BIOL 102 General Biology II - Chp 24: The Origin of Species

Chapter 24The Origin of Species BIOL 102:General Biology II Rob SwatskiAssociate Professor of Biology HACC- HACC-York 1

Speciation Explains how new species originate & how populations evolve Microevolution: adaptations that evolve within a population’s gene pool Macroevolution: evolutionary change above the species level Macroevolution is the cumulative effect of many speciation &2 extinction events Microevolution

Macroevolution 3

Macroevolution of Technology 4

How is PhylogenyDetermined? Morphology Physiology Biochemistry DNA sequences 5

Biological Species Concept A group of populations whose members have the potential to interbreed in nature … ... & produce viable, fertile offspring They do not breed successfully with other populations Gene flow between populations holds the phenotype together 6

Eastern meadowlark Western meadowlark Similarity between two different species 7

Diversity within a species The biological species concept8 is not based on physical similarity

Reproductive Isolation Biological factors (barriers) that prevent 2 different species from mating & producing offspring (hybrids) Reproductive isolation is classified by whether factors act before or after fertilization Prezygotic barriers & Postzygotic barriers 9

Prezygotic Postzygotic Barriers Barriers Habitat Temporal Behavioral Mechanical Gametic Reduced Hybrid Reduced Hybrid Hybrid Isolation Isolation Isolation Isolation Isolation Viability Fertility BreakdownIndividuals VIABLE, of MATING different FERTILIZATION FERTILE ATTEMPT species OFFSPRING (a) (c) (e) (f) (g) (h) (i) (l) (d) (j) (b) (k) 10

Prezygotic Barriers Block fertilization by: Preventing the HinderingImpeding different successful fertilization if species from completion of mating isattempting to mate mating successful 11

Prezygotic Barriers Habitat Temporal Behavioral Mechanical Gametic Isolation Isolation Isolation Isolation IsolationIndividuals of MATING different ATTEMPT FERTILIZATION species (a) (c) (e) (f) (g) (d) (b) 12

HabitatIsolationTwo species rarely or never encounter each other … … because they occupy different habitats … … but are not isolated by physical barriers Ex: sticklebacks & garter snake species 13

St. Lawrence Seaway 14

Water-dwelling garter snake Thamnophis Terrestrial Thamnophis 15

TemporalIsolation Species that breed at different times of the day, … seasons or years … … & cannot mix their gametes Ex: toads & spotted skunks 16

Bufo americanusBufo fowleri 17

Eastern spotted skunk Western spotted skunk (Spilogale putorius) (Spilogale gracilis) - mates in late winter - mates in late summer 18

Behavioral Isolation Behaviors unique to a species are effective barriers Courtship rituals Displays Vocalizations 19

Blue-Blue-Footed Booby Courtship Ritual 20

Bush Cricket MatingDisplay 21

Vocalization 22

Mechanical Isolation Morphological differences can prevent successful mating Anatomical structures evolve differently Body plans are misaligned 23

Bradybaena species with shells spiraling inopposite directions Genital openings are not in alignment 24

Spider copulatory organs 25

GameticIsolation Sperm from one species cannot fertilize eggs of another species Proteins on gamete surfaces cannot bind to each other Ex: sea urchins 26

Postzygotic BarriersPrevent hybrid zygote from developing into a viable, fertile adult Reduced Reduced Hybrid hybrid hybrid fertility breakdown viability 27

Postzygotic Reduced Hybrid Reduced Hybrid HybridBarriers Viability Fertility Breakdown VIABLE, FERTILIZATION FERTILE OFFSPRING (h) (i) (l) (j) (k) 28

Reduced HybridViability Genes of different parent species mayinteract & impair hybrid developmentMay lead to incompletedevelopment of youngResults in weak, frail, & infertile offspring Ex: salamander (Ensatina) hybrids 29

Reduced HybridFertility Hybrid developmentmay also be impaired in other ways Even if hybrids arevigorous, they may be sterileMeiosis in hybrids does not produce normal gametes Ex: donkeys & horses have different #’s of chromosomes 30

Mule (sterile hybrid) 31

HybridBreakdown Some 1st generation hybrids can be fertile… … but, when they mate with another species (or with either parent species) … … offspring of the next generation will be feeble or sterile Offspring carry too many recessive alleles 32

Hybrid Rice Cultivars 33

Limitations of the Biological Species Concept The biological species concept cannot be applied to: Fossils Why Not? Asexual organisms Prokaryotes34 Why not?

