chapter 24 the origin of species. hummingbirds of costa rica species

Chapter 24

The Origin of Species

Hummingbirds of Costa Rica

Species

Biological Species Concept

Species

A population whose members can potentially interbreed in nature

to produce viable, fertile offspring

In practice, we recognize two populations as separate species if each has distinguishing

characteristics relative to the other, and members of each population lack the potential to interbreed in nature with members of the other

population

Reproductive Barriers

A complete barrier would result in no

gene flow

An incomplete barrier could still reduce

gene flow

Isolate populations from one another

Reproductive Barriers

Pre-zygotic vs. post-zygotic

A complete barrier would result in no

gene flow

An incomplete barrier could still reduce

gene flow

Reproductive Barriers

Pre-zygotic

Habitat isolation Geographic isolation

Roseate spoonbill

Eurasian spoonbill

Pre-zygotic

Habitat isolation Geographic isolation

Reproductive Barriers

North America

Central America

Madagascar

Reproductive Barriers

Pre-zygotic

Habitat isolation Geographic isolation Ecological isolation

Hawthorns or apples for oviposition

Rhagoletis pomonella

Reproductive Barriers

Pre-zygotic

Habitat isolation Geographic isolation Ecological isolation Behavioral (mate choice) isolation

Blue-footed boobies

Red-footed booby

Galapagos Islands

Satin Bowerbirds & their bowers

Tooth-billed Catbird’s leaf display

Australia

Reproductive Barriers

Pre-zygotic

Habitat isolation Geographic isolation Ecological isolation Behavioral (mate choice) isolation Temporal isolation

Periodical(12 year)

Dog-day(17 year)

Reproductive Barriers

Pre-zygotic

Habitat isolation Geographic isolation Ecological isolation Behavioral (mate choice) isolation Temporal isolation Mechanical isolation

C. wapleri Thompson Creek, W. Feliciana Parish

Reproductive Barriers

Pre-zygotic

Habitat isolation Geographic isolation Ecological isolation Behavioral (mate choice) isolation Temporal isolation Mechanical isolation Gametic isolation

acrosome

head

midpiece

tail

ovum

Buffon (1811)

Reproductive Barriers

Post-zygotic

Reduced hybrid viability Reduced hybrid fertility Hybrid sterility (in the extreme)

x =

sterile

♀

♂

Reproductive Barriers

Post-zygotic

Reduced hybrid viability Reduced hybrid fertility Hybrid sterility (in the extreme) Hybrid breakdown (reduced viability or fertility occurs in the offspring of hybrids)

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Figure 24.4

Individualsof differentspecies

Matingattempt

Habitat isolation

Temporal isolation

Behavioral isolation

Mechanical isolation

HABITAT ISOLATION TEMPORAL ISOLATION BEHAVIORAL ISOLATION MECHANICAL ISOLATION

Reproductive Barriers

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Viablefertile

offspring

Reducehybrid

viability

Reducehybridfertility

Hybridbreakdown

Fertilization

Gameticisolation

GAMETIC ISOLATION REDUCED HYBRID VIABILITY

REDUCED HYBRID FERTILITY HYBRID BREAKDOWN

Reproductive Barriers

Figure 24.4

Speciation

The process by which new species form

Two requirements:

Reproductive isolation of populations (gene flow sufficiently reduced) Genetic divergence (divergent evolution)

Two main modes:

Allopatric vs. sympatric

Allopatric speciationDivergence occurs in geographic isolation

Sympatric speciationDivergence occurs despite lack of geographic isolation

Allopatric vs. sympatric speciation

Figure24.5

Hawthorns or apples for oviposition

Rhagoletis pomonella

Sympatric speciation

Sympatric speciationDivergence occurs despite lack of geographic isolation

Polyploids

Organisms with extra sets of chromosomes; can result in sympatric speciation in one generation

The origin of a polyploid individual is usually a mistake in meiosis or mitosis

Autopolyploidy vs. allopolyploidy

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An autopolyploid

Is an individual that has > two chromosome sets, all from a single species

Figure 24.8

2n = 64n = 12

2n

4n

Failure of cell divisionin a cell of a growing diploid plant produces a tetraploid branch.

Gametes produced by flowers on this branch will be diploid.

If offspring are viable and fertile, it is a new biological species.

Sympatric speciation

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

An allopolyploid

Is an individual with > two chromosome sets, derived from different species

Meiotic error;chromosomenumber notreduced from2n to n

Unreduced gametewith 4 chromosomes

Hybrid with7 chromosomes

Unreduced gametewith 7 chromosomes Viable fertile

hybrid

Normal gameten = 3

Normal gameten = 3

Species A 2n = 4

Species B 2n = 6

2n = 10

Sympatric speciation

Figure 24.9

Polyploidy is especially common in

plants

From Micro- to Macro-Evolution

Microevolution – Population and species-level

evolution, including speciation

Macroevolution – Speciation and all

broader-scale evolutionary patterns and

processes

Anagenesis Cladogenesis

Sufficient micro-evolutionary changes may occur that the earlier population is considered a separate species from the later population

timeBranchingevolutionoccurs as

speciationevents

accumulate.

The formationof each new

branch is amacroevolutionary

event.

Figure24.2

Anagenesis Cladogenesis

Sufficient micro-evolutionary changes may occur that the earlier population is considered a separate species from the later population

timeBranchingevolutionoccurs as

speciationevents

accumulate

The formationof each new

branch is amacroevolutionary

event

Broad patterns acrossthe resulting tree are also within the scope

of macroevolutionFigure24.2

Adaptive Radiation

One species gives rise to many others in a geologically short period of time

E.g., Darwin’s finches

Islands are good places to find adaptive radiations

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

E.g., Hawaiian silverswords

Figure 24.12

Adaptive Radiation

Gradualism Punctuated

Equilibrium

Tempo of Evolution

time

Figure 24.13

Gradualism Punctuated

Equilibrium

Tempo of Evolution

time

Figure 24.13

Evolutionary Novelties

Evolutionary novelties usually arise as modifications of existing traits

Figure 24.14

Evolutionary Development (Evo-Devo)

Slight alterations in development can have profound effects on adults

Heterochrony = change in the rate or timing of development, relative to an ancestor

E.g., paedomorphosis = heterochronic retention of juvenile structures in adulthood

Evolutionary Development (Evo-Devo)

Slight alterations in development can have profound effects on adults

Heterotopy = change in the physical position of a trait during development, relative to an ancestor

E.g., feathers from one part of a bird’s body may become expressed on another part

Evolutionary Development (Evo-Devo)

Allometric growth = relative growth rates of different body parts within a species during development

Evolutionary Development (Evo-Devo)

Allometric growth = relative growth rates of different body parts within a species during development

E.g., allometric growth in horned scarab beetles; certain clusters of cells grow faster than others

Evolutionary Development (Evo-Devo)

Phanaeus imperator

Evolutionary Development (Evo-Devo)

Evolution is not “goal oriented”

Evolution is a genetic response to the interaction between the individuals of a population and their

current environment (which includes other individuals)

Natural selection can only act on the phenotypic variation present, and selection can only cause

evolutionary change if phenotypic variation results (at least in part) from genetic variation

Evolution is not “goal oriented”

Therefore, even if female tigers in a population would prefer blue males, blue tigers will never evolve if the

population lacks variation that includes blue fur

He’s not blue, but he’s better than nothing!

YES! But he exists only

in my dreams.