THE ORIGIN OF SPECIES

THE ORIGIN OF SPECIES

• HOW DOES EVOLUTION LEAD TO THE FORMATION OF ALL THE DIFFERENT ORGANISMS, OR SPECIES, WE SEE ON THE PLANET?

• FIRST WE MUST DEFINE A “SPECIES”

THE ORIGIN OF SPECIES

• SPECIES– BIOLOGICAL SPECIES CONCEPT

• A SPECIES AS A POPULATION OR GROUP OF POPULATIONS WHOSE MEMBERS HAVE THE POTENTIAL TO INTERBREED AND PRODUCE FERTILE OFFSPRING

– MORPHOLOGICAL SPECIES CONCEPT• CLASSIFICATION IS BASED MAINLY ON OBSERVABLE AND

MEASURABLE PHENOTYPIC TRAITS– GENEALOGICAL SPECIES CONCEPT

• A SET OF ORGANISMS WITH A UNIQUE GENETIC HISTORY– ECOLOGICAL SPECIES CONCEPT

• IDENTIFIES SPECIES IN TERMS OF ECOLOGICAL NICHES

THE ORIGIN OF SPECIES

• REPRODUCTIVE BARRIERS KEEP SPECIES SEPARATE– A BIOLOGICAL FEATURE

OF THE ORGANISMS THEMSELVES TO PREVENT POPULATIONS BELONGING TO CLOSELY RELATED SPECIES FROM INTERBREEDING EVEN WHEN RANGES OVERLAP

THE ORIGIN OF SPECIES

• REPRODUCTIVE BARRIERS

THE ORIGIN OF SPECIES

• REPRODUCTIVE BARRIERSREPRODUCTIVE BARRIERS BETWEEN SPECIES

Prezygotic Barriers: Prevent Mating or FertilizationTemporal Isolation Mating or flowering occurs at different seasons or times of day

Habitat Isolation Populations live in different habitats and do not meetBehavioral Isolation There is little or no sexual attraction between males and females

Mechanical Isolation Structural differences in genitalia or flowers prevent copulation or pollen transfer

Gametic Isolation Male and/or female gametes die before waiting or fail to unite

Postzygotic Barriers: Prevent the Development of Fertile AdultsHybrid Inviability Hybrid zygotes fail to develop or to reach sexual maturity

Hybrid Sterility Hybrids fail to produce functional gametesHybrid Breakdown Offspring of hybrids are weak or infertile

THE ORIGIN OF SPECIES

• WHY DO THESE REPRODUCTIVE BARRIERS ARISE?– GEOGRAPHIC ISOLATION CAN LEAD TO

SPECIATION• ALLOPATRIC SPECIATION GENE FLOW IS BLOCKED BY THE EXISTENCE OF A GEOGRAPHIC BARRIER

THE ORIGIN OF SPECIES

• ALLOPATRIC SPECIATION EXPERIMENT

THE ORIGIN OF SPECIES

• ISLANDS ARE LIVING LABORATORIES FOR SPECIATION– ADAPTIVE

RADIATION THE EMERGENCEOF NUMEROUS SPECIES FROM A COMMON ANCENSTOR INTRODUCTED TO NEW AND DIVERSE ENVIRONMENTS

THE ORIGIN OF SPECIES

• WHY DO THESE REPRODUCTIVE BARRIERS ARISE?– REPRODUCTIVE ISOLATION CAN LEAD TO

SPECIATION (OVERLAPPING GEOGRAPHY)• SYMPATRIC SPECIATION REPRODUCTIVE ISOLATION

DEVELOPS AND NEW SPECIES ARISE WITHOUT GEOGRAPHIC SEPARATION

THE ORIGIN OF SPECIES

• SYMPATRIC SPECIATION– TYPICALLY THE RESULT OF SOME GENETIC

CHANGE (I.E. POLYPLOIDY)

THE ORIGIN OF SPECIES

• AS ORGANISMS BECOME MORE ISOLATED (GEOGRAPHICALLY OR REPRODUCTIVELY) THE BARRIERS BETWEEN THEM INTENSIFY

• THIS EVENTUALLY IN RESULTS IN ORGANISMS THAT ARE SEPARATE SPECIES, AND CONTINUE ON SEPARATE EVOLUTIONARY PATHS

• HOWEVER; THE RATE OF THIS CHANGE IS NOT CONSISTENT!!

THE ORIGIN OF SPECIES

• RATE OF SPECIATION– GRADUALISM VSPUNCTUATED EQUILIBRIUM

• GRADUALISM POPULATIONS EVOLVEDIFFERENCES SLOWLY (GRADUALLY) AS THEYBECOME ADAPTED TO THEIRLOCAL ENVIRONMENT, NEWSPECIES EVOLVE GRADUALLYFROM ANCESTRAL SPECIES

• PUNCTUATED EQUILIBRIUM EVOLUTION OCCURS INSPURTS (SHORT, QUICK, LARGE)

THE ORIGIN OF SPECIES

• WITH ALL THIS SPECIATION OCCURING, HOW DO WE KEEP TRACK OF ALL THESE DIFFERENT ORGANISMS?

• THAT’S WHAT YOU GET TO FIND OUT IF YOU COME BACK TO CLASS!!!