Speciation and Macroevolution• Speciation• Divergent Evolution• Convergent Evolution

Evolutionary change of a species over time

Creation of new groupspeciation diversity of living things.

Speciation & Macroevolution

• Microevolution = evolution on small scale• changes in allele frequency in a population over time

• Speciation = formation of new species• Bridges micro and macro-evolution

• Macroevolution = large scale evolution• broad patterns of evolutionary change; species formation and larger

What is a species?

• biological species concept: • A group of individuals (i.e., multiple pops.) that have the potential to interbreed in

nature and produce viable, fertile offspring.• Based on reproductive compatibility and isolation• Weakness of this def:

• Other species definitions:• Morphological species concept: based on structure• Ecological species concept: based on niche (i.e., role in ecosystem)• Phylogenetic species concept: based on common ancestor (evolutionary relationship)• More…..

Reproductive Isolation• Reproductive isolation : inability to mate and produce viable, fertile

offspring• Classification/Types of Isolation:• Prezygotic Barriers• Pre-mating attempt• Post-mating attempt

• Post-zygotic Barriers

Figure 24.13-2

Gene flow

Population Barrier togene flow

Isolatedpopulationdiverges.

Gametes don’t uniteMating doesn’t occur

Offspring doesn’t survive or can’t perpetuate species

• Prezygotic barriers block fertilization from occurring by• Impeding different species from attempting to mate• Preventing the successful completion of mating• Hindering fertilization if mating is successful

• Postzygotic barriers prevent the hybrid zygote from developing into a viable, fertile adult• Reduced hybrid viability• Reduced hybrid fertility• Hybrid breakdown

Two forms of Speciation:• Allopatric: speciation with

geographic separation• Non-overlapping populations• “Barrier” is relative to dispersal

ability of organism• Even if contact is restored,

interbreeding is prevented

• Sympatric: speciation within the same geographic location/area• Overlapping

Allopatric Speciation: A tale of two fuzzy animals

Figure 24.7

Experiment

Results

Some flies raised on starch medium

Initial populationof fruit flies(Drosophila

pseudoobscura)

Mating experimentsafter 40 generations

Some flies raised on maltose medium

FemaleStarch

population 1Starch

population 2

Female

Starch Maltose

9

208

22

Star

chM

alto

seM

ale

Mal

eSt

arch

popu

latio

n 1

Star

chpo

pula

tion

2

18

12 15

15

Number of matingsin control group

Number of matingsin experimental group

• Reproductive barriers can develop when laboratory populations are experimentally isolated and subjected to different environmental conditions

Figure 24.6

(a) Under high predation (b) Under low predation

Females from each pop show strong preference for their own body shape in mate selection

Sympatric Speciation

• Mechanisms for sympatric speciation• Habitat differentiation• Sexual selection• Polyploidy

A “tale” of two squirrels

Sexual Selection• Preference for specific traits (e.g., morphological or behavioral) by

subset of females can lead to reproductive isolation.• E.g. Sexual selection for mates of different colors has likely contributed to

speciation in cichlid fish in Lake Victoria

Orange noses are dreamy

I love a man with a red

nose

Figure 24.11

Normal lightMonochromatic

orange light

P. pundamilia

P. nyererei

Experiment

Polyploidy

• Polyploidy is the presence of extra sets of chromosomes due to accidents during cell division• Polyploidy can produce new biological species in sympatry within a

single generation• Autopolyploid: from a single species• Allopolyploid: from hybrids of two species

• An autopolyploid is an individual with more than two chromosome sets, derived from a single species

Celldivisionerror

Tetraploid cell4n

2n = 6

2n

2n

Meiosis

New species(4n)Gametes produced

by tetraploids

Autopolyploid speciation Figure 24.UN02

• An allopolyploid is a species with multiple sets of chromosomes derived from different species

Species A2n = 6

Normal gameten = 3

Normal gameten = 2

Species B2n = 4

Sterile hybrid with5 chromosomes

Mitotic or meiotic errordoubles the chromosomenumber.

New species:viable, fertile hybrid(allopolyploid)2n = 10

Figure 24.9-3

Figure 24.10T. dubius(12)

Hybrid species:T. miscellus(24)

Hybrid species:T. mirus(24)

T. pratensis(12)

T. porrifolius(12)

Rate of speciation

• It can happen quickly (punctuated equilibrium model)• It can happen slowly (gradualism)• The interval between speciation events can range from 4,000 years (some

cichlids) to 40 million years (some beetles), with an average of 6.5 million years

Figure 24.16

(a) Punctuated model

(b) Gradual model

Time

Studying the Genetics of Speciation• How many genes change when a new species forms?• As few as a single gene or in other cases many genes• For example, in Japanese Euhadra snails, the direction of shell spiral affects mating

and is controlled by a single gene

• In monkey flowers (Mimulus), two loci affect flower color, which influences pollinator preference• Pollination that is dominated by either hummingbirds or bees can lead to reproductive

isolation of the flowers

• In other organisms, speciation can be influenced by larger numbers of genes and gene interactions

Figure 24.19

(a) Mimulus lewisii M. lewisii withM. cardinalis allele

(b)

M. cardinalis withM. lewisii allele

(c) Mimulus cardinalis (d)

Preferred by hummingbirds

Preferred by bumblebees

68x more hummmingbrid visits than wild-type M. lewisii

74x more bumblebee visits than wild-type M. cardinalis

Convergent Evolution• When similar selective forces cause similarities (similar traits) in

unrelated species• E.g., body shape of aquatic organism (shark and dolfins) • Similar structure of desert plants cacti & euphorbs