In chapter 6, "How Sex Drives Evolution," Coyne mentions that in species that practice female choice, some traits preferred by females provide direct benefits,such as a mate that will help care for offspring, or indirect benefits, such as a mate that will pass on healthier genes. Even seemingly random traits, such as brighter colors in birds, can sometimes signal to the female that the male can provide direct or indirect benefits to the offspring. Conversely, females may also discriminate against certain traits that would signify that the male would not be a good parent, such as the "lousy" male sage grouse (page 165).
Choose a species that exhibits female choice (it's okay if you are a male), and examine one trait that the females of the species seem to prefer or discriminate against. Relate this trait to how the male could (or could not) provide direct or indirect benefits to the offspring.
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Coyne gives on example species on page 164: the house finch. Geoff Hill, a biologist at the University of Michigan, performed experiments observing sexual selection within finches. Hill found a local population of finches with brown females and males that varied from pale yellow to bright red. It was first established that brighter males did in fact obtain significantly more mates when, after dying the birds' hair brighter or paler, the newly brighter finches found more mates.
ReplyDeleteBrightness correlates with overall good health. Male finches only become red when eating seeds with carotenoid pigments. As observed by the females, eating more means better health and better ability to provide for and feed the offspring. Better health also means less risk of diseases or viruses that can be passed on to the offspring and damage chances of survival. Thus, sexual selection increases the number of red finches because the advantage of finding more mates is desirable and beneficial enough to risk the danger of becoming more obvious to predators. On the other hand, females remain dark because the have no advantage in becoming brighter, and they still face the disadvantage that the males risk.
http://www.auburn.edu/academic/science_math/cosam/departments/biology/faculty/webpages/hill/8.pdf
Eilrayna mentioned a great example of female choice in the finch; in this case, the choosing of the male brought direct benefits: more food to the female for example. However, if we look at indirect benefits this time, there is another species that Coyne brings up to demonstrate female choice. Coyne describes the test done on the gray tree frog in order to experiment with the "good-genes model" (165): namely, that a common indirect benefit provided by males is his genes. The hypothesis is that females want genetically well-endowed males and will choose accordingly.
ReplyDeleteFor the gray tree frog, males attract females by giving loud calls - an example of sexual dimorphism as we learned in the Ecology unit. It was found that females preferred males whose calls were longer. Further, the males whose calls were longer clearly had better genes. The tadpoles from the long-callers grew faster, survived better, and grew larger. Thus, a long call is a sign of a male with good genes, and females choose these males for these "good genes" that can be passed on to offspring (http://www.ronaldecker.com/acrecall.htm). This relates to the biological theme of evolution: females will choose the most genetically strong male because the combinations of those genes will make offspring that is more likely to survive and reproduce. Eventually, offspring will evolve to have the most selectively advantagageous characteristics. The concept of "survival of the fittest" as Darwin would say, naturally favors the longer calling frogs.
Eilrayna and Connie both give good examples of animals that exhibit female choice. In Eilrayna's example of the finch, the female chooses a mate that more colorful and more beautiful. The brightness of the bird displays its overall health which is a determining factor for the female because his genes would be in their babies genes. In Connie's example with the frog, the female is attracted to the male by his loud calls. The louder the call the better genes the frog has. Having better genes like with the finch is necessary because the female wants their child to have good genes and be able to survive. Having good genes in the male is always a major determining factor in any animal that exhibits female choice because the female is choosing a male to mate with. If the male doesn't have good genes, then their baby together won't be healthy, and the female should not mate with that male and thus not choose that male.
ReplyDeleteAn example of another animals that displays female choice is the northern elephant seals. The male seals fight with each other trying to showoff their strength to the females. The male that wins the fight proves to the female that he is the strongest of the pack. The female will choose the strongest male because the female wants the male to be able to protect her and their child in case of predators. The female will also choose the strongest male because the strongest male will most likely have the best genes for their child together. If their child has good genes, like in the previous examples in the post above mine, the child will be able to survive longer and be able to reproduce so the specie of that organism won't die out (http://science.jrank.org/pages/48375/Cryptic-Female-Choice.html).
The idea of female's choice relates to theme structure and function. Each male has a different structure that attracts the female. With birds, each male is a bit different colored. Depending on the brightness of the bird, the bird health can be different. With the example of the frog each frog call is different, so each frog's genes are different. With the seals, each seal's strength is different so each seal ability to protect its family different. Because the same organism has so many differences withing themselves in their structure, their function is also different which can attract or repel females.
Another specie that exhibits female choice that Coyne mentions is the peacock, on pg 166. Similar to Eilrayna's finch example, where strong colors indicated better health, the abundancy of eyespots on the tail of a male peacock indicates the likelihood of stronger offspring (the physical trait indicating a benefit, indirect or direct). Female peacocks have shown a tendency to choose males with more eyespots.
ReplyDeleteThe female selection of male peacocks with more eyespots on their tails is not because the male provides direct benefits; the male does not help care for the offspring. However, Marion Petrie observed while working at Whipsnade Park that the offspring of males with more eyespots tended to survive better and grow faster than the offspring of males with fewer eyespots. Therefore, the female selection of males with more elaborate tails provides an indirect benefit that allows her offspring to be more likely to survive.
This female choice relates to the theme of evolution, where the females choose males that are more likely to give rise to offspring that are healthier, stronger, and more likely to survive to adulthood in order to reproduce. So the more eyespots the male, the more likely that that male will find a mate and pass on good genes of being strong and able to survive well, as well as the trait of having many eyespots. As time goes on, therefore, all the males with many eyespots will leave offspring behind, whereas the males with fewer spots might not leave any (because no female wanted to choose them ): ), so all the offspring will have many eyespots, and so all the offspring of THOSE males would be stronger and be more likely to mate and leave MORE strong offspring, and eventually, all the peacocks will get stronger and stronger with each generation of growing numbers of males with many eyespots, and so on and so forth.
Eilrayna’s finches are layer with the vibrant spectrum of colors that illustrate how healthy the finch is. The bright color of the male finch illustrates how healthy the finch is. Samantha’s peacocks are very much like the finch. The peacocks are attracted the number of eye spots because the greater the amount of eyespots present on the peacock, the greater the likely-hood of generating superior children. Connie’s gray tree frogs determine their mates on a different set of criteria. The gray tree frogs attract mates using long calls. In the case of the gray tree frog, the longer a gray tree frog can sustain a call, the better the genes for the survival of the lucky frog. Reproduction with the healthy male will copy some of the traits allowing the production of genetically healthier children.
ReplyDeleteThe bower birds are subjected female selection too. “Several studies have shown that the types of bower decorations, which differ in species, are correlated with mating success. Satin bower birds, for example, get more mates if they put more blue feathers in their bowers” (Campbell 154). The females look at each of the bower’s home while noting the concentration of their favorite color. In the case of the female Satin bower birds, the birds scout the male Satin bower bird’s territory for numerous blue objects. If the female likes the architecture of the male bower bird’s home, then the female Satin bowers birds will mate with the male Satin bower bird’s and reproduce. Thus the creative trait of the Satin bower birds will be copied into their offspring and help the next generation to reproduce.