15. Speciation Hybridization

Speciation

• The “formation” of a new species over geological time, when members of a population can no longer successfully interbreed

• Requires: Reproductive isolation related to behavioral traits, habitat use, physiology, etc.

Allopatric Speciation

• The evolution of a new species through the process of geographic isolation

• Over time, populations become so different that, cannot interbreed, evolve into new speices

Process of Allopatric Speciation

Geographic seperation: creates two populations who are isolated from each other as a result, no genetic exchange can occur between them

Allopatric Speciation

occrus whena opulation is divded into geograhically isolated populations

Vicrance allopatric speciation

geographic subpopulations, river divding

Disperal allopatric Speceiation

indivudals colinaiize a remote area

Gene pool os isolated populations may diverge through

mutation, natural selection, and genetic drift

Allopatric Speciation etc.

• reporduive isolation may arise as a by-porudct of genetic divergence

• Allopatric speceation is the most comon form of specation

Divergence invovles

• accumulation of indepedent genetic difference between groups (often after population shave become repordviley ioslated.

Evidence of allopatric speciation

• isolated/highly subdivded regions usally have more species that those with fewere barriers

• Ex: hawaiian islands have many uniqe plants and animals

Allopatric speciation examples

• isolated populations of mosqutiofish have become repdorucitley isoaltes as a reuslt of slesection under differente levels or predation

• predaiton selected for different body shapes

• perenrefre for mating with individuals that have a similar body shape

Sympatric Specation

• The evolution of a new species without geographic isolation

• Ex: chchild fish in lake Tanganikya have veolved into 200 unique speices from a single common ancestor

• Distint micrhabitats throughout the lake, distnics types of food resrources, speiclaizations, etc.

Porcess of sympatric speciation

• populations live in the same geographic area

• gene flow is reducced by factros such as

• poluplodiy

• sexual selection

• habitat differentation

Drivers of Sympatric Speciation: Polyploidy

• Polupiodiy: accidents during cell dividsio, the presence of extra sets of chromosomes

• This process can form a new speices withing a single gnereation

• can happen with (allopolopolidy) and withouth (autopoluplody) hubridzation

• Many importnat agriculatral crops are polyploids

Examples of polploid speciation

• at least five new plant speices have orginated by polypiod specation since 1850

• ex: two allopolpios speices have evolved from three diploid parent speices in the genus trgopogon

Drivers of sympatric Speciation Seciaul Selection

• Sympatric specation can be riven by seicual selection

• Speciaton of chcilids Lake Victroia was likely driven by female mate choise based on male breeding coloration

Drivers of sympatris speication: Habitat Differentiation

• Sympatric speciation can also result from the exloitation of new habitats or resources

• Apple magoot flies evolved in North America after swithciing hosts from hawthorn to apple

How fase does speication happen?

• rate of speceation

• fossile record invldues manu eposies where new speices apperar suddenly, persit uncahged throuhgl several strate then dissaper

• Puncutrated equilibira describes periods of apperant stasis (squilibrieum) follwer by sudden change

• Rather than a puncatred pattern, other speices appear to have changed gradually over timeS

Speication in the lab

• Reporudtive barriers develope between isolated laboratroy populations subjected to different envriomenttal condtions for only 40 generations

• Fruti flies taken from a sinlge parent population but fed different dies over several generations perfer mates adapted to the same diet

Speciation can be rapid or slow

• the puncturated pattern in the fossile recor, evidence form lab studies, and instatnaenous polyploid specation show that speication can be rapis

• in a sudy of 84 groups of plants and animals, the interval between speication events ranged from 4,000 years (chichilids) to 40 million years (beetles)

• The average time between speciation events was 6.5 million years

What happens when geogrhaically isoalted speices come back into contact

• Hybris are the result of mating bwettne speices with icnomplte reprodutive barries

• a hybruz zone is a region in whcih members of differente speices mate to produdce hybird offpsring

• hybis zones are located where habitats of intrebreeding speices meets

• often occurs as islates pathes scattered across the lansdacpe, rahter than a continous ban

Possible outocme ina hybriz zone: reinfornemcnet

• hybrids are less fit than the parent speices, then there will be astrong selection for prezygotic barries sthat reudced hybrid production

• refornces reoductive barries

• ex: male pied flycahters closesly reseme male collared flycahters in allopatric but no sympatric populations

Possible outcomes in a hybriz zone stability

• Extenseive gene flow from outside they hybrid zone can overwheml seletion for increased repordutive isoaltion inside the hybirz zone

• ex: members of both parent speices of Bomiba todas rotuntley migrate into narrow hybriz zone, resulting in ongoing hybrization and production of fir hybirds

Possible ourcomes in ahybird zone: hybri speciation

Hybirs in a hybrz zone may becoome repodurive islaoted from both parental types (fusion)

Ex: sunflower, hellanthsu anomalues ws formed by hybrization bweent tow other sunflower speices follwed by rapid seceation