BIO 111 Exam 3 flashcards

Concept of Speciation

If gene flow stops, allele frequencies in isolated populations can diverge. the populations begin to evolve independently, divergence will occur as a result of mutation, natural selection, and genetic drift, eventually leading to the formation of new species.

Speciation

is a splitting event that creates two or more distinct species from a single ancestral species.

Species

defined as evolutionarily independent population or group of population

3 approaches of identifying species

1. Biological species concept

2. morphological species concept

3. phylogenetic species concept

Biological Species Concept

the main criterion for identifying species is reproductive isolation which means

• results in lack of gene flow between populations

• members in population do not interbreed, or fail to produce viable, fertile offspring after mating.

mechanisms that stop gene flow between population

are known as reproductive isolating mechanisms, which can be prezygotic or postzygotic isolation.

Prezygotic isolation

individuals or different species are prevented from mating successfully due to various barriers such as temporal, habitat, behavioral, mechanical, or gametic barrier.

Postzygotic isolation

the hybrid offspring do not survive or reproduce successfully due to various mechanisms such as hybrid viability, hybrid sterility.

Disadvantages of Biological Species concept

reproductive isolation cannot be evaluated in fossils like Trilobites and species that preproduce asexually

Temporal Isolation

population are isolated because they breed at different times ex: Spotted skunks they mate different time of the year

Habitat isolation

population are isolated because they breed in different habitats ex: garter snakes, different species live in different habitats

behavioral isolation

populations do not interbreed because of different mating behaviors or rituals, such as specific calls or dances that attract mates. ex: Blue and red footed booby - different courtship

Gametic Isolation

mating fails because sperm and egg are incompatible, preventing fertilization. This can occur in many species, including some types of sea urchins.

Mechanical Isolation

mating fails because male and female reproductive structures are incompatible ex: in drosophila species there are subtle differences in genitalia that prevent successful mating.

Hybrid (in) viability

hybrid offspring do not develop normally and die as embryos ex: salamanders

Hybrid Sterility

hybrid offspring mature but are sterile as adults ex: mules, which are hybrids of horses and donkeys.

Haldane’s Rule

when in F1 offspring of two different animal races one sex is absent, rare, or sterile that sex is the heterozygous sex

• males are sterile in XY taxa (flies, mammals)

• females are sterile in ZW taxa (birds, butterflies)

Morphospecies Concept

individual lineages differ in size, shape, or other morphological features

• it is widely applicable

  • when there is no data on the extent of gene flow

  • Equally applicable to sexual, asexual, and fossil species

Disadvantages of Morphospecies concept

1. one polymorphic species maybe classified as more than one species

2. it cannot identify cryptic species that differ in non morphological traits

3. The features used to distinguish species under this concept is subjective

Phylogenetic species Concept

identifies species based on evolutionary history

• based on the rationale that all species are related by common ancestry

• Only on phylogenetic trees, a monophyletic group consists of an ancestral species and all its descendants.

• Also called a clade or lineage

monophyletic group

defined as an ancestral population and all descendants

synapomorphy

defined as a trait unique to a monophyletic group (unique forms)

Advantages of phylogenetic species concept

1. it can be applied to any type of population (e.g fossils, sexual or asexual)

2. It is logical because different species have different synapomorphies due to lack of gene flow and independent evolution 

Disadvantages of phylogenetic species concept

1. phylogenies are currently available for only a tiny  (through growing) subset of population on the tree of life

2. critics point out that it would probably lead to recognition of many more species than either of the other species concepts. 

Why do researchers use all 3 species concepts?

1. crosses to test compatibility

2. population genetics to characterize genetic exchange

3. phylogenetic to identify evolutionary history

3 modes of speciation

1. allopatric speciation

2. parapatric speciation 

3. sympatric speciation

Allopatric speciation

speciation that begins with geographic isolation

• It occurs when a populations become geographically separated.

• population that live in different areas are in allopatry

• the most common mode

geographic isolation occurs in 2 different ways

1. dispersal

2. vicariance

Dispersal

A population moves to a new habitat, colonizes it, and found a new population

Vicariance

a physical barrier splits a population into subgroups that are physically isolated from each other. 

