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I just learned that all hornets and bumblebees except for the queen die at the end of the year and the queen starts a new nest in spring.

But that means the next generation of queens have only brothers to breed with.

Should this lead to severe inbreeding, which over a couple of years would cause serious problems for survival?

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    $\begingroup$ As far as I know, the drones leave their nests before the end of the season and try to mate with the young queens that arise at the end of the summer. This way there is mixing of genes and also they avoid inbreeding. $\endgroup$ – Chris May 24 '15 at 10:08
  • $\begingroup$ @Chris this should be an answer I think. $\endgroup$ – Jens Schauder May 24 '15 at 10:51
  • $\begingroup$ I can do that, but I have to at least look up where I read this. $\endgroup$ – Chris May 24 '15 at 20:20
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Queens do not generally breed with their brothers, but with males from other nests. In the life cycle of bees (and other social Hymenoptera), new queens are born late in the season along with haploid male drones. These all leave the nest and disperse in the landscape to find mates to reproduce with. After mating, all males die and the queens overwinter to start new colonies next spring. The situation is therefore not all that different compared to other annual, semelparous (single reproductive event) species, since you have population mixing before mating and reproduction.

Here are a couple of mechanisms that bees avoid inbreeding:

  • Population mixing before reproduction (see above).

  • Inbreeding avoidance
    That queens prefer not to mate with close relatives has been shown in several species, see e.g. Foster (1992) and Whitehorn et al (2009).

  • Polyandry
    Each queen generally mates with several males (regulary more than 10 in honey bees, see Palmer & Oldroyd, 2000) and stores their sperm to fertilize eggs during the next year, which means that workers and the queens of next year will have different fathers (increasing genetic variability).

References:

  1. Foster. 1992. Nestmate Recognition as an Inbreeding Avoidance Mechanism in Bumble Bees (Hymenoptera: Apidae). Journal of the Kansas Entomological Society 65(3)
  2. Whitehorn et al. 2009. Kin recognition and inbreeding reluctance in bumblebees. Apidologie, 40(6)
  3. Palmer & Oldroyd. 2000. Evolution of multiple mating in the genus Apis. Apidologie 31(2)
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