Chapter 24: The Origin of Species

1. Chapter 24: The Origin of Species

2. Defining a “Species” • Species comes from Latin word meaning “kind” or “appearance” Red Cardinal Red Cardinal FL Scrub Jay Blue Jay

3. Defining a “Species” Eastern Meadowlark • Morphological Species Concept • Classification scheme based on physical characteristics • However… • Some species look very similar to one another • Some species have a lot of variation for morphological characteristics • Some species have sexual dimorphism Western Meadowlark

4. Defining a “Species” • Ecological Species Concept • Classification scheme based on organisms’ role in natural community • Phylogenetic Species Concept • Smallest group of individuals sharing common ancestor

5. Evolutionary Tree: Describes relationship between descendants and ancestors Evolutionary Trees are hypotheses of current understanding of relationships

6. Defining a “Species” • Biological Species Concept • Group of populations with potential for successful breeding in nature and to create fertile offspring • Biological Species Concept is widely accepted and used by biologists today • Some situations require alternative concepts: • Identifying new species in the fossil record • Identifying prokaryotes (reproduce asexually)

7. Reproductive Barriers • Reproductive Isolation= prevents gene flow between species and maintains “separate” species • Prevents closely related species from successfully mating • Hybrids= offspring of 2 species mating “Grolar” Bear Polar Bear Grizzly Bear

8. Reproductive Barriers • Two Types of Barriers: • Prezygotic Barriers= prevents mating or fertilization from happening • Postzygotic Barriers= happens after fertilization occurs, prevents viable, reproductive offspring

9. Prezygotic Barriers: Temporal Isolation • Mating occurs during different seasons • Mating occurs during different times of day • Diurnal vs Nocturnal

10. Prezygotic Barriers: Habitat Isolation

11. Prezygotic Barriers: Behavioral Isolation Birds of Paradise

12. Chromosome #= 36 Prezygotic Barriers • Mechanical Isolation • Gametic Isolation Chromosome #= 44

13. Postzygotic Barriers • If zygote forms, barriers can prevent continued hybridization • Hybrid inviability • Reduced hybrid viability

14. Postzygotic Barriers: Reduced Hybrid Fertility Hybrid is viable but sterile Female Horse Male Donkey Mule

15. Postzygotic Barriers: Hybrid Breakdown Viable Offspring First generation (F1) offspring are viable and fertile Second generation (F2) has reduced viability # of live offspring at birth Species 1 Hybrid Species 2

16. Development of Reproductive Barriers • Once separated, populations may experience different environmental factors • Natural selection can act on genetic variation and lead to development of reproductive barriers • Once reproductive barriers are in place, separated populations become different species • If populations come into contact again, individuals will not be able to interbreed

17. Speciation • New species can arise from reproductive isolation between populations • No migration or gene flow • Process of one species separating into 2 or more species • Development of new species leads to biodiversity • The original species is the “ancestor” species • New species share many characteristics due to common ancestor

18. Evolution of a Population Generations 1 2 3 • Change over time • Types of Natural Selection • Directional Selection • Highest reproduction in one extreme phenotype • Stabilizing Selection • Highest reproduction of intermediate phenotypes • Disruptive Selection • Highest reproduction of two extreme phenotypes Most likely to lead to speciation

19. Speciation • Allopatric Speciation= New species arise from reproductive isolation of one population from another population • Sympatric Speciation= New species arise in the same location as original population

20. Figure 24.5 (a) Allopatric speciation. A population forms a new species while geographically isolated from its parent population. Sympatric speciation. A subset of a population forms a new species without geographic separation. (b)

21. Allopatric Speciation • New species arise from reproductive isolation of one population from another population • Different environments have different selection pressures • Often results from a geographic barrier • Blocks gene flow

22. Geographic Barriers River Formation Mountain Formation Colonization Continental Drift

23. Habitat Fragmentation • Separation of populations into smaller, isolated populations • Usually result of conversion of habitat or creation of a barrier • Habitat fragmentation reduces overall area, resources, and population sizes of species • Reduces migration of individuals between distance populations N = 100 N=50 N=70 N=30

24. Allopatric Speciation • Once separated, individual populations can evolve due to differences in • Natural selection • Mutation • Genetic Drift

25. Sympatric Speciation • New species arise in the same location as original population • 3 Methods of Sympatric Speciation: • Polyploid Speciation= individual has too many chromosomes, isolating individual from rest of population • Habitat Differentiation= population of species separate because of different uses of habitat • Sexual Selection= females choose mates based on specific characteristics

26. Polyploid Speciation • Polyploidy= errors in meiosis resulted in more than 2 sets of chromosomes in offspring • Autopolyploid= an individual with more than two chromosome sets, derived from one species • An allopolyploid is a species with multiple sets of chromosomes derived from different species • Hybridization + errors in meiosis • Common in plants • Plants can self-fertilize, allowing reproduction despite error in chromosome number • ~50% of plants are polyploid • Wheat, potatoes, apples, cotton

27. Polyploid Speciation • Individual has more chromosomes than others • Reproductive isolation from rest of population • Creates a new species

28. Habitat Differentiation • Population of species isolated because of different uses of habitat • Genetic trait allows some of the population to exploit resources differently • Often related to food sources • Subset of population obtains food in one location • Another subset obtains food in different location • Over time, reproductive barriers can develop • Habitat isolation • Temporal isolation

29. Habitat Differentiation Original Habitat: Native Hawthorn Tree • North American apple maggot fly • Species currently separated into 2 subspecies Apple Trees

30. Sexual Selection • Individuals choose mates based on specific characteristics • If females choose mates based on coloration and different females prefer different colorations, eventually lead to reproductive isolation

31. Sexual Selection • African cichlids in Lake Victoria • As many as 600 different species within one lake

32. Rates of Evolution • Gradualism Model: slow change in population through time • Punctuated Equilibrium Model: sudden change leading to new species followed by periods of stability

33. Figure 24.17 (a) Punctuated pattern Time (b) Gradual pattern

34. Types of Evolution • Macroevolution= change in groups above the level of species, often results in new taxonomic groups • Methods of Macroevolution • Adaptive radiation= periods of change when many new species originate from a common ancestor • Mass extinctions= large number of species go extinct within a relatively short amount of time • Environmental change • 5 mass extinctions have occurred through geological time with 50% or more species lost • Plate tectonics and Continental drift= movement of Earth’s plates

35. Mass extinction led to adaptive radiation of mammals 70% of species lost Cretaceous –Tertiary Extinction Event 1.8 mya 65 mya 145 mya 199 mya Total Number of Species: 5,448 mammal species (IUCN, 2008)

36. Speciation leads to increases in biodiversity 1.8 million named species