Microevolution Microevolution: changes in allele frequencies and physical traits within a population and species So we know that alleles that allow cheetahs to run faster will be favoured But how did the cheetah arise as a new species?

What is a Species? All members of a population with a common gene pool These members are able to interbreed under normal conditions and produce fertile offspring

How Species Arise In the formation of a new species, one constant is always seen: Distinct features arise that isolate the new species reproductively (and therefore genetically) from other species

How Species Arise For a variety of reasons, members of the new species are not able to produce fertile young with other species This is known as Reproductive Isolation

Mechanisms of Reproductive Isolation Any behavioural, structural, or biochemical trait that prevents individuals from reproducing successfully Two types – Prezygotic Mechanisms – Postzygotic Mechanisms

Prezygotic Mechanism Prezygotic Mechanism: A reproductive isolating mechanism that prevents fertilization and zygote formation

Prezygotic Mechanism These are traits between species that prevent them from being able to create a zygote (fertilized egg) These species may live in the same region, but these factors prevent breeding from occurring There are five types of prezygotic mechanisms

1. Behavioural Isolation Different species use unique courtship rituals to find a mate Example: Birds of Paradise

2. Temporal Isolation Different species breed at different times Example: Field Crickets

3. Ecological Isolation Similar species may inhabit different habitats within a region Example: Eastern and Mountain Bluebirds

4. Mechanical Isolation Differences in physical features that make two species unable to mate Example: Damselflies

5. Gamete Isolation Male gametes are unable to recognize and fertilize egg cells of another species Example: Marine Animals

Postzygotic Mechanism Postzygotic Mechanism: An isolating mechanism that prevents maturation and reproduction in the offspring of interspecies reproduction

Postzygotic Mechanism In this case, species are able to mate and create a zygote The zygote is either unable to make it to term, or the offspring is sterile

Postzygotic Mechanisms There are three types of postzygotic mechanisms:

1. Zygotic Mortality Mating and fertilization are possible Genetic differences result in a zygote that is unable to develop Example: Sheep and Goats

2. Hybrid Inviability A hybrid individual develops, but cannot survive to maturity – May die before birth – May die before reaching maturity Example: Tigers and Leopards

3. Hybrid Infertility Hybrid offspring remain healthy and viable but are sterile – Unable to reproduce and have their own offspring Example: Mules

Allopatric Speciation Allopatric Speciation: the formation of a new species as the result of evolutionary changes after a period of geographic isolation Physical isolation means that these species are no longer able to exchange genetic info – Mutations that arise in one population will not be shared with the other

Allopatric Speciation After some time has passed in geographic isolation, a reproductive isolating mechanism will develop

Mechanisms of Allopatric Speciation How does this occur? – Isolated on remote islands – Mountain ranges form between populations – Continental drift

Sympatric Speciation Sympatric Speciation: The formation of new species within the same geographic area This occurs as populations become genetically isolated from the larger population

Sympatric Speciation This can occur through human action The Hawthorne Fly: – Apples were introduced to North America from Europe between 1800 and 1850 – Some flies started laying eggs on apples – Today there are two species: one whose maggots feed mostly on apples One whose maggots feed mostly on hawthorn

This is an example of disruptive selection!

Sympatric Speciation Instant Sympatric Speciation Occurs in species that can reproduce asexually A random mutation in an individual may eventually lead to the formation of a new species This has probably happened many times in plants – many are able to sexually and asexually reproduce

Polyploidy Remember meiosis? cells should have 2n chromosomes: one from each parent Problems during meiosis can lead to cells with more than 2n chromosomes: – A cell may actually end up with 3 or 4 copies of a chromosome

Polyploidy Polyploids can successfully breed with other polyploids but not with the original 2n ancestor

Polyploidy Incredibly important in the evolution of plants

Polyploidy Eastern Treefrog has four sets of chromosomes – nearly identical to the Cope’s Gray Treefrog, which has two sets of chromosomes – Suggests that the Eastern Treefrog has evolved from the Cope’s Treefrog

Homework Q’s PG. 340 #2, 5, 6 PG. 372 #20, 37