Mom, Dad… There’s something you need to know… I’m a MAMMAL! The Origin of Species

Mom, Dad…There’s something you need to know…

I’m a MAMMAL!

The Origin of Species

“That mystery of mysteries…”

• Darwin never actually tackled how new species arose…

• Darwin never actually tackled how new species arose…

Both in space and time, we seem to be brought

somewhat near to that great fact—that mystery of mysteries—

the first appearance of new beings on this Earth.

So…what is a species?• Biological species concept

– defined by Ernst Mayr– population whose members can

interbreed & produce viable, fertile offspring

Western MeadowlarkEastern Meadowlark

Distinct species:Distinct species:songs & behaviors are different songs & behaviors are different enough to prevent interbreedingenough to prevent interbreeding

Distinct species:Distinct species:songs & behaviors are different songs & behaviors are different enough to prevent interbreedingenough to prevent interbreeding

Other “species” definitions

• Morphological

• Phylogentic

Why are these needed?

How and why do new species originate?

• Species are created by a series of evolutionary processes– populations become isolated

• geographically isolated • reproductively isolated

– isolated populations evolve independently

• Isolation– allopatric

• geographic separation

– sympatric• still live in same area

The flightless cormorant (Nannopterum harrisi), one of many new species that have originated on the isolated Galápagos Islands

• Obstacle to mating or to fertilization if mating occurs

PRE-reproduction barriers

behavioral isolationbehavioral isolation

geographic isolation ecological isolation temporal isolation

mechanical isolation gametic isolation

Geographic isolation• Species occur in different areas

– physical barrier– allopatric speciation

• “other country”

Harris’s antelope Harris’s antelope squirrel inhabits squirrel inhabits the canyon’s south the canyon’s south rim (L). Just a few rim (L). Just a few miles away on the miles away on the north rim (R) lives north rim (R) lives the closely related the closely related white-tailed white-tailed antelope squirrel antelope squirrel

Harris’s antelope Harris’s antelope squirrel inhabits squirrel inhabits the canyon’s south the canyon’s south rim (L). Just a few rim (L). Just a few miles away on the miles away on the north rim (R) lives north rim (R) lives the closely related the closely related white-tailed white-tailed antelope squirrel antelope squirrel

Habitat (ecological) isolation• Species occur in same region, but occupy different

habitats so rarely encounter each other– reproductively isolated

2 species of garter snake, 2 species of garter snake, ThamnophisThamnophis, occur , occur in same area, but one lives in water & other is in same area, but one lives in water & other is terrestrialterrestrial

2 species of garter snake, 2 species of garter snake, ThamnophisThamnophis, occur , occur in same area, but one lives in water & other is in same area, but one lives in water & other is terrestrialterrestrial

lions & tigers could lions & tigers could hybridize, but they hybridize, but they live in different live in different habitats:habitats: lions in grasslandslions in grasslands tigers in rainforesttigers in rainforest

lions & tigers could lions & tigers could hybridize, but they hybridize, but they live in different live in different habitats:habitats: lions in grasslandslions in grasslands tigers in rainforesttigers in rainforest

Temporal isolation• Species that breed during different times of

day, different seasons, or different years cannot mix gametes– reproductive isolation– sympatric speciation

• “same country”

Eastern spotted skunk Eastern spotted skunk (L) & western spotted (L) & western spotted skunk (R) overlap in skunk (R) overlap in range but range but easterneastern mates mates in in late winterlate winter & & westernwestern mates in mates in late summerlate summer

Eastern spotted skunk Eastern spotted skunk (L) & western spotted (L) & western spotted skunk (R) overlap in skunk (R) overlap in range but range but easterneastern mates mates in in late winterlate winter & & westernwestern mates in mates in late summerlate summer

Behavioral isolation• Unique behavioral patterns & rituals isolate

species– identifies members of species – attract mates of same species

• courtship rituals, mating calls

Blue footed boobies mate Blue footed boobies mate only after a courtship display only after a courtship display unique to their speciesunique to their species

Blue footed boobies mate Blue footed boobies mate only after a courtship display only after a courtship display unique to their speciesunique to their species

sympatric speciation?sympatric speciation?

firefly courtship displaysfirefly courtship displaysfirefly courtship displaysfirefly courtship displays

courtship display of courtship display of Gray-Crowned Cranes, KenyaGray-Crowned Cranes, Kenya

courtship display of courtship display of Gray-Crowned Cranes, KenyaGray-Crowned Cranes, Kenya

courtship songs of sympatriccourtship songs of sympatricspecies of lacewingsspecies of lacewings

courtship songs of sympatriccourtship songs of sympatricspecies of lacewingsspecies of lacewings

Recognizing your own species

Mechanical isolation• Morphological differences can prevent

successful mating

Even in closely related Even in closely related species of plants, the flowers species of plants, the flowers often have distinct often have distinct appearances that attract appearances that attract different pollinators. different pollinators. These 2 species of monkey These 2 species of monkey flower differ greatly in shape flower differ greatly in shape & color, therefore cross-& color, therefore cross-pollination does not happen.pollination does not happen.

Even in closely related Even in closely related species of plants, the flowers species of plants, the flowers often have distinct often have distinct appearances that attract appearances that attract different pollinators. different pollinators. These 2 species of monkey These 2 species of monkey flower differ greatly in shape flower differ greatly in shape & color, therefore cross-& color, therefore cross-pollination does not happen.pollination does not happen.

