chapter 24 - speciation Flashcards
define sympatric speciation
when speciation occurs in the same geographical space
why does sympatric speciation occur? give an example
species may be isolated by factors such as preferences for different habits, mating, natural selection
eg. disruptive selection and assortative mating could lead to reproductive isolation
define polyploidization
- instant speciation!
- genetic isolation created by formation of polyploid individuals that can breed only with each other
define autopolyploidy
- polyploids that have duplicate chromosome sets from SAME species
- spontaneous gene duplication
(eg. chromosome doubling to produce a tetraploid)
define allopolyploidy
- polyploids that have duplicate chromosome sets from DIFFERENT species
- hybridization event, followed by chromosome doubling
name the 2 types of polyploids
autopolyploids and allopolyploids
tetraploids
autopolyploidy: offspring of a parent that produced diploid gametes and then SELF FERTILIZED
allopolyploidy: error in meiosis or mitosis
explain how allopolyploid species form (requires hybridization event)
- 2 species mate
- error in meiosis or mitosis leads to UNREDUCED GAMETES (with more than one set of chromosomes)
- if egg is fertilized, results in polyploid offspring
why can polyploidy lead to reproductive isolation?
- diploid + tetraploid = TRIPLOID
- uneven (dysfunctional) amounts of chromosomes when gametes combine
- offspring can’t survive
why is polyploidization more common in plants than animals?
- plant somatic cells undergo MORE rounds of MITOSIS making it more common that errors would occur
- self-fertilization more common
define hybrid zones
zones where hybrids are made
diverged species/populations that come together to produce cross-fertilized offspring
what can happen when isolated populations come in contact?
- when prezygotic isolation does not exist, populations may interbreed, produce hybrids
- gene flow may cause homogenization between populations
- gene flow may result in adaptive introgression (advantageous genes transferred across species)
define adaptive introgression
advantageous genetic variation is transferred from one species (or population) to another
the good stuff gets shared
name outcomes of hybridization
- homogenization (via gene flow)
- adaptive introgression (good genes transferred)
- reinforcement (NS for reproductive isolation)
- development of hybrid zones
- speciation by hybridization
define reinforcement
selection for traits that isolate populations reproductively
- if two populations of different species are very diverged, their hybrid offspring may have lower fitness
= incomplete postzygotic isolation - if hybrid fitness low, may be strong NS against interbreeding
can hybrids speciate?
yes!
and sometimes they actually have higher fitness
define the biological species concept (BSC) and its issues
- assigns individuals to the same species if they actually or potentially interbreed
- populations evolutionarily independent if they are reproductively isolated from each other (NO GENE FLOW)
ISSUES:
- difficult to apply to natural systems (seemingly different species can still interbreed)
- asexual organisms?
what mechanisms stop gene flow between populations?
PREZYGOTIC or POSTZYGOTIC mechanisms
List and describe mechanisms of reproductive isolation
PREZYGOTIC (can’t mate)
- temporal: diff breeding times
- habitat: diffbreeding habitats
- behavioural: diff mating rituals
- gametic barrier: eggs + sperm incompatible
- mechanical: genitalia incompatible
POSTZYGOTIC (offspring die or have low fitness)
- hybrid variability: offspring don’t develop normally, die as embryos
- hybrid sensitivity: sterile offspring
define the morphospecies concept (MSC) and its issues
- morphological traits distinguish species
- based in idea that distinguishing features more like to happen with no gene flow
ISSUES:
- features are subjective
define the phylogenic species concept (PSC) and its issues
- species defined as smallest monophyletic group on a tree that compares populations
ISSUES
- may end up over diagnosing species (not all clades are really species)
define allopatry
populations or species that live in different places
OVERALL THEME:
name the ways genetic isolation can happen
ALLOPATRIC SPECIATION (physically separated)
- allopatry (physical separation)
- geographic distance (change of mating over long distance)
SYMPATRIC SPECIATION (in one physical space)
- reproductive isolation (pre/postzygotic)
define the two types of allopatry and why they occur
DISPERSAL
- population moves to new habitat, colonizes, forms new population
- age of barrier pre-dates speciation event
VICARIANCE
- physical barrier splits population into isolated groups
- age of barrier ~same as speciation event
genetic isolation happens because of
- genetic drift
- natural selection
- mutation
- NOT gene flow
how to find out which species are more closely related on phylogenic tree
find most recent common ancestor!
mechanisms of sympatric speciation
- disruptive selection + assortative mating
- polyloidization (auto/alloploidy)
what is a polyploid?
species with more than 2 sets of homologous chromosomes
what is assortative mating?
biased mating with other individuals with similar traits
define allopatric speciation
solation happening when species become physically separated
- DISPERSAL (one group of pop moves away)
- VICARIANCE (physical barrier of separation)
