Lecture 11. Species and Speciation Flashcards
What is the species concept ?
What is a species ? When does it stop being a sub-species, or a distinct population ?
What does a species describe ?
A group of individuals sharing a common gene pool.
What can those who share the same gene pool not do ?
They cannot diverge from each other
When can a population diverge ?
When it stops exchanging genes and as a result it can follow a separate evolutionary trajectory.
What are the five main ways scientists have considered defining a species ?
- Biological species concept
- Evolutionary species concept
- Recognition species concept
- Morphological species concept
- Genetic difference
What is another name for the biological species concept ?
Isolation species concept
What is the biological species concept ?
Species are groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups
What are some problems with the biological species concept ?
- Does not specify that the young need to be fertile
- Inappropriate for asexual organisms
- Too difficult to apply to fossils, as we cant know who they would have bred with
- Species isolated on islands are problematic as they never get the chance to show whether they would breed
- Organisms which just release gametes - if mating is never observed, it is hard to tell who is mating with whom
- Some species which do occasionally interbreed, are clearly good species
What is the evolutionary species concept ?
A group of organisms that share an ancestor - a lineage that maintains its integrity with respect to other lineages through both time and space
What are some issues with the evolutionary species concept ?
- May or may not recognise sub species and recognise sister-species only when they have become distinct enough to be clearly different.
- Depends on the evolutionary history being known and the phylogenic tree being correct
What is the recognition species concept ?
Species are separated by differences in their fertilisation system
What is the problem with the recognition species concept ?
Does not cater for asexual organisms
What is the morphological species concept ?
Taxonomists look for discontinuities in the morphological variations between the populations
What are the problems with the morphological species concept ?
- Polymorphisms
- Sexual dimorphisms
- Cryptic diversity
- Use of genetic markers
How would you determine genetic distance between sister species ?
Look at the number differences in bases within the same genes
What are barcoding genes ?
Genes used by geneticists for species comparisons
What are barcoding genes ?
Genes used by geneticists for species comparisons
What is integrative taxonomy ?
Uses several lines of evidence together to make a case to the taxonomists community
What is the Tobias criteria scoring system ?
A popular method, using morphology, song, plumage and behavioral traits for separating species
What does speciation need to occur ?
The two populations need to stop breeding for long enough for them to become different to breed any more
What are the 3 possible methods of speciation ?
- Allopatric speciation
- Parapatric speciation
- Sympatric speciation
What is allopatric speciation ?
Some form of barrier splits the population, or part of the population gets stranded on an island
Why do isolated populations change ?
- Founder effect
- Genetic drift
- Natural selection (in conditions different from those experiences by the founder population)
What is a founder effect ?
Founding population is unlikely to have all the variation present in the parent population
What is genetic drift ?
The effect of chance on tiny populations
Why is natural selection different on islands ?
- Traits spread faster in smaller populations
- Reduced predation pressure as fewer predators
- Niche expansion because of less food of any one type on the island
- Less interspecific competition as less species on island
- More intraspecific competition because where a species reaches an island, it tends to flourish
What is parapatric speciation ?
Speciation at a border which does not prevent gene flow entirely
When does a hybrid zone narrow ?
If hybrid offspring are less fit that the pure breed of each type
When does a hybrid zone widen ?
If they are equally fit with pure bred offspring
What do you often get in hybrid zones ?
Character displacement
What is character displacement ?
Exaggeration of signals, especially those related to breeding, to make the signal stronger and prevent hybridisation
What is sympatric speciation ?
Requires isolation of a subset of the population within the original population
What is founder effect ?
A change in allele frequency due to the foundation of a sub-population by an unrepresentative sample of the parent population
What is genetic drift ?
A change in allele frequency due to chance events
What is meant by selectively neutral ?
A gene with no fixed effect on fitness
What is effective population size ?
Those individuals of a population which breed
What is fixation ?
When one allele survives at a locus
What is a population bottleneck ?
When a population is reduced to very few individuals
What is meant by polymorphic ?
Having more than one form
What is meant by monomorphic ?
Having only one form
What is inbreeding depression ?
Reductions in fitness due to breeding with close relatives due to increased expression of rare deleterious recessives
What is the heterozygote advantage ?
Extra vigor due to the genotype being heterozygotic
What is assortative mating ?
Mate selection on the grounds of sharing the same allele
What is disassortative mating ?
Mate selection on the grounds of having a different allele
What is a stable polymorphism ?
A species with more than one form in the population
