Chapter 24 Flashcards
when does speciation begin
when gene flow between populations is reduce or eliminated
what does an elimination of gene flow cause
genetic isolation
allopatry
populations that are geographically separated
what is the term for speciation that begins with geographic isolation
allopatric speciation
allopatric speciation
speciation that occurs when population of same species become geographically isolated, often due to dispersal or vicariance
what are the two ways speciation starts
- dispersal
- vicariance
dispersal
movement of individuals from one place to another
- disperse to new habitat, colonize it, and found new population
vicariance
physical splitting of a habitat
- new geographic barrier can split population into 2 or more subgroups
biogeography
study of how species and populations are distributed geographically
Allopatric Speciation by Dispersal Case Study
- ground finches
- migration from home island to Daphne Major during breeding season
- some individuals remained on Daphne Major and produced offspring
- these individuals represented a new population, allopatric with migrant source population
why were the ground finches of the case study who remained on the island represent allopatric speciation
- the two populations bred and nested on different islands
- when compared, the two populations of ground finches had different beak sizes
- genetic drift and natural selection were at play
what is though to lead to speciation in many island groups, including finches
- dispersal and colonization
- genetic drift
- natural selection
Allopatric Speciation by Vicariance Case Study
- collected tissue samples from trumpeters throughout the Amazon and compared DNA sequences of four genes to estimate phylogeny
- compared phylogenetic data to biogeographical analysis of formation of Amazon river system
How did the creation of the Amazon river cause vicariance speciation in the trumpeters case study
when the river was formed, it split the population in two, limiting gene flow
- since trumpeters cannot fly over the distance of the Amazon river, they were isolated from one another
what is the first requirement of speciation
genetic isolation
sympatry
condition in which two or more populations live in the same geographic area, or close enough to permit interbreeding
sympatric speciation
speciation that occurs even though populations live within the same geographical area
what does sympatric speciation not require
geographic isolation
what two factors can initiate the process of sympatric speciation
- extrinsic factors (external)
- intrinsic factors (internal)
extrinsic factors example
disruptive selection for extreme phenotypes based on different ecological niches or mate preferences
example of intrinsic factors
chromosomal mutations
what does disruptive selection favor
extreme phenotypes
if disruptive selection persists over time, what happens to the two subsets of the population
can become genetically isolated and diverge from each other
case study for disruptive selection (sympatric speciation)
- currently described as single species
- two groups of travelers: larger and smaller
- transient killer whales looked different from the resident killer whales
- ecotypes were not mixing
what were the killer whales in the case study separated by
feeding cultures
niche
describe range of ecological resources that a species can use and range of conditions that it can tolerate
what did the two ecotypes of killer whales occupy
different niches within the same area of ocean
what is the particular type of mutation that is extremely important in speciation
polyploidy
polyploidy
condition of possessing more than two complete sets of chromosomes
- caused by massive error in mitosis or meiosis
what are the two types polyploids
- autopolyploid
- allopolyploid
autopolyploid
individuals are produced when a mutation results in doubling of chromosome number and chromosomes all come from same species
allopolyploid
individuals are created when parents of different species mate and then an error in mitosis occurs
- results in viable, nonsterile offspring with two full sets of chromosomes
what is the hey even leading to autopolyploid
nondisjunction during meiosis resulting in diploid gametes
autopolyploid is the duplication of
the same genome
speciation occurs with what generation and when
single generation and instantaneously
allopolyploid is the combination of
two genomes
when is speciation by polyploidy common
in plants
what is speciation by polyploidization driven by
chromosome level mutations and occurs in sympatry
what is the simplest outcome of 2 populations coming into contact
populations fuse over time as gene flow erases any distinctions between them
if two populations have diverged and are distinct genetically, what is expected of their hybrid offspring
have lower fitness because they will not be well adapted to either habitat
when should their be a strong selection
when postzygotic isolation occurs because hybrid offspring have reduced fitness
reinforcement
natural selection for traits that prevent interbreeding among populations
- selected traits reinforce differences that evolved while populations were isolated from one another
if closely related species are sympatric, what will the mating pattern be? (study on fruit fly species)
individuals from the two species will seldom mate with one another in lab
if species are allopatric, what will the mating pattern be (study on fruit fly species)
individuals from the two species will often mate with one another in lab
hybrid zone
geographic area where interbreeding occurs and hybrid offspring are common
what can determine if hybrid zones are narrow or wide, long or short lived, and move over time?
