Introductory Questions #32 1)How can allele frequencies change in a population and increase variation? Give three examples. What do we call this when this

Introductory Questions #321) How can allele frequencies change in a population and

increase variation? Give three examples. What do we call this when this is happening?

2) Does natural selection operate directly on the phenotype or genotype of organisms? Briefly explain your choice.

3) Name the three modes of selection. Explain how each mode is different and draw a graph representing each mode.

4) Define what genetic polymorphism is and why balanced polymorphism is unique. Give the two mechanisms observed for balanced polymorphism.

5) If the frequency of the heterozygote is 48% and the frequency of the recessive allele is greater than the frequency of the dominant allele, what is the frequency of the dominant allele? Show all of your reasoning in addition to the answer.

Macroevolution & Speciation

Chapter 24 & 26• Define a Species• Isolation• Extinction Events• Geological Timetable• Phylogenetics

• The origin of new species, or speciation– Is at the focal point of evolutionary theory,

because the appearance of new species is the source of biological diversity

• Evolutionary theory– Must explain how new species originate in

addition to how populations evolve

• Macroevolution– Refers to evolutionary change above the

species level

The biological species concept emphasizes reproductive isolation

•Species– Is a Latin word meaning “kind” or “appearance”

– Species= as a population or group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring but are unable to produce viable fertile offspring with members of other populations

Macroevolution: the origin of new taxonomic groups

• Speciation: the origin of new species

• 1- Anagenesis (phyletic evolution): accumulation of heritable changes. Ancestral species becomes extinct.

• 2- Cladogenesis (branching evolution): budding of new species from a parent species that continues to exist (basis of biological diversity)

Overview of the Existence of Species

• Estimated number of 13-14 million different species• Only 1.75 million have been scientifically named• The breakdown:

-250,000 Plants

-42,000 Vertebrates

-750,000 Insects

How would you define a species?

What is a species?• Biological species concept (Ernst Mayr):

a population or group of populations whose members have the potential to interbreed & produce viable, fertile offspring (genetic exchange is possible and is genetically isolated from other populations)

Other definitions of Species pg 476

Limitations of the Biological Species Concept

• The biological species concept cannot be applied to– Asexual organisms– Fossils– Organisms about which little is known regarding

their reproduction

• Considered separate species Considered separate species if they if they cannot interbreedcannot interbreed (or (or are reproductively isolated)are reproductively isolated)

What is a Species?What is a Species?

How Does a new Species Emerge?

• There has to be some ISOLATION event that separates a population of individuals

• Separation has to be maintained with barriers

• Applies to sexually reproducing organisms

• Asexual reproducers: species concept is difficult to apply

-classified by structural & biochemical differences

Problem With “Species” Problem With “Species” Definition:Definition:

If they never have the If they never have the opportunity to interbreed, opportunity to interbreed, how do you know if they how do you know if they can?can?

What if they breed, but don’t What if they breed, but don’t produce viable offspring?produce viable offspring? (mules)(mules)

We Can Separate Species We Can Separate Species Based On % Of Shared DnaBased On % Of Shared Dna

How Much of a difference is How Much of a difference is needed to call 2 organisms needed to call 2 organisms

separate species?separate species?

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Other Definitions of Species

• The morphological species concept

– Characterizes a species in terms of its body shape, size, and other structural features

• The paleontological species concept

– Focuses on morphologically discrete species known only from the fossil record

• The ecological species concept

– Views a species in terms of its ecological niche

• The phylogenetic species concept

– Defines a species as a set of organisms with a unique genetic history

Prezygotic Barriers

• Prezygotic barriers: impede mating between species or hinder the fertilization of the ova

• Habitat (snakes; water/terrestrial)

• Behavioral (fireflies; mate signaling & courtship)

• Temporal (salmon; seasonal mating)

• Mechanical (flowers; pollination anatomy)

• Gametic (frogs; egg coat receptors)

