Altruism refers to any behavior by an individual that increases the fitness of another while decreasing their own fitness. Altruism can evolve as a result of benefiting both parties involved, although it may not be immediate for one, in the long run the altruist also benefits. Such an example is seen in vampire bats. They will share acquired blood meals with others who were unsuccessful hunting one evening in securing their own meal. They do this not because they are ‘Kind” and ‘Loving” but instead have ulterior motives. Sharing their meal with those who have none will increase the likelihood that if they were placed in a similar situation one night where food was not found they will secure the same help from those that they have helped in the past. However this behavior will only persist throughout time is if memory and learning also co-evolve. They must have the capability to recognize individuals whom helped and or hurt them in the past. This “learning” mechanism allows there to be a punishment of cheaters and reward to cooperators.
This time of scenario is called the prisoner’s dilemma.
By the prisoner’s dilemma the best way to receive the greatest reward is to be the individual who defects the other and gains all benefits while the other is punished. If both individuals cooperate, the punishment is still present but at a much lower amount along with a small benefit. The latter scenario is thought best for a first-time encounter between altruistic animals who can distinguish between individuals who have helped and punish those who cheated. It is always best to cooperate at the first time encounter although the greater benefit is to defect and run, it will only be advantageous for that particular time. Later on in the future the individual you betrayed will remember and punish you for cheating before by not helping you this time around.
Tuesday, October 27, 2009
Saturday, October 24, 2009
Blog 5: Queen-Worker-Bee Conflict
Explain the conflict between queens and workers. Who wins and why? Are there any exceptions?
There exists and reproductive conflict between worker daughters and their queen mother. In social insects--such as bees--here occurs a very distinct sex-determination system that governs where selective pressure is placed when speaking in terms of reproduction. This system is called haplodiploidy. The father only has one set of genes to pass along, so the probability that an ant will share the same paternal genes as her sister is 100%. So the degree of relatedness for two sisters is:
(1 x ½) + (½ x ½) = ¾.
A typical female bee is genetically more closely related to her sister than to her mother or her daughters. This is why female workers would favor a 3:1 ratio, of producing more sisters rather than their own daughters. But this comes with a caveat-- their mother queen must only mate with one drone in order to ensure greater relatedness between the offspring sisters. If the queen is inseminated by more than one male, selective pressures will shift and cause daughter workers to reproduce their own young, since it guarantees a greater degree of genetic relatedness and therefore greater percentage of genetic fitness.
The queen’s genes however can benefit best if she invests equally in both sexes, supported by Fischer calculations on optimal sex ratios done by Trivers and Hare. Using 20 species of ants, Trivers and Hare estimated sex ratios in terms of investment in reproductives and found a 3:1 female to male ratio. “Workers are running the show for their own benefit.” With this study Trivers and Hare found that it was the workers who “won” the conflict between workers and queen because it was them who had the greatest investment in the offspring.
Since the workers were the ones making the greatest investment in caring for the offspring –they could therefore manipulate the sex ratio towards their benefit, that is, to a 3:1 female : male ratio. Exceptions to this included that in species that have “slaves” (ants from other colonies) caring for the offspring the queen has a greater ability to manipulate the ratios through the slaves since the queen can escape the slaves’ countermeasures because they do not work on her, being that she is totally unrelated to them.
There exists and reproductive conflict between worker daughters and their queen mother. In social insects--such as bees--here occurs a very distinct sex-determination system that governs where selective pressure is placed when speaking in terms of reproduction. This system is called haplodiploidy. The father only has one set of genes to pass along, so the probability that an ant will share the same paternal genes as her sister is 100%. So the degree of relatedness for two sisters is:
(1 x ½) + (½ x ½) = ¾.
A typical female bee is genetically more closely related to her sister than to her mother or her daughters. This is why female workers would favor a 3:1 ratio, of producing more sisters rather than their own daughters. But this comes with a caveat-- their mother queen must only mate with one drone in order to ensure greater relatedness between the offspring sisters. If the queen is inseminated by more than one male, selective pressures will shift and cause daughter workers to reproduce their own young, since it guarantees a greater degree of genetic relatedness and therefore greater percentage of genetic fitness.
The queen’s genes however can benefit best if she invests equally in both sexes, supported by Fischer calculations on optimal sex ratios done by Trivers and Hare. Using 20 species of ants, Trivers and Hare estimated sex ratios in terms of investment in reproductives and found a 3:1 female to male ratio. “Workers are running the show for their own benefit.” With this study Trivers and Hare found that it was the workers who “won” the conflict between workers and queen because it was them who had the greatest investment in the offspring.
