Thursday, April 8, 2010
Fighting for the Females
In chapter 6 "How Sex Drives Evolution," Jerry Coyne suggests that one of two forms of sexual selection occurs through the process of "direct competition between males for access to females" (148). In direct competition, males fight using there adaptations to overcome other males. The victors would have access to the females and be able to reproduce with them. "Selection will favor any trait that promotes such victories so long as the increased chance of getting mates more than offsets any reduced survival. This kind of selection produces armaments: stronger weapons, larger body size, or anything that helps a male win physical contests" (149). Please provide examples of organism that perform direct competition during courtship and explain how their physical adaptations developed.
Subscribe to:
Post Comments (Atom)
Examples of animal species that fight for mates include squids (as we saw in the molluscs video) and northern elephant seals (Baird, 2004).
ReplyDeleteAdaptations like "stronger weapons, larger body size, or anything that helps a mate win physical contests" (Coyne, 2008, 149) obviously increases the likelihood of any individual with the adaptations of survival and reproduction. Therefore, in accordance with the theme of continuity and change, in which traits can be inherited in the form of genes, the fighting adaptations are more likely to be inherited by offspring. There are also non-physical adaptations that have proliferated due to the reproductive success that the adaptations brought. For example, in many species in which males fight for mates, levels of hormones that promote or facilitate fighting are higher during mating season than in the rest of the year (Wright, 2007). The genes that regulate these hormones, and the ways in which the genes are expressed, may be passed down from parent to offspring.
However, superiority in physical strength is not always a direct product of genes. Just as human soldiers undergo military training to improve their fighting skills, many species, such as dogs, engage in play fighting to practice fighting and improve their fighting skills. The pleasure that comes from winning play fights (or thirst for revenge that comes from defeat) encourages individuals to continue play fighting ("Play Fighting", 2009). Thus, behavioral adaptations such as play fighting can lead to greater physical strength.
This comment has been removed by the author.
ReplyDeleteAn example of an animal that performs direct competition during courtship is the polar bear. Male polar bears follow the tracks of a breeding polar bear for around 60 miles. Once the male finds the female, the male will fight for other males competing for the same female polar bear over mating rights. The fights of the polar bear usually resolves in scars and broken teeth (http://www.hickerphoto.com/bear-fight-7807-pictures.htm). The males have to be really strong and really big to win a fight against the other males. The female will want to mate with the male that has won the fight because that would be the strongest male. The female wants a strong male because the female wants her kin to have strong genes like its father. Like Yiding had said in his post, most animals get heir genes from the parents, so a male's strong body probably came from his father who had a strong body.
ReplyDeleteMale polar bears have a polygamous mating system. A polygamous mating system is when "an individual of one sex is mating with several of the other sex" (Campbell 1134). Because the males are always competing for females their entire life, the males have to remain strong after all the fights. It is important for the males to have a large body size and a good immune system to fight off diseases and infections to win a many fights and be able to mate with the female.
Another example are deers. Male deers fight each other for the female of choice. Just like with polar bears, the female will choose the male that wins the fight. The two male deers circle each other and then attack head on. The deers attack each other using their antlers, which grow a few months before mating season and fall off at the end of mating season (http://www.wildanimalfightclub.com/). It is important for male deers to have big antlers so they can win the fight and get the female deer. Like with the polar bear, the male deer probably got his big antlers from his father because they share the same genes.
Like Yiding had said in his post, the idea of adaptions that increase the survival and reproduction rate is associated with the theme continuity and change. Continuity and change relates to when DNA molecules carry biological information from one generation to the next (Campbell ix). Strong genes from the father are transferred into the child so the child will also have good genes. The female will choose the "best" male so their child will have the best genes and will have a better chance of surviving and reproducing.
Stag beetle mating involves intense competition among the males. Once they have found a female to mate with, male stag beetles circle around her with antlers open wide, showing off. When one must compete with another male for a certain female, the two potential courters fight each other using these antlers.
ReplyDeleteSimilarly, male stag beetles use their jaws (mandibles) to fight other organisms desiring a certain mating space.
Both of these portions of stag beetle anatomy are much larger in males than in females. Also, mandibles and antlers are larger in the sexually selected, victorious stag beetles than in the losing organisms. From this information, the conclusion has been drawn that these adaptations came about as a result of sexual selection and a pattern of these larger parts in the winning males. These adaptations relate to the theme of structure and function: because the antlers and mandibles of winning beetles are large, they are better able to fight off opponents and show greater strength.
http://www.ypte.org.uk/animal/beetle-stag-/53
http://www.wildlondon.org.uk/Habitatsandspecies/Species/Londonspriorityspecies/Stagbeetle/tabid/176/language/en-US/Default.aspx