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Lecture 17

Biology 1001A Lecture 17.pdf

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 17 Sexual Selection –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Consequences of Sex: Sexual Selection - sexual selection explains - sexual dimorphism – differences in appearance of males and females - traits that reduce survival or have no survivorship advantage - for example, frogs that call loudly to attract mates put themselves in danger to reproduce sexually because their loud call also attracts predators - traits like this persists because they are favoured by sexual selection Intersexual & Intrasexual Selection - intrasexual selection is when many of one sex competes for access to the other; examples would be the convergent evolution of horns, weapons or large body size in many different taxa - intersexual selection is when individuals of one sex are selected by individuals of the other sex; this is often called female-choice because it is often the females that are choosy about the males that they mate with - both intersexual and intrasexual selection can occur at the same time therefore the distinct can be blurry - an example of this is the bower-bird where intersexual selection is present because females choose who to mate with based on the quality of the structure and the amount of blue things present, and intrasexual selection is also present because males will attempt to sabotage each other’s bowers - for males the best way to maximize fitness is to mate with many females; the number of mates that can be accessed is usually what limits male fitness - for females on the other hand, it is better to mate with only one male because females are more concerned with offspring quality than with quantity, therefore females typically make careful choices about who they mate with Direct & Indirect Benefits - direct benefits - males provide direct benefits to females such as gifts - some males have decoration which is preferred, in house finches: the males with more red make better fathers because they are better able to forage for food - indirect benefits - some species are more extravagantly ornamented because they are of greater genetic quality, therefore there are heritable genetic benefits to be had by the offspring, and this makes the individual attractive to females - females try to mate with the highest quality males to produce the greatest quality offspring Biology 1001A | 2012 Why Are Females Often the Choosy Ones? - females tend to select the male, but why? - anisogamy is the inequality of gamete size between males and females - eggs are metabolically expensive to produce relative to the cost of producing sperm - it tends to be the females that have a higher parental investment in the offspring - sex differences in parental investment and potential fitness determine which sex chooses, and which sex competes - o
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