Transition to Group Living

cyanobacteria that divide into nitrogen fixers and photosynthetic cells. In these cases, the division of labor favors the organism. All symbiotic relationships involve division of labor. Anytime that division of labor is more efficient, this will be the favored relationship.

Cells that have aggregated need to communicate with one another. One of the things that can complicate this is that there can be cheaters” that signal dishonestly or that don t respond to signaling efforts. This means that the communication must be honest. Signaling mechanisms cannot be easily faked and must be costly to fake. Both the sender and receiver must share common interests.

There also must be minimal conflict between the different cells in a group. The goal of cooperation and minimal conflict is maximization of the fitness of the entire group. In the case of workers in a cooperative, conflict can be avoided if the helping worker is just as related to another worker s offspring as if it had the offspring itself. In other cases, competition is repressed, as is seen in some bee colonies where workers destroy the eggs laid by other workers.

In some cases, a cooperative group can break up but the individuals can still reproduce. This would not be an advantage that favors mutual dependence. Mitochondria, for example, cannot reproduce by itself if separated from the cell. Termite queens can t reproduce if the workers don t cooperate. The thing that most favors mutual dependence is extreme division of labor. Exactly how this occurs isn t known.

TRANSITION TO GROUP LIVING

What about organisms—plants, animals, or others—who live in a group setting? Why do they do this and why to animals help each other out when it is costly to their own survival? Some animals are inherently asocial. These include polar bears and mosquitoes. Others are very social. These include wolves, who live in packs, and fish, who live in schools. Ants, bees, wasps, and termites are the most social of all animals because they live in tightly woven colonies.

Social behavior can be very adaptive, meaning that increases the fitness of the parts, usually through improved reproductive success. Social behavior can provide protection against predators. Think about bird flocks, schools of fish, and herds of wildebeests, which can escape predators by living in groups. It basically decreases the odds of any one organism getting killed by a predator.

There are risks and benefits to forming social groups. One of the benefits happens when one organism does something to aid another. This is called altruism. With altruism, there is some

cost to the organism providing the help or at least there is a potential cost. This happens in squirrels, when one squirrel cries out to warn others about a predator. Sharing nesting space and raising another s young are also examples of altruism. There is an individual cost but an overall advantage to the group.

When a group of vampire bats, for example, involve those that get food and those that don t after a hunting expedition, those that get food share it with those that don t. This is an example of both altruism and reciprocity. Reciprocity means that, on another expedition, the one who previously gave food to others will, at another time, be the receivers of food. Bats who don t share are less likely to get fed at a later date.

Because of kin selection, the same bats are more likely to share with relatives than with nonrelatives. This allows researchers to see the relatedness of different bats in a group. The advantage to kin selection is that there is an increased chance of the donor s DNA getting passed from one generation to another.

Eusocial animals are those that live in colonies. In these types of colonies, only a few of the members have the opportunity to reproduce. These include the naked mole rate, certain reefdwelling shrimp, termites, ants, some bees and some wasps. It is a feature of these colonies that they usually produce large numbers of offspring and the benefit is greater than it would be if the individuals had the opportunity to reproduce themselves. There are often large structures for these organisms, which is where they live. These colonies are well-defended and tend to do very well.