1. Chapter 24 The Origin of Species

2. Concepts
Speciation is the origin of new species and is at the focal point of evolutionary theory
Evolutionary theory must explain how new species originate and how populations evolve

3. Biological Species Concept
Species is a Latin word meaning “kind” or “appearance”
Archaeopteryx lithographica
Morphology, physiology, biochemistry, and DNA sequences are compared when grouping organisms

4. Definition of Species
Species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring; they do not breed successfully with other populations

5. Concept of Species Biological species concept: reproductive barriers
Ecological species concept: ecological niche
Pluralistic species concept: unique factors depending on the species
Genealogical species concept: genetic history

6. Biological Species Concept: Similarity and diversity

7. Reproductive Isolation
Reproductive isolation is the existence of biological factors (barriers) that impede two species from producing viable, fertile offspring
Hybrids are the offspring of crosses between different species
Reproductive isolation can be classified by whether factors act before fertilization (prezygote) or after fertilization (postzygote).

8. Prezygotic (before the zygote)
Prezygotic barriers block fertilization from occurring by:
Impeding different species from attempting to mate
Preventing the successful completion of mating
Hindering fertilization if mating is successful

9. Types of Prezygotic Barriers
Habitat isolation
Behavioral isolation
Temporal isolation
Mechanical isolation
Gametic isolation

10. Habitat isolation
One lives in water the other on land

11. Behavioral isolation
The dancing and singing are completely different

12. Temporal Isolation
One diurnal and the other nocturnal

13. Mechanical isolation
Spirals in opposite directions

14. Gametic Isolation Gametes are not compatible
Timing of gamete release may be different
Conditions in the female womb of a different species may not be ideal for the sperm
Gamete recognition hampered due to molecules arround the ovum

15. Postzygotic Barriers Reduced hybrid viability Reduced hybrid fertility
Hybrid brakedown

16. Reduced hybrid viability
Ensantia hybrid shows to be frai, may not survive

17. Reduced hybrid fertility
Mule: sterile hybrid of donkey and horse

18. Hybrid brakedown
Hybrid (center sample) is stunt and may not survive or reproduce

19. Speciation Based on Gene Flow
(a) Allopatric speciation
(b) Sympatric speciation

20. Allopatric
In allopatric speciation, gene flow is interrupted or reduced when a population is divided into geographically isolated subpopulations

21. The definition of barrier depends on the ability of a population to disperse
Separate populations may evolve independently through mutation, natural selection, and genetic drift

22. Allopatric speciation in the Grand Canyon
A. leucurus
A. harrisi

23. Reproductive isolation between populations generally increases as the distance between them increases
Barriers to reproduction are intrinsic; separation itself is not a biological barrier

24. Millions of years ago (mya)
Mantellinae
(Madagascar only):
100 species
Rhacophorinae
(India/Southeast
Asia): 310 species
Other Indian/
Southeast Asian
frogs
100 80 60 40 20 1 2 3
Millions of years ago (mya) 1 2 3
India
Madagascar
88 mya
65 mya
56 mya

25. Sympatric Speciation Sympatric means “same country”
Speciation takes place in geographically overlapping populations
Occurs because of
Polyploidism
Habitat differentiation
Sexual selection

26. Polyploidism
Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division
Autopolyploidy
Allopolyploidy

27. Autopolyploidy in plants
2n= n=12
Failure of cell division after chromosome duplication gives rise to tetrapliod cells which
may be viable and self-fertile

28. Allopolyploid
An allopolyploid is a species with multiple sets of chromosomes derived from different species
Many important crops (oats, cotton, potatoes, tobacco, and wheat) are polyploids

29. Ancestral species: AA BB DD Triticum monococcum (2n = 14) Wild
T. tauschii
(2n = 14)
Product:
AA BB DD
T. aestivum
(bread wheat)
(2n = 42)

30. Habitat differentiation
Sympatric speciation can also result from the appearance of new ecological niches
North American maggot fly can live on native hawthorn trees as well as more recently introduced apple trees, so food preference may isolate the two populations

31. Sexual selection Sexual selection can drive sympatric speciation
Sexual selection for mates of different colors has likely contributed to the speciation in cichlid fish in Lake Victoria

32. Hybrid Zones
region in which members of different species meet and mate
Patterns
abnormal, more fragile offspring, less fit (mule is sterile)
more fit than the parents for both environments (paco vicuña)

33. Reinforced Barriers
less fit hybrids might show a reinforcement in the barriers
stronger in allopatric than sympatric species
mule is sterile

34. Fusion barriers are not strong enough
hybrids are more likely (red wolf= coyote x grey wolf)

35. Stability the hybrid production is stable
barriers haven't happen or are too weak
stil hybrids are not the norm because the location where they occur are the extremes of the normal habitat where the original species exist
The End