1 / 50

The Origin of Species

The Origin of Species. chapter 24 Campbell and Reece. Speciation. process by which one species splits into 2 or more species Speciation explains both the diversity of life and the unity of living things. Speciation : forms bridge between:. MICROEVOLUTION

morrison
Download Presentation

The Origin of Species

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. The Origin of Species chapter 24 Campbell and Reece

  2. Speciation • process by which one species splits into 2 or more species • Speciation explains both the diversity of life and the unity of living things.

  3. Speciation : forms bridge between: MICROEVOLUTION • Evolutionary change below species level • Example: • change in allele frequencies in population over generations MACROEVOLUTION • Evolutionary change above the species level • Examples: • origin of new group of organisms • impact of mass extinctions

  4. Biological Species Concept • Species: a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring • members of a species cannot produce viable, fertile offspring with other groups • emphasizes the separateness of species due to reproductive barriers

  5. What holds the gene pool of a species together? • Gene Flow: transfer of alleles between populations of same species • exchange of alleles tends to hold populations together genetically

  6. Reproductive Isolation • existence of biological barriers that keep members of 2 populations from interbreeding over long periods of time

  7. Reproductive Isolation • hybrids: offspring that result from the mating of individuals from 2 different species or from 2 true-breeding varieties of same species

  8. Prezygotic Barriers • block fertilization from happening by: • impeding members of different species from attempting to mate • preventing attempted mating from being completed successfully • hindering fertilization if mating was completed successfully

  9. Postzygotic Barriers • reproductive barrier that prevents hybrid zygotes produced by 2 different species from developing into viable, fertile adults • lethal developmental errors • infertility in viable offspring

  10. Types of Prezygotic Reproductive Barriers • Habitat Isolation 2 species that occupy different habitats w/in same area may rarely interact example:

  11. Types of Prezygotic Reproductive Barriers 2. Temporal Isolation: species breed during different times of day, different seasons, or different years

  12. Types of Prezygotic Reproductive Barriers 3. Behavioral Isolation: Courtship rituals used to attract mates are effective barriers

  13. Types of Prezygotic Reproductive Barriers 4. Mechanical Isolation: • morphological differences prevent successful completion even if attempted

  14. Types of Prezygotic Reproductive Barriers 5. Gametic Isolation: • Sperm of 1 species may not be able to fertilize egg of another: • Reproductive tract hostile to sperm • Sperm does not have enzymes to penetrate zonapellicida of another species

  15. Types of Postzygotic Reproductive Barriers • Reduced Hybrid Viability: hybrids development or survival is impaired

  16. Types of Postzygotic Reproductive Barriers 2. Reduced Hybrid Fertility: hybrids may develop and be healthy but they are not fertile

  17. Types of Postzygotic Reproductive Barriers • Hybrid Breakdown: Some 1st generation hybrids are fertile but those offspring are feeble or sterile

  18. Species • There is no single, universally applicable species concept that can define, explain, and identify all species. • There are multiple ways to think about & define species.

  19. Biological Species Limitations • unable to use these characterisitics on fossils of extinct species • only applies to organisms that reproduce sexually • only applies where there is no gene flow

  20. Other Definitions of Species • These dfns emphasize the unity w/in a species. • morphological species concept: • characterizes a species by a structural feature • applies to species that reproduce sexually or asexually • how scientists distinguish most species • disadvantage: subjective

  21. Morphological Species Concept • Problems: • domestic dogs may look very different but are still same species • mouse lemurs look very similar but there are 18 species of them • grey mouse lemur lesser mouse lemur

  22. Ecological Species Concept • views species in terms of its niche • the sum of how members of the species interact with the nonliving & living parts of their environment • asexual or sexual species • emphasizes role of disruptive NS as organisms adapt to different environmental conditions

  23. Phylogenetic Species Concept • defines species as smallest group of individuals that share a common ancestor, forming one branch on the “tree of life” • determining degree of differences is difficult

  24. Species • There are >20 other ways to define species

  25. Speciation can take place with or w/out geographic separation • Speciation can occur in 2 main ways: • Allopatric Speciation • Sympatric Speciation

  26. ALLOPATRIC SPECIATION • “other country” • Gene flow is interrupted when population is divided into geographically isolated subpopulations

  27. Allopatric Speciation Process • Once geographic separation has occurred, the separated gene pools will each have their own mutations • NS & genetic drift may alter allele frequencies in different ways in each subpopulation group

  28. Allopatric Speciation

  29. Evidence of Allopatric Speciation • There are many studies & examples supporting this type speciation • Indirect support: regions that are isolated or highly subdivided have more species than regions w/out those features

  30. Drosophila Experiment

  31. Sympatric Speciation • “same country” • occurs in populations in same geographic area • less common than allopatric • occurs if gene flow is reduced by factors like: • polyploidy • habitat differentiation • sexual selection

  32. POLYPLOIDY • means extra sets of chromosomes • can occur in animals • gray tree frog (Hylaversicolor) • around Great Lakes

  33. Polyploidy • much more common in plants • estimate: 80% of today’s plants species have ancestors that formed by polyploid speciation • 2 forms

  34. 1. Autopolyploid • Individual has >2 chromosome sets all derived from a single species • Plant polyploidy

  35. Plant Polyploidy • tetraploid plant can produce fertile tetraploid offspring by self-pollinating or mating with other tetraploids

  36. 2. Allopolyploid • 2 different species interbreed making a hybrid • hybrid reproduces asexually • over generations sterile hybrid  fertile polyploid (called an allopolyploid)

  37. Allopolyploids • can breed with each other but not with either of their parents so are a new species • rare: 5 new plant species since 1850 documented • Mimulusperegrinus

  38. Allopolyploids • include many agricultural crops • Triticumaestivum(bread wheat) has 6 sets chromosomes (2 pair from each of 3 parents), an allohexaploid • 1st polyploidy event probably occurred ~8,000 yrs ago as spontaneous hybrid

  39. Top 2 parentsbottom: Triticumaestivum

  40. Allopolyploids • plant geneticists “create” new polyploids making hybrids with desired characteristics • use chemicals that induce meiotic & mitotic errors

  41. Habitat Differentiation • Sympatric speciation can occur when genetic factors enable a subpopulation to exploit a habitat or resource used by the parent population

  42. Rhagoletispomonella • North American apple maggot fly • Original habitat was the native hawthorn tree

  43. Habitat Differentiation • As apples mature faster than hawthorn fruit, NS has favored flies with rapid development • have an allele that benefits flies that feed off only 1 or the other not both (post-zygotic barrier to reproduction) • The flies feeding on apple trees now show temporal isolation from flies still eating hawthorn fruit (prezygotic restriction to gene flow)

  44. Sexual Selection • can also drive sympatric speciation: • cichlid fish Pundamiliapundamilia

  45. Cichlid Fish • >600 species found in Lake Victoria • originated in past 100 000 yrs • hypothesis : subgroups of original population adapted to different food sources  genetic divergence • female preference for mates may also be a factor: 1 species breeding males have blue back another species has orange back

  46. Breeding Cichlids Colors

  47. Sexual Selection Study • placed the 2 subspecies in same tank • used monochromatic orange light so both appeared very similar • females bred with either • Conclusion: mate choice by females is based on male coloration so it’s the main reproductive barrier (prezygotic behavior)

  48. Allopatric & Sympatric Speciation are the 2 main modes of speciation • Allopatric • geographic isolation • NS • genetic drift • sexual selection • Sympatric • requires emergence of a reproductive barrier that isolates a subgroup • less common • polyploidy • sexual selection

  49. Hybrid Zones

More Related