15.2 Species and Speciation OverviewI. Evolution

I. Results of evolutionI. New species (speciation)

II. Causes of evolutionI. Barriers between same species (gene pools)

I. Geographical isolation -> leads to allopatric speciationII. Temporal isolation -> leads to sympatric speciationIII. Behavioral isolation -> leads to sympatric speciationIV. Hybridization -> leads to sympatric speciation

III. Types of EvolutionI. Adaptive radiationII. Convergent evolutionIII. Divergent evolution

IV. Pace of EvolutionI. GradualismII. Punctuated equilibrium

• Gene pool – all of the genetic information present in the reproducing members of a population at a given time– A large gene pool exists in a population which

shows high variation– A small gene pool exists in a population which

shows little variation (ex: inbreeding)

• Allele frequency – measure of the proportion of a specific variation (allele) of a gene in a population; this can be stated as a proportion or a percent– Remember, Hardy-Weinberg discussed this in

terms of p and q where: p = frequency of the dominant allele q = frequency of the recessive allele and together p + q = 1

– If there are no changes in allele frequency over time, then no evolution

– If there is big change in allele frequency over time, evolution has occurred

Review of what can change allele frequencies (and therefore the gene pool) within a

population:1. Mutations2. Immigration and emigration3. Nonrandom mating (ex: inbreeding/selective

breeding)4. Some alleles are more advantageous than

other alleles5. The population is small and therefore the

allele frequencies are easier to manipulate

• Species – the basic unit for classifying an organism

• A species is made up of organisms which:– Have the ability to interbreed and produce fertile

offspring– Share the same ecological niche– Have the same karyotypes– Have a common phylogeny (share common

ancestor(s))– Share a unique collection of structural and

functional characteristics

Barriers between Gene Pools

Barriers may exist where populations of members of the same species can be stopped from reproducing together; such barriers can be geographical, temporal, behavioral, or related to infertility caused by hybridization

This slide is an overview of what is to come, no need to write it down!

Allopatric Speciation• When a new species forms from an existing species

due to a geographic barrier

1. Geographical Isolation

• Occurs when physical barriers such as land or water formations prevent mating– Ex: tree snails in Hawaii, 1

population lives on trees on one side of a volcano, the other population lives on trees on the other side of the volcano

Type of Allopatric Speciation!

Sympatric Speciation• When a new species is formed

from an existing species while living in the same geographic area– This is much rarer than allopatric

speciation

1. Temporal Isolation• Occurs when two populations

mate or flower at different times of the year– Ex: the female parts of one

flower’s population reach maturity before the pollen of another flower’s population gets released

– Ex: one population of mammals is still hibernating while another population is ready to mate

Type of Sympatric Speciation

2. Behavioral Isolation• Occurs when one population’s lifestyle and habits

are not compatible with those of another population– Ex: many birds rely on courtship displays to attract

mates; if one population has a version of the courtship display which is significantly different from another population, they may not consider each other to be seductive enough to mate with

Type of Sympatric Speciation

3. Hybrids• Hybrids are typically infertile and

therefore cannot pass on their karyotype– This goes for plants and animals– female horse + male donkey = mule– male horse + female donkey = hinny– female tiger + male lion = liger– male tiger + female lion = tigon

How polyploidy leads to speciation:• Speciation is when a population

evolves significantly enough so that the production of offspring with the original population becomes impossible

• Haploid – sex cells are monoploidy (n)

• Diploid – somatic cells are diploidy (2n)

• Polyploidy = more than 2 sets of chromosomes; 3n, 4n, 5n, ect.

•Ploidy changes among angiosperms are common including banana tree, tobacco plant, apple trees

•Also seen in animal kingdom with salamanders, frogs, and leeches

• Studies have shown after polyploidy formation rapid changes in gene structure and expression can occur; if one population evolves enough to have significant change, then a new species can be formed

• NOTE: two similarly polyploidy organisms can interbreed ex: 8n sugar cane with another 8n sugar cane

Adaptive Radiation• It is when many similar but distinct species evolve

relatively rapidly from a single species or from a small number of species– These organisms will share homologous structures with various functions– Occurs due to variation, natural selection, and the exploitation of various niches

Lemurs of Madagascar• Lemurs were able to

survive (no other primates present) and adaptive radiation allowed them to fill all the islands niches– On ground– In trees– In desert– In rainforest

Divergent Evolution• Divergent evolution is where organisms

have a common ancestor, but have become more different as time goes by– Example:• The pentadactyl limb – the homologous

structure in many vertebrates including the human arm, the fin of a whale, and the wing of a bird

Convergent Evolution

• Convergent evolution is where distantly related organisms evolve similar traits as they adapt to similar environments; they become more alike– Example:• Marsupials and placental organisms evolved

separately on different continents, but both types evolved into all the niche of the area

• In both types of evolution, it is the process of natural selection that allowed the organisms to adapt to their environments in the ways that they did

The Pace of Evolution

• Gradualism – the idea that evolution occurs over small, continuous, and slow changes

• First proposed in late 1700’s and was adopted by Darwin– Supporters argue:• fossil record shows a succession of small changes that

is steady and ongoing• must be gradual since we don’t witness it

http://wiki.district87.org/index.php/Image:Gradualism.jpg

Discuss ideas on the pace of evolution:

• Punctuated equilibrium – the idea that evolution occurs relatively quickly and is followed by long periods of little or no change

• Theory developed 1900’s– Supporters state • speciation happens quickly, often in response to

environmental changes• fossils of animals like sharks and cockroaches show

little change thru time

http://wiki.district87.org/index.php/Image:Gradualism.jpg

Problems with Either Arguments

• Only evidence we can use is fossil evidence; can’t use characteristics such as pigmentation, behavior, mating calls/songs

• Just b/c a fossil looks like a modern day organism, doesn’t mean they are related

Describe one example of transient polymorphism

Polymorphisms – different versions of a species

This Virginia Springbeauty flower shows

polymorphism with its flower

color

• Transient polymorphism – where two or more forms of a species exist in the same population; it results in one form dominating the other form; can be result of mutation

• Ex: peppered moth

Peppered form

Melanic form

The phenomenon of factory pollution changing the population of peppered moths is called Industrial melanism.

Shows how natural selection works in nature and no one trait is always good or bad

Transient because the results can change over time

• Balanced polymorphism – when the two different forms in a species are not changing, but are stabilized by natural selection

• Ex: sickle cell• For sickle cell (homozygous recessive):– AA = normal red blood cells, susceptible to malaria– AS = normal and sickle blood cells, some resistance to

malaria– SS = sickle-shaped blood cells, highly resistant to malaria

• Due to the benefit of the sickle cell allele against malaria, the presence of the sickle allele is relatively stable and shows balanced polymorphism; one side shows pressure towards the allele, the other side shows pressure against the allele