One Species … or Two? 35

Grizzly bear (U. arctos) Polar bear (U. maritimus)Hybrid “grolar bear” 36

Alternative Definitions of “Species”Emphasize the unity within a species, not the separateness between different speciesMorphological Ecological Phylogenetic species species species concept concept concept 37

Morphological Species Concept Defines a species by it’s anatomical features Applies to both asexual & sexual species … but relies on subjective criteria Which structures distinguish a species? 38

Ecological Species ConceptDefines a species byits ecological nicheAlso applies to both asexual & sexual speciesEmphasizes the role of disruptive selectionEx: barnacle species 40

Phylogenetic Species Concept Defines a species as the smallest group of individuals on a phylogenetic tree Also applies to both asexual & sexual species It can be difficult to determine the degree of difference required for separate species Ex: slime molds 42

SpeciationAllopatric SympatricSpeciation speciation Speciation with Speciation withoutgeographic isolation geographic isolation (“other country”) (“same country”) 44

Allopatric speciation Sympatric speciation 45

AllopatricSpeciation Gene flow is interrupted or reduced … … when a population is divided into geographically isolated subpopulations Ex: habitat fragmentation 46

Habitat Fragmentationin the Amazon Rainforest 47

A. harrisi A. leucurusHarris’s antelope White-tailed squirrel antelope squirrel (South rim) (North rim) 49

Mechanisms of Allopatric Speciation Natural Mutation Genetic Drift Selection 50

(a) Under high predation (b) Under low predationReproductive isolation as a by-product of selection: Mosquitofish 51

Evidence of AllopatricSpeciation Regions with many geographic barriers … … usually have more species than regions with fewer barriers Ex: tropical rain forest frogs 52

A. formosus A. nuttingi Atlantic Ocean Isthmus of Panama Pacific OceanAllopatric speciationin snapping shrimp (Alpheus) – A. panamensis A. millsae sibling species 53

Reproductive isolation increases as the distance between populations increases Dusky salamandersDegree of reproductive isolation 2.0 1.5 1.0 0.5 0 0 50 100 150 200 250 300 Geographic distance (km) 54

Sympatric Speciation Occurs in geographically overlapping populations Habitat SexualPolyploidy Hybrid Zones Differentiation Selection 55

Polyploidy The presence of extra sets of chromosomes due to accidents of cell division Much more common in plants than in animals (flatworms, leeches, salamanders, tree frogs) Occurs in many important crops: oats, cotton, potatoes, tobacco, & wheat Autopolyploidy & Allopolyploidy 56

Autopolyploidy A new species with 2 or more chromosome sets, derived from one species 2n = 6 4n = 12 2n 4n Failure of cell Gametes Offspring with division after produced tetraploid chromosome are diploid. karyotypes may duplication gives be viable & fertile rise to tetraploid & become new species cells 58

Allopolyploidy A new species with multiple sets of chromosomes, derived from 2 different species Species B Unreduced 2n = 4 gamete Unreduced with 4 Hybrid gamete chromosomes with 7 with 7 chromosomes chromosomes Meiotic error Normal New viable fertile Normal gamete hybrid species* Species A n=3 gamete n=3 (allopolyploid) 2n = 6 2n = 10 *The 2n chromosome # of the new species = the sum of the 2n chromosome #’s of the parent species 59

HabitatDifferentiation Sympatric speciation can also result from the appearance of new ecological niches Ex: North American maggot fly Lives on native hawthorn trees & more recently introduced apple trees 60

Apples (new habitat) Hawthorns (original habitat) 61

SexualSelection Can also drive sympatric speciation Selection for mates of different colors led to speciation Ex: cichlids in Lake Victoria 62

EXPERIMENT Monochromatic Normal light orange lightPundamiliapundamiliaP. nyererei Females only mated with males Females mated with of their own species males of both species 64

HybridZones Regions wheremembers of different species mate & produce hybrids Provide opportunities to study factors thatcause reproductive isolation Ex: swordtails (Xiphophorus) 65

