Adaptation & Speciation

Pregunta	Respuesta
Negative Frequency Dependence	It is better to be rare. But this will then become common as it is selected for & increases in the pop. It goes in cycles, so as it becomes common, fitness decreases and the next rare morph is selected for etc. This is balancing selection. E.g. Hawaiian Happy Face Spider has 3 colour morphs which fluctuate. RARE = ADVANTAGE
Positive Frequency Dependence	Fitness increases as it becomes more common - rarer morphs are eliminated. Batesian mimicry & warning colouration in hoverflies. It's better to be rare because predators think you're toxic. If you're a rare morph you get eaten as they're willing to test it.
Human Sex Ratio	1:1 sex ration so each parent contributes equally to next generation. As soon as 1 sex is rarer, it contributes more heavily & ratio is restored. But sex ratio can differ where indivs. are more related. Hamilton showed some spiders who live in close kin groups have a heavily female biased sex ratio.
Frequency Dependence vs. Actual Numbers	It may not be freq. dependence but actual numbers. In New World Monkeys, colour vision is determined by number of X chromos. Females can be dichromatic or trichromatic, but males can only be dichromatic. The gene is X-linked so Fs will get an extra allele. In foraging groups it is better to have a mixture of di&tri. Di-vision is better for predator awareness, as tri-vision is distractinng. but it's good for foragin as can see colours clearer..
Density Dependent Selection	Can speed up adaptation. E.g. in bacteria, if 4 out of 100 indivs have antibiotic resistance, then all will die apart from those 4. These 4 are contributing to the next generation & so teh resistance will spread v. rapidly.
Time Dependence	Prolonged insecticide use have increased resistance. But decreasing the use will probably reduce resistance. This is because resistance is a trade-off & is costly, so those not harbouring resistance will probably have an advantage elsewhere and be selected for.
Polymorphisms & Adaptation	Not all polymorphisms are adaptive. E.g. Partula snaims of diff. spp. are diff. shaped/coiled/coloured. This was though to be adaptive in some way(CLARKE, 1960). But on Moorea, there are higher than expected numbers of variation & this was shown to be as a result of hybridisation from prev. isolated pops. This was NOT NS.
Polymorphic Pleiotropy	Polymorphisms that influence more than 1 trait. E.g. leg length & abdomen size in spiders. They cannot evolve independently of one another. The body size constrains the leg length. But this can be adapted - Harvestman spiders spread their legs out so they have legs that are thin, but spread out to support their body.
Mimcry	Batesian & Mullerian & Cryptic. Organisms adapt in response to their biotic environment (other spp. around them). Mimicry is unlikely to escape the affects of density & freq. dependence
Batesian Mimicry	Non toxic mimicking toxic spp. E.g. Hoverflies mimicking a toxic wasps.
Mullerian Mimcry	Unpalatable spp. mimicking other unpalatable spp. E.g. Butterflies to speed up predator response & learning to avoid them
Cryptic Mimicry	Looks like something else. E.g. Jumping spiders look like flies. Crab spiders on flowers.
Super-Genes	Polymorphism can be maintained within a supergene for mimicry. A supergene refers to a collection of genes that are physically in close proximity & that are unlikely to be split up through combination.
Adaptive Radiation	The rapid diversification & speciation of new species to occupy different ecological niches. Massive on islands. E.g. Hawaiin Honey Creepers & evolution of tube feeding mechanism.
Speciation	The process by which new species arise
Species	Have limited or 0 genetic exchange with other 'species' - but are difficult to define due to things like geo. isolation. If they come together again can the reproduce successfully? New species are largely reproductivley isolated from one another & they are no longer freely exchanging genes.
Factors of Reproductive Isolation	Prezygotic barriers = mating calls, morphological differences, sinistral/dextral snails. Postzygotic barriers = failure to develop embryo, auto-abortion, infanticide, unviable offspring. Or both.
Allopatric Speciation	A physical barrier develops & splits the original pop. Changes occur due to drift, local adaptation to environment, founder effect etc. Over time thins causes reproductive isolation & if they come together again & can't reproduce viably = Allopatric speciation. Microallopatric speciation occurs in different sections of the same habitat. E.g. trunk, leaf, twig of a tree.
Sympatric Speciation	Where the original population is divided through reproductive isolation in the absence of a physical barrier. E.g. Cichlids in Lake Victoria - 500 species 15,000 years. Same environment yet speciation occurs - Disruptive selection model where changes in pop. genetics lead to extreme trait values being favoured over intermediate ones. So the 2 ends of the spectrum diverge.
Parapatric	Where 1/2 the original population moves into a new, but adjacent territory & over time repro. iso. occurs & a new range equilibrium occurs. Genetic exchange is then limited so the 2 pops. diverge. E.g. Anolis Lizards in Caribbean have parapatric dist. They occupy similar niches & hybridise when in sympatry.
Host-Shifts	Adaptation driven by host-shifts. E.g. R. pomonella flies on hawthorn. the intro. of apple treees led to a divergence. Hawthorn & apple fruit @ diff. times so larvae of 2 flies hatch @ diff. times so genetic exchange no longer occurs. Totally diverged.
Ecological Release	Adaptation driven by ecological release is when changes in the external environment offers new opportunities for adaptation.
Resource Availability	Adaptation driven by changes in resource availability. E.g. Island dwarfism/gigantism. No top predators so things get big/flightless. Or things get small due to limited resources & intense competition.
Diversification Rate Limits	Factors limiting diversification rates = pleiotropy, trade-offs, time-frame & past history

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	Creado por Alice Burke hace más de 11 años