Biogeography

the study of how species and populations are distributed geographically, it can tell us how dispersal and vicariance events occur

Allopatric Speciation by Dispersal

• Colonization events can lead to speciation

• Colonists represented a new allopatric population, but could have led to speciation

• The Grants concluded that both mechanisms contributes the change in beak size in the large ground finches

• New population is not a sepatate species yet, because there is still some gene flow

• Over time the populations could continue to diverge

Allopatric Speciation by vicariance

• When there is a physical barrier such as a mountain range uplifting or a river splitting the geographic range of a species, vicariance has occurred.

Example: Researchers compared the DNA sequences of trumpeters from different areas of the Amazon basin to the geological events that occurred

• They found evidence of isolation of populations by vicariance

• Initially, the formation of the Amazon split the ancestral population

• The formation of the river systems then subdivided the population

Parapatric Speciation

• Genetic isolation happens when populations change gradually along a cline

• Geographic features such as latitude, or elavation impose a gradient of selection pressures

• Phenotypic and genetic change result 

cline

spatial gradient of character change along an environmental variable

sympatry

Populations or species that live in the same geographic area - close enough to interbreed

Isolation and Divergence in sympatry

researchers believed that speciation could not occur among sympatric populations because gene flow would overwhelm any differences among populations,

Sympatric Speciation has two types of events

• External

  • Disruptive selection

• Internal

  • chromosomal mutations

Disruptive Selection

different ecological niches or mate preferences

niche

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

Sympatric speciation by polyploidization

Polyploidy can cause speciation where an error in meosis or mitosis result in more than two sets of chromosomes

Autopolyploid

• a doubling of chromosome number

• Chromosomes are all from the same species

• New tetraploid species may be created when two diploid species hybridize.

• Offspring are usually sterile. Offspring has two copies of each of two sets of chromosomes.

Allopolyploid

• parents of different species mate and an error in mitosis occurs, resulting in viable non sterile offspring

• Produces offspring with two different sets of chromosomes. 

tetraploid

individuals can sucessfully breed eith other tetraploids but not with diploids

Advantages of polyploid

• have higher levels of heterozygosity

• can tolerate higher levels of self-fertilization because they are not as affected by inbreeding depression

• genes on duplicated chromosomes cab diverge independently

What happens when isolated populations come into contact?

If separation has occurred and prezygotic isolation exists, then mating between the population is rare, and populations continue to diverge

What happens when isolated populations do not come into contact?

When prezygotic barriers do not exist, populations may interbreed and potentially erase distinctions between the two populations. Other possible outcomes are reinforcement, development of hybrid zones.

Reinforcement

Natural selection of traits that prevent interbreeding among populations

selection for prezygotic isolating mechanism

evidence of reinforcement

Several studies show that prezygotic isolation mechanisms are found between species that overlap geographically.

Hybrid Zones

A Geographic area where interbreeding between two populations occurs, which sometimes shows that the hybrid offspring of separated populations can mate and produce viable, fertile offspring. Their hybrid zones can be either narrow or wide, long or short-lived

stable in one place or move over time

Hybrid zones data shows

Data from the mitochondrial DNA show that most hybrids form when Townsend’s warbler males mate with hermit warbler females. The males invade hermit territories, drive off hermit males, and mate with hermit females.

Phylogeny

The evolutionary history of a group of organisms

Phylogenetic Tree

is a graphical summary of history, it can show evolutionary relationship among genes, species, higher taxa

Tree of life

• can be used in taxonomy to define species

• can be used in medicine to study the spread of disease

• can aid in identifying species that are in conservation priority

• can be used in agriculture to identify wild relatives for breeding with current crops

A branch in the phylogenetic tree represents

a population through time

A node in the phylogenetic tree represents

A point where a branch splits - that is hypothetical most recent ancestor, represent speciation events

a tip in the phylogenetic tree represents

The endpoint of a branch which is a living or extinct taxon

A root in the phylogenetic tree represents

ancestral branch

An out group in the phylogenetic tree represents

A taxon that is separated before the taxa of interest did,when they evolve they donot represent other taxa in the tree

Polytomy

is a node that divides into 3 or more branches

Taxa

Always located in the brach tips, never within the tree because none of the taxa are presumptive ancestors of others. Related taxa are sister groups that share a common ancestor.

