Bio unit 4: macroevolution, relationships, polygentic trees

microevolution

a change in allele frequencies in a population

• observed over one or a few generations

• caused by mutation, natural selection, gene flow, genetic drift

macroevolution

origins of new species or groups of species (clades)

• speciation

• usually occurs over very long periods of time

• has same evolutionary mechanisms as microevolution

  • mutation, natural selection, gene flow, genetic drift

fluid, not straightforward

since species evolve, a species itself is a ___ entity capable of change and is _____

appendix I, no

species threatened with extinction

• ____ trade

ex: howler monkey

appendix II, limited

species that may become threatened

• ____ trade

ex: Ebony

appendix III, cities

trade allowed by ___

Ex: asian water snake

biological species concept

distinguished species based on reproductive isolation

• species are groups of actually or potentially interbreeding populations that are reproductive isolated from other groups

• reproductive isolation may be prezygotic or postzygotic

mate with each other, produce fertile offspring

to be members of the same species …

prezygotic isolation

prevent fertilization from taking place at all

• temporal

• habitat

• behavioral

• gametic barrier

• mechanical

temporal

populations are isolated because they breed at different times

Ex: bishop pines and monterey pines

habitat

populations are isolated because they breed in different habitats or separated by geographical barriers

ex: mainland mice and beach mice

behavioral

populations do not interbreed because their courtship differ

ex: to attract females, male songbirds sing species specific songs

gametic barrier

matings fail because eggs and sperm are incompatible—don’t have the right proteins to mate

ex: bindin protein

mechanical 

matings fail because male and female reproductive structures are incompatible

Ex: large dogs and small dogs

postzygotic isolation

prevent fertilized egg from developing into a viable or fertile individual

• occurs after fertilization and zygote is formed

• hybrid viability

• hybrid sterility

• based on genetic incompatibility

hybrid viability

hybrid offspring do not develop normally and die as embryos

ex: ring neck dove and rock dove= <6% of eggs hatch

hybrid sterility

hybrid offspring mature but are sterile as adults

ex: horse x donkey= mule

limits of the biological species conceppt

• some organisms (bacteria) reproduce asexually and do not mate with one another

• the ability to make cannot be evaluated for extinct species

• sometimes plants of different species can interbreed and produce

morphospecies concept

identifies species based on their appearance (morphology)

• this data can be quantified and qualitative

• members of the same species usually look alike and be distinguished from other species

• widley applicable

• subjective

limitations of the morphospecies concept

• sexual dimorphism: males and females look different

• similar appearances of different species (coral snake and milk snake)

• varaiation within a species: different look but can still breed with each other

phylogenetic species concept

based on shared evolutionary history

• each species is a group of organisms that 

  • share a common ancestor (relations through evolution)

  • can be distinguished from other groups that do not share this ancestor

advantages of the phylogenetic species concept

• can be applied to any type of population (fossil, assexual, sexual)

• it is logical because different species have different unique traits (synapomorphies) due to lack of gene flow and independent evolution 

• widely applicable 

• testable

disadvantages of the phylogenetic species concept

• phylogenies are currently available for a tiny (although growing) subset of populations on the tree of life

• critics point out that it would lead to recognition of many more species than either of the other species concept

• what is the scale?—can be significant

different

application of different species concepts may result in ____ conclusions

speciation

results from genetic isolation—populations that are geenetically isolated will diverge from each other

• no longer reproduce together

• accumulation of genetic differences 

• through allopatry or symatry

allopatric speciation

occurs when opopulations are geographically separated/isolated from each other due to being different geographic areas

• mechanisms

  • vicariance

  • dispersal

vicariance

physical splitting of a habitat

1. geographic isolation: change event physically separates population into subgroups

2. divergence: isolated population beg to diverge due to mutation, genetic drift, and selection

3. genetic isolation: eventually the two populations are genetically isolated

ex: trumpeter birds

dispersal

colonization of a new habitat and new population 

1. geographic isolation: some individuals disperse from their population and colonize a new habitat

2. divergence: isolated population beg to diverge due to mutation, genetic drift, and selection

3. genetic isolation: eventually the two populations are genetically isolated

ex: galapagos mockingbirds

symatric speciation

occurs when populations that live in the same location diverge from one another

• mechanisms

  • disruptive selection (external events)

