If anyone is still interested, the results of my OCD searching:

QUOTED MATERIAL

Inbred drones

The drone is a good subject to use for investigating the occurrence of non-genic inbreeding effects. Drones result from unfertilized eggs, and therefore get only a single copy of the mother-queen genome.

During development, they multiply their set of chromosomes per cell which results in highly polyploid tissue (i.e. with many sets of chromosomes per cell). Only a few tissues, such as the sperms, remain haploid in drones. Hence inbreeding depression, resulting from a decrease of genetic variability, would have no effect in drones if only gene interactions are the source of inbreeding depression. On the other hand, if drones show a depressive response to inbreeding, this must be due to factors other than genes.

During a four-year experiment, we produced six inbred lines of Apis mellifera carnica by instrumental insemination. We established five levels of inbreeding in each line. Using a 'piggy back' technique the inbred queens were wintered in non-inbred colonies; the non-inbred vigour of these colonies lead to fewer losses than from colonies with inbred workers which hence have reduced vitality. Despite this precaution. often more than 80% of queens were lost during the winter. Drones produced by inbred queens were tested for their reproductive capacity, physiological performance (resistance to extremes in temperature), and the activity of key enzymes in their haemolymph, to quantify their fitness.

The results show that there are severe inbreeding effects in drones which affect their fitness; inbred drones showed a worse flight performance than non-inbred drones -- they made fewer flights and these were of shorter duration. Also, the number of sperm produced by inbred drones decreased dramatically as the level of inbreeding increased.

Clearly, inbreeding does effect the behaviour, physiology and metabolism of drones. In all cases workers showed a stronger inbreeding effect than drones. This difference can be interpreted as the genic inbreeding depressive effect which is additional to the cytoplasmatic effects.

EXCERPTED FROM:

MORITZ RFA (1986): The origin of inbreeding depression in honeybees. Bee World 67: 157-163

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