evolution - chapter 23 and 24 microevolution, macroevolution

Agents of microevolution (5)

• Mutation

• Natural selection of fittest

• Gene flow between pops through migration (interbreeding assumption)

• Genetic drift (random force in small population, limited variation)

• Non random mating

Stable gene pool implies (6)

• pop is not evolving

• no gene flow

• large populations (no gen drift)

• random matings

• no natural selection

• no new mutations

Hardy weinberg law

predicts if stable (close to 1) or evolving

p2 + 2pq +q2 = 1

p+q=1

means frequency of:

p: allele 1

q: allele 2

p2: pp

q2: qq

2pq: pq

microevolutionary forces (5)

• Mutations: only significant if paired with natural selective (preadaptive, random)

• Natural selection 

• Migration results in gene flow: interchange of alleles between populations (reverses gen drift of isolated pops) (interbreeding must occur)

Ex: black squirrels from toronto causing grey squirrels in montreal

• Small populations likely to experience genetic drift: limited variation

• Non random mating: this and interbreeding lead to homozygosity and interbredding depression. Homozygous usally less fit and selected against (e.g inbred dogs vs pure bred, marriage of cousins)

genetic drift effects (2)

• Founder effect: isolated population, descendant from a few founders shopws uncommon phenotype (ex: amish ellis van syndrome, leigh syndrome in canada)

• bottleneck effect: catastrophic elimination of individuals from small population, produce offspring with reduced variation (ex: loss of habitat of prairie chicken, hunting elephant seals

Macroevolution

an original species. a barrier appears that blocks gene flow.

microevolutionary changes become amplified until sub population have diverged enough to become different species

allopatric speciation

• physical barrier

• differences in genetic drift, mutations, natural selection

ex: bering straight, grand canyon with chipmunk species

sympatric speciation

populations diverge in the same space

• barriers of:

natural selection: competition for resources leads to exploration of new niches

non random mating sexual selection (timing of breeding, behaviour type etc) 

• absence of gene flow from non geographic regions

for example a new mating call appears that females prefer. 

ex: darwins finches on island, african chichlids, humminbirds in the andes.

Range

geographic area occupied by a speciesq

habitat

portion of range

niche

portion of habitiat used by one species

polyploidy

• changes in chromosome number causes inability to breed with normal 2n in plants

• this becomes the gene flow barrier

Reproductive isolation

happens when speciation is complete and two species cant breed

prezygotic isolation methods (zygote cant be produced) (5)

• Habitat isolation: occupy different niches in habitat. (maggot on different fruit, gardner snakes in land vs water)

• Temporal isolation: no interbreeding because of seasonal preferences (frogs)

• Behavioural isolation: incompatible behaviour (boobies need right coloured feet and mating call)

• Mechanical isolation: lack of mechanical fit between male and female (some insects cant pollinate flowers because cant fit in, bat penis sizes)

• Gametic isolation: mating occurs but fertilisation doesn’t due to gamete mortality or molecular incompatibility.

Postzygotic isolation + chromosome math (3)

• Hybrid inviability: hybrids form but wont survive to reproductive age (salamander hybrids)

• Hybrid sterility/reduced fertility: hybrids produced sterile (mule)

• Hybrid breakdown: healthy hybrid produced but unable to produce healthy offspring (will die in a few generations)

if chromosomes of both species added is odd, then sterile and if even then fertile.

Levels of biodiversity (3)

• Genetic diversity: number of alleles per gene in 1+ populations of a species. Decreases ability of population to recover if faced with habitat loss.

• Species diversity: number of different species in each community and ecosystem, or globally.

• Ecosystem diversity: number of different ecosystems in a geographic region (ex number of coral reefs)

define extant, extinct, extirpated, threatened, endangered

extant: current species

extinct: no longer exists

Extirpated: extinct locally

Threatened: at risk of becoming endagnered

endangered: at risk of becoming extinct.