  • polyploidy (internal events)

disruptive selection

sexual selection that when it acts on traits that have a normal distribution, individuals at both ends of the distribution have higher fitness (greater reproductive success) than individuals with the intermediate phenotype

• opposite of stabilizing selection

• overall amount of genetic variation in the population is increases

• favors extreme phenotype at both ends raise of the range of phenotype variation

• speciation—overtime only 2 distinct population instead of 1

ex: ciclid fishes—sexual selection and different food sources

polyploidy

occurs when an error in meiosis or mitosis results in more than 2 sets of chromosome

• important in plants: hybridization event

hybridization event

hybrid (offspring from 2 parents of different species) spontaneously doubles its chromosome number (becoming polyploid), it will have chromosomes that occur in pairs, but it will be unable to breed with either parent species

• hybrid will not be considered a new species

community

consists of all the populations of interacting species living in a defined area

• populations are dynamic—change and split

outcomes of interactions

1. influence the distributions and aundance of the interacting species

2. they are agents of natural selection which therefore influence the fitness of individuals within populations of species within the community

3. outcome of interactions among species is dynamic and conditional

commensalism

Commensals gain a fitness advantage but don’t affect he species they depend on

• +/0

• tricky to observe/describe because it is hard to demonstrate an absence of effect on fitness

• conditional

• short term impact: population size and range of commensal may depend on population size and distribution of host

• long term impact: strong selection on commensal to increase fitness benefits in relationship, no selection on host

Competition

the act of competing uses resources, in turn, those resources are not available for foraging, mating, or other activities to increase fitness

• -/-

• lowers fitness for both organisms involved

• short term: reduce population size of both species

  • may lead to extinction—asymmetric

• long term: niche differentiation via selection lowers competition

• interspecific and intraspecific

• direct and indirect

intraspecific competition

occurs between members of the ssame species

interspecific competition

occurs when members of different species use the same limiting resource

• occurs when niches of 2 species overlap 

resource

substance or factor that an organism consumes or occupies adn that leads to increase population growth

limiting resource

when a resource ,or combination, leads to competition

• depends on availability of resource

intraspecific, density dependent growth

because ___ competition for resources intensifies as a population’s density increases, it is a major cause of _____

niche

the range of resources that species can use and the range of conditions it can tolerate

disadvantage

in a partial niche overlap individuals who regularly use joint resource is at ___ compared to individual who use other resources

symmetric competition 

occurs when both species have a similar decrease in fitness due to the overlap of their niches, but both species may persist in the area of overlap 

• similar disadvantages

asymmetric competition

occurs when one species suffers a greater fitness decline than the other species

• outcome depends on the amount of overlap 

• may lead to extinction of the weaker species

competitive overlap principle

2 species that occupy the same niche cannot coexist

• stronger competitor drives out the weaker competitor because of overlap of niches

fundamental niche

total theoretical range of environmental conditions that a species can tolerate

• both strong and weak competitors have this

realized niche

a portion of fundamental niche that a species actually occupies

• limited by factors: competition with other species

• only weaker competitor has this

natural selection, avoid

because competition is a -/- interaction, there is a strong ____ on both sides to ___ it

niche differentiation

an evolutionary change in resource use, caused by competition over generations

• natural selection selects against individuals that comepete

• reduces overlap

  • changes frequency of traits in using limiting resources

consumption

based on the type and size of species involved, the extent of ___, and the duration of the interaction 

• + / -

• herbivory, predation, parasitism 

• short term: impact on prey population depends on predator density, prey density, and effective defenses

• long term: strong selection on prey for effective defenses, strong select on consumer for traits that overcome defenses, coeveolutionary arms races result

herbivory

herbivores (plant eaters) consume plants and algae

predation

a predator kills and consumes most or all of another individual (prey)

• can also refer to consumption of plants and seeds

parasitism

a parasite consumes relatively small amounts of tissue or nutrients from another individual (the host); often takes place over a long period of time

• often not fatal

• can spread diease

constitutive/standing defense

present event in the absence of predators

• cryptic coloration and object resemblence: escape detection

• escape behavior: run, fly, jump, swim

• toxins and other defense chemcials

• schooling/flocking

• defense armor and weapons

• effective by energetically costly

inducible defenses

physical, chemical, or behavioral defense traits that are induced in the prey in response to the presence of a consumer (not always present)

