Species and Speciation BIOL 1407 Biological Species Concept

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 Ø Parents offspring • Horizontal gene transfer Ø Individual individual Ø Not 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: H 7 has picked up Shiga toxin gene from Shigella • Up to 25% genetic difference among E. coli strains • Photo Credit of E. coli 0157: H 7: 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=4 MPf. Tz. XEZd. Y • Photo Credit: Richard 001, 2007, Wikimedia Commons

Behavioral Isolation Eastern and Western Meadowlarks • Isolated by Songs • Listen to both species (Links to songs are below the picture): • http: //www. lewis-clark. org/content-article. asp? Article. ID=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, 8 th ed. Pearson Benjamin Cummings.