Chapter 24 The Origin of Species

1. Chapter 24The Origin of Species

2. Macroevolution • the origin of new taxonomic groups Speciation: the origin of new species

3. Anagenesis: accumulation of changes within a population, transforming that population into a new species • Cladogenesis: branching evolution, whereby a new species arises from a parent species

5. Biological Species Concept • Defines a species as a population or group of populations that have the potential to breed with each other in the wild and produce viable, fertile offspring

6. What are some of the limitations of the biological species concept?

7. Ecological Species Concept • Defines a species in terms of its ecological niche

8. Morphological Species Concept • Characterizes each species in terms of its unique set of structural features

9. Genealogical Species Concept • Defines species in terms of its unique genetic history

10. Pluralistic Species Concept • The factors that are most important for the cohesion of a species vary

11. Reproductive Isolation • Factors that prevent interbreeding Note: These are factors that intrinsic to the species itself and does not include geographic isolation

12. Reproductive barriers can either be prezygotic or postzygotic • Zygote: fertilized egg

13. Prezygotic barriers • Impede mating between species or hinder fertilization of ova if two members attempt to mate

14. Prezygotic Barriers • Habitat isolation – if two species live within the same area but different habitats • Behavioral Isolation – often depends upon courtship rituals

15. Prezygotic Barriers, cont’d • Temporal Isolation: if two species mate during different times of the day, different seasons, or different years • Mechanical isolation: two species are not anatomically compatible • Gametic isolation: two gametes meet but fail to fertilize

16. Postzygotic Barriers • Reduced hybrid viability: hybrids are not very healthy, don’t live to maturity • Reduced hybrid fertility: hybrids are sterile • Hybrid breakdown: first-generation offspring are fertile and viable but when these offspring mate with either each other or parent species, offspring are feeble or sterile

17. Modes of Speciation • Based on how gene flow is interrupted

18. Allopatric Speciation • Speciation takes place in populations with two geographically separate ranges

20. Sympatric Speciation • Speciation takes place in geographically overlapping areas • How might these barriers arise?

22. Punctuated Equilibrium Model • Argues that species diverge in spurts of relatively rapid change instead of slowly and gradually

23. Exaptations • Structures that evolve in one context but becomes co-opted for another function • Ex: feathers in birds

24. Evo-devo • The link between evolutionary biology and the study of how organisms develop is called “evo-devo” • Allows us to understand how small changes in the genome can lead to dramatic changes in an organism

25. Toolkit Genes • Subset of genes used to pattern the body • Proteins encoded by these genes control the formation, design, and patterning of most major features of animal design and diversity

26. Homeotic Genes • Control placement and spatial organization of body parts

27. Hox genes

28. Ultrabithorax mutation

30. Eyeless • First discovered in Drosophila. Humans have a homologous protein called Pax6. • Homeotic gene. Responsible for turning on other genes (transcription factor) • Loss of eyeless leads to a loss of eyes. (Flies without eyes)

31. If you turn on eyeless in another part of the fly - Ectopic eyes! Halder et al, 1995

32. Paedomorphosis • When the adult species retains structures that were juvenile structures in an ancestral species Ex: axolotl

33. Heterochrony • Evolutionary change in the rate or timing of developmental events

34. Allometric Growth • The relative growth rates of different parts during development

35. Allometric Growth Example – human and chimpanzee skulls