Behavior of Ants
It is often argued whether ants and other social
insects are altruistic in their contribution to the colony rather than
trying to reproduce and directly pass on their own genes to their offspring.
Yes, they seem to be altruistic, in they are helping their sisters at
their own expense without directly passing on their genes. No, they aren't
altruistic, in that they are passing on their own genes by allowing the
colony to survive and expand to new colonies. This type of natural selection
is called Kin Selection. Genes are selected in nature according to their
ability to contribute to the success of the species. If an altruistic
gene helps a colony to survive, then that gene will be passed onto kin
which will in turn have the altruistic gene that will help that colony
survive. If the gene for altruism works against the success of the colony
then the individuals with the gene will not be successful and the gene
will be selected against.
One possible explanation for kin selection arises from the fact that all
workers are females. It turns out that the workers are more closely related
to each other than they would be to their own offspring. This means that
they are more successful in making more genetically similar individuals
by helping the colony than by having their own offspring.
Specifically, males arise from unfertilized eggs so they have only a half
complement of genes, all from their mother. Female workers arise from
fertilized eggs and therefore have a full complement of genes of which
half come from their mother and half come from their father. Workers always
get the exact same half of their gene complement from their father since
he only has a half to begin with. Workers are, therefore, at least fifty
percent related to each other since half of their genes always come from
their father. Workers can end up with either half of their mother's genes
which means that they will be on average 75 percent related to each other.
If the workers did have the opportunity to reproduce, (which they don't),
the best they can do is to contribute 50 percent of their genes to their
Ants need to be able to communicate for an array of reasons.
The following is a list of the 12 major reasons for communication that
researchers have identified (Holldobler and Wilson, p. 227).
- Simple attraction
- Recruitment, as to a new food source or nest site
- Grooming, including assistance at molting
- Trophallaxis (the exchange of oral and anal liquid)
- Exchange of solid food particles
- Group effect: either facilitating or inhibiting a given
- Recognition, of both nestmates and members of particular
castes, including (broadly) discrimination of injured and dead individuals.
- Caste determination, either by inhibition or by stimulation.
- Control of competing reproductives
- Territorial and home range signals and nest markers
- Sexual communication, including species recognition,
sex recognition, synchronization of sexual activity, and assessment
during sexual competition.
The majority of communication seems to be chemical. Ants also tap each
other, feel each other out with their antennae, straddle each other to
give certain messages, and grasp and stroke each other as well.
One gland, the pygidial gland on the gastor, is used to lay down trails
for the same individual or for others to follow in the same track. It
also seems to be used to warn colony members of danger and as a pheromone
to attract fellow foragers to food sites. In fire ants, the Dufour's gland
is the source of trail- laying chemicals. Some trail pheromones can last
several days. In leaf cutter ants, they may create a main trunk trail
leading away from the colony only to branch out in several directions
a short distance later. They continue to branch out like arteries to capillaries
until single ants are foraging for leaf material. When they obtain their
leaf fragment, they turn around follow their pheromone trail back along
the path to the main trunk and then the colony.