lecture 1

What is Evolution?

Changes in allelic or genotypic frequencies from one generation to the next

What are the 2 different types of Evolution?

Microevolution and Macroevolution

What is Microevolution?

Changes in allelic or genotypic frequencies within a population from one generation to the next

At what taxonomic level does microevolution occur?

Below the species level

What is Macroevolution?

Evolutionary change on a grand scale involving major evolutionary trends such as speciation

What are the 5 key things found within Microevolution?

Natural selection, mutations, gene flow, genetic drift, and non-random mating

What are the 4 key observations of Darwin's theory of natural selection?

Overproduction, limited resources, individual variation, and differential reproductive success

What is the meaning of Darwin’s 1st Observation (overproduction)?

All species tend to produce excessive numbers of offspring

What is the meaning of Darwin’s 2nd Observation (limited resources)?

Environmental resources are finite and cannot support unlimited population growth

What does the combination of overproduction and limited resources lead to?

A struggle for existence

What is an example of a species encountering the first 2 of Darwin’s observations?

Taraxacum sp. (dandelion)

What is the meaning of Darwin’s 3rd Observation (individual variation)?

Variation exists among individuals in a population, and much of this variation is heritable

What is an example of heritable morphological variation in plants?

Flower colour variation in Cylindropuntia sanfelipensis (cactus)

What is the meaning of Darwin’s 4th Observation (differential reproductive success)?

Those individuals with traits most successful in the local environment will leave more fertile offspring

What does differential reproductive success ultimately lead to?

Adaptation

What is mutation in the context of microevolution?

The ultimate source of all genetic variation within species and populations

What is an example of a mutation?

Morphological floral differences between two different Morning Glories

What is gene flow?

The exchange of alleles between populations resulting in changes in allelic frequencies

How can gene flow counteract the effects of natural selection?

By decreasing genetic differences between populations

What animal pollinators facilitate gene flow in plants as shown in lecture examples?

Insects (bees), rodents (mice), and bats

What is genetic drift?

A change in allelic frequency due to chance (random events)

What does this diagram depict?

A random reduction where only a fraction of plants leave offspring by chance, shifting allele frequencies across generations until an allele is fixed

What are two specific mechanisms or manifestations of genetic drift?

Bottleneck effect and founder effect

What is the bottleneck effect?

A sharp, random reduction in population size caused by a bottlenecking event (extreme environmental events or human activities) that drastically reduces genetic diversity in the surviving population

What plant species is an example of an extreme bottleneck effect where all known individuals are nearly genetically identical?

Wollemia nobilis (Wollemi Pine)

What is the founder effect?

When a small group of new arrivals establishes a new population and does not represent the genetic diversity of the ancestral population from which they came

Regarding glacial maximums in North America, how does genetic diversity compare between regions?

Populations and species south of the glacial maximum are more genetically diverse than those north of the maximum

What is non-random mating in plants?

Mating where individuals do not pair randomly, including self-pollination or mating exclusively with immediate neighbours

What is Self-pollination or selfing?

When an individual plant fertilizes itself

What can selfing lead to?

Inbreeding, which increases the frequency of homozygotes

What is inbreeding?

Mating between closely related individuals or self-fertilization

What genetic consequence results from selfing and inbreeding?

The frequency of homozygotes increases

Why is inbreeding particularly common in plants?

Because plants do not move (sessile) and therefore mate with their immediate neighbours

What is the literal Latin meaning of the word species?

Kind or appearance

What is the Morphological Species Concept?

Defining and grouping species based on structural features and phenotypic appearance

What is the Biological Species Concept (BSC)?

Defines a species as a group of populations from which the members can interbreed and produce fertile offspring and is seperated from other species through reproductive barriers

What major evolutionary implication arises from the Biological Species Concept?

Two individuals of different species cannot produce fertile offspring (their baby cannot reproduce)

What is an example of a sister species that showcases the BSC?

Mimulus lewisii and Mimulus cardinalis (monkey-flowers) which are 2 different sister species who live in the same place but do not interbreed because of reproductive isolation barriers

Why does the Biological Species Concept frequently fail in plants?

Because plants hybridize widely and can produce fully fertile offspring

What is hybridization?

The crossing of unlike parents (which can be individuals within a species or even different species)

What is Platanus × hybrida (London Plane Tree)?

