In Chapter 6 “How Sex Drives Evolution” (more specifically on pgs. 144-146 and 159-161), Coyne discusses sexual dimorphisms. Coyne explains the selective advantage more decorated males have because they are more likely to find a mate (and thus reproduce and pass on their genes). Coyne later acknowledges that not all species follow this pattern of more decorated males. Explain the correlation between polyandry, polygamy and monogamy and the physical appearance of the males and females. (This part should be easily found in Coyne’s book, as well as Campbell).
Furthermore (now using outside knowledge!), explain how the way of polygyny, polyandry or monogamy is a selective advantage for different species. (For example, why is it advantageous for some bird species to be monogamous, it is advantageous for other bird species to be polygamous?) In your explanation it may be helpful to include discussion of survival rates/curves, competition for mates, parental investment (both maternal and paternal), r/K selection, and/or a specific example of a species.
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ReplyDeletePolygamy: One male, multiple female mates
ReplyDeletePolyandry: One female, multiple male mates
Monogamy: Us! One male and one female
Usually, in a polygamous species, the male would be more ornamented (having a mane like a lion, or huge antlers like an elk). It's the other way around for a polyandrous species, with the female being highly ornamented. For monogamous species, neither males nor females are highly ornamented
Well, for a lot of species, it's an advantage for them to be polygamous. Lions in a pride, for example, are polygamous. The lion could mate with the females so the females could all produce offspring.
There was a debate topic like a year ago that was discussing polygamy in humans. Of course, we all view it as morally wrong to be polygamous. However, if you look back into history, such as the Mormons, polygamy actually could potentially increase the number of humans multifold. It's that our society views polygamy as "ethically wrong" that we don't do it.
If you look at it with a scientific perspective, polygamy is actually very good for the survival of a species. Like Coyne said, "a male could produce large quantities of sperm, and so can potentially father a huge number of offspring, limited only by the number of females he can attract and the competitive ability of his sperm. Eggs are expensive and limited in number, and if a female mates many times over a short period, she does little - if anything - to increase her number of offspring" (156). Considering the Mormon society as a case study, after a man mates with many women and the women have their children, as long as the other Mormons help out to raise the children (since humans need high parental care), then the small number of Mormons suddenly will increase very quickly.
But what about polyandry, Henry Lin? In most cases of polygamy and monogamy, it is the females, as the child-bearers, that invest more energy. As a result, it is logical that the males in these relationships would expend more energy in competition, either through combat or with elaborate displays and physical dimorphisms that might reduce the male’s selective advantage. In contrast, it is logical that in the polyandrous pipefish, where the males carry the eggs and invest more parental care than the females, it is the females that expend energy by being more decorative (Coyne 160).
ReplyDeleteHowever, polyandry (the mating of one female with more than one male) can also have a selective advantage. Campbell mentions on page 1136 that certain species of birds practice polyandry; this is because in animals that engage in external fertilization, the certainty of paternity is much higher. Therefore, the males, which assume a parental role, can be more certain that they improving their reproductive success by caring for their own offspring. (To add to Henry Lin’s example, when a male lion takes over in a new pride, it will often kill all of the cubs of the previous male and fertilize the females, so that energy is not being expended (by the male and females) to care for cubs that do not bear the male’s genes. This also contributes to the idea that “adaptations always increase the fitness of the individual, not necessarily of the group or the species” (Coyne 121)).
Other polyandrous species include bees, ants, and naked mole rats, in which there is only one breeding female, the queen, and many sterile female workers that are often descendents of the queen. In this mating system, the queen is often larger, although she doesn’t necessarily have to compete for a mate.