MST1102 Flashcards
(17 cards)
Species concept
a group of individuals which normally reproduce to create viable offspring, and are unable to produce viable offspring with another group”.
What is disturbance?
“a discrete event, a sudden physical destruction, causing mortality faster than populations can be replaced” -
What is anagenesis?
- Individual lineage changes over time
- Subsequent generations sufficiently different - separate species
- No net gain of species
Describe cladogenesis.
- Splitting of ancestral line into two (or more) new species.
- Budding of new species from ancestral lineage
- Net gain of numbers of species
- Both can be gradual accumulation of evolutionary experience, or sudden jumps (mutations) with no apparent benefit
Describe directional selection.
Directional selection - favours advantageous characteristic; genetic diversity lost. There will always be pressure to be better (faster, stringer ect)
Describe stabilising selection.
Stabilising selection - favours intermediate characteristic; genetic diversity lost. (Snails ^ green shells are easiest to produces, without the predation pressure to camouflage all the snails would end up with green shells.
Describe disruptive selection.
favours extreme characteristics, more pressure to be yellow or black rather than green; genetic diversity lost - this is cladogenesis.
Describe genetic dispersal and gene flow.
Genetic dispersal and gene flow - homogenise genetic diversity (no longer advantageous to be a certain skin colour, therefore humans skin colour will homogenise)
Mutation creates genetic diversity; selection and drift reduce diversity
What is allopatric speciation.
Allopatric - geographical separation of a previously continuous population (common)
- Separation of populations
- Physical barrier (Island with three mountains becomes three Islands - Darwin’s Finches)
- Extinction of middle range
- Jump dispersal
- Barrier prevents gene flow
- Adaptive divergence and/or genetic drift
What is peripatric speciation.
Peripatric - variant of allopatric involving isolation of a peripheral population (fairly common). It is very similar to allopatric speciation but involves a much smaller portion of the population, therefore you end up with founder effects and a limited bottleneck genetic diversity. For example when a small population of invasive species has been pinched of from the normal population and adapts in isolation.
- Isolation of peripheral population
- Peripheral populations create specific features:
- Limited genetic diversity
- Head start to divergence
- Founder effects
What is parapatric speciation.
Parapatric - speciation of adjacent populations stretched over an environmental gradient (rare). The example below shows how the flowers have been fertilised by different insects, depending on the time of day.
- Creation of genetic gradients by:
- Variation throughout range of a species
- Local adaptation
- Decrease in gene flow across gradient
- Development of hybrid zone and reproductive isolation
- Driving force is distance over range of populations
What is sympatric speciation?
Sympatric - no separation during speciation (very rare in multicellular organisms), if the yellow snails only breed with the yellow snails even when there is nothing stopping them breeding with the green or black snails. Lake with fish that are separated due to feeding habitats.
- No spatial separation of populations
- Establishment of separate genotypes while in contact with each other
- Disruptive selection - selection of phenotypes controlled by one gene; natural selection encourages reproductive isolation (polymorphism into speciation)
- Competitive speciation - variant of disruptive selection; competition within a species selects for phenotypes
- Polyploidy - multiplication of whole sets of chromosomes (extreme mutation)
What is taxonomy?
The classification of organisms in an ordered system that indicates natural relationships”
Describe an asconoid structure
Asconoid
Simple and continuous choanoderm, with just one layer. (many newly settled calcareous sponges ≤ 10cm high). Mostly micrscopic, rarely bigger than a mm and often take on a more complex form as they grow.
Describe a sycinoid structure
Syconoid
Simple folding of pinacoderm and choanoderm (some calcareous species display this form all the time)
Describe a leuconoid structure.
Leuconoid
Folding and subdivision of choanoderm (most calcareous, all demispongiae)
The increased complication is because the chaonocytes are driving the aquiferous system, and as each choanocyte is only very small it can only produce a very small amount of water which leads to lower pressure and in larger sponges it would create a dead zone. The increased complexity will prevent this dead zone.
