L4 & L5 Sexual Selection Flashcards
What is sexual selection?
It is a mode of natural selection
How does sexual selection act?
It acts on an organisms’s ability to obtain or successfully copulate with a mate. It is not about features that function to improve survival, but function to maximise an individuals reproductive success.
What is asexual reproduction?
One sex, usually no genetic recombination e.g hydra
What is sexual reproduction?
Two sexes, male and female may be found in the same individual (e.g. slugs & snails). Sexes may be separate (e.g. vertebrates, insects). Individuals may change sex during their lifetime (e.g. some fish).
What does sexual selection create?
Sexual conflict, asymmetry in investement. Males and females do not share interests over reproduction. Female gametes - large, motile, few produced. Male gametes - small, motile, many produced.
What is a monogamous mating system?
Low comp for mates, both sexes may compete for mates. Sexes similar in size and appearance. Both sexes often care for young.
What is a polygynous mating system?
High comp for mates between males, high levels of dimorphism (males larger, ornamentation etc). Females care for young
What is a polyandry mating system?
Females compete more intra-sexually for mates. Sexes similar size and appearance (low dimorphism) - but females may be larger or have ornamentation if competition is high. Both sexes, or males only, care for young
What is sexual selection (pre-mating)?
Intrasexual (male-male) selection - secondary sexual characteristics. Intersexual selection (mate choice) - ornaments, colouration.
What are intersexual selection mechanisms?
Indicator traits, sensory bias, runaway selection, genetic compatibility.
What are indicator traits?
Female stickleback fish (Gasterosteus aculeatus) prefer redder males. Redder males are healthier. Plumage brightness as an indicator of parental care in northern cardinals. Great tits, Parus major, ‘females with more immaculate patches bred significantly earlier.
What is sensory bias?
The preference for a trait evolves in a non-mating context and is then exploited by one sex in order to obtain more mating opportunities. Females prefer to mate with more orange males. Outside of a mating context, both sexes prefer animate orange objects. Orange fruits are a rare treat that fall into streams where the guppies live.
What is Runaway selection?
Assumes genes for male traits and female choice are linked, i.e. if female prefers males with a certain trait then her sons are likely to have that trait. Leads to positive feedback.
What is genetic compatibility?
Major histocompatibility complex (MHC). They scored male body odours as more pleasant when they differed from the men in their MHC than when they were more similar. Our results suggest that contraceptive pill use could disrupt disassortative mate preferences.
What is sexual selection (post-mating)?
Cryptic female choice, sperm competition
What is cryptic female choice?
Influence of female behaviour, morphology and physiology on post copulatory competition between sperm of multiple males. Females preferentially choose sperm (birds, arachnids, gastropods, reptiles, insects)
What is sperm competition?
Females may mate with several males during a single fertile period. Male that deposits the most sperm has the most chance of siring the offspring. Sexual selection favours greater sperm production (larger testes)
Case study - How can big, costly, bums evolve?
Sexual swellings are probabilistic signals of the timing of ovulation. The swelling size within-cycle indicator of the probability of conception. Swellings size signals enduring differences between females in their individual ability to conceive and raise offspring. Once sexual swellings have evolved as fertility signals, they can, in certain socio-sexual systems, be further selected to act as quality signals.
What factor may impact sexual selection?
Sex ratios
What is the peacock example of sexual selection? What are females choosing?
How can we show female choice for male ornamentation? Demonstrate that there is a correlation between the degree of elaboration of peacocks’ trains and their mating success. If the number or arrangement of eye-spots in the peacock’s train influences mating success, then how can we test this experimentally. Change the no. of eye spots, more eye spots should increase mating success. Peacocks with eye spots removed showed a significant decline in mating success between seasons compared with a control group.
What is the peacock example of sexual selection? What does the tail reveal about males?
Are males with more eye spots or bigger tails actually better mates. Correlative data showed peacocks with a large number of tail eyespots had low levels of circulating heterophils, suggesting better health status.
What is the peacock example of sexual selection? How are females benefitting?
If females choose healthier males with more eye spots how do they benefit? Improved growth and survival of offspring of peacocks with more elaborate trains. Improved growth and survival of offspring controlling for female quality
What is polygyny?
One male, multiple females.
What is polyandry?
One female, multiple males.
What is polygynandry?
Many males, many females
What can testes size relative to body weight be dependent on?
Mating type, smaller if they have already competed before mating for access to female
