Monday, March 15, 2010
Asexual vs. Sexual Reproduction
In the chapter entitled “How Sex Drives Evolution,” Coyne discusses the evolution of sexual reproduction. On pg. 155-156, Coyne begins to explain the evolutionary advantages of both asexual and sexual reproduction. Expand on Coyne’s list of reasons one type of reproduction is more advantageous than the other using outside knowledge from class. Furthermore, when do organisms that can reproduce in both manners reproduce asexually? When do they reproduce sexually? What does this demonstrate about the two methods of reproduction?
Subscribe to:
Post Comments (Atom)
Sometimes, asexual reproduction is more advantageous than sexual reproduction. As Coyne says, "Any individual who reproduces sexually sacrifices 50% of its genetic contribution to the next generation compared to an individual who reproduces asexually" (155). In other words, the offspring won't be an exact copy of the parent.
ReplyDeleteThe reason why an organism would want to reproduce asexually is to reproduce faster than reproducing sexually. For example, molds are able to spread across food more quickly if they reproduce asexually than sexually. Campbell says that "molds typically grow rapidly and produce many spores asexually, enabling the fungi to colonize new sources of food” (640). It takes more time for sexual reproduction than asexual reproduction because during sexual reproduction, a mold's mycelia has to meet with a + and – mycelia. Otherwise, there is no genetic exchange.
However, there are times when molds choose to reproduce sexually. When molds are done eating away at the food and need to colonize some other food, then they have to do sexual reproduction to be able to find new substrates.
Organisms that reproduce both asexually and sexually demonstrate that there are different reasons for choosing which way to reproduce. If an environment is favorable, asexual reproduction is the fastest way to go. However, if environments are not the same, then sexual reproduction is advantageous because it allows for that powerful asset of sexual reproduction.
Thematically, whether an organism performs sexual or asexual reproduction depends on how the environment regulates its lifestyle. If the environment is favorable, then that’s a green light for asexual reproduction. However, the environment will begin to regulate the mold’s lifestyle when the environment is not inhabitable anymore.
As Henry stated, if an organism has a choice, then asexual reproduction will take place when the environment is favorable, and sexual reproduction will take place when there is a need to adapt.
ReplyDeleteSexual reproduction relates to the theme of evolution by facilitating adaptation. The main advantage of sexual reproduction is that sexual reproduction "might promote faster evolution to deal with aspects of the environment that are constantly changing" (Coyne, 2009, p. 156) by increasing genetic diversity. Each offspring created by sexual reproduction has a unique set of genes. While asexual reproduction, in favorable conditions, would rapidly produce large numbers of offspring that are suitable for living in the current environment, a population of offspring produced asexually, unlike a population of offspring produced sexually, would be less prepared for changes in the environment, as the sexually produced population, with more genes, has a higher chance of having at least one individual with the correct genes to adapt to changes in the environment. The adapting gene then proliferates as the individual with the gene reproduces and individuals without the gene die.
The Red Queen hypothesis, which emerged in the 1980s, is a hypothesis that demonstrates the importance of sex. Just as Alice from Alice in Wonderland was instructed by the Red Queen to run as fast as she could just to stay in the same place, species need to constantly evolve just to maintain the status quo in terms of rate of survival and reproduction. For example, pathogens have protein "keys" that bind to recognition protein "locks" on the external membranes on the surface of target cells in order to take advantage of the target cell. Pathogens are constantly changing, producing individuals with different keys. If the target organism were to reproduce asexually, then the locks on the target cells would remain the same from one generation to the next, and eventually a day will come when a pathogen with the key that fits into the target organism's lock (which can consequently cause disease in the target organism) emerges. To fight against the pathogen, the target organism needs to evolve to produce new locks that are not compatible with existing keys, and in order to target the target organ, pathogens need to evolve to produce new keys that might open the target cells' locks. As large animals such as humans are unable to mutate their DNA via mechanisms like conjugation or transformation, sexual reproduction is essential in accelerating evolution and helping the target species maintain the upper hand (or at least parity) with the pathogen in this competition (Ridley, 1993, p. 3).