lecture 10 and 11- sexual selection Flashcards
whats is the difference between natural selection and sexual selection?
natural selection= causes the evolution of traits, morphological or behavioural
sexual selection=the evolution of traits that gives individuals mating advantages over other individuals within that sex.
what is the impact of sexual selection traits on overall survival?
they do not always contribute
when the male has the higher rate of reproduction, which sex is choosier?
the female
why does the male usually compete for breeding opportunities? 4 reasons
- theres a difference in gamete size.eggs are more costly
- males have the faster potential rate of reproduction
- the operational sex ratio is often more skewed towards lesser females (for example females are less available due to longer gestation periods)
- females have greater parental investment
explain the differences in gamete size between males and females
female investment in gametes in relatively high. eggs are large,and expensive in terms of resource use
sperm is cheap in terms of resource use, and comes in large numbers
what factors cause asymmetry between sexual selection of males and females
females have greater parental investment and limited number of gametes
what is the difference inlimitations to mating potential in males and females
females=gametes quantity
males=access to mates
what is the operational sex ratio?
the ratio of sexually available females to males. when resources (eg. females) are in short supply, there is competition for them.the sex with the greater potential rate of reproduction competes whilst the other is choosy
what are the two types of sexual selection?
inra-sexual selection
inter-sexual selection
what is intrasexual selection?
competition between members of the same sex for access to members of the opposite sex.this involves passive females
what is intersexual selection?
mate choice by members of the opposite sex, females are often the “choosy” ones.
what are secondary sexual characteristics?
traits which differ between the two sexes, and are unconnected to gamete transfer or production
what are secondary sexual characteristics unrelated to?
gamete transfer or production
what are some examples of secondary sexual characteristics?
- weapons (antlers,horns)
- size dismorphism
- elaborate displays and colours
Explain the gene process and size dimorphism
Males compete to win the right to reproduce. They then pass on their phenotypes, and natural selection occurs. As the larger males continuously win, their larger characteristics are passed on
What is the size dimorphism between male elephant seals and females
Males are 10x larger than females
What are the benefits of being choosy in intersexual selection? (There’s five)
- The right species can be mated with, instead of accidentally mating with a similar genus.
- better resources can be obtained by a mate( territory, food, nest sites etc)
- Better parental care
- Less harassment by competitive males
- offspring of better genetic viability, as the best quality male can be obtained
What are the benefits of sizing up in intersexual selection?
It doesn’t cause any damage to physical health like fighting in intra-sexual selection does
What is the difference between antlers and horns
Antlers are a temporary growth
Horns are bones grown from the skull
Explain the reasoning behind antlers/ horns evolving for sexual selection opposed to natural
- Moose have antlers but their main defence form is kicking, suggests it’s used for sexual selection
- females do not have antlers/ horns
Explain the intrasexual selection selection process in red deer mating
Step 1. The two males roar. Large males produce deeper roars. The two males can size eachother up and decide to walk away if they desire
Step 2. If one hadn’t backed off, they engage in a series of parallel walks
Step 3. If neither have backed off, a fight for access to territory and females occurs
Why do male dear engage in a series of parallel walks during intrasexal selection
It gives them an opportunity to size the other up, by seeing relative body sizes. This gives the smaller one the opportunity to walk off without engaging in the fight
why do males normally compete for mates?
- eggs are more costly
- they have the greater potential rate of reproduction
- the operational sex ratio is often skewed towards less available females
- females have greater parental investment
explain the hybridisation importance of choosing the correct mate
- accidentally mating with another species and creating a hybrid species can have serious implications for the offspring in terms of postzygotic barriers(hybrid invitaility,hybrid sterility, hybrid breakdown)
- it reduces the parents reproductive success
explain the indirect benefits of being choosy
-allows for the acquisition of good genes, leading to higher quality offspring
what ae the two modes of female preference?
- sensory bias
- arbitary bias
explain sensory bias (give frog example)
- preference may exist from females who simply go towards the “easiest to find mate”
- eg. female frogs follow a sound gradient. the male frog with the loudest call will sound closest, and attract the nearest mate
explain the link between arbitary bias and natural selection
-when the females bias causes selection on a trait that benefits the male, it becomes natural selection. this fitness advantage results from the female selection pressure
quickly define linkage disequilibrium
-when non random mating results in the gene for preference and the trait being found within the same genome of the same individuals
explain how linkage disequilibrium occurs
- females have preference for a particular male trait (eg. a large tail), so will “choose” this male and mate with him
- the genes for preference and the trait are then passed onto the offspring, and now exist within the same genome
- how these genes are expressed depends on the sex
explain fishers runaway process
- females have preference for a particular trait, so these males have a mating advantage over others lacking it and produce a greater proportion of offspring
- the genes for preference and trait become linked via linkage disequilibrium
- those lacking the traits do not pass them on, and are subsequently selected out of the population due to lesser mating opportunities
- the magnitude of the trait (eg. size of tail) is continually amplified in a population due to its greater mating advantage
- natural selection eventually puts the breaks on, as the trait becomes a hinderance to survival and its no longer advantageous
explain Zahavis handicap principle
- extravagant traits are a hinderance to survival (eg. they cause increased predation), so those who possess them and survive are seen to have a greater fitness
- this indicates to the females that the male is “high quality”, and makes the male a more attractive choice as his benefits can be passed onto offspring
- this signal is an “honest one”, as males are unable to produce fake signals of having a greater fitness as they wouldn’t be able to avoid the costs
