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Chapter 6

chapter 6 coyne.doc

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June Larkin

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Coyne chapter 6 how sex drives evolution for lec 6 and 7 - Peacock with its blue tail violates every aspect of Darwin because the traits that make him beautiful is making him maladaptive for survival because the tail produces a problem in it not being able to fly to escape predators especially when their tail so wet it’s hard to drag. The sparkling colours also make it attract praetors especially compared to the females who are short tailed and camolfauged to have a more drab greenish colour and a lot of the energy is gone into to the male’s tail which must be re-grown each year - How could the peacocks feathers be an adaptation when it is a barrier? Also if the males evolved by natural selection why the females aren’t as bright as the males are? - These unique traits and behaviours are only seen in one sex - Another example would be the frog of central America where the male sing at night time to attract the attention of the females but also in doing so they are attracting predators like flies that prey on these frogs and get their attention more than the intended no calling females they are after - These examples shows us that just as Darwin thought these traits do reduce survival - Let’s take a look at the red colored widowbird who have long talk feathers longer than their bodies and so a university group captured them as they would see them flying in struggle so what they did was cut an inch in one group and another 4 inch in another and recapturing them in the breeding season they found that: longer tailed males lost more weight than shorter ones making te longer tailed ones a disability for them - Another example would be the footlong lizard where the males and females look different meaning the males are bright colours having yellow head while the females were grayish colour and lightly spotted. An experiment was done to test a hypothesis to see that the males bright colours attracts more predators and after the experiment the male models showed bite marks by birds and snakes while none were on the female models - Sexual dimorphisms – traits that differ between males and females of a species such as colour, and songs - biologists have found that sexual dimorphic traits that are found in males seem to violate the evolutionary theory because they waste time and energy and reduce survival look at the colours of the species in males we have seen in experiments that they are eaten more than the plain females - If selection is responsible for these traits we need to explain how? - Before Darwin sexual dimorphism was a mystery that not even creationist could explain how one sex should produce features that are harmful for their survival - Darwin finally noted an explanation- if traits he said differed between males and females such as their behaviours, ornaments, or structures only being done to the males these costly traits have evolved for a reason and it is not for survival - selection we have to remember is not only for survival but it is also for successful reproduction and by having fancy tail or singing doesn’t help you to survive but it does enhance your chances to have offspring’s which answers why these traits have Rosen - Darwin was the first to recognize this trade off and said that this type of selection responsible for sexually dimorphic features are called sexual selection - Sexual selection- it’s a selection that increases an individual’s chance of getting a mate which is a division of natural selection but has a unique way of operating and is also nonadaptive adaptation that it produces - Sexually selected traits evolve more when there is a increase in reproduction like the widowbird noted before have long tails because the females prefer the longer tailed males as mates even though it is hard for the males to run from predators or look at deers with big antlers where they too might struggle with a burden but the win contests more to create more offspring’s - Sexual selection comes in 2 forms: - 1)direct competition between males for access to females (huge antlers) - 2) female choiceness – widowbird long tail among possible mates - Male-male completion is the easiest to understand with almost all animals between the males for the possession of the female and when the males battle directly it is usually clashing antlers of the deer, the stabbing horns of stag beetle , head butting of stalk eyed flies - Selection will favour any trait that promotes victories so getting more mates for pffsprings producing armaments- stronger weapons, larger body size or anything that helps the male win physical contest - Whereas bright colours, ornaments are more for mate choice - To female eyes not all males are the same because they find that some male traits and - behaviours more attractive so genes that produce those favourites are accumulated in the population - Another indirect completion among males is that they have the loudest voice, brightest colours and then the winner is decided by the female in contrast to the male- male competition - Why is it that in sexual selection males competes for females and not the other way around? Because of the differences in sizes of the sperm and the egg - Is this theory true though those males who are winners have the best displays because if they do not the whole sexual selection theory fails!! - Don’t worry evidences support the theory - Sexual selection promotes the evolution for large, fierce males because the bigger males pass on their genes to the next generation where the smaller ones don’t - Females who do not have to fight are close to their original weight for reproduction - So sexual dimophorims of body size even in our own may be due to competition between males for access to females - Male birds compete for estate as well to attract females by controlling a patch of land one with good vegetation that is goof for nesting and when the males have it they defend it with vocal sounds to keep other males away - look at elephant seals who are polygynous with the males having more than 15 females nesting in their territory - many other males are called floaters (players) trying to invade territories so that they can copulate with females - beside the males protecting their turf they also they sing complex songs and making threats with their ornaments which is a bright red epaulet on the shoulder and when a experiment was done colouring it black 70% males lost their territories and so it is not to attract females but to warn males away to say this territory is occupied - we can tell how selections are done are by going in the fields to instead of labs - sexual selection doesn’t end after sex because males can still compete even after mating because females mate with more than one male in a short period of time so a male has to protect his paternity by post mating competition by the male hanging around after mating guarding his female against other suitors just like a dragon fly attached its the male g
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