A fully fertile hybrid tree produced from crossing 2 trees from different continents which made fully fertile hybrid

How does hybridization apply to “monkey-flowers”?

Mimulus lewisii and Mimulus cardinalis can be crossed in lab to yield fertile F1 and diverse F2 hybrid generations

What is the Phylogenetic Species Concept (PSC)?

defines a species as a group of living things that have been on their own evolutionary path long enough to develop their own permanent, distinct signature.

Does the Phylogenetic Species Concept require complete genetic isolation or breeding tests?

No, it implies genetic isolation through its difference in diagnostic traits, but a breeding test or complete genetic isolation is not required

How does the PSC apply to “monkey-flowers”?

Even though Mimulus species can produce fertile hybrids when crossed, they maintain diagnostic trait differences in nature, distinguishing them as separate species under the PSC

What morphological pattern is commonly observed in plant hybrids?

Hybrids tend to be intermediate (mixed just in between) in morphology and other traits relative to their parents

What is an example of intermediate morphological traits in a plant hybrid?

2 different oak trees (genus Quercus) create a hybrid with a mixture of both leaf shapes in different ways

Where do hybridizing plant parents meet and cross while maintaining distinct identities?

At contact points or hybrid zones (places where 2 distinct species are right next to eachother)

What is an example of a hybrid created on an elevation gradient?

Iris flowers where one type of iris grown on the top of the hill, the other type grows at the bottom, where they meet in the middle is a “hybrid zone” where they hybridize through contact points

What is required for plant hybrids to successfully speciate?

They need to establish reproductive barriers from either parent so it branch off on its own and stop breeding back into one of its parents. for example changing its blooming season, moving to a new area, or changing color to attract a totally different pollinator

What is mechanical reproductive isolation (barrier) in plants and one of its examples?

A structural barrier where an insect pollinator does not fit into the flower to transfer pollen. example: a bee unable to pollinate a flower because its too narrow.

What is temporal reproductive isolation (barrier) in plants and one of its examples?

A barrier where mating or flowering structures are not mature at the same time. example: plants that bloom in fall cannot cross with ones that bloom in spring.

What is geographic (physical) isolation in plants and one of its examples?

A barrier where mating is impossible due to physical distance or geographic barriers. example: the lotus species from east asia cannot cross with the lotus species all the way in northern america

What is the gradualistic model of speciation?

A model where evolutionary change and speciation occur slowly and continuously over long periods as an extrapolation of microevolution

Who created the gradualistic model?

Charles Darwin

What are transitional species (intermediate forms) in the gradualistic model?

Morphologically intermediate forms that bridge (in the middle of) ancestors to descendant species over time

What is the punctuated equilibrium model of speciation?

A model where species experience long periods of evolutionary equilibrium interrupted by rapid bursts of speciation

Who co-developed the punctuated equilibrium model?

Stephen J. Gould

What essential condition is required for a species to evolve?

The creation of a reproductive barrier (genetic isolation)

What are the two major geographic modes of speciation?

Allopatric speciation and sympatric speciation

What is allopatric speciation?

Speciation that occurs when a population becomes geographically separated and evolves through natural selection and/or genetic drift

Which mode of speciation is considered the most common in nature?

Allopatric speciation

What is an example of allopatric speciation over many continents.

The breakup of Gondwana (Antarctica, South America, and Australia) 50 to 30 million years ago caused the ancestral nothofagus tree to speciate across the different continents due to the different climates creating 43 new species.

What is an example of an Arcto-Tertiary distribution?

The breakup of a continuous deciduous forest through global cooling. As the Earth cooled and glaciers/deserts expanded, the middle parts of this giant forest died off. This left two isolated pockets of survival thousands of miles apart: one in East Asia and one in Eastern North America. Because the 2 trees were seperated in different climates, they evolved independently into new species. the most common example is the liriodendron.

What occurs when two allopatrically separated populations become sympatric again after evolving complete genetic isolation?

They coexist in the same geographic range without interbreeding as they are now 2 different species. examples: the sugar maple and red maple and the Pinus coulteris and sabiniana (pine trees)

What are distinctive morphological features of Pinus coulteri cones?

Massive seed cones weighing up to 2.3 kg and measuring up to 36 cm long

What are distinctive features of Pinus lambertiana (Sugar Pine) cones?

Very long seed cones (25-66 cm) that are much lighter in weight

What is adaptive radiation?

