Speciation

Speciation

the origin of new species is at the focal point of Darwin’s evolutionary theory

Evolutionary theory must explain

how new species originate and how populations evolve

Microevolution

Consist of adaptations that evolve within a population, confined to one gene pool

Macroevolution

refers to evolutionary change above the species level

Reproductive isolation

is the existence of biological factor(barriers) that impede two different species from producing viable, fertile offspring.

Hybrids

are the offspring of crosses between different species

Reproduction isolation can be classified by

where factor act before or after fertilization

Prezygotic Barries

block fertilization from occurring by:

• Impeding different species from attempting to mate

• Preventing the successful completion of mating

• Hindering fertilization if mating is successful.

Prezygotic barries

maintain reproductive isolation and includes

• Temporal habitat, Behavioral, Mechanical, and gamete isolation

Habitat isolation

two species(genetically similar) encounter each other rarely because they occupy different habitats even though not isolated by physical barriers.

Temporal Isolation

Species that breed at different timed of the day, different seasons, or different years cannot mix their gametes

Behavioral isolations

Courtship ritual and other becahiors unique to a species are effective barriers

Mechanical Isolation

Morphological difference can prevent successful mating (shells)

Gametic(sperm and egg) isolation

Sperm of one species may not be able to fertilize to fertilize eggs of another species

Postzygotic barriers

prevent the hybrid zygote from developing into a viable fertile adult

• reduced hybrid viability (weak)

• Reduce hybrid fertility( sterile )

• Hybrid breakdown

Speciation occurs in two ways

• Allopatric speciation: geographic barrier operates populations

• Sympatric speciation: no geographic barrier

In allopathic speciation gene flow is

interrupted or macroevolution is the cumulative effect of many speciation and extinction events

Reduced when a population is divided intro geographically isolation subpopulations

A geographic barrier separated the original population

Separate population may

evolve independently through mutation, natural selection, and genetic drift

Barriers to repoduciron are insteisci(naturally happens)

seperation itself is not a biological barrier

Autopoluloid is a species with

multiple steps of chromosomes(always have to been even) derived from different species

Polyploidy

is common in plants

Sympatric speciation

can also result from the appearance of new ecological niches

For example

the North American maggot fly can live on notice hawthorn trees as well as more recently introduces apple trees

Sexual selection

can drive sympatric speciation

Sexual selection form aged of different color has

likely contribute to the speciation in cichlid fish in lake Victoria.

hybrid zone

is a region in which members of different species mate and produce hybrids.

where adjacent species meet?

A hybrid zone can occur in a single band

Hybrids often have

reduced fitness compared

with parent species.

The distribution of hybrid zones can be more

complex

if parent species are found in multiple

habitats within the same region.

When closely related species meet in a hybrid

zone, there are three possible outcomes:

• Reinforcement -- Strengthening of reproductive barriers reducing gene flow.

• Fusion -- Weakening of reproductive barriers with eventual fusion into one species.

• Stabilizing -- Continued formation of hybrid individuals.

The Time Course of Speciation

Broad patterns in speciation can be studied using the fossil record, morphological data, or molecular data.

The fossil record includes

examples of species that appear suddenly, persist essentially unchanged for some time, and then apparently disappear

punctuated equilibrium

to describe periods of apparent stasis (no change) punctuated by brief periods of rapid change.

The explosion of genomics is

enabling researchers to identify specific genes involved in some cases of speciation. (speciation might require the change of only a single allele or many alleles.)