speciation

speciation

formation of new species

→ occurs when populations of the same species become reproductively isolated

→ they can no longer interbreed to produce fertile offspring

geographical isolation

reproductive isolation

g

occurs when a physical barrier separates populations of the same species, preventing them from interbreeding.

r

individuals in a population cannot interbreed to produce fertile offspring.

[Even if two organisms are similar, they are reproductively isolated if they:

do not mate, cannot produce offspring, or produce offspring that are infertile]

difference between geographical and reproductive isolation

-g uses physical barrier

-g- populations are in different areas. r- populations are in the same area

geographical isolation can lead to reproductive isolation

types of speciation

allosteric [most common]

occurs when a population of a species is geographically isolated by a physical barrier

sympatric [rare. common in plants]

occurs when a population of species is reproductively isolated within the same geographical area

does not require a physical barrier

conditions required for speciation to occur

-natural selection

-mutation

-populations must experience different selection pressures

-time [requires many generations]

How does allopatric speciation occur?

-population of the same species becomes separated by a physical barrier. They are geographically isolated

-The separated populations cannot interbreed. This leads to reproductive isolation and no gene flow

-in each population, there’s genetic variation due to mutation

-Each population experiences different selection pressures

-Individuals with advantageous alleles for their environment survive and reproduce.

-The advantageous alleles are passed on to offspring.

-the frequency of the advantageous alleles increases in each population.

-Over many generations, the allele frequencies in each population change due to natural selection

-eventually, the two populations can no longer interbreed to form fertile offspring so two different species are formed

examples of how reproductive isolation can occur

behavioural changes

→Populations have different courtship or mating behaviours.

[courtship→ a behaviour animals use to attract a mate e.g. bird singing, flies dancing]

seasonal changes

→Populations breed at different times of day, season, or year.

mechanical changes

→Physical differences in reproductive organs prevents successful mating. e.g. flowers can only be pollinated by certain insects due to shape. e.g. Some beetle species cannot mate with others because the male organ does not fit the female organ.

How does sympatric speciation occur?

-population of the same species live in the same geographical area

-mutation occur within the population. This forms new alleles.

-mutation leads to change in [mating behaviour, flowering times etc]→ depends on context of q]

-this change prevents some individuals from reproducing with other individuals of the species. This leads to reproductive isolation and no gene flow

-different alleles pass to offspring

-over time, allele frequencies changes due to natural selection

-eventually, the two populations can no longer interbreed to form fertile offspring so two different species are formed

Changes in colour and body shape are believed to occurred for 1000 years during which the grey wolf species evolved into the domesticated dog species. Suggests different types of isolating mechanisms allowed dogs to evolve separately to wolves.

geographical isolation

→Humans kept dog populations separate from Wolf populations.

→Wolves lived in the wild

→Dogs lived near human settlements

→this prevented mating

behavioural isolation

→Dogs may have developed different mating or courtship behaviours compared with wolves. Therefore, they don’t recognise each other as mates.

mechanical isolation

→Wolves are generally large.

→Some dogs are very small.

→Physical differences prevent successful mating.

seasonal isolation

→ species breed at different times so mating will not occur