Lec 9: species speciation& hybridisation Flashcards
Sympatric vs allopatric speciation
Fairly easy to identify within a region (sympatric)
* arise from gradual differences across regions (allopatric)
What is the biological species concept and some of its main points?
- a group of interbreeding natural populations that are reproductively isolated from other such groups
- Geographic isolation alone is NOT sufficient
- Isolation does NOT have to be absolute
- Must be possibly interbreeding IN THE WILD
- Does not apply well to bacteria, asexuals, highly self-fertilizing species …or fossils
What are some pre-zygotic reproductive isolating barriers?
NB Pre-zygotic barriers prevent mating or fertilization so no zygote gets formed
- Geographical, ecological
- Temporal, behavioural (mate recognition)
- Mechanical (genital structure compatibility)
- Cellular (sperm-egg compatibility)
What are some post-zygotic isolating barriers?
NB. Post-zygotic barriers prevent proper
functioning of zygotes once they are formed
- Caused by combinations of genes with low fitness in the
hybrid - Intrinsic: – Inviability, sterility, or abnormal development of hybrids eg mules and hinnies
- Extrinsic: – Ecological mismatch of hybrid phenotype to environment - hybrid butterflies with aberrant colour patterns makes them a higher risk of predation and lowers mating success
Cannot be directly favoured by natural selection:
* Arise as an indirect byproduct of evolution acting separately in different populations
what is genetic distance?
(D) is a measure of the degree
of genetic differentiation between samples
How and why do organisms diverge and diversify?
Populations diverge genetically as a result of evolutionary forces (mutation, natural selection, genetic drift)
* Become reproductively isolated, often as an incidental byproduct of evolutionary change within populations
What is adaptive radiation?
The evolution of ecological and phenotypic diversity within a rapidly multiplying lineage as a result of speciation
Features of adaptive radiation
1) Recent common ancestry from a single species
2) Phenotype-environment correlation
3) Trait utility
4) Rapid speciation
What causes adaptive radiation?
1) Ecological opportunity
* Abundant resources
* Few competitors
* Often encountered on oceanic islands or their aquatic
counterparts e.g. African rift lakes
2) Origin of a key innovation
* e.g. toepad in Anoles; floral nectar spur in Columbines
3) High rates of speciation characterize the clade
* Test by comparing island to mainland clade
* e.g. Darwin’s finches & Hawaiian honeycreepers also
radiated on mainland (although not as much), whereas Galápagos mockingbirds have not radiated on islands or continents
what is hybridization?
The exchange of genes between species as a result of occasional inter-species mating
– Sometimes can reverse speciation process to merge two groups into one
What is polyploidy
An organism, tissue,or cell with more than two complete sets of homologous chromosomes
Allopolylpiody vs autopolyploidy
Allopolyploidy (e.g. AA x AA–AA AA) – Arises from duplicated karyotype following hybridization between species – the Commonest type of polyploidy
- Autopolyploidy (e.g. AA–AA AA)
– Arises from duplicated karyotype within a species (e.g. non-disjunction)
Evolutionary Significance of Polyploidy
- Polyploids are reproductively isolated from their diploid parents
– Hence a form of sympatric speciation - Polyploids exhibit novel phenotypes – Allows exploitation of new habitats
- Polyploids often show hybrid vigor due to heterozygosity, particularly in allopolyploids
- Polyploid origin for approx 50% of flowering plants – Many crops plants & invasive species
Biological vs taxonomic species concept
Taxonomic (or morphological)
* Based primarily on distinct measurable differences
Biological
* Based on inter-fertility among individuals
what is a clad
a group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics
