Speciation Flashcards
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Speciation
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The formation of different species from a common ancestor
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Species
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a group of organisms that can interbreed to produce fertile offspring
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Population
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a group of organisms of the same species, which live in the same place at the same time
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Gene pool
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All the inheritable alleles present in a population
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First thing needed for speciation to occur
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- there must be genetic variation in the original population to begin with
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Second thing needed for speciation to occur
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- then there must be no gene flow between a group and the original population so that they can change independently
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Third thing needed for speciation to occur
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- then evolutionary processes must increase the genetic variation between the group and the original population.
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Fourth/last thing needed for speciation to occur
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- and they must become different enough that RIMs develop so that they can no longer successfully interbreed/produce fertile offspring with the original population
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Two types of speciation
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Allopatric and Sympatric speciation
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Allopatric speciation
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The formation of different species due to a geographical barrier separating the original ancestral population into two or more geographically isolated populations
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Sympatric speciation
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the formation of different species from an ancestral species in the same geographical area without prior geographical isolation (= no geographical barrier involved)
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process of allopatric speciation
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- Initially a population with genetic variation occupies the same geographical area
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process of sympatric speciation
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- Initially a population with genetic variation occupies the same geographical area
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Sympatric species
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species that have previously diverged from a common ancestor and now exist in the same area but remain reproductively isolated (note: can occur via allopatric or sympatric speciation
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Allopatric species
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species that are geographically isolated
16
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Polyploidy
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when an organism has more than two complete sets of chromosomes in its somatic cells e.g. 3n, 4n, etc
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What causes polyploidy
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caused by non-disjunction during cell division
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non-disjuction
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chromosomes are not pulled apart correctly during cell division and so causes polyploidy
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What is needed to be fertile?
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It requires an even number of chromosome SETS and the chromosomes need to be able to form homologous pairs
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Allopolyploidy
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two different but closely related species contribute chromosomes to a polyploid (if the species were not closely related a hybrid could not form)
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Autopolyploidy
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one species contributes all the chromosomes in a polyploid.
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triploid
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when a cell/individual has 3 sets of chromosomes
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Diploid
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when a cell/individual has 2 sets of chromosomes
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haploid
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when a cell/individual has half the original number/sets of chromosomes
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A way instant speciation and sympatric speciation can occur
when polyploidy results in the formation of hybrid sterility RIM in one generation, so they immediately become separate species
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advantages of polyploidy
Polyploidy can produce different phenotypes that might provide a survival advantage and so increase reproductive success for the polyploids
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hybrid vigour
individuals that have this often grow larger and faster, and are more robust/resilient e.g. produce more flowers and fruit, or are better able to tolerate harsh conditions
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Reproductive Isolating Mechanism (RIM)
any factor that stops organisms from breeding together, so prevents gene flow between groups of organisms (so can result in speciation or keeps species isolated).
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Examples of reproductive isolating mechanisms
geographical, ecological, temporal, behavioural, structural barriers, polyploidy
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Geographical isolation
when physical barriers (e.g. oceans, mountain ranges, rivers, deserts) separate populations so they cannot come in contact to reproduce and so there is no gene flow
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Ecological isolation
individuals of a species live in the same geographical area but occupy different ecological niches to reduce competition and so they rarely come into contact, so they do not reproduce and so there is no gene flow between them.
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Temporal isolation
differences in the timing of their behaviour e.g. mating is prevented because the two species breed at different times of the year or day.
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Structural isolation
structural shape or size means that mating is not possible.
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Behavioural isolation
results from differences in behaviour, such as different courtship rituals, so do not recognise each other as a possible mate; or they do not select each other as a mate because of physical appearance (sexual selection); or one species might be nocturnal and the other diurnal so they do not come into contact (note this is also timing of behaviour so could be regarded as temporal isolation as well);
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hybrid sterility
each chromosome does not have a homologous pair so they cannot undergo meiosis to produce viable gametes
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Evolutionary processes
processes that cause changes in allele frequencies in a population over time (so cause evolution). They include: Mutation, Natural Selection, Gene Flow, and Genetic Drift (which includes Founder Effect and Bottle Neck Effect), and sexual reproduction
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Evolution
change in allele frequencies in a population over time
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Genetic variation / diversity
the differences in the genotypes and characteristics of individuals in a species.
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Benefit of more genetic variation/diversity in a population
greater chance the population has to survive changes in the environment because there is more likely to be a variation present that is suited to the environmental change and so will survive
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consequence of low genetic variation/diversity in a population
less likely to survive changes in the environment, and speciation is unlikely to occur in the population because there is less/no GV for evolutionary processes to work on.
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mutation
a random and permanent change in the base sequence of DNA.
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The effects of mutation on genetic variation/diversity
If it is a gametic mutation, it will produce a new unique allele that is inheritable, and so will increase the size of the gene pool and the genetic variation in the population.
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Harmful mutations
these do not provide a survival advantage, so are selected against and so decrease in frequency in the population
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Beneficial mutations
these provide a survival advantage, so are selected for and so increase in frequency in the population.
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different selection pressures in different environments
causes isolated groups that have no gene flow to diverge from each other and become different species
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Natural selection
a process where environmental factors select for the phenotype that is best suited to the environment
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How natural selection affects gene pools
Individuals with the phenotype best suited to the environment have a survival advantage (are 'fitter'), so are more likely to survive and successfully reproduce, and therefore pass on their favourable characteristics/alleles to offspring more often, which means the frequency of the beneficial allele(s) increases in the gene pool.
