Lecture 4- Fitness Flashcards
species
a population of reproducing organisms that is isolated from other populations (but there are multiple definitions)
when can this definition of species not be used
- prokaryotes and eukaryotes that aren’t strictly sexual
-with extinct organisms
-with bacteria and archaea that have horizontal gene transfer
where can species appear
-in a long-time lineage (e.g. humans/ chimps and our common ancestor)
-In space due to geographic isolation (e.g. animals on an island)
-Various genetic effects can play a role
how can species be identified/ detected
by comparing populations using population genetics
allopatric speciation
allo- other, patra- homeland
Not necessarily different selection pressures and adaptations in two zones, leading to speciation
-populations are geographically isolated
-e.g diff species of antelope squirrels on either side of the Grand Canyon
what can occur when populations are isolated?
-directional selection
-disruptive selection
-stabilising selection
genetic drift
-random effects causing major changes in small populations ( by chance only some individuals reproduce)
-in large randomly mating populations, large fluctuations are unlikely
founder effects/ bottle necks
founder effect- type of genetic drift, loss of genetic variation (species evolved from a small group)
bottleneck- environment causes a small population
sympatric speciation
- (sym = same, patra = homeland)
- Much debated in animals from a theoretical point of view, few examples (parasites, perhaps?)
- Plants can easily show these effects
examples of speciations in progress
blackcap (breeds in central Europe, over-winters in Spain, and for the last 30 years in the UK)
how do black caps show temporal isolation
-black caps have assortative mating where Spanish birds mare with Spanish birds and UK mate with UK which is a result of arrival time on breeding grounds
-strong signs of genetic and morphological differences in Spanish and UK populations
-rapid genetic change= raw material of speciation
comparison of hooded crow and carrion crow
have different distributions (83 base differences)
can hybridise
81 in same genetic region
why do plants show polyploid species
have greater genetic, physiological and developmental flexibility
example of sympatric speciation in Shortcleuch Waters
-appearance of Mimulus peregrines in Scotland
-Mimulus peregrinus originated from interspecific hybrids: hybrids were triploids (three sets of chromosomes usually prevents meiosis)
-A genome duplication event occurred in one of these triploid hybrids (entire set of chromosomes was doubled, creating a hexaploid individual -with six sets of chromosomes)
-This duplication restored the ability of the plant to undergo meiosis effectively because it now had an even number of chromosome sets, allowing the usual pairing and separation of chromosomes during reproduction.
-The hexaploid individual could reproduce and create offspring, forming a new, self-sustaining population (new species)
what genetic factors can lead to speciation
-sampling and statistical effects e.g. drift and bottlenecks
is speciation an adaptation
no, it’s an event
-consequence of particular conditions which can involve the by-products of subsequent selection
how long can speciation take
up to 5,000,000 years (Mean time taken to go from single eukaryotic population to two reproductively isolated populations)
how many species are there?
-unknown
-estimated based on sampling
-massive unknown in the sea
why are there so many insect species?
-unknown
-appearance has been linked to evolution of plants
-the evolution of the larval stage enables insects to exploit new niches
-evolution of flowering plants coincides with radiation of the butterflies
-changes in ecology means new niches
isolating mechanisms
barriers that prevent different species or populations from interbreeding and producing fertile offspring
-These barriers help maintain species as distinct groups by stopping gene flow between them.
-types: prezygotic and postzygotic
what are the different prezygotic barriers
premating (habitat isolation, temporal isolation and behavioural isolation)
post-mating (mechanical isolation, gametic isolation)
postzygotic barriers
-reduced hybrid viability, reduced hybrid fertility, hybrid breakdown (fertile hybrids but reproductive failure at F2 or afterward)
hybrid zones
-regions where two distinct meet and interbreed as a consequence of gene flow (movement of genes between groups)
fitness
the reproductive success of hybrids or parents
hybrid zones: fusion
-lots of gene flow
-groups are highly interfertile, no barriers to breeding
-lead to a single population
hybrid zones: reinforcement of isolation
If there is moderate gene flow, but hybrids experience reduced fitness (e.g., they are sterile, weak, or poorly adapted to the environment), natural selection will act against hybridization
-more reproductive barriers (e.g. mating preferences to prevent producing unfit hybrids)
-push the groups further apart genetically and more isolation
hybrid zones: stability
-If gene flow is limited and hybrids experience no significant fitness disadvantage, the hybrid zone can remain stable over time.
-This means that the two groups remain distinct but continue to produce hybrids in the overlap area. The hybrid zone persists because neither fusion nor complete reproductive isolation occurs.