Prezygotic barriers

Figure 24.4

Prezygotic barriers impede mating or hinder fertilization if mating does occur

Individualsof differentspecies

Matingattempt

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION

(b)

(a)(c)

(d)

(e)

(f)

(g)

Postzygotic BarriersPostzygotic Barriers: fertilization occurs, but the hybrid

zygote does not develop into a viable, fertile adult

Reduced hybrid viability- mixed genes impair hybrid developmentfrogs; zygotes fail to develop or reach sexual maturity

Reduced hybrid fertility –hybrid is sterilemule; horse x donkey; cannot backbreed

Hybrid breakdown – 1st generation fertile and viable; 2nd are feble or sterilecotton; 2nd generation hybrids are sterile

Viablefertile

offspring

Reducehybrid

viability

Reducehybridfertility

Hybridbreakdown

Fertilization

Gameticisolation

GAMETIC ISOLATION REDUCED HYBRID VIABILITY

REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

(h) (i)

(j)

(k)

(l)

(m)

Other Definitions of Species

• The morphological species concept– Characterizes a species in terms of its body shape, size,

and other structural features

• The paleontological species concept– Focuses on morphologically discrete species known only

from the fossil record

• The ecological species concept– Views a species in terms of its ecological niche

• The phylogenetic species concept– Defines a species as a set of organisms with a unique

genetic history

Modes of Reproductive IsolationPgs. 474-475

Speciation can take place with or without geographic separation

1. Allopatric: populations segregated by a

geographical barrier; can result in adaptive radiation (island species)

2. Sympatric: reproductively isolated subpopulation in the midst of its parent population (change in genome);

-polyploidy in plants (wheat)

-cichlid fishes (pg 480)

2 Modes of speciation (based on how gene flow is

interrupted)

Adaptive Radiation• Adaptive radiation– Is the evolution of diversely adapted species

from a common ancestor upon introduction to new environmental opportunities

Figure 24.11

Adaptive RadiationAdaptive Radiation

• The Hawaiian archipelago– Is one of the world’s great showcases of

adaptive radiation

Figure 24.12

Dubautia laxa

Dubautia waialealae

KAUA'I5.1

millionyears O'AHU

3.7millionyears

LANAI

MOLOKA'I

1.3 million years

MAUI

HAWAI'I0.4

millionyears

Argyroxiphium sandwicense

Dubautia scabra Dubautia linearis

N


• An autopolyploid

– Is an individual that has more than two chromosome sets, all derived from a single species

Figure 24.8

2n = 64n = 12

2n

4n

Failure of cell divisionin a cell of a growing diploid plant afterchromosome duplicationgives rise to a tetraploidbranch or other tissue.

Gametes produced by flowers on this branch will be diploid.

Offspring with tetraploid karyotypes may be viable and fertile—a new biological species.


• An allopolyploid

– Is a species with multiple sets of chromosomes derived from different species

Figure 24.9

Meiotic error;chromosomenumber notreduced from2n to n

Unreduced gametewith 4 chromosomes

Hybrid with7 chromosomes

Unreduced gametewith 7 chromosomes Viable fertile hybrid

(allopolyploid)

Normal gameten = 3

Normal gameten = 3

Species A 2n = 4

Species B 2n = 6

2n = 10


Habitat Differentiation and Sexual Selection

• Sympatric speciation

– Can also result from the appearance of new ecological niches


• In cichlid fish

– Sympatric speciation has resulted from nonrandom mating due to sexual selection

Figure 24.10

Researchers from the University of Leiden placed males and females of Pundamilia pundamilia and P. nyererei together in two aquarium tanks, one with natural light and one with a monochromatic orange lamp. Under normal light, the two species are noticeably different in coloration; under monochromatic orangelight, the two species appear identical in color. The researchers then observed the mating choices of the fish in each tank.

EXPERIMENT

P. nyererei

Normal lightMonochromatic

orange light

P. pundamilia

Under normal light, females of each species mated only with males of their own species. But under orange light, females of each species mated indiscriminately with males of both species. The resulting hybrids were viable and fertile.

