18.2 & 18.3 Formation of New Species & Reconnection and Speciation Rates

What is the order of evolution?

Individual organism → Population (Species) → Community → Ecosystem

Species

 Group of organisms that are able to breed, and produce fertile, viable offspring

• Individuals of the same species have the same number and composition of chromosomes

Hybrids

Offspring of organisms that would not normally breed with each other

Gene Flow

Movement of alleles within and between populations

Speciation

Formation of two separate species from one original parent population

Which traits evolve?

Only heritable traits can evolve

Allopatric Speciation

Physical separation of the two new populations from the parent population, caused by physical isolation

What are the two types of allopatric speciation?

Dispersal- Few members of a population move to a new area

Vicariance- Geographic barrier physically divides the population, limited to no gene flow

Sympatric Speciation

Populations inhabiting the same geographical range diverge into

• Caused by reproductive isolation

• Leads to behavioral isolation

What are the 3 types of reproductive isolation?

• Temporal – Variation in time of day or seasonality of mating

• Behavioral – Different mating cues

• Habitat – Individuals specialize within their environment

Adaptive Radiation

 Relatively rapid evolution of many species from a single ancestor

• Typically occurs when new resources or new habitats are available

• Islands are ideal sites for adaptive radiation

What are the two patterns of speciation?

• Gradual Speciation- Species diverge gradually over time

• Punctuated Equilibrium- New species diverge quickly from the parent species and then remain unchanged for long periods of time

What are the primary drivers of the rate of speciation?

Environmental Conditions

Reproductive Isolation

Prevents individuals from different species from interbreeding or, if they do interbreed the resultant offspring will be nonviable or infertile

• Prevents gene flow

What are the two types of reproductive isolation?

• Prezygotic Barrier- Prevents mating from occurring, or fertilization from occurring

• Postzygotic Barrier- Zygote does not develop and dies or offspring is sterile

What are the 4 types of prezyogtic barriers?

Temporal, Habitat, Behavior, Mechanical

Temporal Barrier

Reproduce at different times of the day or year

Habitat Barrier

Individuals inhabit close but different habitats

Behavior Barrier

Mating cues are different

Mechanical Barrier (Aka Gametic Isolation)

Incompatible reproductive structures & incompatible gametes (Cant reproduce with each other)

Hybrid Zone

Closely related species interact

• Less-fit hybrids reinforce the speciation

  • As the speciation progresses in time, fewer hybrids are produced until there are no hybrids (Reinforcement)

• If reproductive barriers weaken, then the two species may fuse back into one species (Fusion)

•  If hybrids are fit and reproduce only with each other, stabilization results

  • The two new species remain separate, but they can interbreed and produce hybrids

  • Oftentimes the hybrids differentiate into a third species 

Hybrid Inviability

Hybrid zygote does not develop

Hybrid Sterility

Hybrid is sterile (infertile)

Hybrid Breakdown

First generation of hybrid offspring is viable and can reproduce, however, viability or sterility problems arise with their offspring.

Polyploidy

Condition in which a cell or organism has an extra set, or sets, of chromosomes

Autopolyploidy

A polyploid individual will have two or more complete sets of chromosomes from its own species