L10 - Diversification: Origin of Species Flashcards
1
Q
Define species?
A
- The most specific unit of taxonomic classification (domain; kingdom; phylum; class; order; family; genus; species)
- Also, a biological classification
- Classifying individuals based on a set of characters
2
Q
Define gene flow?
A
Movement of new alleles (variants) of a gene from one population to another.
3
Q
Define speciation?
A
- Creation of new species
- Dependent on limited or absent gene flow between populations
- If gene flow does occur between populations, both populations will remain genetically similar
4
Q
What are the mechanisms of speciation?
A
- Change in gene flow
- Mutation
- Genetic drift
- Natural selection
5
Q
What factors might cause a population to separate?
A
- Geographic or physical barriers (mountains, rivers and deserts that can be newly formed) reduce/eliminate gene flow between populations
ALSO - Different courtship behaviours (mating rituals)
- Different breeding seasons
- Different period of activity
6
Q
What processes might contribute to changes in allele frequency?
A
- Natural selection
- Genetic drift
- Mutation
7
Q
Where does the variation that natural selection acts upon come from?
A
Chance mutations: random change that happens when DNA is replicated that express new traits in an organism.
8
Q
What is Genetic Drift?
A
- Frequency of genes in a population can change over time, even when not under strong selective pressure
- Random inheritance can shift gene frequency
- Likely to occur in small populations, by chance
- Whole alleles (traits) may even be lost :(
9
Q
What will happen to these isolated populations when they come back into contact? Are the different species now?
A
- Depends on how you define “species”
- Morphological
- Biological
- Phylogenetic
10
Q
Morphological species concept
A
- Things that have a similar physical appearance/internal anatomy (size, shape function) are likely to be of same species
11
Q
Pros & Cons to Morphological species concept
A
- LIMITATIONS:
- Oldest method of defining species
- Doesn’t take modern genetics into account
- Not very accurate
- ADVANTAGES
- Good for examining the fossil record
12
Q
Biological species concept
A
- Defines a species as members of populations that actually or potentially interbreed (mate with each other) in nature and produce offspring that are fertile (can also reproduce)
13
Q
Pros & Cons to Biological species concept
A
- Not all species reproduce sexually
- Not a practical method (nor ethical): can’t test the ability to mate between every pair of species
14
Q
Phylogenetic species concept
A
- Species are groups of individuals that share a unique common ancestor
- Determined by showing that individuals share traits (previously morphological, now genetically) unique to that species
- Causes them to cluster distinctly and form other groups
15
Q
Why do we care how many species of [ X ] there are?
A
- Important for conservation discussions
- The more distantly related these species are, the greater the pool of genetic diversity
- If we define them as entire species, we look at losing an entire pool of genetic information
16
Q
How/why can gene flow be halted between populations? How do populations become new species?
A
- Allopatry: species in geographic location
- Parapatry: species with ranges directly adjacent to each other, ranges overlap slightly
- Sympatry: species existing in the same geographic location
17
Q
What is allopatric speciation?
A
- Speciation caused by the GEOGRAPHIC ISOLATION of two different populations
- Low gene flow can occur between populations but must be rare
- Geographic barrier depends on the type of organism (river, mountain, desert)
- Theory believed to explain the greatest number of species
- Believed to be the primary form of speciation that occurs on islands
18
Q
An example of allopatric speciation
A
- Break up of the Pangea
- Speciation increases after super continent division
- Limited to no gene flow, speciation can occur
Islands
19
Q
What is parapatric speciation?
A
- Ranges of two speciating populations are actually overlapping, but GENE FLOW IS REDUCED
- A contentious theory: not all evolutionary biologists believe that parapatric speciation can occur
20
Q
Parapatric Speciation
A
- Speciation occurs when the ranges of two speciating populations are actually overlapping, but gene flow is reduced
- A contentious theory: not all evolutionary biologists believe that parapatric speciation can occur
21
Q
How might Parapatric Speciation occur?
A
- New niche opens
- Population moves into new niche
- Niche causes evolution in the new populations
- Eventually, enough difference to speciate
- Large range in habitat = increased environmental differences = evolutionary differences
- Populations at far edges become very distinct
- Individuals in hybrid zone either disappear or become one of the two distinct populations
22
Q
What happens in the hybrid zone during parapatric speciation?
A
- Cannot be steady gene flow, or new species will hybridize out of existence
- Hybrids will be less fit for either habitat
23
Q
Example of parapatric speciation
A
- Phragmites australis: plant that lives over a very large geographic range
- In Siberia: it flowers after 1 month of growth
- In Mediterranean: flowers after 8 months of growth
- Differences in flowering timing prevents gene flow between populations
24
Q
Sympatric speciation
A
- A species arises from within a range overlapping with its origin species
- Also controversial
- How is gene flow restricted to a sub-population from within a larger population?
- Cues that animals use to decide who they want to mate with?
- Chemical signals
- Communication signals (bird songs)
- Sexual compatibility
- Mutations in physical appearance (pigmentation)
25
Sympatric speciation
- A species arises from within a range overlapping with its origin species
- ALSO CONTROVERSIAL
- Cues that animals use to decide who they want to mate with?
26
How is gene flow restricted to a sub-population from within a larger population?
- Reproductive Isolation
- Incompatible reproductive methods reduce gene flow in even completely overlapping populations
- Different courtship rituals (birdsongs)
- Different reproductive structures
- chromosome duplications in plants
- often arise from mutations
- infertile hybrid offspring
27
What is a hybrid?
- Organisms that we consider to be different species can interbreed
- Offspring are often sterile
- Hybridization is fairly common among plants
28
What is hybrid speciation?
- Some interbreeding can create viable offspring which can survive and mature
- Why we have some Neanderthal DNA
- Hybrids between polar bears and grizzly bears that can produce viable offspring
29
Why don’t we see more hybrids in the wild?
- Ranges do not overlap, do not come into contact with each other
- Changing for polar bears and grizzlies - climate change
- May have different courtship rituals
- Some of the traits of each parent will not be advantageous in the environment (brown polar bears would not be successful in the arctic)
30
What is despeciation?
- When two species become one
- HYBRIDIZATION can cause distinct lineages to collapse into a single lineage with an admixed mosaic genome
- RARE but there are a few examples: stickleback fish
31
Which mode of speciation?
- Do the ranges of species overlap?
- Is the entire range of one of the species found within the other?
- Are sexual practices compatible?
- Are two species becoming one instead of one species becoming two?
32
What is the primary requirement for speciation to occur?
- Minimal to no gene flow between two populations
- If populations begin to interbreed, they will lose their distinctness and become one species