RESULTS

The researchers concluded that mate choice by females based on coloration is the main reproductive barrier that normally keeps the gene pools of these two species separate. Since the species can still interbreed when this prezygotic behavioral barrier is breached in the laboratory, the genetic divergence between the species is likely to be small. This suggests that speciation in nature has occurred relatively recently.

CONCLUSION

Introductory Questions #11) How would you define a species? What are two key factors

you must consider?2) Explain the difference between a prezygotic barrier and a

postzygotic barrier.3) How is allopatric speciation different from sympatric

speciation? Why is sympatric speciation more common in plants vs. animals?

4) Which model (gradualism or punctuated equilibrium) is more reflective of the fossil record? Briefly explain why?

5) Define these terms and provide an example: allometric growth, paedomorphosis, Hox genes, and allopolyploidy

6) What is an index fossil?7) When was the last mass extinction event? How many have

occurred in the last 600 million years?

2 modes for the tempo of speciation

• Tempo of speciation: gradual vs. divergence in rapid bursts; Niles Eldredge and Stephen Jay Gould (1972); helped explain the non-gradual appearance of species in the fossil record

See pg. 482

Gradualism Punctuated Equilibrium

(mutations/sudden environmental changes)


Evolutionary Novelties

• Most novel biological structures

– Evolve in many stages from previously existing structures


• Some complex structures, such as the eye

– Have had similar functions during all stages of their evolution

Figure 24.14 A–E

Pigmented cells(photoreceptors)

Epithelium

Nerve fibers

Pigmentedcells

Nerve fibers

Patch of pigmented cells.The limpet Patella has a simplepatch of photoreceptors.

Eyecup. The slit shellmollusc Pleurotomariahas an eyecup.

Fluid-filled cavity

Epithelium

Cellularfluid(lens)

Cornea

Optic nerve

Pigmentedlayer (retina)

Opticnerve

Pinhole camera-type eye.The Nautilus eye functionslike a pinhole camera(an early type of cameralacking a lens).

Cornea

Lens

RetinaOptic nerve

Complex camera-type eye. The squid Loligo has a complexeye whose features (cornea, lens, and retina), though similar to those of vertebrate eyes, evolved independently.

(a) (b)

(d)(c)

(e)

Eye with primitive lens. Themarine snail Murex has a primitive lens consisting of a mass of crystal-like cells. The cornea is a transparent region of epithelium (outer skin) that protects the eyeand helps focus light.


Evolution of the Genes That Control Development

• Genes that program development

– Control the rate, timing, and spatial pattern of changes in an organism’s form as it develops into an adult


Changes in Rate and Timing

• Heterochrony

– Is an evolutionary change in the rate or timing of developmental events

– Can have a significant impact on body shape


• Allometric growth

– Is the proportioning that helps give a body its specific form

Figure 24.15 ANewborn 2 5 15 Adult

(a) Differential growth rates in a human. The arms and legs lengthen more during growth than the head and trunk, as can be seen in this conceptualization of an individual at different ages all rescaled to the same height.

Age (years)


• Different allometric patterns

– Contribute to the contrasting shapes of human and chimpanzee skulls

Figure 24.15 B

Chimpanzee fetus Chimpanzee adult

Human fetus Human adult

(b) Comparison of chimpanzee and human skull growth. The fetal skulls of humans and chimpanzees are similar in shape. Allometric growth transforms the rounded skull and vertical face of a newborn chimpanzee into the elongated skull and sloping face characteristic of adult apes. The same allometric pattern of growth occurs in

humans, but with a less accelerated elongation of the jaw relative to the rest of the skull.


• Heterochrony

– Has also played a part in the evolution of salamander feet

Ground-dwelling salamander. A longer timeperoid for foot growth results in longer digits andless webbing.

Tree-dwelling salamander. Foot growth endssooner. This evolutionary timing change accounts for the shorter digits and more extensive webbing, which help the salamander climb vertically on treebranches.

