Evolution Lecture 5 Flashcards
Darwin’s Origin of species?
It’s answers where the many species on earth come from and how come there is so many. Darwin saw speciation when he went to the islands and saw species similar to the ones on the mainland.
Species
Difficult to make universal definition. But typically it’s related organisms that share common characteristics and are capable of interbreeding.
Morphological species concept
Based on morphological (physical) similarity. Historically, most commonly used concept. How much difference is enough (it’s very subjective)? It’s unity within a species. Extinct animals are described by this.
Morphological species concept example?
Two intents that look mostly the same but have one major difference. How do you know it’s a new species and not just a new population of a species that’s already been made.
Ecological Species Concept
Views a species in terms of its ecological niche, the sum of how members of the species interact with the nonliving and living parts of the environment.
Molecular Sequence similarity
Looking at the DNA sequence but it’s also subjective.
Biological Species Concept
Separateness of a species. Can a set of organisms reproduce to sexually produce viable, fertile offspring. Species are designated by the absence of gene flow. Based on inter-fertility, not similarity. Not always applicable, but usually most useful concept (eg, can’t work with asexual organisms.
Inter-fertility
Populations that interbreed to produce fertile offspring. They are a species if they can do this.
Reproductive Isolation
Do not normally successfully interbreed in nature with other species = No/few ‘Hybrids.’ Not the same species.
Hybrids
One parent in one population and one in the other. They are often less fit than parent species.
Speciation
The making of new species. Makes diversity. Forms the bridge between micro and macro evolution.
Clade agenesis
When one species becomes two.
Anna genesis
Where one species changes so much that you wouldn’t think it was the same species.
Reproductive barriers
Inhibit gene flow between populations, allowing evolutionary divergence. Feature of its biology that prevent them with breeding with one another.
Speciation event
Where new species arise (the branch points on the tree of life).
Prezygotic Barriers
Acts before fertilization that blocks it.
Postzygotic barriers
Acts after fertilization. Prevents a healthy, fertile adult offspring.
Example of Prezygotic Barriers (in order of the chain)?
Habitat Isolation (live in different habitats)
Temporal Isolation (breed at different times)
Behavioural Isolation (have different mating cues)
Mechanical Isolation (tried, but won’t form a zygote)
Gametic isolation (gamete incompatibility)
Liger example?
Hybrid that grow to adult and typically are fertile. Not found in nature (a lot of barriers between them).
Example of Postzygotic Barriers (in order of the chain)?
Hybrid inviability (Zygote has a low chance of surviving adulthood because of genes)
Hybrid infertility (sterility) (It becomes an adult but is infertile)
Hybrid breakdown (they are viable and fertile offspring but when they mate with one another the offspring will be sterile)
Mules example?
Bred by famers to pull things. They are infertile. Since they are descended from a common ancestor, there is change in the arrangement of genes on chromosomes. So the chromosomes don’t pair properly when put together, during meiosis when you try and pair up those chromosomes get massive non-disjunction.
Evolution of reproductive barriers?
May arise ‘accidentally’ as result of evolution in isolation (two lineages become separate species and reproductive barriers evolved as a consequence of other evolutionary change (adaptive to different environments).
May evolve through natural selection to reduce inter-species mating that lowers reproductive success.
(e.g. ‘Reinforcement’) (Where there is existing barriers to reproduction (post), you can get the additional pre barriers, through natural selection).
Two ways of speciation?
Allopatric and Sympatric
Allopatric speciation
Geographic barrier blocks gene flow between populations. It’s more common. Barriers to reproductive evils while they aren’t experiencing gene flow.
Geographic barriers
Features of landscape that separate populations physically.
Example of geographic barriers for land animals?
Rivers, Seas between islands or continents, Mountain ranges
Example of geographic barriers for sea animals?
Landmasses. Isthmus of Panama that isolated population of marine species when it formed.
Evolution after separation?
Natural selection to different environments (i.e. adaptive evolution). Genetic drift (especially in small isolated populations). The founder effect on species from mainland to island, island becomes new species with no gene flow (peripheral isolates).
How can we tell allopatry has occurred?
Unless they come together again and can breed together again. Many things could happen when they reform and it depends how viable and fertile the hybrids are.
If contact re-established between evolved allopatric populations (2 things)?
Complete reproductive barriers evolved: Populations now classic biological species (two disinct species)
Partial reproductive barriers evolved: Formation of hybrids where species contact.
Hybrid zones
Located wherever the habitats of the interbreeding species meet. Environment conditions can alter the habitats of interbreeding species meet.
Fusion
Hybrids form readily; have high fitness: the incipient species merge into one again. Have gene flow and weakening reproductive barriers.
Reinforcement
Hybrids have low fitness: Natural selection strengthens barriers - Hybridisation gradually ends =
Two good Biological Species. Strengthing of reproductive barriers.
Long-lasting Hybrid zone
Hybrids have variable fitness or are uncommon. Hybrids are continued to be produced.
Species formed on the tree of life?
It takes a lot of time, it’s not sudden like it shows.
Introgression
Hybrids that breed back with one of the new species can introduce alleles from the other species. Opportunities for genes pass from one species to another. Important for understanding genetic makeup of many populations around. Incomplete separation of species.
Sympatric speciation
Requires a barrier to gene flow within a geographic region. Requires some mechanism to generate a barrier to gene flow. Can be done by sexual selection.
Habitat differentiation
Where genetic factors are enable a subpopulation to exploit a habitat or resources not used by the parent population.
Examples of Sympatric speciation?
Host switching by specialist herbivores or parasites.
Disruptive selection: favouring evolution of reproductive barriers between individuals with different phenotypes?
Polyploid speciation, especially in plants.
Autopolyploid
Where it mates with itself and has a cell division failure doubling the # of chromosomes so new species is made.
Polyploid speciation (Allopolyploid)
Where two species with different # of chromosomes mate and produce viable but infertile hybrid. But then mitotic error double the chromosome number so now it’s fertile. But it’s unlikely it will find another one like it, so it can’t sexually produced. Van’t produce with either parent. So it uses stealthing to start a new population. This is an example of hybrid speciate and is common in plants and an exception to a strict “tree-of-life.”
Speciation and tree-of-life?
Each branching on the tree-of-life began with a speciation event.
