Lecture 34- Population genetics + speciation

How can do we define a species

Biological, morphological, chemospecies, ecological species

For 2 species to be separate, a mechanism must be in place that keeps them from breeding and mixing their genes via..?

Via gene flow

Prezygotic barriers prevent?

Prevent mating or fertilization between species

Postzygotic barriers operate after?

Operate after hybrid zygotes are formed

Habitat isolation

2 species that occupy different habitats within the same area may encounter each other rarely, even though they are not separated by obvious physical barrier

Temporal isolation

Species that breed at different times in the day, different seasons or different years cannot mix their gametes

Behavioural isolation

Species have different behaviors that are not preferred by individuals of other species, enables mate recognition (different courtship rituals)

Mechanical isolation

(Physical incompatibility oof reproductive parts) matin is attempted, but morphological differences prevent its successful completion

Gametic isolation

(Molecular incompatibility of eggs and sperm) mating is attempted, but molecular differences prevent its successful completion

Reduced hybrid viability, development or survival

Hybrids do not develop fully or are unable to reproduce due to interaction of parental genes

Reduced hybrid fertility

Hybrids, even if vigorous (healthy) cannot produce offspring

Hybrid breakdown

Some first generation hybrids are fertile and viable, but when they breed with one another or with the parental species, the F2 generation are feeble or sterile

Allopathic speciation

When a population is divided into geographically isolated populations due to changes in geography or water bodies

Often one population is small, which leads to ? (Allopatric speciation)

Founder effect

genetic drift in common

What can trigger natural selection? (Allopatric speciation)

Differential environmental pressures between 2 locations

Sympatric speciation

When a population is divided without geological isolation

How can sympatric speciation arise?

Can arise through polyploidy, habitat differentiation or sexual selection

Polyploidy

Cels/organisms contain more than 2 paired (homologous (sets of chromosomes (more than 2n)

Autoploidy

Doubling off chromosomes in the same species (most common in plants)

Allopolyploidy

Hybridization of 2 different species, followed by cell division error

Habitat differentiation

When a subpopulation of a species start to exploit a habitat or resource bolt not used by the parent population

Sexual selection occurs..?

Occurs both allopatrically and sympatrically

What speciation does not require geographic isolation?

Sympatric

How does sexual selection occur alopatrically ?

Separatd by geography, separated populations develop new mating behaviours thus will not interbreed withthe original population if reintroduced

How does sexual selection occur sympatrically?

Changing in mating behaviours in the same habitat led to restrictions in gene flow leading to speciation over time

What can lead to bot Allopatric and sympatric speciation ?

Sexual selection