The rapid diversification of a single ancestral lineage into many ecologically diverse species adapted to different habitats

What plant group is a classic example of island adaptive radiation in Hawaii?

Silverswords, where more than 28 species evolved from a single sunflower family ancestor

Why did Hawaiian silverswords rapidly adapt to diverse habitats such as arid zones and volcanic alpine slopes?

Because of a lack of competition on the islands

What continental-scale plant radiation occurred following the uplift of the Andes mountains?

The rapid diversification of the genus Lupinus

What is sympatric speciation?

Speciation that occurs within the same geographic area when a genetic change produces a reproductive barrier between mutants and the parent population (mainly occuring in plants)

What major genetic mechanism drives instant sympatric speciation, especially in plants?

Polyploidy

What is polyploidy?

The presence of three or more chromosome sets in an organism (greater than the diploid number, 2n), very common in plants

Approximately what proportion of flowering plants have polyploidy in their evolutionary history?

Up to 80%

What plant species holds the record for high chromosome numbers with how many pairs?

Ophioglossum reticulatum with 630 chromosome pairs (2n = 1260 chromosomes per cell)

What process is mitosis usually used for?

Growth and repair

What cells are the result of mitosis?

Creates 2 cells identical to its mother cell (it duplicates it) resulting in 2n diploid cells (contains 2 genomes (1 genetic instruction from mom and 1 from dad = 2n)

What process is meoisis usually used for?

Reproduction

What cells are the result of meiosis?

Creates 4 cells different from the mother cell, resulting in 1n haploid cells (sex cells/gametes such as sperm cells and ovules)

What does the variable “n” stand for?

# of genomes

What is the fertility status of odd-numbered polyploids (e.g., triploid 3x, pentaploid 5x)?

Infertile (sterile)

What is the fertility status of even-numbered polyploids (e.g., tetraploid 4x, hexaploid 6x)?

Fertile

Why are odd-numbered genomes (like triploids) sexually infertile?

There are not enough homologous chromosomes for meiosis to divide evenly twice and produce balanced gametes (sex cells)

Why can an odd-numbered polyploid organism survive and grow vegetatively despite being sterile?

Because mitosis only requires chromosomes to double once and divide in two, which functions normally

What is autopolyploidy?

Polyploidy involving multiple sets of chromosomes derived from a single species

What is allopolyploidy?

Polyploidy involving multiple sets of chromosomes derived from two or more different species

Which form of polyploidy represents hybrid speciation and is more common?

Allopolyploidy

Why is polyploidy described as "instant speciation"?

Because genetic and reproductive isolation from the parental population is established immediately in a single generation

What cellular accident during cell division causes polyploidy?

Nondisjunction during meiosis

What is nondisjunction?

An accident during cell division where chromosomes or sister chromatids fail to separate properly during meiosis

What is an example of sympatric speciation by autopolyploidy in plants and a prominent figure who investigated it?

Oenothera (Onagraceae) “Evening Primroses”, investigated by Hugo de Vries

What morphological difference is commonly observed between polyploids and their diploid ancestors?

Polyploids are often larger because cells containing twice the DNA are twice the size

What type of speciation is Allopoplypoidy an example of?

Hybrid speciation (and instant sympatric speciation)

What weed genus provides a classic wild example of allopolyploid hybrid speciation studied by Marion Ownbey in the 1950s?

Tragopogon (Goat's Beard)

What are the polyploid stages in the evolution of modern bread wheat (Triticum aestivum)?

Diploid Triticum monococcum (14 chromosomes) crossed with wild Triticum (14 chromosomes) to form tetraploid T. turgidum (28 chromosomes), which crossed with T. tauschii (14 chromosomes) to form hexaploid T. aestivum (42 chromosomes)

What are examples of domesticated crops that are polyploid?

Bananas (3x), apples (3x), pears (3x), ginger (3x), potatoes (4x), cotton (4x), peanuts (4x), tobacco (4x), sugarcane (8x), and strawberries (8x)

What chemical compound derived from Colchicum autumnale is used to induce polyploidy in plant breeding?

Colchicine

How does colchicine induce polyploidy in plant tissue?

It inhibits chromosome segregation during meiosis/cell division

What cross produces seedless triploid (3n) watermelon seeds?

Crossing a diploid (2n) male parent with a tetraploid (4n) female parent