Species and Speciation

BIOL 1407

Biological Species Concept

• A group of organisms that can interbreed and produce viable, fertile offspring

• Photo Credit of Galápagos Marine Iguanas: Putneymark, 2008, Wikimedia Commons

Biological Species Concept

• Assumes – Common

characteristics – Genetically compatible– Interbreed under

natural conditions– Sexual Reproduction

• Photo Credit of Iguana iguana: Ianare, 2007, Wikimedia Commons

Drawbacks of Biological Species Concept

• Cannot be used with exclusively asexual organisms – Prokaryotes– Amoeba & some

other protists– Some animals,

plants & fungi• Photo Credit of Amoeba proteus: Angel, BIOL 1407

student, fall 2008

Drawbacks: Isolated Populations

• How do you test for interbreeding under natural conditions?

• Can a deer in Florida interbreed with one in Wisconsin?

• Photo Credit of Key Deer: Scott Bauer, 2006, USDA• Photo Credit of Deer Running: Paul Frank, 2006, USFWS

Drawbacks

• Can a Great Dane interbreed with a Chihuahua?

• Photo Credit: David Shankbone, 2006, Wikimedia Commons

Drawbacks• Some species look

and behave differently

• Can interbreed and have viable, fertile offspring

• Example: coyotes, wolves, dogs

• Picture Credits: Courtesy of Smithsonian National Zoo @ nationalzoo.si.edu (coyote and wolf); Pam Wolfe (dog)

Drawbacks:Horizontal Gene Transfer

• Vertical gene transfer Parents offspring

• Horizontal gene transfer Individual individualNot parent-offspring

• Diagram Credit: Gregorius Pilosus, 2009, Wikimedia Commons

Horizontal Gene Transfer

• Can occur between organisms:– Different species – Different kingdoms– Different domains

• Diagram Credit: Barth F. Smets, Ph.D., with permission, 2005, Wikimedia Commons

Horizontal Gene Transfer in Bacteria

(1) Transformation

Horizontal Gene Transfer

in Bacteria

(2) Transduction

Horizontal Gene Transfer in Bacteria

(3) Conjugation

Horizontal Gene Transfer

• E. coli 0157:H7 has picked up Shiga toxin gene from Shigella

• Up to 25% genetic difference among E. coli strains

• Photo Credit of E. coli 0157:H7: E. H. White, Centers for Disease Control, 1995, Wikimedia Commons

Horizontal Gene Transfer

• Normally, 25% genetic diversity different species

• Human and chimp genomes differ by only 1.2%

• Photo Credit: Thomas Lersch, 2005, Wikimedia Commons

Drawbacks: Fossil Species

• Cannot tell if fossil organisms were capable of interbreeding

• Photo Credit of Harlan’s Ground Sloth: Doyle Cross, 2006, UT Memorial Museum

Fossils

• Normally can’t compare genes of different fossil species

Morphological Species Concept

• Group of individuals that share common characteristics

• Used for:• Fossils • Exclusively asexual• Traditional method

for sexual organisms• Photo Credit of Orchid: Bernd Haynold, 2004, Wikimedia

Commons

Biological Species Concept:Reproductive Isolation

• Barriers between species• Prevent viable fertile

offspring• Photo Credit (Lesser Bird of Paradise): Roderick Eime, 2005; (Greater

Bird of Paradise): Andrea Lawardi, 2008, Wikimedia Commons

Reproductive Isolating Mechanisms

• Prezygotic mechanisms – Before fertilization

• Postzygotic mechanisms – After fertilization

Prezygotic Mechanisms

• Prevents: – Prevent mating from

occurring – Prevents gametes

from forming a zygote

• Photo Credit for Sperm fertilizing an ovum: Wikimedia Commons, 2008

Prezygotic Mechanisms: Temporal Isolation

• Isolated by time• May breed:

– Different times of day– Different seasons – Different years

• Photo Credit: Alan Zomerfeld, 2006, Wikimedia Commons

Temporal Isolation

Late Winter Late Summer

Prezygotic Mechanisms: Habitat Isolation

• Same geographic area• Different habitats

Prezygotic Mechanisms: Behavioral Isolation

• Different courtship rituals

• Blue-Footed Booby Video: http://www.youtube.com/watch?v=4MPfTzXEZdY

• Photo Credit: Richard001, 2007, Wikimedia Commons

Behavioral IsolationEastern and Western Meadowlarks

• Isolated by Songs• Listen to both species (Links to songs are below the picture):• http://www.lewis-clark.org/content/content-article.asp?ArticleID=401

Prezygotic Mechanisms: Mechanical Isolation

• Structural differences prevent mating

• Example:

Genital openings (arrows) not aligned No Mating

Prezygotic Mechanisms: Gametic Isolation

• Sperm cannot fertilize eggs

• Very important in aquatic species (broadcast spawners)

• Example: Sea Urchins

Postzygotic Mechanisms

• Prevents hybrid zygotes from developing into viable, fertile adults

• Photo Credit of Zeedonk: Ondrejk, 2004, Wikimedia Commons

Postzygotic Mechanism: Reduced Hybrid Viability

• If Sheep and goats mate Hybrid zygotes

• Die before birth.• Photo Credit: Missouri NRCS Photo

Gallery

Postzygotic Mechanism: Reduced Hybrid Fertility

• Male donkey x Female horse Mule

• Mules:– Healthy (viable)– Sterile.

Postzygotic Mechanism: Hybrid Breakdown

• First generation hybrids are viable and fertile.

• Offspring of hybrids are feeble or sterile.

Speciation

• Process of species formation

• Two main mechanisms:

– Allopatric speciation

– Sympatric speciation

Allopatric Speciation

Geographic separation Genetic

exchange Populations

become genetically different

Reproductive isolation

Sympatric Speciation

• Populations not geographically separated

• Can be due to rapid genetic changes:– Alter morphology – Alter behavior– Alter habitat

preferences

Example: Sympatric Speciation

• Euhadra snails• Mutation in one

gene Shell spirals in opposite direction

• Instant mechanical isolation

Two species

Adaptive Radiation

• A common ancestor Many new species

• Relatively rapid• Common in island

chains– Isolated– Numerous habitats &

resources• Map Credit: M. Minderhoud, 2006, Wikimedia Commons

Galápagos Finches

• Ancestral finch from South America Several finch species– Different diets– Different beak

shapes – Different beak sizes

Galápagos Finches

Hawaiian Silverswords

• Tarweed arrived from North America ~ 5 mya

• Common ancestor Silverswords

• Map Credit: M. Minderhoud, 2006, Wikimedia Commons

Hawaiian Silverswords

The End

Unless otherwise specified, all images in this presentation came from:

Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.