Origin of Species Lecture 5 Winter 2014

Transcription

1 Origin of Species Lecture 5 Winter 2014

2 The beauty and genius of a work of art may be reconceived, though its first material expression be destroyed; a vanished harmony may yet again inspire the composer; but when the last individual of a race of living things breathes no more, another heaven and another earth must pass before such a one can be again" - William Beebe, Naturalist,

3 IUCN the World Conservation Union 20,219 species on the IUCN Red List of threatened species (2012) 2

4 History of Extinction % of all species that have ever lived are extinct Background rate = ~1 to 10 species per year assuming 10 million species Mass extinctions extinctions in many different environments and across many different species

5 4 Ordovician Period 444 mybp 25% of all families extinct Devonian Period 370 mybp 19% of all families extinct Permian Period 250 mybp 54% of families, 90% of

6 5 Triassic Period 210 mybp 23% of all families, ½ of species extinct Cretaceous Period 65 mybp 17% of all families, ½ of species extinct

7 What were the causes of the five major deep time extinction events? 6 Changes in sea level Volcanic eruptions Asteroid impact Climate change

8 Extinctions Near time 7 Pre-60,000 y.b.p. Africa and Eurasia few extinctions, spread over a long time 50,000 y.b.p. Indonesia 50% of large mammals go extinct 60,000 40,000 y.b.p. Australia 55 vertebrate species go extinct

9 Extinctions Near time 8 12,000 10,000 y.b.p. North and South America 70% of large mammals megafauna go extinct years

10 Extinctions Near Time 9 1,600 to 1,400 y.b.p. Hawaiian Islands two-thirds of vertebrates go extinct 90% of bird species go extinct 1, y.b.p. New Zealand 30 bird species (including 11 species of Moa and two raptors), other animals large & small. Haast s eagle and Moas. John Megahan, BBC, 2005.

11 Extinctions 10 Two main hypotheses for near time extinctions Pleistocene overkill Large vertebrates go extinct due to overhunting by humans Disease hypothesis Humans introduce new diseases Human vectors Animals brought with humans

12 The Sixth Extinction? 11 Current Rate= times faster than background rate? Quartenary Period Present The Sixth Mass Extinction event??

13 Causes of Current Extinction 12 Invasive species Population growth (human) & resource use Pollution Overharvest Climate Change Fig

14 What is a Species? 13 Species: A distinct identifiable group of individuals that regularly breeds together and is thought to be an evolutionarily independent group Generally distinct from other species in appearance, behavior, habitat, ecology, genetic characteristics, etc

15 What is a Species? 14 Limitations of species concepts?

16 15 Genetic Variation and Populations AVERAGE HETEROZYGOSITY average percentage of loci that are heterozygous FRUIT FLY East Africa, Cheetah % Drosophila melanogaster 14%

17 Genetic Variation and Populations 16 CLINE A graded change in a genetic based character along a geographic axis

18 Speciation 17 Speciation An evolutionary process in which one species splits into two or more species Requires reproductive isolation Allopatric The formation of new species in populations that are geographically isolated from one another Sympatric The formation of new species in populations that live in the same geographic area Fig. 24.5

19 Allopatric Speciation 18 Geographic isolation of populations No gene flow Population diverges genetically Genetic drift Natural selection Mutations Reproductive isolation occurs (biological barrier) Prevents gene flow if populations reunited

20 Allopatric Speciation 19

21 Allopatric Speciation: Geographic Barriers 20 Harris s antelope squirrel Fig White-tailed antelope squirrel Would this be a barrier to bird populations?

22 Allopatric Speciation: Geographic Barriers 21 Regions with many geographic barriers typically have more species than do regions with fewer barriers

23 Allopatric Speciation 22

24 23 Allopatric Speciation Plate Tectonics (Continental Drift)

25 Allopatric Speciation 24 Fig Variation in reproductive isolation with distance between populations of dusky salamanders

26 Sympatric Speciation 25 How can reproductive barriers form when there are no geographic barriers? Need to reduce/prevent gene flow Polyploidy Habitat differences Sexual selection

27 Sympatric Speciation: Polyploidy 26 Reproduction in plants Sexual vs. asexual Self-fertilization (self-pollination) vs. cross-fertilization (cross-pollination)

28 Sympatric Speciation: Polyploidy 27 Remember Polyploidy? Chromosomal alteration in which an organism possess more than two complete chromosome sets (e.g., 3n, 4n) Autopolyploidy Fertile individual with more than two chromosome sets derived from a single species Self-fertillization or cross with another tetraploid

29 28 6n 4n 4n Polyploidy is much more common in plants than in animals

30 Sympatric Speciation: Polyploidy 29 Infertile, can asexually reproduce Error in meiosis Allopolyploid A fertile individual with more than two chromosome sets resulting from two different species interbreeding Can self-pollinate, cross-pollinate with other allopolyploids

31 Polyploidy: the Tragopogons 30 T. pratensis T. dubius T. porrifolius T. miscellus T. mirus

32 Sympatric Speciation 31 Habitat differentiation Genetic factors allow a subpopulation to exploit a new habitat or food resource not used by other members of the population E.g., soapberry bug

33 Sympatric Speciation 32 Sexual selection E.g., Cichlids Pundamilia pundamilia and P. nyerei Results of experiment? Separate species? Fig

34 33 Allopatric Speciation: Review In allopatric speciation, geographic isolation restricts gene flow between populations Reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations Even if contact is restored between populations, interbreeding is prevented

35 34 Sympatric speciation: Review In sympatric speciation, a reproductive barrier isolates a subset of a population without geographic separation from the parent species Sympatric speciation can result from polyploidy, natural selection, or sexual selection

36 Activity: As the worm turns

37 Do subspecies matter? The Florida Panther 35

38 Do subspecies matter? 36

39 What is a Species? 37 Does the dusky Seaside Sparrow need to be protected? (Ammodramus maritimus nigrescens)

40 Hybrids & Speciation 38 Hybrid zone Geographic area where interbreeding occurs and hybrid offspring are common incomplete reproductive barriers Fig

41 Hybrid Zones No geographic barrier in zone, so why don t we see more Yellow bellied alleles in fire-bellied toads? Postzygotic barriers Adaptations to local environment 39 Fig

42 Hybrids & Speciation 40 Fig

43 Hybrid Zones: Reinforcement 41 Hypothesis: Where reinforcement occurs, reproductive barriers should be stronger for sympatric than allopatric species. Reasoning? Test: Pied flycatchers and collard flycatchers Allopatric: similar males Sympatric: different males

44 Hybrid Zones: Reinforcement 42 Fig

45 Hybrid Zones: Fusion 43 Chichlids in Lake Victoria Species extinction Fusion? Fig

46 44 Hybrid Zones: Fusion Fig

47 45 Hybrid Zones: Stability Hybrid vigor Migration and gene flow

48 Speciation Rates 46 Limitations of fossil Fig

49 Speciation Rates 47 Time between speciation events? Varies by species Average 6.5 million years 40 million years (some beetles) Few shorter than 500,00 years 4,000 years (some cichlids)

50 Speciation Rates 48 Rapid speciation Helianthus anomalus (wild sunflower) Hybrid, but not allopolyploid Laboratory experiments Fig

51 Speciation Rates 49 Reproductive isolation How many genes change when a new species forms? One gene for Euhadra snails Wild sunflower: 26 chromosome segments (unknown # of genes) Mimulus example (see fig, in text)

52 Consequences of Mass Extinction 50 Fig

53 Adaptive Radiation 51

54 Adaptive Radiation 52 Fig