Concept/Content kin selection, inclusive fitness / honeybees
Information caption The outcome of kin selection is well illustrated by honeybees (Apis melifera). Each hive is typically dominated by one large "queen" bee that reproduces. The other bees are her offspring. While also female, they are sterile and work in the hive supporting their sisters, rather than mating on their own. This behavior reflects the bees' distinctive genetics. The queen is haploid, the female workers (and males) diploid. Paradoxically from a human perspective, workers are more closely related to their sisters (75%) than to their own children (50%)! When a honeybee dies defending the hive, she increases the chances that the queen and her many sisters the lineage expressing her traits all continue. Through indirect kin selection, the helping behavior, while costly, increases her inclusive fitness. Many other insects exhibit similar genetics and, not surprisingly, also similar social organization.
Inquiry caption Honeybees, and many wasps and ants, along with naked mole rats from eastern Africa include individuals that do not reproduce. Rather, they contribute to the reproduction of a single individual in a social setting. The failure to perpetuate one's own lineage seems to contradict the principle of natural selection. But consider the more inclusive lineage of collateral relatives. Contributions to the survival and reproduction of kin may well outweigh the individual's own. Costly helping traits might be preserved and proliferate through relatives, not direct offspring. Natural selection would be indirect: kin selection. The benefits would depend, of course, on the degree of relatedness, or the likelihood that the helping genes were passed on through relatives. How much genetic information does an individual share with its offspring? —with its siblings? —with its siblings' offspring? —with its cousins? Using this information, what combination of benefits to others would (genetically) outweigh one's own cost?
The genetics of honeybees, pictured here, are unlike humans'. Females are diploid, while males are haploid (developing from unfertilized eggs). Accordingly, a female is generally 75% related to her sisters, 50% to her own offspring and brothers. How would you expect this to affect the natural selection of helping and reproductive behavior in females?
[Honeybee hives are indeed composed of groups of cooperating sisters, or workers, all descended from a common mother, the "queen bee". Males are not part of the hive. The female workers are sterile.]
Target Concept: Some cases of costly helping are explained by genetic relatedness.
Photographer Waugsberg
Credit public domain [wikipedia]
SIZE in pixels [file size] 670x446

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