15 3 Mechanisms of EVOLUTION 15 3 Speciation

15. 3 Mechanisms of EVOLUTION

15. 3 Speciation The formation of a new species

What is a species? A group of organisms with similar characteristics capable of producing fertile offspring

What is a species? Members of a species share the same gene pool (sum of all the genes + their different forms – alleles)

Speciation New species are formed when a population diverges into two populations AND

Speciation New species are formed when a population diverges into two populations AND the gene pools of two populations become reproductively isolated

Speciation New species are formed when a population diverges into two populations AND the gene pools of two populations become reproductively isolated = the populations can’t produce a fertile offsprings

Speciation There are several different ways speciation can occur. . .

Modes of Speciation Allopatric Speciation Peripatric Speciation Parapatric Speciation Sympatric Speciation

Allopatric Speciation Is a type of geographic isolation A population is split in two (or more) by some kind of physical barrier (mountain, river, wall…)

Allopatric Speciation The separated populations undergo changes in their genes as they begin to adapt to different environments or as they undergo mutations.

Allopatric Speciation After that time they are no longer capable of interbreeding (exchanging the genes)

EXAMPLE 1 – Allopatric Speciation A population of wild fruit flies minding its own business on several bunches of rotting bananas. They also lay eggs inside of bananas.

EXAMPLE 1 – Allopatric Speciation A hurricane washes the bananas and the fruit flies’ eggs out to sea. The bananas eventually wash up on an island off the coast of the mainland

EXAMPLE 1 – Allopatric Speciation The fruit flies mature (eggs became flies) and emerge onto the lonely island. The two portions of the population, mainland island, are now too far apart for gene flow to unite them.

EXAMPLE 1 – Allopatric Speciation At this point, speciation has not occurred yet — any fruit flies that would fly back to the mainland could mate and produce healthy offspring with the mainland flies.

EXAMPLE 1 – Allopatric Speciation The populations diverge: Ecological conditions are slightly different on the island, and the island population evolves differently than the mainland population does.

EXAMPLE 1 – Allopatric Speciation Morphology (eye color), food preferences, and mating behaviours change over the course of many generations of natural

EXAMPLE 1 – Allopatric Speciation When another storm reintroduces the island flies to the mainland, they will not be able to mate with the mainland flies since they’ve evolved different mating behaviours.

EXAMPLE 1 – Allopatric Speciation The flies’ lineages has split now that genes cannot flow between the populations

EXAMPLE 2 – Allopatric Speciation Darwin’s Finches Darwin thought that a long time ago there must have been a common ancestor to the finch species.

EXAMPLE 2 – Allopatric Speciation Darwin’s Finches As the Galapagos islands were formed, the common ancestor slowly dispersed and broke away from one another.

EXAMPLE 2 – Allopatric Speciation Darwin’s Finches Genetic variations amongst the finches were then selected for by the environment (natural selection).

EXAMPLE 2 – Allopatric Speciation Darwin’s Finches This resulted in the formation of new species on each island

EXAMPLE 3 – Allopatric Speciation Blue headed wrasse and Cortez Rainbow wrasse

EXAMPLE 3 – Allopatric Speciation Blue headed wrasse and Cortez Rainbow wrasse Original population was split by the formation of isthmus of Panama about 3. 5 million years ago

EXAMPLE 3 – Allopatric Speciation Blue headed wrasse and Cortez Rainbow wrasse Since that time, genetic changes happened in the both populations. These changes led to creation of different species

EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers Very similar to Galapagos’ finches

EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers On each island of Hawaii, we can find different species of honeycreeper

EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers It is thought that they all descended from a single species of honeycreeper

EXAMPLE 4 – Allopatric Speciation Hawaiian honeycreepers

Peripatric Speciation a special version of the allopatric speciation - It happens when one of the isolated populations has very few individuals - genetic drift (the founder effect) plays a major role in this speciation

Peripatric Speciation A population of wild fruit flies minding its own business on several bunches of rotting bananas also laying eggs inside of bananas.

Peripatric Speciation A hurricane washes the bananas and the fruit flies’ eggs out to sea. The bananas eventually wash up on an island off the coast of the mainland

Peripatric Speciation But only a few eggs have survived the journey to end up colonizing the island.

Peripatric Speciation These few survivors just by chance carry some genes that are very rare in the mainland population.

Peripatric Speciation One of these rare genes causes a slight variation in the mating behaviour and changes in sexual organs. (REMEMBER? it’s an example of the founder effect)

Peripatric Speciation After a few generations, the entire island population ends up having these rare genes.

Peripatric Speciation As the island population grows, flies experience natural selection that favours individuals better suited to the reproductive behaviour, climate and food of the island.

Peripatric Speciation After some generations, the island flies become isolated from the mainland flies. Peripatric speciation has occurred

Peripatric vs Allopatric Speciation WHAT IS THE DIFFERENCE BETWEEN THEM?

Peripatric vs Allopatric Speciation It is the size of the populations involved!

Peripatric vs Allopatric Speciation In allopatric speciation, a population is separated into two relatively large independent populations. In peripatric speciation, only a small fraction of the original population becomes geographically isolated.

Parapatric Speciation There is no specific barrier (mountain, river…) to gene flow, but the population does not mate randomly

Parapatric Speciation Individuals are more likely to mate with their geographic neighbours than with individuals in a different part of the population’s area

Parapatric Speciation The two species may come in contact from time to time but (after some time), species can no longer produce offspring together anymore

EXAMPLE 1 – parapatric Speciation A grass species Anthoxanthum odoratum

EXAMPLE 1 – parapatric Speciation Some of these plants live near mines where the soil has become contaminated with heavy metals.