Since the workers were the ones making the greatest investment in caring for the offspring –they could therefore manipulate the sex ratio towards their benefit, that is, to a 3:1 female : male ratio. Exceptions to this included that in species that have “slaves” (ants from other colonies) caring for the offspring the queen has a greater ability to manipulate the ratios through the slaves since the queen can escape the slaves’ countermeasures because they do not work on her, being that she is totally unrelated to them.
Tuesday, October 13, 2009
Blog 4: Natural Selection vs. Sexual Selection
Natural Selection is the process by which a slight variation in a trait of an individual increases its likelihood of surviving relative to that of an individual not possessing the trait. Fitness describes an organism’s ability to survive and reproduce viable offspring. It is this second component of fitness (production of viable offspring) that gives sexual selection its relevance in terms of evolution. In contrast to natural selection, sexual selection is not dependent on a struggle for existence between individuals, but instead on a struggle between individuals of the same species and sex (usually males) for possession of the other sex.
In the On the Origin of Species, Darwin elucidates on Natural selection when he says: "It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, wherever and whenever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life." Here he states how Natural Selection is the evolutionary process by which species confer advantages over time and in slight variations. Therefore the slightest differences in structure can turn the scale for the struggle of existence; in turn, individuals possessing advantageous traits will survive and reproduce more. He uses the example of prey hawks and how natural selection gives them. Characteristics of natural selection that differ from sexual selection, by being utilitarian, functional, sensible, economical and constructive.
Sexual Selection is elucidated by Darwin when he discuses “We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.” Here sexual selection is seen as conferring advantages for a particular sex in the SAME species versus the entire population. Its characteristics include showy, elaborate displays that cause a preference for one mate over another and therefore increasing the reproductive fitness of that particular individual who posses that trait. This in turn causes treats preferences as adaptive.
Dawkins takes a similar stance on natural and sexual selection, but tends to make fewer distinctions between the two. He reinforces how the best genes continue and prosper throughout time and are selected for. He further explains since females begin with a disadvantage due to the fact that they invest more in the offspring from fertilization, there in turn must be selective pressure on the males—this comes in the form of sexual selection. Females begin to form preferences for certain males that have certain traits and only those who posses them secure copulations. An example is the domestic-bliss strategy, where females select their males carefully, searching for fidelity and domesticity traits. By insisting a long courtship/waiting period, they weed out casual suitors and only copulates with those who are faithful and will stick around. So here patience is a virtue and their genes for sexual selection will then be passed on to the next generations and will be favored in the gene pool.
In the On the Origin of Species, Darwin elucidates on Natural selection when he says: "It may be said that natural selection is daily and hourly scrutinizing, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good; silently and insensibly working, wherever and whenever opportunity offers, at the improvement of each organic being in relation to its organic and inorganic conditions of life." Here he states how Natural Selection is the evolutionary process by which species confer advantages over time and in slight variations. Therefore the slightest differences in structure can turn the scale for the struggle of existence; in turn, individuals possessing advantageous traits will survive and reproduce more. He uses the example of prey hawks and how natural selection gives them. Characteristics of natural selection that differ from sexual selection, by being utilitarian, functional, sensible, economical and constructive.
Sexual Selection is elucidated by Darwin when he discuses “We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.” Here sexual selection is seen as conferring advantages for a particular sex in the SAME species versus the entire population. Its characteristics include showy, elaborate displays that cause a preference for one mate over another and therefore increasing the reproductive fitness of that particular individual who posses that trait. This in turn causes treats preferences as adaptive.
Dawkins takes a similar stance on natural and sexual selection, but tends to make fewer distinctions between the two. He reinforces how the best genes continue and prosper throughout time and are selected for. He further explains since females begin with a disadvantage due to the fact that they invest more in the offspring from fertilization, there in turn must be selective pressure on the males—this comes in the form of sexual selection. Females begin to form preferences for certain males that have certain traits and only those who posses them secure copulations. An example is the domestic-bliss strategy, where females select their males carefully, searching for fidelity and domesticity traits. By insisting a long courtship/waiting period, they weed out casual suitors and only copulates with those who are faithful and will stick around. So here patience is a virtue and their genes for sexual selection will then be passed on to the next generations and will be favored in the gene pool.
Subscribe to:
Comments (Atom)