1.C.2 Reproductive Isolation Speciation may occur when two populations become reproductively isolated from each other.

Speciation is the origin of new species and the source of biological diversity.

A species is a group of populations whose members have the potential to produce fertile offspring.

In reproductive isolation barriers impede members of two different species from producing fertile offspring. Stops gene flow.

Reproductive isolation Prezygotic Barriers Postzygotic Barriers

Prezygotic barriers impede mating or hinder fertilization.

In geographic isolation, the populations are separated by a physical barrier, such as a mountain range or body of water.

In habitat isolation populations encounter each other rarely.

In temporal isolation populations breed at different times of day, season, or years

In behavioral isolation populations have incompatible courtship rituals, pheromones, bird songs.

In mechanical isolation morphological differences between the genitalia prevent fertilization.

In gametic isolation the sperm and egg are incompatible. Very important in aquatic species which release their gametes into the water.

Postzygotic barriers prevent the hybrid zygote from becoming a fertile adult

In reduced hybrid viability genes of different species may interact and impair hybrid development.

In reduced hybrid fertility sterile hybrids are created due to uneven chromosome number.

In hybrid breakdown the hybrid is fertile, but the next generation sterile.

Sometimes, reproductive barriers are not sufficient to explain speciation, as in fossils and prokaryotes.

The morphological species concept characterizes species by body shape, size and other features. can be applied to asexual organisms can be used without knowing extent of gene flow but it is subjective can be applied to asexual organisms can be used without knowing extent of gene flow but it is subjective

The paleontological species concept defines morphologically distinct species from the fossil record.

The phylogenetic species concept defines a species as a set of organisms with a unique genetic history (one branch on tree of life). A species shares common physical characteristics or molecular sequences.

Learning Objectives LO 1.22 The student is able to use data from a real or simulated population(s), based on graphs or models of types of selection, to predict what will happen to the population in the future. [See SP 6.4] LO 1.23 The student is able to justify the selection of data that address questions related to reproductive isolation and speciation.