EXAMPLE 1 – parapatric Speciation Some plants around the mines have experienced natural selection and are now tolerant of heavy metals.

EXAMPLE 1 – parapatric Speciation The neighbouring plants that don’t live in polluted soil have not experienced natural selection for this trait (they have NO tolerance of heavy metals)

EXAMPLE 1 – parapatric Speciation Both plants are close enough that they could fertilize each other (mate with each other)

EXAMPLE 1 – parapatric Speciation However, the two types of plants have evolved different flowering times. This change is the first step in cutting off gene flow between the two groups = SPECIATION

Sympatric Speciation In sympatric speciation, species diverge while inhabiting the same place.

Sympatric Speciation It does not require large area to reduce gene flow between parts of a population

Example of Sympatric Speciation 200 years ago, the ancestors of apple maggot flies laid their eggs only on hawthorns Maggots Hawthorns

Example of Sympatric Speciation but today, these flies lay eggs on hawthorns and domestic apples (which were introduced to America by immigrants) Hawthorns Apples Maggots

Example of Sympatric Speciation Females generally choose to lay their eggs on the type of fruit they grew up in, and males tend to look for mates on the type of fruit they grew up in.

Example of Sympatric Speciation So hawthorn flies generally end up mating with other hawthorn flies + Hawthorns

Example of Sympatric Speciation and apple flies generally end up mating with other apple flies. + Apples

Example of Sympatric Speciation Hawthorn flies and apple flies never mate together + Hawthorns Apples

Example of Sympatric Speciation This means that gene flow between parts of the population that mate on different types of fruit is reduced. + Hawthorns Apples

Example of Sympatric Speciation This host shift from hawthorns to apples may be the first step toward sympatric speciation —in fewer than 200 years, some genetic differences between these two groups of flies have evolved + Hawthorns Apples

Evidence for Speciation? Speciation is a long process, but we can find evidence for it in PATTERNS OF EVOLUTION

PATTERNS OF EVOLUTION Adaptive radiation Convergent Evolution Coevolution Rate of Speciation

Coevolution • Many species evolve in close relationship with other species.

Coevolution • The relationship might be so close that the evolution of one species affects the evolution of other species. This is called coevolution. • For Example: Mutualism - when two species benefit each other.

Coevolution – EXAMPLE 1 • comet orchids and the moths that pollinate them have coevolved an intimate dependency • the foot long flowers of this plant perfectly match the foot -long tongue of the moth

Coevolution – EXAMPLE 2 • One species can evolve a parasitic dependency on another species. • This type of relationship is often called a coevolutionary arms race

Coevolution – EXAMPLE 2 • A plant and an insect that is dependent on the plant for food. – The plant population evolves a chemical defense against the insect population. – The insects, in turn, evolve the biochemistry to resist the defense. – The plant then steps up the race by evolving new defences, the insect escalates its response, and the race goes on.

PATTERNS OF EVOLUTION Adaptive radiation Convergent Evolution Coevolution Rate of Speciation

Adaptive Radiation = divergent evolution • can occur in a relatively short time when one species gives rise to many species in response to the creation of new habitat or another ecological opportunity.

Adaptive Radiation = divergent evolution • Adaptive radiation often follows large - scale extinctions (such as the extinction of dinosaurs and subsequent rise of mammals) • These different species have homologous structures

Adaptive Radiation – EXAMPLE 1 • More than 300 species of cichlid fish once lived in Africa’s Lake Victoria. • Data shows that these species diverged from a single ancestor within the last 14, 000 years.

PATTERNS OF EVOLUTION Adaptive radiation Convergent Evolution Coevolution Rate of Speciation

Adaptive Radiation = divergent evolution Produces Homologous Structures

Convergent Evolution common adaptations to similar environments

Convergent Evolution occurs when organisms that are NOT closely related (they have no common ancestors) live in the SAME environment in different parts of the world.

Convergent Evolution – Example 1 • all of these animals live or lived in an ocean but they are not closely related

Convergent Evolution These species independently evolved similar traits or structures which are adapted to that same environment What similar traits or structures these three animals gained during the course of evolution?

Convergent Evolution Flippers, streamlined body, ability to swim What similar traits or structures these three animals gained during the course of evolution?

Convergent Evolution Prickles, thorns and spines

Convergent Evolution They have evolved independently to prevent or reduce herbivory (eating of plants by organisms)

Convergent Evolution Produces Analogous Structures

Adaptive Radiation = divergent evolution Produces Homologous Structures

Analogues Structures VS. Homologues Structures

Analogues Structures Different internal structures Same Function Similar Environments Result of Convergent Evolution VS. Homologues Structures Same internal structures Different Functions Different Environments Result of Divergent Evolution

PATTERNS OF EVOLUTION Adaptive radiation Convergent Evolution Coevolution Rate of Speciation

Rate of Speciation • Evolution is a dynamic process: traits might change rapidly OR traits might remain unchanged for millions of years. • Some scientists think that evolution proceeds in small, gradual steps = gradualism. A great deal of evidence favors this theory. # of specie s Time

Rate of Speciation • However, the fossil record contains instances of abrupt transitions. • Certain species of fossil snails looked the same for millions of years, then the shell shape changed dramatically in only a few thousand years = punctuated equilibrium

Rate of Speciation • However, the fossil record contains instances of abrupt transitions. • Certain species of fossil snails looked the same for millions of years, then the shell shape changed dramatically in only a few thousand years = punctuated equilibrium # of specie s Time