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Summary Evolution 2 dt1+2
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Summary of all lectures & additional study material for both sections of Evolution 2.
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Evolutie 2Geography of evolution
Geographic distributions can best be explained by historical circumstances in some cases or
ecological factors in others
Historical
- Extinction of populations can reduce distributional ranges
- Dispersal can lead to expansion of distributions
- Vicariance can separate populations, dividing ranges
Ecological
- Dispersal limitation limits range expansion
- Niche availability changes potential ranges
- Competitive exclusion can lead to range decline and even (local) extinction
Biogeographic realms: taxa binnen realms zijn veel meer verwant dan tussen realms
Wallace’s line: eilanden – een kant deelt meer met de orientaalse realm, andere kant deelt meer
met de australische realm
Phylogeography: principles and processes governing distributions of genealogical lineages, within
and among closely related species, providing insight into past movement and current distribution
Disjunct distribution: gaten in de verspreiding van een soort
Saxifraga cernua komt alleen voor in hoge gebieden – dispersal, extinction, vicariance
Potential niche vs realizes niche: competitive exclusion – andere taxa gebruike potential niche space
Hoe meer verschil tussen soorten, hoe sneller ze samen zullen voorkomen
,Explanations for diversification differences
- Difference in species carrying capacity Ktrop > Ktemp
- Difference in diversification rate (S – E)trop > (S – E)temp
- Difference in time for diversification Ttrop > Ttemp
The evolution of biodiversity
Problems with estimating biodiversity
1. Rare species are more likely in larger samples
2. Imprecise estimate of duration because of the use of geological stages
3. A fossil is a minimum (origination) and maximum (extinction) age
4. Count of living species is more complete – pull of the recent: the more recently a taxon
arose, the more likely it is to still be extant, diversity will seem to increase as we approach
the present. Reducing the bias: counting only fossil occurences of each living taxon and not
listing it for time intervals between its last fossil and the Holocene
5. Singletons
Rates of background extinction & origination have declined during the Phanerozoic
- Bigger taxa? Pas uitgestorven als alle leden zijn uitgestorven
- Volatility of clades? Soorten die snel specieren gaan ook sneller extinct
Key adaptations / innovations: grote diversificatie ten gevolge van een nieuwe eigenschap – bijv.
vleugels van vogels
- Increase probability of speciation
- Novel niche / resource use
Models for replacement
- Competitive displacement: C2 caused the extinction of C1 (A)
- Incumbent replacement: C1 prevented the diversification of C2 (B)
Mutation and variation
Codon bias: veel codons voor dezelfde aminozuren
Segregation: the selection of one of the two copies of a locus in gamete formation
When segregation is the only factor changing genotype frequencies this leads to a Hardy Weinberg
equilibrium
Hardy-Weinberg
2 implications:
1. Genotype frequencies attain HW values after a single generation of random mating
2. Not only genotype but also allele frequencies remain unchanged from generation to
generation
, Most important assumptions:
- Random mating
- Population is infinitely large
- No migration
- No mutation
- No selection
Recombination: the process that combines a gene copy at one locus inherited from the mother to
another inherited from the father (during meiosis)
When alleles are found together more often than expected based on chance, they are in linkage
disequilibrium
D = PA2B2 – PA2PB2
Recombination causes linkage disequilibrium to decrease. With speed depending on r
Why can there be linkage disequilibrium?
- Nonrandom mating
- New mutations linked to other loci
- Recent population fusion
- Low or absent recombination
- Genetic drift
- Natural selection (if association results in higher fitness)
Many mutations have no effect on fitness but some do and their effect can be deleterious or
beneficial
Genetic drift
Genetic drift is the evolutionary process resulting from chance events of survival, reproduction and
inheritance
Key features of genetic drift:
- Drift is unbiased
- Effects are larger in small populations
- Drift causes genetic variation to be lost
- Drift causes populations initially identical to divert
Census population: the number of individuals we count
Effective population: the number of individuals that actually contribute genes to the next
generation. Populatiegrootte waarbij de verwachte mate van drift gelijk is aan wat je ziet
Causes:
- Variation in number of progeny
- Sex ratio deviates from 1:1
- Natural selection
- Overlapping generations
- Fluctuations in population size
Drift interacts with selection
When a new mutation enters a population, not only selection determines its faith
- Advantageous alleles can be lost
- Disadvantageous alleles can be fixed
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