Monday, April 12, 2010
Don't Judge The Books By Their Covers
On page 159 Coyne further discusses about the theory of sexual selection. In the beginning paragraph, Coyne shows how the socially monogamous species do not actually exhibit the monogamous behavior. This is shown in many aspects of evolution where the initial physical appearance does not exhibit the matching behavior. What would be a reason for the contradiction or rather mismatching? Is there any examples, can be sexual selection or any other parts of evolution, that shows this mismatching? Explain.
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When Coyne talks about species that are “socially monogamous”, he’s saying they appear from the outside like they’re all coupled together with only one partner for life. Revealed in the text, when female and males look less alike there is more chance that they’re not monogamous at all. I’ll explain this reason with the fairy wren example that Coyne discusses. As said above, the fairy wren from the outside looks like it’s completely bonded with its mate for life. From observations of the wren they appear to, “spend their entire adult lives socially bonded to each other, and they codefend their territory and share parental care” (159). The males and females of this species though look very different. The males are blue and black, while the females are a simple gray. When there is a contrast in plumage like this, you have to assume the male must be competing a lot for several females attention. Why would that be though if he only had one mate? This is because in the end the females don’t necessarily reproduce with their mate, but instead reproduce with other males. If the female doesn’t always reproduce with her mate, it would make sense that the male wrens would try to stand out more and shows an increase in dimorphism. Overall when males or females are showing extravagant acts of courtship or showing of disguising features (color birds, big antlers in deer), they are competing for a mate. If they are like geese and ducks where the females and males look more alike, there is more of a chance that the couples are completely monogamous as there is no sexual competition.
ReplyDeleteAnother mismatching of sexual selection would be the reverse roles of seahorses. Many know that male seahorses fertilize and hold the female’s eggs in their pouch, and actually are the one that ends up being pregnant. In result, instead of males competing for females, females are competing for males. Males are the ones that will be carrying the young and there is a competition for a male seahorse that isn’t already carrying someone else’s eggs. The males are also fewer than females and they have to do more of the child bearing. In result, like males of other species, these female seahorses must become colorful and decorative in order to get the attention of a potential male.
Sources:
Why Evolution Is True
http://en.wikipedia.org/wiki/Seahorse
There are several examples, other than sexual selection, throughout nature of where the physical appearance of an organism does not match it's actual behavior. This is the idea of mismatching has proved to be a selective advantage in many cases, such as with animals exhibiting the concept of mimicry. Two main types of mimicry are Mullerian mimicry and Batesian mimicry. Mullerian mimicry is when two harmful species (relatively unrelated) mimic the warning signs of the other. This is advantageous because allows predators to learn the dangers of those species faster. This mimicry does not correspond with the idea that one's appearance is different than its behavior. Batesian mimicry, however, does. Batesian mimicry is when a harmless species mimics the appearance of a harmful species. This dissuades predators from attacking, thus increasing that organism's chance of survival. This idea was proven in an experiment conducted by David Pfenning and William Harcombe who set out to experiment with snake replicas. In North and South Carolina, the scarlet kingsnake (nonpoisonous) and the eastern coral snake (poisonous) both reside. The nonpoisonous kingsnake closely resembles the poisonous coral snake having the same colors and lines. The poisonous coral snake and the nonpoisonous kingsnake overlap in territories of southern North and South Carolina. The experimenters made fake snakes to resemble the nonpoisonous kingsnake (as the experimental variable) and plain brown snakes (as the control) and set them in areas all over the Carolinas. The dependent variable was the percent of total attacks on artificial snakes. In areas where the poisonous coral snakes were absent, 83% of the artificial kingsnakes were attacked and 17% of the brown artificial snakes were attacked. In the areas where coral snakes were present, 16% of the artificial kingsnakes were attacked compared to the 84% of artificial brown snakes. These results show that in areas where predators know the danger of the coral snake, they will also avoid attacking a harmful snake that looks just like it. Where as in an area void of that comparison, predators have not learned to stay away from a "harmless" snake.
ReplyDeleteOther organisms that appear a way different than their actual nature would be Cryptic Katydids which camouflage themselves as leaves, and Hawkmoth larva which takes the appearance of a green parrot snake to keep predators away.
Biology, Campbell
http://en.wikipedia.org/wiki/M%C3%BCllerian_mimicry
http://www.thewildones.org/Animals/camo.html
http://en.wikipedia.org/wiki/Batesian_mimicry
Fidelity vs infidelity
ReplyDeleteMany times, natural selection favors the ornamented female that selectively chooses the right partner to proliferate “good” genes to the offspring (Coyne 161). But sometimes, it is the male that ornamented. But why?
According to Coyne, evolution works to benefit the individual; therefore, some species that are truly monogamous seeks monogamy where the male actually provides extensive parental care, sharing that responsibility with the female. In many birds, while one parent forages for food, the other needs to take care of the little birds, or if not yet hatched, incubate the eggs. Other times, the female may be larger than the male simply because the female needs more energy to produce large eggs (energy costly) – explains such dimorphism in lizards (Coyne 159).
Like what Sara stated with the example of the promiscuous wren, this may be attributed to maintaining the successful passing on of genes. Like the theory of kin selection, individuals may also seek to help out their relatives because in essence, this behavior benefits them at the same time.
Extensive research has led to three classes of monogamy: social, sexual, and genetic. Sexual monogamy is very rare because socially monogamous species also engage in extra-pair copulations; unless certainty of paternity is high, many offspring are raised by someone other than the real “father”. But as a result, gene diversity increases. (source: http://webcache.googleusercontent.com/search?q=cache:bzmFQmHRb5AJ:en.wikipedia.org/wiki/Animal_sexual_behaviour+socially+monogamous+not+actually+monogamous&cd=2&hl=en&ct=clnk&gl=us)
Stephanie’s explanation brings up an important point; like mimicry that benefits an individual or collective group of species, sexual monogamy also seeks to favor and support the choice an animal is able to make on how to “get the best genes.” An article on softpedia.com claims that it is very difficult for an individual to invest its entire reproductive potential on just a single mate, and that is a valid point (source: http://news.softpedia.com/news/Monogamy-is-an-Oddity-42006.shtml).
Therefore, on the surface, it may seem that within species, females and males are being disloyal to one another, but with regards to evolution, it makes sense.