usocial Insects1. The mother, along with individuals that may or may not be directly related, conducts cooperative care of young.
2. A reproductive division of labor evolves from sterile castes which often have certain propensities or characteristics associated with helping behavior.
3. There is an overlapping of generations which allows for the older generations of offspring to help related, younger generations.
Table 1: Examples of Eusocial Insects
| Specifics | Example Species | |
|---|---|---|
| Ants | All ants are eusocial. They have morphologically distinct workers and queens. In some ants, the workers do not even have ovaries. Other workers can lay male eggs. | Fire Ants, Solenopsis invicta Pharoahs ants, Monomorium minimum Carpenter Ants, Camponotus Pseudomyrmex in acacia galls Leaf Cutter Ants, Atta |
| Bees | Many bees are not social at all. | Sweatbees, Lasioglossum Bumblebees, Bombus Honeybees, Apis mellifera Carpenter Bees, Xylocopa |
| Wasps | Some wasps are eusocial, but many are not. | Paper Wasps, Polistes Yellowjackets, Vespula Stenogastrine wasps Tropical Wasps, Epiponines, Polybia |
| Termites | All termites are social. They have male and female workers and, unlike most social insects. are diploid rather than haplodiploid. Often they have a king and a queen. | |
| Aphids and Thrips | Some aphids and thripes are are eusocial. When they form a gall, some soldiers will not reproduce. This form of eusociality tends to be restricted to a few soldiers, because the sterile forms only defend and do not care for the young. Therefore, there is less potential for the development of advanced societies. |
Relatedness and the Origin of Eusociality
Many eusocial insects, including ants, bees, and wasps, are haplodiploid. Therefore, each female has two alleles at a locus, while each male has only one. This leads to a different kin relatedness than that which diploid species exhibit. For example, whereas a diploid female is related to her sister only 1/2, a haplodiploid female is related to her sister 3/4. Other degrees of relatedness are charted below:
Table 2: Genetic Relatedness in Haplodiploid and Diploid Species
| Mother | Sister | Daughter | Father | brother | son | Niece or Nephew | |
|---|---|---|---|---|---|---|---|
| Haplodiploid | |||||||
| female | 0.5 | 0.75 | 0.5 | 0.5 | 0.25 | 0.5 | 0.375 |
| male | 1 | 0.5 | 1 | 0 | 0.5 | 0 | 0.25 |
| Diploid | |||||||
| female | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.25 |
| male | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.5 | 0.25 |
The relatedness differences in haplodiploid species lead to differences in their display of kin selected behavior as compared to diploid species. On the basis of kin selection, eusocial females would be expected to prefer to help their mothers raise their sisters, increasing their indirect fitness, rather than concentrating on increasing their direct fitness by raising their own offspring. This explains why there are sterile castes in eusocial insects; these workers may give up potential direct benefits associated with raising their own children, because indirect benefits are so beneficial. The indirect benefits preference in social wasps can be used as a basis of comparison and analysis of the balance of indirect and direct benefits in other species.
Differences in genetic relatedness among the various individuals within a eusocial colony also make social insects important in the study of parent-offspring conflict. As mentioned above, female haplodiploids benefit from helping raise their sisters which they are related to 3/4. These females, on the other hand, are related to their brothers only 1/4. Therefore, they will prefer for their mothers to have daughters. Since the mother is related to both sons and to daughters 1/2, she will have a tendency to not show preference towards daughters, leading to a conflict of interest between the mother and her daughters.