Flashcards in Natural and sexual selection Deck (15)
Reproductive success is
The number of viable, fertile offspring an individual leaves
Direct fitness: the number of copies of an allele that will be represented in the next generation.
Indirect fitness: also inclusive fitness (kin selection)
Has also been defined as: weighted average of the reproductive success of the phenotypes the allele appears in.
Relative fitness is
Difference in fitness between alleles. If one allele has a higher fitness than the other, it will leave more copies of itself in the next generation (at the expense of the one with less fitness). That means that selection is taking place, and the allele frequency will increase.
Change in allele frequencies because of relative fitness: is it faster in recessive or dominant alleles and why?
Faster in dominant alleles, because if recessive alleles have higher fitness, the organism will only reap its benefits if it's homozygous.
Types of selection?
1. purifying: harmfull alleles do not survive because they are less fit.
2. stabilizing: current population average is the optimum, higher or lower will be reduced.
3. directional: optimum is higher or lower than the population average, selection will occur in that direction.
4. disruptive: optimum is at two points, high extreme and low extreme but not the intermediate form
5. balancing: maintains 2 or more forms in the population
Examples of balancing selection
1. Heterozygote advantage: sickle cell in malaria countries. (and Malaysia ;p)
2. frequency dependent selection: eg high fitness only when rare, as in the case of left handedness in close combat fights. -> stabilizes at intermediate frequency.
What other ways can allele frequencies change?
1. genetic drift: bottleneck and founder effects
2. gene flow: reduces genetic variance between population, increases genetic variance within population.
Selection reduces variation. However, variation may persist, due to:
1. heterozygote advantage
2. frequency dependent selection
4. inconsistens selection bc of changing environments
5. sexually antagonistic selection
Designs we see currently may not be optimal. Why?
1. Time lag
2. Genetic correlation: hitchhiking genes, trade offs
3. inconsistent selection (changed environment)
4. there might be local peaks in covariation of a trait with fitness. It needs to have a continuation of positive gradients in between intermediate subtypes to continue to evolve. If intermediate types are less adaptive, it will not happen.
The individual with the higher reproductive costs/parental investment (humans: females) will be the ones who are picky in mates, the other sex will then be the one who best mates a lot and has to compete. The males then will have larger variance in reproductive success.
Why is sexual dimorphism a thing?
1. Intrasexual competition: The differences in reproductive cost causes (in many species) the males to compete amongst each other: It is then adaptive to be large, agressive (for fighting).
2. Intersexual competition: also adaptive to have the most fancy ornamentals (for the female to choose).
Best for reproductive success of males to have high libido. For females its better to have lower libido and be more picky about their sexual partners.
DIfferent theories of ornamentation in sexual partners?
1. Sexy son hypothesis: females mate with good looking males because it means their male offspring will also be good lookin' and have more reproductive success and thus, inclusive fitness states the genes will get passed on more. Needs an initial slight preference for the ornamentation for the theory to work. The preference will then co-evolve with the ornamentation.
2. Good genes: because ornamentation is expense energy wise, those who can afford it are thought to have good genes.
Different sources of selection?
1. natural selection
2. sexual selection
3. artificial selection
4. genetic drift
5. gene flow
Galapagos finches example: they inspired scientists as a form of adaptation & selection. Why?
A reduction in the number of finches was correlated with a change in the average beak size of finches. This happened after a drought: during this period, plants produced bigger seeds, and bigger beaks were adaptive. Thus the average beak size was bigger than before. Selection had happened because one trait was more adaptive than the other.