Transcript Speciation - inetTeacher.com

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/MuleC
olt05Right.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_i
mages/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
QuickTime™ and a
decompressor
are needed to see this picture.
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