How do biologists estimate phylogenies?

1. character-state data

2. genetic distance data

Character state data

A character or trait is any genetic, morphological, physiological or behavioral characteristic to be studied

ancestral trait

character that existed in an ancestor

derived trait

One that is a modified form of an ancestral trait, found in a descendant species.  

homology

similarity in traits due to common ancestry

Synapomorphy

a shared, derived trait

homoplasy

Similarity in organisms due to reasons other than common ancestry

polyphyletic group

An unnatural group that does not include the most recent common ancestor

paraphyletic group

A group that includes a common ancestor and some, but not all, of its descendants.

homologies

traits shared among related species

homoplasies

traits shared among unrelated species

convergent evolution

Similar design solutions to environmental challenges that arise independently in different evolutionary lineages.

Parsimony

The principle of logic states that the most likely explanation or pattern is the one that implies the least number of changes. the trees with the least number of evolutionary changes is likely the one that most accurately reflects what occured during evolution 

Principle of parsimony

in the absence of other data, the best hypothesis minimizes the number of evolutionary changes (minimizes the number of extra changes on tree due to homoplasy) 

molecular clock

a technique used by evolutionary biologists to estimate the timing of evolutionary events by measuring the accumulation of genetic mutations in DNA or protein sequences

Fossil Record

It is the total collection of fossils that have been found throughout the world 

Fossil

physical evidence from an organism that lived in the past

The Fossil record provides evidence about

• what organisms that lived in the past looked like

• where they lived

• when they existed

how do fossils form?

most of the processes that form fossils begin when part or all of an organism is buried by sediment, which then hardens over time, preserving the organism's remains.

intact fossils

Decomposition does not occur, and organic remains are preserved

compression fossils

when sediments accumulate on top of the material and compress it into a thin carbonaceous film

Cast fossils

form when the remains decompose after burial and dissilved minerals create a cast in the remaining hole

per mineralized fossils

when the remains decompose slowly and dissolved minerals slowly infiltrate the cells’ interiors and harden into stone

Trace Fossils

When sedimentation and mineralization preserve indirect evidence of an organism 

how do fossils form?

fossils form only under ideal conditions

• they must be buried rapidly 

• they must decompose slowly 

limitations of fossil record

1. habitat bais

2. taxonomic and tissue bias

3. temporal bias

4. abundance bais

habitat bais

Organisms that live where sediment is actively being deposited are more likely to fossilize than those living aboveground. in these habitats burrowing organisms are more likely to fossilize compared to organisms living aboveground

taxonomic and tissue bais

some organisms those with hard shells such as bones or shells are more likely to decay slowly and leave fossil evidence

temporal bias

more recent fossils are more common than ancient fossils

Abundance bais

Organisms that are abundant, widespread, and present for a long time leave evidence much more often than do species that are rare, local, or ephemeral

precambrian era

interval from earth’s formation to the apperance of most animal groups about 543 million years ago

• unicellular until late

phanerozoic eron

• Spans the interval between ~543 mya and the present

• Is divided into three eras—the Paleozoic, the Mesozoic,

and the Cenozoic

Paleozoic Era

 Begins with the appearance of most major animal lineages

• Includes the initial diversification of animals, land plants, and fungi

• Land animals first appear

• Ends with the obliteration of almost all multicellular life-forms at

the end of the Permian period

• ~543 mya – 248 mya

Mesozoic era

 Begins with the extinction events at the end of the Paleozoic and

ends with the extinction of dinosaurs

• Dinosaurs and gymnosperms were the most dominant terrestrial

vertebrates and plants, respectively

• 252 mya – 66 mya

cenozoic era

mammals and angiosperms were the largest terrestrial vertevrates and plants, respectively

Adaptive Radiation

 the rapid production, from a single lineage, of many descendant species

Extinctions

dramatic reduction in the number of species due to environmental change

 Two general mechanisms can trigger adaptive radiations

1. Extrinsic factors such as favorable new conditions in the

environment (Ecological opportunity)

2. Intrinsic factors such as evolution of key morphological,

physiological, or behavioral traits (Key innovation)

 Ecological opportunity

the availability of more or new types of resources—has driven a wide array of adaptive radiations

•  By being able to disperse into new environments, they could radiate into lots of species