Speciation Flashcards
biological definition of species
population of reproducing organisms that is isolated (cant exchange genes) from other populations
what problems apply to the biological definition of species
prokaryotes and eukaryotes that arent strictly sexual, doesnt apply to them
impossible to use with extinct organisms
and also bacteria/archaea w/ horizontal gene transfer
what situations can species appear
- in TIME along a lineage splitting off during evolutions
- in SPACE due to geographical isoltion
- GENETIC EFFECTS could be even a single bp change
can be identified using pop. gneetics)
allopatric speciation
classic form of speciation
pop geopgraphically isolated from each other –> reproductive islation (no gene floe)
doesn’t have to be diff selection pressures but can be
types of selection effects
directional selection - one extreme version of a population survives
disruptive selection - only extreme forms survive
stabilizing selelction - extreme forms disappear
see one note for example
Genetic drift
no selection pressure
prurely randome effects
more likely in small populations - theyre more at risk
Founder effect/bottleneck
an event causes a reduction in a pop’s size and gene pool
founder effect:
new pop established by small number of indivudals
e.g. a bird gets blown away to some islands,
an entire type of allele can be left behind cuz the bird doesnt have it
sympatric speciation and its potential causes
populations that aren’t geograhpically isolated, but reproductively isolated
minimal evidence for animals doing this
but plants more likely
assortative mating + an exmaple
selection where individuals with similar pheno/genotypes interbreed more frequently than ocmplete random mating
e.g. Blackcap birds - spanish birds breed with each other, UK birds with each other
probs due to arrival time on breeding grounds
but it saw reproductive isolation between 2 groups
polyploid speciation
happens in plants only
cells of an organism have more than one pair of homologous chromosomes
its a failure of cell division,
basically it forms diploid gametes (so DNA doubles in offspring instead of being identical)
therefore the next generation are genetically isolated from the normal population
see one note for diagram
Barriers in mating - prezygoting barriers
blocks reproduction by preventing fertilisation
caused by:
(pre mating)
habitat isolation
temporal isolation
behavioural isolation
(post mating)
mechanical isolation
gametic isolation
so no mating can take place, or if it does - not compatible
Barriers in mating - postzygotic barriers
blocks reproduction after fertilization
causes:
reduced hybrid viability (doesnt survive)
reduced hybrid fertility (can’t reproduce)
hybrid breakdown (can reproduce once but not again)
Hybrid zones
after speciation occurs, it’s the possible outcomes if the two species interbreed and make hybrids (very likely if they’re still in the same habitat)
possible outcomes:
Reinforcement - remains as 2 distinct species, hybrids are less fit so they eventually die out, the species contirnue to diverge until hybridisation cant occur
Fusion - reproductive barriers weaken, the two species eventually become one again
Stability - Two species remain distinct, fit hybrids continue to reproduce, everyone lives happily ever after
see one note for diagrams
In what situation would natural selection act to reinforce reproductive isolation?
When 2 pops are diverged enough to produce hybrids
But the hybrids are unfit
nat selec will act to prevent the formation of these unfit hybrids
By strenthening reproducitve isolations
via REINFORCEMENT