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Selecting agents/pressures
environmental factors (abiotic and biotic) that affect the survival of an organism, so influence reproductive success, and so they select for the successful phenotype
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Stabilizing selection
when the middle/mean of the phenotype range is selected for, so it decreases variation in a population (= more individuals show the mean phenotype)
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Disruptive selection
when both ends of the phenotype range are selected for, creating two distinct groups with different phenotypes in a population (can be the start of forming separate sympatric species / sympatric speciation)
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Directional selection
when a phenotype towards one end of the range is favoured over other phenotypes, causing the allele frequency to shift in the direction of that phenotype over time
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Gene flow
movement of alleles between populations/gene pools when individuals migrate (immigrate and emigrate) between populations and interbreed
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The effect/impact of gene flow on gene pools
immigration can introduce new alleles into a gene pool increase genetic variation/diversity, emmigration can remove unique alleles from a gene pool decreasing genetic variation. It has more of an affect in small populations.
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Genetic drift
random changes in allele frequency in a population due to random chance events.
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The effect/impact of genetic drift on gene pools
decreases genetic variation in gene pools because an allele frequency may decrease, or alleles may become fixed in the gene pool, due to the random loss of individuals from the population due to a chance event. It has more of an affect in small populations.
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Founder Effect
occurs when a small group of individuals leaves a larger original population and starts a new population somewhere else
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The impact of founder effect on the gene pool
reduces genetic variation because it is a random small sample of the original population that leaves and so it is likely the allele frequencies will be different to (not reflective of) the original larger population, or it won't have an allele from the original population
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Bottleneck Effect
the sudden reduction in the size of a population
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The impact of bottleneck effect on the gene pool
it reduces genetic variation in a gene pool because it is likely the allele frequencies in the remaining smaller population will be different to (not reflective of) the original larger population and it can often result in the loss of unique alleles from the population
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Patterns of Evolution
Divergent evolution
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Divergent evolution
the splitting of a common ancestor into two or more species due to different selection pressures in different ecological niches favouring different phenotypes, and so homologous structures are evidence of this pattern
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Homologous structures
structures in different species that were inherited from (present in) their shared common ancestor, so have a shared structural origin, but have evolved to have different forms and functions in the different species due to different selection pressures in their niches. So evidence of divergent evolution.
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Adaptive radiation
occurs when a common ancestral species evolves into a large number of new species in a short period of time due to the availability of many new ecological niches (due to extinction events or environmental changes) - associated with divergent evolution
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Convergent evolution
when two or more species from different direct ancestors (i.e. do not share a recent common ancestor) evolve similar phenotypes/adaptations due to similar selection pressures in their niches, and so analogous structures are evidence of this pattern
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Analogous structures
structures in different species that were not inherited from (present in) their shared common ancestor, so have different structural origins but have evolved to have similar form and function due to similar selection pressures in their niches. So evidence of convergent evolution.
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Co-evolution
when different species have close ecological relationships, so that they exert selection pressures on each other, and so any change in one species can lead to reciprocal changes/adaptations in the other species (= influence each other's evolution).
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Different rates of evolutionary change
Punctuated equilibrium and Gradualism
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Punctuated equilibrium
a rate of evolution where species stay unchanged for a long period of time (in stasis) and then rapid speciation/divergence occurs in a short period of time often because an environmental change results in different ecological niches becoming available and so they experience different selection pressures. It is associated with adaptive radiation
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Gradualism
a rate of evolution where species constantly undergo slow adaptive change due to the constant action of evolutionary processes and so new species will continually appear spread out over time
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Evidence for evolution
Fossils, comparative anatomy (homologous and analogous structures), molecular biology (proteins and DNA analysis), biogeography
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Fossils
the preserved remains or traces of organisms in sedimentary rock.
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The evolutionary evidence fossils provide
evidence of the change in structures and form over time, with the oldest ones showing the most primitive features. Help identify evolutionary relationships, and the timing of evolutionary changes/divergence.
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Biogeography
investigating the evolutionary relationships of species based on knowledge of how the geography of Earth has changed over time and so influenced the distribution of living species today.
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The evolutionary evidence that biogeography provides
evidence that species found on land masses that were joined together for longer periods of time are more closely related to each other and that modern forms evolved from a shared ancestor that spread (radiated) out into new environments and then diverged.
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How DNA analysis works as evidence of evolution
All life on Earth shares the same 4-base DNA code. The more closely related the species are (= the more recently they shared a common ancestor) then the more similar their base sequence of DNA
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Genetic distance
a measure of the genetic divergence between species/individuals/populations - the distance is small if they share many similar alleles/genes/ or a similar base sequence, and so they are more closely related and have a more recent common ancestor.
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mtDNA
only inherited from the mother and does not undergo recombination, so only changed by mutation
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How mtDNA analysis works as evidence of evolution
its mutation occurs at a known rate, so it acts as a molecular clock, so by analysing how different it is between two species, it can be worked out how long it would have taken for that amount of variation to arise and therefore approximately how long ago they diverged from a common ancestor
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How protein analysis works as evidence of evolution
They are coded for by the base sequence of DNA, so a change in the DNA base sequence will make these different, and so their similarity in different species can be used to tell how genetically similar the species are and so how closely related they are
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Phylogeny/Cladistics
the grouping of organisms based on shared derived characteristics that can be traced back to a common ancestor and that are not in more distant ancestors. It is based on physical characteristics, molecular biology (DNA analysis especially mtDNA)
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NZ geographical history
split from Gondwana (South America, Africa, India, Antarctica, Australia, NZ) before mammals evolved, NZ sinks so mostly underwater (lots of small isolated islands), then mountain uplift separates land into new environments (cool high alpine areas), then ice ages occur ->lowering sea level -> creating land bridges, making new habitats South cooler North warmer, then warming climate -> rising sea levels separates into North and South Island, Sth warms but still has cooler high alpine regions
