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  1. Lecture 13 The source of novelty

  2. Lecture 13 The source of novelty Natural Selection Adaptive Radiation Mutations Hybridization Polyploidy

  3. Introduction Every species is adapted to a combination of factors (Phy. Environment, Range of variation, food supply, competition, occasional losses due to disease, predation) Puts demands on the Structure or Physiology of the organism Some are obvious and some are more complex

  4. Introduction Early 19th Century “accepted that each species had always existed precisely as we now see it” God was thought to have created each one (including adaptations, and that these remained unchanged through time)

  5. “It (biological design) indeed doesdestroy the most powerful arguments of God”. Famous Reply of French Mathematician Pierre Simon de Laplace (1749-1827) to Napoleon is now truer than ever. Laplace argued for Biological design by natural selection rather than divine creation.

  6. Introduction Explanation for Fossils God had destroyed the species during Catastrophes! e.g. The Biblical Flood

  7. Darwin’s Journey Around the World-HMS Beagle Two Observations: Galapagos Islands/Mainland South America Reconsidered the assumptions of the day (Finches and Fossils)

  8. Darwin’s Journey Around the World-HMS Beagle

  9. Natural Selection: Basic Philosophy of Biological Science Published by Darwin in 1858. Natural selection is the evolutionary process by which favorable traits that are heritable become more common in successive generations of a population of reproducing organisms and unfavorable traits that are heritable become less common.

  10. Natural Selection: Natural selection acts on the phenotype, or the observable characteristics of an organism, such that individuals with favorable phenotypes are more likely to survive and reproduce than those with less favorable phenotypes.

  11. Natural Selection: “The favorable phenotypes will have a natural advantage in the competition for life” “They will survive at the expense of their less fortunate Relatives,” “by their survival and eventual mating the process of NS will to the persistence of these favorable characteristics”

  12. Natural Selection: So why should each species not be able to evolve to one single answer to the demands that the environment makes upon it? All flowers of a particular plants species would then have the same color? every sparrow have the same beak size? Such a simple solution is not possible, because the Env. is neither stable nor uniform

  13. Natural Selection in Action Darwin's Finches (Flock from SA 2-3 mya) Darwin's finches are an excellent example of the way in which species' gene pools have adapted in order for long term survival via their offspring. Once thought that evolution took place too slowly for it to be detectable over the timescale of scientific studies of living organisms-but no! Adaptive Radiation: evolve and radiate into ways not formerly available to it

  14. Adaptive Radiation In an adaptive radiation, a "founder" species enters a new environment with many unoccupied niches. This species expands (radiates) and evolves adaptations to fit these niches better. The process of becoming adapted to these different niches may lead to, and in these cases has led to, the formation of new species.

  15. Natural Selection in Action Darwin's Finches The finches hold a unique place in the history of science. The birds, which live only on the Galapagos, were studied closely by Charles Darwin on his Beagle voyage in the 1830s. Observations on the shapes of the birds' beaks were central in helping Darwin formulate his theory of evolution.

  16. Natural Selection in Action Darwin's Finches Among the Darwin's finches, there is general agreement as to the existence of 13 Galapagos species, although there may be one or two more or one or two less, depending on how one assesses several unusual populations.

  17. Darwin's 13 Finches Narrow Bills -live on the ground and feed on insects, snails etc Strong, heavy bills -live in cactus thickets, feed on cactus seeds, flowers, pollen Most live in bushes/trees -feed on seeds, nuts, fruits

  18. Darwin's Finches Difficult to separate out! Even for Ornithologist’s

  19. Natural Selection in Action

  20. Natural Selection in Action Darwin's Finches All the species of finches on the Galápagos Islands appear morphologically very similar, varying mostly in terms of beak size and behavior; they all look very much like a species of finch from the mainland of South America. This suggests that all the finches on the Galápagos are descended from one original colonist species that went through an adaptive radiation.

  21. Natural Selection in Action Darwin's Finches The Darwin's Finches diagram illustrates the way the finch has adapted to take advantage of feeding in different ecological niche's.

  22. Natural Selection in Action Darwin's Finches Their beaks have evolved over time to be best suited to their function. For example, the finches who eat grubs have a thin extended beak to poke into holes in the ground and extract the grubs.

  23. Natural Selection in Action Darwin's Finches

  24. Natural Selection in Action Darwin's Finches Finches who eat buds and fruit would be less successful at doing this, while their claw like beaks can grind down their food and thus give them a selective advantage in circumstances where buds are the only real food source for finches.

  25. Galápagos Islands

  26. Galápagos Islands Because of the small, isolated environment of the Galápagos, the finches have become the topic of extensive study into natural selection. The studies that have been conducted on the finches show strong selection for larger beaks during droughts (e.g. 1977).

  27. Galápagos Islands The studies that have been conducted on the finches show strong selection for larger beaks during droughts (11 mm ideal for drought years).