PatternsWithin Hybrid Zones Hybrids can occur in a single band where adjacent species meet Hybrids often have reduced fitness compared with parent species Hybrid zone distribution can be more complex if parent species are found in multiple habitats within the same region 67

Fire-bellied toad range Hybrid zoneYellow-bellied toad range 68

0.99B. variegata-specific allele Hybrid zone 0.9 Frequency of 0.5 Yellow-bellied Fire-bellied toad range toad range 0.1 0.01 40 30 20 10 0 10 20 Distance from hybrid zone center (km) 69

Possible Outcomes of Hybrids Over TimeReproductive barriers Reproductive barriers Hybrid individuals become stronger become weaker continue to form 70

Possible Isolated population outcomes: diverges Hybrid zone Reinforcement OR Fusion Gene flow OR Hybrid Barrier toPopulation gene flow Stability(5 individuals are shown) 71

Reinforcement Occurs when hybrids are less fit than their parent species Over time, hybrids gradually stop forming Reproductive barriers become stronger 72

Sympatric male Allopatric malepied flycatcher pied flycatcher 73

28 Pied flycatchers Number of females 24 Collared flycatchers 20 16 12 8 4 (none) 0Females mating Own Other Own Otherwith males from: species species species species Sympatric males Allopatric males 74

Fusion Pundamilia nyererei Pundamilia pundamilia Occurs when hybridshave the same fitnessas both parent species There can be significant gene flow between speciesReproductive barriers weaken If gene flow is high enough, parent Pundamilia “turbid water,”species can fuse into a hybrid offspring from a location single species with turbid water 75

StabilityContinued production of hybrid individualsExtensive gene flow from outside the hybrid zonecan overwhelm selection for increased repro isolation inside the hybrid zone The resulting 1st or 2nd generation hybridoffspring are less fit than either parent species 76

Speciation Can occur slowly or rapidly Can result fromchanges in few or many genesHow long does it take for new species to form?How many genes need to differ between species? 77

Speciation Patterns Can Be Studied Using:The Fossil Morphological Molecular Record Data Data 78

Patterns in the Fossil Record Species may appear suddenly, persist essentially unchanged for some time, & then apparently disappear Niles Eldredge & Stephen Jay Gould coined the term punctuated equilibrium to describe periods of apparent stasis punctuated by sudden change This contrasts with the gradual change model 79

(a) Punctuated pattern Time(b) Gradual pattern 80

Speciation Rates The punctuated pattern in the fossil record & lab studies suggests that speciation can be rapid The interval between speciation events can range from: 4000 years (cichlids) to… 40 million years (some beetles) 81

Rapid Speciation of Helianthus anomalus 82

EXPERIMENTH. annuus H. petiolarusgamete gamete F1 experimental hybrid (4 of the 2n = 34 chromosomes are shown)RESULTS H. anomalusChromosome 1 Experimental hybrid H. anomalusChromosome 2 Experimental hybrid 83

Studying the Genetics of Speciation Genomics enables researchers to identify specific genes involved in some cases of speciation Speciation might require the change of only one allele … … or many alleles 84

Single-Single-Gene Speciation 85

A Locus That Influences Pollinator Choice: Monkey flowers (a) Typical Mimulus lewisii (b) M. lewisii with an M. cardinalis flower-color allele 86

(d) M. cardinalis with an M. lewisii(c) Typical Mimulus cardinalis flower-color allele 87

Credits by Rob Swatski, 2013 Visit my website for more Biology study resources! http://robswatskibiology.wetpaint.com http://www.flickr.com/photos/rswatskiPlease send your comments and feedback to: rjswatsk@hacc.eduImages used in this work bear a This work bears an Creative Commons license and Attribution-Noncommercial are attributed to their original Share Alike Creative authors. Commons license. 88

BIOL 102 General Biology II - Chp 24: The Origin of Species

by Rob Swatski on Feb 11, 2010

Accessibility

Categories

Upload Details

Usage Rights

3 Embeds 59

Statistics

BIOL 102 General Biology II - Chp 24: The Origin of Species Presentation Transcript

http://robswatskibiology.wetpaint.com	49
http://www.slideshare.net	8
http://pinterest.com	2