each end of the phenotypic range. Retained Eliminated Frequency Variation in phenotype Frequency

9. Directional Selection After selection there is a reduction in variation at one extreme of the range while favoring variants at the other end. Retained Eliminated Variation in phenotype

10. Dwarf elephants evolved to a fraction of the size of their modern relatives. Insular dwarfism is a biological phenomenon by which the size of animals isolated on an island shrinks dramatically over time. Fossil remains of dwarf elephants have been found on the islands of Cyprus, Malta, Crete, Sicily, Sardinia, Sulawesi, Flores, Timor and other islands of the Lesser Sundas.

13. Disruptive Selection intermediate Individuals at both extremes of a phenotypic range are favored over intermediate variants (two peaks). Disruptive selection may occur when environmental conditions are varied or when the environmental range of an organism is large. This leads to speciation. Retained Eliminated Retained Variation in phenotype Frequency Two peaks Frequency

14. The African and Asian elephants and the woolly mammoth all evolved from a common ancestor, Primelephas. The ancestors of the woolly mammoth migrated to Europe and North America.

15. Woolly Mammoth (Mammuthus primigenius) Thick layer of 1 meter long shaggy hair plus a find underwool. Their ears are also smaller than modern elephants- only 30 cm long. Hump of stored fat.

16. Sites where mammoths have been found

17. Baby mammoth found frozen in Russian permafrost in 2007

18. Remember Snuffy?

19. Genetic Drift Due to random chance, not all individuals in a gene pool pass on their genes to the next generation. This causes random changes in the gene frequencies. Alleles may become: Lost Fixed (present in all individuals) Genetic drift is greater in small populations.

20. The foot stomping on some beetles is a random event- there was no selection of specific beetles to be squashed. Yet it has led to a change in the gene pool.

21. Allele Frequencies and Population Size The allele frequencies of large populations are more stable because they are less affected by changes involving few individuals. Small populations have fewer alleles to begin with and so the severity and speed of changes in allele frequencies are greater. Small population Large population AA Aa aa Aa AA Aa aa AA Aa aa Aa AA Aa AA Aa AA Aa AA aa AAaa Aa AA Aa Cheetahs have a small population with very restricted genetic diversity

22. The Founder Effect Occasionally, a small number of individuals may migrate away or become isolated from their original population. This colonizing or founder population will have a small and probably non- representative sample of alleles from the parent population’s gene pool. The colonizing population may evolve in a different direction than the parent population. The marine iguana of the Galapagos has evolved in an isolated island habitat Offshore islands can provide an environment in which founder populations can evolve in isolation from the parental population.

23. Population bottlenecks A population bottleneck occurs when the breeding population is reduced by 50% or more. Population bottlenecks increase genetic drift (change), as the rate of drift is inversely proportional to the population size. They also decrease genetic diversity Example: cheetahs

25. Population Bottlenecks The original gene pool is made up of the offspring of many lineages (family groups and sub-populations) All present day descendants of the original gene pool trace their ancestry back to lineage B and therefore retain only a small sample of genes present in the original gene pool Genetic bottleneck Only two descendants of lineage B survive the extinction event Extinction event such as a volcanic eruption

26. Genetic Bottlenecks & the Cheetah Population Cheetahs appear to have narrowly escaped extinction at the end of the last ice age: 10- 20000 years ago. All modern cheetahs may have arisen from a single surviving litter, accounting for the lack of diversity. The lack of genetic variation has led to: sperm abnormalities decreased fecundity (female fertility) high cub mortality sensitivity to disease Since the genetic bottleneck, there has been insufficient time for random mutations to produce new genetic variation.

27. Speciation A species is a group of organisms able to interbreed and produce fertile offspring. A population of one species can only evolve into more than one species if groups within the population become isolated from each other by barriers that prevent exchange of genes.  no gene flow

28. Splitting & Budding Splitting: A species could split fairly equally into two populations that evolve differently until they eventually become separate species. Budding: A small part of the species population could “bud off” from the main part and evolve rapidly to form a new species. Species B Small population buds off Species A Budding Species A BA A Splitting Species A Population splits equally Species C Species B B C A

29. Types of isolation Geographical Features such as rivers or mountain ranges isolate groups. Ecological Although groups are not geographically isolated from each other they may be isolated by such things as occupying different habitats or breeding areas. Reproductive Breeding between groups within a population may not be possible because of differences in courtship behaviour, physical differences which prevent mating, or failure of gametes to fuse.

32. Rate of evolution Gradual- If the environment remains stable, organisms undergo very little change over time & evolution is slow & gradual. Punctuated- After long periods with little or no change, an isolation event separates a small population of individuals. With a different gene pool or a burst of mutations, this isolated group rapidly evolves into a separate species.

34. A good example of punctuated evolution is the explosion of birds and mammals after the dinosaur extinction 65mya

35. Adaptive (divergent) radiation A common ancestor evolves into a number of species. These have adaptations allowing them to occupy different niches. Speciation in honeycreepers The islands of Hawaii were colonised by a single species of finch-like birds. Populations were isolated from each other on separate islands. They evolved into modern honeycreeper species with beak shapes, which adapt them for different feeding methods.

36. The radiation of the mammals occurred after the extinction of the dinosaurs, which made niches available for exploitation. Megazostrodon an early mammal ancestor Flying predator/ frugivore niche Freshwater predator niche Underground herbivore niche Marine predator niche Arboreal herbivore niche Terrestrial predator niche Browsing/ grazing niche

37. Divergent Evolution of the Ratites The ratites are a group of birds that evolved from one ancestor and lost their powers of flight early in their evolutionary development. Their distribution can be explained by continental drift following the break-up of Gondwana. Kiwi New Zealand Emu Australia Cassowary Australia/New Guinea Elephantbird Madagascar (extinct) Moa New Zealand (extinct) Rhea South America Ostrich Africa

38. Convergent evolution Where similar environmental conditions exist, initially different organisms evolve to have similar physical characteristics, to suit the similar environment. E.g. Wolf (placental mammal) & Thylacine (marsupial)

39. Convergent Evolution in Mammals Marsupial and placental mammals have evolved separately to occupy equivalent niches on different continents; they are ecological equivalents. Marsupial Mammals Australia Wombat Flying phalanger Marsupial mole Marsupial mouse Tasmanian wolf Long-eared bandicoot Placental Mammals North America Wood chuck Flying squirrel Mole Mouse Wolf Rabbit

40. Marine predators Sharks Dolphins Penguins Which class is each from? What physical features do they have in common?

41. Grades and Clines Even for sexually reproducing organisms, a species may grade (show a gradual change) in phenotype over a geographic area. Such a continuous gradual change is called a cline and often occurs along the length of a country or continent. All the populations are of the same species as long as interbreeding populations link them. Cline Light shells Dark shells

42. Ring species The range of gulls forms a ring around the North Pole. Within the ring, neighbouring birds can mate with each other, even though they look slightly different. Birds at the two ends of the ring - the Herring Gull and Lesser Black-backed Gull - are so distinct that they can't mate with each other although they live side by side.