1 Origin of Species Lecture 5 Winter 2014 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, 1906 2 History of Extinction 3 IUCN the World Conservation Union 20,219 species on the IUCN Red List of threatened species (2012) 99.9% 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 4 5 Ordovician Period 444 mybp 25% of all families extinct Devonian Period 370 mybp 19% of all families extinct Triassic Period 210 mybp 23% of all families, ½ of species extinct Cretaceous Period 65 mybp 17% of all families, ½ of species extinct Permian Period 250 mybp 54% of families, 90% of species 1
What were the causes of the five major deep time extinction events? Changes in sea level Volcanic eruptions Asteroid impact Climate change 6 Extinctions Near time 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 7 Extinctions Near time 8 Extinctions Near Time 9 12,000 10,000 y.b.p. North and South America 70% of large mammals megafauna go extinct 400 1000 years 1,600 to 1,400 y.b.p. Hawaiian Islands two-thirds of vertebrates go extinct 90% of bird species go extinct 1,200 800 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. Extinctions 10 The Sixth Extinction? 11 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 Current Rate= 10-1000 times faster than background rate? Quartenary Period Present The Sixth Mass Extinction event?? 2
Causes of Current Extinction 12 What is a Species? 13 Invasive species Population growth (human) & resource use Pollution Overharvest Climate Change 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 Fig. 25.17 What is a Species? 14 Genetic Variation and Populations 15 Limitations of species concepts? AVERAGE HETEROZYGOSITY average percentage of loci that are heterozygous FRUIT FLY East Africa, Cheetah 0.0004-0.014 % Drosophila melanogaster 14% Genetic Variation and Populations CLINE A graded change in a genetic based character along a geographic axis 16 Speciation 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 17 3
Allopatric Speciation 18 Allopatric Speciation 19 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 Allopatric Speciation: Geographic Barriers 20 Allopatric Speciation: Geographic Barriers 21 Harris s antelope squirrel Fig. 24.6 White-tailed antelope squirrel Would this be a barrier to bird populations? Regions with many geographic barriers typically have more species than do regions with fewer barriers Allopatric Speciation 22 Allopatric Speciation Plate Tectonics (Continental Drift) 23 4
Allopatric Speciation 24 Sympatric Speciation 25 Fig. 24.9 How can reproductive barriers form when there are no geographic barriers? Need to reduce/prevent gene flow Polyploidy Habitat differences Sexual selection Variation in reproductive isolation with distance between populations of dusky salamanders Sympatric Speciation: Polyploidy Reproduction in plants Sexual vs. asexual Self-fertilization (self-pollination) vs. cross-fertilization (cross-pollination) 26 Sympatric Speciation: Polyploidy 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 27 Self-fertillization or cross with another tetraploid 28 Sympatric Speciation: Polyploidy 29 6n 4n 4n Polyploidy is much more common in plants than in animals 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 5
Polyploidy: the Tragopogons 30 Sympatric Speciation 31 T. pratensis T. dubius T. porrifolius 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 T. miscellus T. mirus Sympatric Speciation Sexual selection E.g., Cichlids Pundamilia pundamilia and P. nyerei Results of experiment? Separate species? 32 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 33 Fig. 24.12 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 34 Activity: As the worm turns 6
Do subspecies matter? The Florida Panther 35 Do subspecies matter? 36 What is a Species? Does the dusky Seaside Sparrow need to be protected? (Ammodramus maritimus nigrescens) 37 Hybrids & Speciation Hybrid zone Geographic area where interbreeding occurs and hybrid offspring are common incomplete reproductive barriers 38 Fig. 24.13 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 Hybrids & Speciation 40 Fig. 24.13 Fig. 24.14 7
Hybrid Zones: Reinforcement 41 Hybrid Zones: Reinforcement 42 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 Fig. 24.15 Hybrid Zones: Fusion 43 Hybrid Zones: Fusion 44 Chichlids in Lake Victoria Species extinction Fusion? Fig. 24.16 Fig. 24.04 Hybrid Zones: Stability 45 Limitations of fossil Speciation Rates 46 Hybrid vigor Migration and gene flow Fig. 24.17 8
Speciation Rates 47 Speciation Rates 48 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) Rapid speciation Helianthus anomalus (wild sunflower) Hybrid, but not allopolyploid Laboratory experiments Fig. 24.18 Speciation Rates 49 Consequences of Mass Extinction 50 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, 24.20 in text) Fig. 25.18 Adaptive Radiation 51 Adaptive Radiation 52 Fig. 25.20 9