• energetically efficent but slower reaction time

• decrease in prey species if consumers leave habitats

ex: plants can induce the production of toxins to protect themselves

mutualism

involve a variety of organisms and rewards

• short term: population size and range depend on other species

• long term: strong section on both species to maximize fitness benefits and minimize fitness costs of relationship

• both organisms benefit

Ex: the microbiome in us

evolutionary arms race

• camouflage vs. improved eyesight

• increased speed or agility in prey or predator

• poison/mutations that lead to immunity to poisens

• armor/shells vs. increased bite/beak strength 

favors

natural section strongly ___ traits that allow individuals to avoid being eaten

taxonomy

the study of the classification of organisms

taxon

groupings of different organisms

phylogeny

evvolutionary history of a group of organismsp

phylogenetics

field of study of evolution and genetic relationshipsp

phylogenetic tree

genetic summary of history and helps us see evolutionary relationships

nodes

forks representing hypothetical common ancester

root

ancient ancestor

tip

terminal nodes, end points of branch; representing living or extinct group of genes, species, families, phyla, or taxa

branch 

lienes that represent population through time 

sister groups

occur when a single ancestral lineage gives rise to two daughter lineageso

out group

a taxon that diverge prior to the taxa that are the focus of the story

• can be used to establish whether a trait is ancestral or derived trait

speciateion

nodes of sister groups represent a _____ event; two populations within an ancestral species become genetically isolated and diverse

ancestral trait

a character that existed in an ancestor

derived trait

a modified form of an ancestral trait found in a descendant

relative

ancestral and derived traits are ____

synapomorphy

a trait found in 2 or more taxa that is present in their more recent common ancestor, but is missing more distant ancesters

• allows biologists to recognize clades

clade

an evolutionary unit; a group of organisms that include a single ancestor and all of its descendants 

• aka monophyletic group

one snip test

if you cut any branch on a phylogenetic tree all of the branches and tips that fall off represent a clade/monophyletic group

T

T/F: clades are nested within one another

tipes for reading phylogenetic tree

1. examine which groups share the most common ancestors

2. branches can relate at each node—taxa at the tips can spin around but not the connections which represent relationships

3. the locations of the nodes determine the relatedness of clades, not the order of the tips

4. branches can be added or removed without changing the relationship of the other branches—can be expanded or collapsed to fewer taxa--; counting nodes is not a useful way to decide how closely or distantly related two taxa are

can not; estimates

relationships among taxa ___ be known with absolute certainty. They are ___ of of evolutionary relationships

hypothesis

phylogenetic trees are ___ that can be tested

characters

anatomical, physiological, and or molecular features of organisms

character states

features that have different conditions

Ex: with wings or without wings

• often shown, grouped, and summarized in a data matrix

independently; different

traits can be similar in 2 species not because those traits were present in a common ancestor but because similar traits evolved ____ in two ____ lineages

reversal

sometimes a ___ in character occurs, such as the gain of a trait in one branch folllowed by the loss of hte same trait in a subsequent branch 

one, different

someetimes species is part of one clade according to ___ trait on the matrix, but is part of a____ clade according to a different trait on the matrix

principle of parsimony

the most likely explanation or pattern is the one that assumes the fewest steps

• Occam’s razor: the simplest explanation is the right one

• we do not know what really happened though

character states can be similar for different reasons

1. they share a common ancestor that had wings—homologous structures

2. could have independently evolved wings—homoplastic structures

divergent evolution

share a common ancestor where two descendants have same character

convergent evolution

descendants evolved characters separately of each other

homolgoy

any similarity between characters that is due to their shared ancestry

homoplasy

occurs when characters are similiary bit are not derived from a common ancestor

• convergent evolution

roses and water lilies

• phylogenetic evidence: flowers are inherited from a common ancestor that also had flowers

• structural evidence: most flowers are built upon the same template—sepals, petals, stamen and carpals

• genetic and developmental evidence: the genetic tool kit and developmental patterns of development of floral structures are simlar in different plants involving the same genes

have a key

how do we know if the branch length is arbitrary or not?

monophyletic groups

• clades

• homology

• shared, derived traits—synapomorphy

polyphyletic group

an unnatural group that does not include most recent common ancestor

• not a clade: does not follow the one snip test

• homoplasy: arose independently

• poly” multiple

ex: dolphins and Ichthsyosaurs

paraphyletic group

a group that includes an ancestral population and some of its decesndents but not all

• not a clade: does not follwo the one snip test

• para: apart from