(a)

(b)

Figure 24.16 A, B


• In paedomorphosis

– The rate of reproductive development accelerates compared to somatic development

– The sexually mature species may retain body features that were juvenile structures in an ancestral species

Figure 24.17


Changes in Spatial Pattern

• Substantial evolutionary change

– Can also result from alterations in genes that control the placement and organization of body parts


• Homeotic genes

– Determine such basic features as where a pair of wings and a pair of legs will develop on a bird or how a flower’s parts are arranged


Chicken leg budRegion ofHox geneexpression

Zebrafish fin bud

Figure 24.18

• The products of one class of homeotic genes called Hox genes

– Provide positional information in the development of fins in fish and limbs in tetrapods


• The evolution of vertebrates from invertebrate animals

– Was associated with alterations in Hox genes

Figure 24.19

The vertebrate Hox complex contains duplicates of many ofthe same genes as the single invertebrate cluster, in virtuallythe same linear order on chromosomes, and they direct the sequential development of the same body regions. Thus, scientists infer that the four clusters of the vertebrate Hox complex are homologous to the single cluster in invertebrates.

5

First Hox duplication

Second Hox duplication

Vertebrates (with jaws)with four Hox clusters

Hypothetical earlyvertebrates (jawless)with two Hox clusters

Hypothetical vertebrateancestor (invertebrate)with a single Hox cluster

Most invertebrates have one cluster of homeotic genes (the Hox complex), shown here as coloredbands on a chromosome. Hox genes direct development of major body parts.

1

A mutation (duplication) of the single Hox complex occurred about 520 million years ago and may have provided genetic material associated with the origin of the first vertebrates.

2

In an early vertebrate, the duplicate set of genes took on entirely new roles, such as directing the development of a backbone.

3

A second duplication of the Hox complex, yielding the four clusters found in most present-day vertebrates, occurred later, about 425 million years ago. This duplication, probably the result of a polyploidy event, allowed the development of even greater structuralcomplexity, such as jaws and limbs.

4

MicroevolutionMicroevolution• SmallSmall genetic changes in a genetic changes in a

populationpopulation• Change in frequency of a Change in frequency of a single single

alleleallele due to due to selectionselection

MacroevolutionMacroevolution• Large-scale changes in Large-scale changes in

organismsorganisms• Involves Involves new new generagenera

The End

• The elimination of a species from The elimination of a species from the earththe earth

• Background Extinction RateBackground Extinction Rate - - relatively constant rate of relatively constant rate of extinction in the fossil recordextinction in the fossil record

• Mass ExtinctionMass Extinction - major loss of - major loss of species: climate change, humans, species: climate change, humans, catastrophiescatastrophies

ExtinctionExtinction

Figure 15.5

90 million years ago 80 70 65

Cretaceousextinctions

60

?

- These mass extinctions may have been a result of an asteroid impact or volcanic activity

– Every mass extinction reduced the diversity of life

– But each was followed by a rebound in diversity

Ex. Mammals filled the void left by the dinosaurs

Mass Extinctions

• The Permian extinction killed about 96% of marine animal species and 8 out of 27 orders of insects

• It may have been caused by volcanic eruptions• The Cretaceous extinction doomed many

marine and terrestrial organisms, notably the dinosaurs

• It may have been caused by a large meteor impact

Six Mass Extinction Events in the last 600 m.y. (2) of the major extinctions are:

LE 26-9

NORTHAMERICA

ChicxulubcraterYucatán

Peninsula

• By forming new islands, volcanoes can create opportunities for organisms

– Example: Galápagos

• But volcanic activity can also destroy life– Example: Krakatau

Figure 15.4B, C

Figure 15.1

Pg. 519

Geologic Time Eras-Pg. 521


Concept 26.3: As prokaryotes evolved, they exploited and changed young Earth

• The oldest known fossils are stromatolites, rocklike structures composed of many layers of bacteria (cyanobacteria) and sediment

• Stromatolites date back 3.5 billion years ago

• Living ones in Shark Bay Australia






• We humans are, in simple terms, bags of water filled with proteins and prokaryotic bacteria (the bacteria in your body outnumber the cells in your body about 10 to 1). We humans have descended from organisms that adapted to living in a prokaryotic world, and we humans retain (conserved in evolutionary terms) in our mitochondria the cellular machinery to power our cells that we inherited (i.e., endosymbiosis) from the prokaryotes of deep time on earth.