  28. Galápagos Ground Finches with beaks of different size. (11 mm ideal for drought years). Tribulus Fruits-some Having been opened by Finches, who have removed the seeds leaving holes

  29. Beak depth, which is correlated with body size and the ability to crack larger seeds, varies according to drought conditions, which produce fewer, harder seeds in dry years and more and softer seeds in wet years. The change is ±5% in extreme years. The graph shows a pattern of stabilizing selection, in which beak depth fluctuates around a mean of about 9.6mm.

  30. Galápagos Islands These data show that climatic changes can have profound effects on the morphology of a species and potentially lead to the formation of new species.

  31. Galápagos Islands Short term climatic change Rainfall Finch population Biomass of small seeds

  32. The difficulty in identifying the finches is rooted in precisely what makes them so interesting and important -the evolutionary process. If we believe that two species share a common ancestor, then as one traces the species back in time, they should become closer and closer in form. At the branch point, the species should become ambiguous. That is precisely the point at which we find the Darwin's finches.

  33. They are in the process of separating, but they haven't completely done so at this point in time. The definition of the term "species" includes the presence of a fertility barrier between individuals of different species. • In the case of Darwin's finches, those barriers are not completely • formed yet, and there is a certain amount of documented • hybridization between species. • This also contributes to the ambiguity of the birds.

  34. Our current understanding of evolution is that new species are born when the population of the ancestor species is split. Once the gene pool is separated, the two populations may be subject to different natural selection pressures, and hence, evolve in separate ways.

  35. The splitting of a population followed by subsequent evolution is known as allopatric speciation.

  36. Our current understanding of evolution is that new species are born when the population of the ancestor species is split. Once the gene pool is separated, the two populations may be subject to different natural selection pressures, and hence, evolve in separate ways. The splitting of a population followed by subsequent evolution is known as allopatric speciation. At some point, the populations may come back together again, that is, they may become sympatric.

  37. A variety of possibilities arise when two populations, born in allopatry become sympatric;

  38. A variety of possibilities arise when two populations, born in allopatry become sympatric;

  39. A variety of possibilities arise when two populations, born in allopatry become sympatric;

  40. Darwin's finches have many other evolutionary tales to tell. • Darwin himself used the finches in the The Voyage of the Beagle to • quietly announce the theory of evolution: • "Seeing this gradation and diversity of structure in one small, • intimately related group of birds, one might really fancy • that from an original paucity of birds in this archipelago, • one species had been taken and modified for different ends."

  41. Interesting side note When Darwin visited the Galápagos, he observed and collected some of the finch species, believing that they represented a very diverse set of birds that were not closely related.

  42. Interesting side note When Darwin visited the Galápagos, he observed and collected some of the finch species, believing that they represented a very diverse set of birds that were not closely related. Their significance was not recognized until later, when ornithologist John Gould pointed out that the birds were all closely related finches

  43. Interesting side note When Darwin visited the Galápagos, he observed and collected some of the finch species, believing that they represented a very diverse set of birds that were not closely related. Their significance was not recognized until later, when ornithologist John Gould pointed out that the birds were all closely related finches But because Darwin originally collected some of the specimens and because the finches showed so much evidence for evolution and natural selection, they have been dubbed "Darwin's finches." This has led many people to conclude (mistakenly) that Darwin's theory of evolution was specifically inspired by the finches

  44. Controlling Forces Within the organism Mutations Sudden alterations in the genetic make up of individuals. Sometimes there is a slight error from time to time the in gene duplication during cell division (biological a very complex process and mistakes occur!). Cell-Nucleus-Chromosomes-Genes-Alleles (different versions of the Gene -hair color (brown, red, black, blonde)

  45. Controlling Forces Within the organism Mutations Changes in the genetic system can lead to changes in the characteristics of an isolated population in two ways. Mutations may appear and prove advantageous Second, each ind. carries several thousand genes, and each maybe present in one of its several thousand alleles, no two individuals carries the same genetic code or genotype-unless they are identical twins.

  46. Controlling Forces Within the organism Mutations Inevitably, isolated populations will come to differ from others in its genetic content, some alleles being rarer or absent. As mating continues new combinations appear leading to further differences later

  47. Controlling Forces Within the organism Genetic Drift In small populations, where chance plays a greater role in controlling whether a particular allele becomes common or Rare or disappears. Smaller populations contain less genetic variability and are closely adapted to the environment.

  48. Controlling Forces Within the organism Phenotype The way in which a genotype of an organism is expressed in its morphology, physiology, behavior etc is known as the phenotype. Plasticity of an organism-adapted to the demands of the environment

  49. Hybridization (Hybrids of Two Independent Pops-usually along a narrow zone of contact where the two meet). The offspring of two different species, or of two different genera. Once separated (barriers), they speciate in isolation, but once they are re-united they can still interbreed-resulting in reduced fertility or sterility.