Speciation

How are new species created?

What is a species?

• According to the biological species concept, a species is a group whose members can breed with each other in nature and produce fertile offspring

• It’s all about reproduction!

• Problems with this definition?

What is speciation?

• Speciation is an event that produces two or more separate species.

• In a phylogenetic tree, it is represented by a branching point

• Example: Drosophila

A new species of fruit fly

• Example: Fruit flies

http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_42

A population of wild fruit flies on several bunches of rotting bananas, laying their eggs in the mushy fruit...

A new species of fruit fly

• Disaster strikes: A hurricane washes the bananas and the fruit flies out to sea. The banana bunch washes up on an island off the coast of the mainland. The two portions of the population, mainland and island, are now too far apart for gene flow to unite them.

A new species of fruit fly

• The populations diverge: Conditions are slightly different on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does.

• Food preferences, and courtship displays change over the course of many generations of natural selection.

A new species of fruit fly

• So we meet again: When another storm brings the island flies back to the mainland, they will not mate with the mainland flies since they've evolved different courtship behaviors.

• The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations.

• Two separate species now exist since genes cannot flow between the populations.

Geographic Isolation

• Populations are separated by geographic change or dispersal to geographically isolated places– Rivers change course– Mountains rise– Continents drift– Organisms migrate– Roads are built

• Note: a barrier for one species may not be a barrier for another species

Small populations face risks

• Founder effect: when only a few individuals colonize a new place, genetic variation is low

• Genetic drift: changes in gene pool due to chance (which individuals reproduce)

• Bottleneck effect: disasters that eliminate a large number of individuals and greatly reduce the gene pool

A new species:

• If a group splits off from the main population– evolves to adapt to its environment– the changes accumulated make it unable

to breed with the larger population

• Then a new species has been formed

Other reasons for reproductive isolation:

• Timing: Different breeding seasons– Example: Spotted skunks

• Western skunks breed in the fall, Eastern skunks breed in the late winter

QuickTime™ and a decompressor

are needed to see this picture.

http://s190.photobucket.com/albums/z257/americanwildlife/Mammal/Z-western-spotted-skunk1.jpg

http://www.redorbit.com/modules/reflib/article_images/42_7de29e7e859b48896129c3d380d3cfbb.jpg

Other reasons for reproductive isolation:

• Behavior: Different courtship or mating behaviors– Example: Eastern and Western

Meadowlarks• Different songs

Other reasons for reproductive isolation:

• Habitat: Adapted to different habitats in the same general location– Example: Stickleback fish in British

Columbia• Live in different levels of water, have different

diets

http://ecoreb.org/imgs/o_gasacu2.jpg

Other reasons for reproductive isolation:

• Others: different reproductive structures, insects only transfer pollen to certain plants, hybrid offspring is sterile

http://www.birkenholz.com/IMAGES/MuleColt05Right.jpg

Adaptive Radiation

• Evolution from a common ancestor that results in diverse species adapted to different environments– Diversification happens quickly

• Islands often favor speciation because geographically isolated– Example: Hawaiian honeycreepers

Adaptive Radiation

• Hawaiian honeycreepers: over 40 species have evolved from 1 common ancestral species

• Variation in color and beak shape is related to their habitat and diet

http://www.hawaii.edu/environment/ainakumuwai/assets/src_images/honeycreepers.jpg

Macroevolution

• Describes dramatic biological changes– Origin of new species– Extinction of species– Formation of major new features (wings, flowers)

• Different from microevolution which describes changes in allele frequencies within a population

• Mutation+Natural Selection+3.5 billion years = Macroevolution

Ensatina Salamanders

• California salamanders– Live and lay eggs on land– Studied by R.C. Stebbins in the 1940s

• You will use his data to map the locations of various subspecies

• Video of mating behavior:– http://evolution.berkeley.edu/evolibrary/article/0_0_0/devitt_07

• Pictures of each subspecies:– http://www.indiana.edu/~ensiweb/lessons/stepsal4.html

http://evolution.berkeley.edu/evolibrary/article/0_0_0/devitt_02

Ensatina Salamanders

Qu

ickTim

e™

an

d a

decom

pre

ssor

are

need

ed

to se

e th

is pic

ture

.

Ring Species

• All subspecies interbreed with their immediate neighbors EXCEPT at southern end– E. klauberi and E.

eschscholtzii do not interbreed

• Where should speciation be marked?

http://evolution.berkeley.edu/evolibrary/article/side_0_0/biospecies_01#ring