Evolution - Ch 24 - Speciation Flashcards
What is speciation?
the evolution of two new lineages (species) from a single ancestral species
What can cause speciation?
genetic isolation (NO gene flow) and genetic divergence (caused by natural selection, genetic drift, mutations, and sexual selection)
What is a species? What are four different sets of criteria used to identify species?
an evolutionarily independent population or group of populations
- biological species concept
- morpho-species concept
- ecological species concept
- phylogenetic species concept
What factors cause prezyogtic (reproductive) isolation?
temporal, habitat, behavioural, gametic barrier, and mechanical (and genetic)
What factors cause postzyogtic (reproductive) isolation?
hybrid viability and hybrid sterility
What is temporal isolation?
when populations breed at different times
What is behavioural isolation?
when populations have different courtship displays
What is habitat isolation?
when populations live in different habitats
What is a gametic barrier?
when sex cells are incompatible between mates
What is mechanical isolation?
when male and female reproductive structures are incompatible
What is hybrid viability? Hybrid sterility?
- hybrid viability: hybrid offspring die as embryos
- hybrid sterility: hybrid offspring cannot reproduce
What is the biological species concept?
Advantages? Disadvantages?
(given NO gene flow) populations that can produce viable offspring are the same species
- advantage: clear
- disadvantage: fossil and asexual species; hard to assess if populations do not overlap geographically
What is the morpho-species concept?
Advantages? Disadvantages?
based on differences in size, shape or other morphologies
- advantage: widely applicable
- disadvantage: “cryptic” species; can lead to too many names for one polymorph; subjective
What is the ecological species concept?
Advantages? Disadvantages?
the same species have the same niche (range of resources, and tolerances)
- advantage: applies to asexual species
- disadvantage: different species can have similar ecological roles
What is the phylogenetic species concept?
Advantages? Disadvantages?
smallest monophyletic group on a phylogenetic tree
- advantage: widely applicable, can be tested for
- disadvantage: our data on the tree of life is small; possibly leads to naming of “too many” species
What is allopatry?
when populations are living in different geographical areas
What is allopatric speciation, and what are its two modes?
the divergence and creation of new species by physical isolation
-vicariance and dispersal
What is vicariance?
the physical separation of a population into components via a chance event that splits a habitat (ex. by glaciation)
What is dispersal?
when some individuals migrate to a new habitat, and colonize it to found a new, physically isolated population
What is sympatry?
when populations live close enough together so that interbreeding is possible
What is an ecological niche? What type of selection can lead to speciation?
the range of environmental resources that a species can use, and the range of conditions it can tolerate
-disruptive selection, which can lead to reproductive isolation in a population as individuals adapt to different niches
What is sympatric speciation? What events can cause it?
the formation of new species even though populations live in the same geographical area
- can happen through
(1) external events (ex. disruptive selection) and
(2) internal events (ex. chromosonal mutations)
What specific type of mutation can be very important in speciation?
polyploidism
What is a polyploid?
a condition when mutant individuals have more than two sets of chromosomes
-leads to reduced gene flow between mutant and wild-type individuals
What two ways are polyploid individuals formed?
alloploidy (more common) and autoploidy
What kind of polyploid is produced when the chromosome doubling and chromosomes come from the same species?
autopolyploid
What kind of polyploid is produced when the chromosome doubling and chromosomes come from the different species?
allopolyploid
Compared to other forms of speciation, what is special about polyploidism (in terms of rate)?
it creates species instantaneously!
Why have polyploids been so successful (especially plants)?
- Polyploids suffer less from inbreeding depression
- Polyploids have more heterozygosity
- Genes on duplicated chromosomes can also undergo change, so genetic variation increases in polyploids
Suppose two isolated populations come back together. What are the four possibilities?
- fusion
- reinforcement
- hybrid zones
- speciation by hybridization
- extinction of one population
How does fusion of two once previously isolated populations happen?
if two populations can freely interbreed, populations become more similar to each other
Suppose two isolated populations come back together. How does reinforcement happen?
hybrids have low fitness (N.S. selects against hybrids, preventing interbreeding)
-solidifies the trait differences between populations which happened because of separate evolutions
Suppose two isolated populations come back together. How do hybrid zones happen?
hybrids have medium fitness
Suppose two isolated populations come back together. How does speciation by hybridization happen?
(ex. sunflowers: H. annus and H. petiolaris produce a hybrid called H. anomalus)
hybrids have high fitness because of unique combination of traits
What is a hybrid zone?
a geographical area in which interbreeding happens between populations and (viable) hybrids are common
-it can move over time, and it depends on hybrid fitness and extent of interbreeding
Suppose two isolated populations come back together. How does extinction of one population happen?
if one population outcompetes the other for resources