fitness of hybrid offspring and extent of breeding between parental species
how can hybridization cause speciation
if hybrid offspring can not only survive and reproduce but also possess a unique combination of traits that are adaptive in their environment
secondary contact of two populations can produce…
- fusion of populations
- extinction of one population
- reinforcement of divergence
- founding of hybrid zones
- formation of new species
(look at table 24.4 for summary)
example of fusion of populations
open water whitefish population fused with sympatric benthic whitefish population after introduction of invasive open water competition
example of one population
open water whitefish population may go extinct after fusion
example of hybrid zone formation
hybrid zone between hermit and Townsends warblers appeared to have moved over time
example of formation of new species
hybridization between sunflowers gave rise to a new species with unique characteristics
speciation
splitting event that results from a 2 step process
1. genetic isolation
2. genetic divergence
genetic isolation
occurs when some sort of barrier to gene flow isolates 2 populations within a species
in genetic isolation, what does the absence of gene flow mean for the alleles
alleles are not exchanged
genetic divergence
occurs when mutation, natural selection, and genetic drift occur in each of isolated populations
- populations begin to evolve independently
species
an evolutionary independent population or group of populations generally distinct from other species
what are some ways species will differ or be distinct from each other in
- appearance
- behavior
- habitat
- ecology
- genetic characteristics
what are the three main criteria used to identify species
- biological species concept
- morphospecies concept
- phylogenetic species concept
biological species concept
- main criteria is reproductive isolation
- members of same species cannot interbreed successfully
- no gene flow
what are mechanisms that stop gene flow
- prezygotic isolation
- postzygotic isolation
prezygotic isolation
prevents individuals of different species from mating successfully
postzygotic isolation
hybrid offspring of mating between members of different species either do not survive or reproduce
what are the causes of why mating wouldn’t occur in prezygotic isolation
- temporal- breed at different times
- habitat- breed in different habitats
- behavioral- have different courtship displays
mating occurs bit no zygotes produced because of
- mechanical- male and female repro. structures are incompatible
- genetic barrier- egg and sperm are incompatible
- hybrid inviability- do not develop normally and die during early development
- hybrid sterility- offspring mature but are sterile
what are some disadvantages to biological concept
- criteria of repro. isolation cannot be evaluated in fossils
- concept difficult to apply when closely related populations don’t overlap with each other geographically
- repro. isolation can be a complex gradient
morphospecies concept
identify evolutionary independent lineages by difference in size, shape, or other features
- if populations are independent and isolated from gene flow
- widely applicab;e
what are some disadvantages of the morphospecies concept
- may lead to naming of 2+ species when there is only 1
- cannot identify cryptic species
- subjective
polymorphic species
species that has two or more distinct phenotypes in the same interbreeding population at same time
cryptic species
species that cannot be distinguished from similar species by easily identifiable morphological traits
phylogenetic species concept
- identifies species based on evolutionary history
- all species form a monophyletic group
what does a monophletic group/clade/lineage consist of
- ancestral population
- all of its descendants
- and ONLY those descendants
what is one method to identify monophyletic groups
- one snip test
- imagine cutting one branch with scissors, everything that would fall off is a monophyletic group
how are monophyletic groups identified
traits called synapomorphies
synapomorphies
trait that is formed in certain groups of organisms and their common ancestors but missing in distant ancestors
- example: white fur that identifies polar bears as monophyletic group within bears
what are the disadvantages of phylogenetic concept
- only available for tiny subset of populations
- tends to recognize many more species than the other concepts
- complicates naming of species
