Lecture 5 Flashcards
Discuss one problem of sexual selection
It is a problem for natural selection. If the traits in males are beneficial for survival, why don’t females have them too? Darwin (1871) suggested they serve only to give one male an advantage over another.
Discuss natural selection vs sexual selection
Natural selection = survival of the fittest. Sexual selection = survival of the sexiest. Fundamentally they work in the same way. BUT sexual selection focuses its attention on the selective consequences of sexual interactions within a species. Natural selection operates in the context of other environmental factors.
What were Bateman’s findings in his fruit fly study (1948) and what is his principle
Females mean number of offspring didn’t changes between 1-3 mates, whereas males offspring increased alongside the increase in mates. His principles states that variance in male reproductive success is much greater than females, and male reproductive success depends on number of mates: additional matings may have a reproductive pay-off and a females reproductive success does NOT depend on number of mates. The sex which invests more in the young becomes a resource for which other members of the less parental sex compete.
Discuss sexual selection and sex differences
Males compete for access to females in the majority of species. This competitoin leads to sex differences in both morphology and behaviour. As a generalisation, the bigger the difference in parental investment between sexes, the more different the sexes are
Discuss size dimorphism across species
Increasing polygyny reflects stronger male-male competition. Stronger competition leads to increased sexual dimorphism, males being larger/brighter. Holds true for most mammal and bird species. E.G; elephant seals
What is sperm competition and the different types?
Pre-copulatory sperm competition in male-male competition includes fighting and displays and in female choice is includes choosiness. Post-copulatory sperm competition in male-male competition is sperm competition (sperm displacement) and female choice is cryptic female choice (complexitiy of female tract to selet best quality sperm).
Discuss sperm competition and body size dimorphism in primates
Testis size and body size dimorphism is linked to mating system in primates. Multi-male/multi-female groups provide a lot of opportunity for sperm competition. 45kg chimpanzees = 120gram tests, 160kg gorilla = 30gram testes.
Discuss sperm competition in humans
Spending more time apart from partner will increase mens attraction to partner, interest in sex and belief their partner wants sex too.
Discuss female choice patterns
Females may prefer males with sexondary traits; the power to charm the female. For example, female preference for elaborate feature in african widowbird; the long tail.
What were Anderssons’ 1982 findings
4 groups; elongated tails (artificially lengthened) / control 1 (tails cut and glued back) / control 2 (tails untouched / short tails (artificially shortened plumes). Females preferred males with long tails
Why do females prefer exaggerated male traits?
Runaway selection. Good genes. Sesory exploitation.
What is the Runaway selection (Fisher)?
Some variation in females preference for a male trait. Sons of these females inherit the trait, and daughters inherit the preference for the trait (Genetic covariance). This provides positive feedback in selection: females prefer males with the trait because they enjoy an advantage.
What is meant by good genes in terms of female choosiness
Sometimes females choose even though they don’t seem to gain anything other than sperm; this is often because the males possess good genes that the females want their children to inherit
Discuss the handicap principle
Zahavi (1975); secondary sexual characteristics may be attractive because they are detrimental to survival. THe idea was controversal because it was originally based on verbal argument. An example of this is testosterone dependent traits: immunocompetence hanicap hypothesis.