CRITICAL QUESTION:CRITICAL QUESTION:

How Do Humans Affect How Do Humans Affect Extinction Rates?Extinction Rates?

• SimplifySimplify ecosystems ecosystems –(monocultures/disturbed (monocultures/disturbed

habitats) habitats)

• StrengthenStrengthen pest populations pest populations

• EliminateEliminate predators (can predators (can create new pests)create new pests)


• IntroduceIntroduce new species new species (starlings)(starlings)

• OverharvestOverharvest

• InterferInterfer with chemical cycling with chemical cycling and energy flow (UV/ozone, and energy flow (UV/ozone, heat pollution)heat pollution)


• Continental drift is the slow, incessant movement of Earth’s crustal plates on the hot mantle

Continental drift has played a major role in macroevolution-Pg. 527

Figure 15.3A

PacificPlate

NorthAmerican

Plate

NazcaPlate

SouthAmerican

Plate

AfricanPlate

EurasianPlate

Splitdeveloping

Indo-AustralianPlate

Edge of one plate being pushed over edge of neighboring plate (zones of violent geologic events)

Antarctic Plate

• Plate tectonics, the movements of Earth’s crustal plates, are also associated with volcanoes and earthquakes– California’s

San Andreas fault is a boundarybetween two crustal plates

Connection: Tectonic trauma imperils local life

Figure 15.4A

San Andreas fault

San Francisco

Santa Cruz

Los Angeles

• This movement has influenced the distribution of organisms and greatly affected the history of life

– Continental mergers triggered extinctions

– Separation of continents caused the isolation and diversification of organisms

– Rate : 1-2 cm/yearFigure 15.3B

Mil

lio

ns

of

ye

ars

ag

o

EurasiaCE

NO

ZO

ICM

ES

OZ

OIC

PA

LE

OZ

OIC

North America

AfricaIndiaSouth

America

AntarcticaAustra

lia

Laurasia

Gondwana

Pangaea

Continental Drift/Plate Tectonics

Pangea (Paleozoic)

Laurasia Gondwana (Mesozoic)

• Europe -S. America• Greeland -Australia• N. America -Africa (Cenozoic)

**First Proposed by Alfred Wegner (1912)**Later Reproposed in the 1960’s after WWII and sonar mapping of the ocean

floor

Figure 15.3D

NORTHAMERICA

SOUTHAMERICA

EUROPE

AFRICA

ASIA

AUSTRALIA

= Living lungfishes

= Fossilized lungfishes

• Continental drift explains the distribution of lungfishes

– Lungfishes evolved when Pangaea was intact

Figure 15.3C

Preparing for the Final • Test Breakdown:

– Cumulative 60 Questions (Ch. 1-9 & 11-20)– Evolution 40 Questions (Ch. 22-24 & 26)

• Labs: Review all ten labs (especially AP rec.)

• Researchers, discoveries, & timelines

• Key concepts for each Chapter (summaries)

• Review Online quizzes, Study guide MC Q’s

• Generate a terminology list from each chapter

• Look at diagrams, tables, & charts discussed in class

Final Assignment Packet• Study guide Chapters 22, 23, & 24

• Comp book

• Bring 2 # 2 pencils

• Bring hall passes (late will not be accepted)

• Last chance to Bring pea plants

• Bring extra credit ap/ib tests

Documents

Introductory Questions #32 1)How can allele frequencies change in a population and increase variation? Give three examples. What do we call this when this