Task 3 Flashcards
Define sexual selection
Part of natural selection that focuses on the intra-species aspects of competing for mates and thus reproduction.
What is Thomas Malthus known for?
His 1978 paper called “Essay on the Principle of Population”
-> Populations would grow exponentially, but the fact that they are not, means that there are some factors that stop this from happening
How can reproductive success be quantified?
Number of offspring produced
What are some common misconceptions about evolution / natural selection?
- Natural selection doesn’t change an individual during its life span. The individual merely passes on its traits or not and thus the overall average traits in the population change.
- Evolution doesn’t actively encourage mutations in a certain direction. All mutations are random and only the ones that coincidentally increase reproductive success become more common.
- Fitness of an individual is more about its alleles than the actual phenotypic characteristics.
Relative Fitness of alleles is determined by…
…how their representation in the population changes relatively to other alleles.
What are two factors, that mediate how fast a trait becomes more common?
- Selective Pressure
2. Heritability
Name two reasons why alleles tend to not reach fixation.
- Negative frequency dependent selection
- Heterozygote Advantage (Heterozygotes are sometimes better adapted to environment and fixation requires homozygotes. -> Example: Sickle cell Disease)
Explain the three “directions of selection”
- Directional - having a more extreme trait either in negative or positive direction leads to selective advantage
- Stabilizing - When a medium amount of a trait that is present in the population is most effective, the normal distribution curve will get more focused at this point.
- Disruptive - When both extremes of a trait are advantageous. Leads to a distribution curve with two peaks.
What is a fourth, alternative model of selection direction?
Purifying Selection - Mixture of directional and stabilizing selection - all amounts of the trait get weeded out except for a specific amount, that is more towards on of the ends of the spectrum.
What is sexual dimorphism?
The apparent differences between the genders of a species.
What is the basis of the Bateman’s Principle?
Male reproductive success increase with each new mate, whereas females have a maximum capacity of offspring and also typically have a higher cost of reproducing. This means that they will be more choosy about their mates.
What do the statements of the Bateman’s Principle lead to?
- Intrasexual Selection: Fighting between males in order to compete for more sexual partners
- Size differences between genders: Males need their size in combat.
- Male ornamentation: Increases attractiveness to females and thus increases likelihood of the female choosing this male as their mate.
What are some hypothesises for why a female might prefer ornamented males?
- Sexy son Hypothesis: Picking a mate with a lot of ornamentation will increase the chance of the male offspring also having this trait, which in turn increases his potential reproductive success. (Loop Principle)
- Good genes model: Tail being a sign for (correlating with) better fitness in other domains)
Name some exceptions of the Bateman’s Principle.
- sometimes the roles of male and female in this context are reversed
- Many birds and other species form long term partner bonds.
What is one phenomenon, that appears frequently in long term bonding in animals?
> Extra-Pair matings: mating outside the partnership as a mean of maximizing reproductive success
- > Choosing a fitting social partner but a genetically superior mate outside the partnership
- > Lower quality males often become nomads, that search for females to have extra-pair matings with in order to secure their reproduction.
