QUEEN NUMBER AND GENETIC RELATEDNESS IN A NEOTROPICAL WASP, POLYBIA-OCCIDENTALIS

We found that genetic relatedness among Polybia occidentalis workers was 26 +/- 0.057, a value high enough to make altruistic behavior by workers relatively easy to explain. This comparatively high level of relatedness can be attributed to close relatedness among queens of .57 +/- 0.077 and to great variation among colonies in numbers of queens. The harmonic mean of queen number is 3.1 queens per colony, which is much lower than the arithmetic mean of 10.6 queens per colony. These results are consistency with a colony cycle called cyclical oligogyny, that is characterized by a reduction in queen number from colony initiation to colony reproduction. We did not find any evidence that one or a few queens monopolized egg laying or that there was any inbreeding, both of which have been hypothesized to increase relatedness among workers. Another factor that can increase relatedness among workers and the brood they rear is within-colony segregation on the basis of relatedness. We found that combmate pupae are significantly more closely related to each other (r = .41) than they are to pupae in other combs (r = .33), but we have not investigated whether workers take advantage of these relatedness patterns. This distribution of relatedness among combs will occur if queens do not lay eggs randomly throughout the nest, but concentrate their egg laying on one or a subset of the available combs.