PlantsPlants


Mechanical isolation

• For many insects, male & female sex organs of closely related species do not fit together, preventing sperm transfer– lack of “fit” between sexual organs:

Damsel fly penises

AnimalsAnimals

I can’t even imagine!

Gametic isolation• Sperm of one species may not be able to fertilize

eggs of another species– mechanisms

• biochemical barrier so sperm cannot penetrate egg– receptor recognition between egg & sperm

• chemical incompatibility – sperm cannot survive in female reproductive tract

Sea urchins release sperm & Sea urchins release sperm & eggs into surrounding eggs into surrounding waters where they fuse & waters where they fuse & form zygotes. Gametes of form zygotes. Gametes of different species— different species— redred & & purple —are unable to fuse.purple —are unable to fuse.

Sea urchins release sperm & Sea urchins release sperm & eggs into surrounding eggs into surrounding waters where they fuse & waters where they fuse & form zygotes. Gametes of form zygotes. Gametes of different species— different species— redred & & purple —are unable to fuse.purple —are unable to fuse.


POST-reproduction barriers• Prevent hybrid offspring from

developing into a viable, fertile adult– reduced hybrid viability– reduced hybrid fertility– hybrid breakdown

zebroid

QuickTime™ and a decompressor

are needed to see this picture.

Reduced hybrid viability• Genes of different parent species may

interact & impair the hybrid’s development

Species of salamander Species of salamander genus, genus, Ensatina,Ensatina, may may interbreed, but most interbreed, but most hybrids do not complete hybrids do not complete development & those that development & those that do are frail.do are frail.

Species of salamander Species of salamander genus, genus, Ensatina,Ensatina, may may interbreed, but most interbreed, but most hybrids do not complete hybrids do not complete development & those that development & those that do are frail.do are frail.


Mules are vigorous, Mules are vigorous, but sterilebut sterile

Reduced hybrid fertility

• Even if hybrids are vigorous they may be sterile– chromosomes of parents may differ in

number or structure & meiosis in hybrids may fail to produce normal gametes

Donkeys have 62 Donkeys have 62 chromosomeschromosomes(31 pairs)(31 pairs)

Horses have 64 Horses have 64 chromosomeschromosomes(32 pairs)(32 pairs) Mules have 63 chromosomes!Mules have 63 chromosomes!

Hybrid breakdown• Hybrids may be fertile & viable in first

generation, but when they mate offspring are feeble or sterile

In strains of cultivated rice, In strains of cultivated rice, hybrids are vigorous but hybrids are vigorous but plants in next generation are plants in next generation are small & sterile.small & sterile.On path to separate species.On path to separate species.

In strains of cultivated rice, In strains of cultivated rice, hybrids are vigorous but hybrids are vigorous but plants in next generation are plants in next generation are small & sterile.small & sterile.On path to separate species.On path to separate species.


Adaptive Radiation

• Islands are laboratories of speciation

• Adaptive radiation is the evolution a number of different new species from a common ancestor

• Archipelago's are the home of adaptive radiations

Adaptive radiation

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 scabraDubautia linearis

N

Ring Species: Allopatric Speciation in Progress

What sort of reproductive barrier is this? Prezygotic

Has reproductive isolation occurred?

Sympatric Speciation

Sympatric Speciation in Animals

Under normal light Under monochromatic light

Niles EldredgeCurator

American Museum of Natural History

Rate of Speciation• Current debate:• Does speciation happen gradually

or rapidly? – Gradualism

• Charles Darwin• Charles Lyell

– Punctuated equilibrium• Stephen Jay Gould• Niles Eldredge

Gradualism

• Gradual divergence over long spans of time– assume that big

changes occur as the accumulation of many small ones

Punctuated Equilibrium• Rate of speciation is

not constant– rapid bursts of

change – long periods of little

or no change– species undergo

rapid change when they 1st bud from parent population

Stephen Jay Gould (1941-2002)

• Harvard paleontologist & evolutionary biologist– punctuated equilibrium– prolific author

• popularized evolutionary thought

Evolutionary Novelties

• Complex structures evolved from simpler versions

Changes in Developmental Rates

Changes in Hox clusters

• Impacts morphology

• Ex changes in hox gene location leads to swimming appendages in one and to feeding appendages in other.

What caused the loss of spines in lake stickleback fish?

2006-2007

Any Questions??

Review Questions

• 1. A biologist discovers two populations of wolf spiders whose members appear identical. Members of one population are found in the leaf litter deep within the woods. Members of the other population are found in the grass at the edge of the woods. The biologist decides to designate the members of the two populations as two separate species. Which species concept is this biologist most closely utilizing?A. EcologicalB. BiologicalC. MorphologicalD. PluralisticE. genealogical

• 2. The formation of a land bridge between North and South America about three million years ago should have resulted in which of the following? I. allopatry of marine populations that were

previously sympatricII. sympatry of marine populations that

were previously allopatric

III. sympatry of terrestrial populations that were

previously allopatric

A. I onlyB. II only• III only• I and II • I and III

For each of the following situations, choose the best answer from the following types of isolating mechanisms:

A. Geographical isolationB. Behavioral isolationC. Mechanical isolationD. Temporal isolationE. Reproductive isolation

•Two species of rats live on different islands.•Referes to all species that adhere to the biological definition.•Two species of fruit fly have different courtship rituals.•The pollen from a Dogwood tree can not penetrate the pine cone of a Douglas Fir.

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Mom, Dad… There’s something you need to know… I’m a MAMMAL! The Origin of Species