WSS/ Indian Chapter Newsletter Vol 2, No. 2 Sept. 1988
Technical Section
THE GENETIC BASIS OF BEHAVIOlJR
To what extent is animal behaviour genetically determined ? This question has been actively investigated since the time of Charles Darwin and especially since the time of another grandson of Erasmus Darwin namely Francis Galdon who might be considered as the Father of behaviour genetics. lntemst in the genetic control of behaviour has become even more strong with the advent of genetic theories for the evolution of behaviour which is what Sociobiology is all about. That genes influence behaviour has always been obvious, but to put our fingers on single well defined genes which determine well defined dilscrete behaviours has not at all been easy. The ma in reason for this must be that because behaviour is a very complex phenomenon, several genes r..robably act in concert to bring about any kiod of behaviour.
An important exception to this was provided in 1964 by Rothenbuhler's study of
"hygenic" behaviour in the honey bee Apis mellifera (Amer. Zool 4, 111-123). Apis mel/ifera brood is sometimes killed by a disease called "American foulbrood '. Normally worker bees uncap cells and remove diseased pupae and thereby control the spread of infection. Some strains of Apis mellifera, appropriately called "unhyganic", fail to check infection by this metl:iod,
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Rothenbuhler crossed "hygenic" with "unhygenic" bees and discovered two interesting facts:
1. Uncapping of the cells and rerrioval of the diseased brood can be dissociated so that he could produce bees which uncapped fells of disease containing pupae but did not remove them and similarly bees which removed diseased pupae if he uncapped the cells for them.
2. By the familiar genetic technique of back-crossing, Rothenbuhler showed that "hygenic"
behaviour was controlled by two genes, one for uncapping and another for removal of the diseased brood. He also showed that "hygenic" behaviour was dominant over "unhygenic"
behaviour.
Although subsequent studies of this phenomenon have been difficult and there are reasons to believe that the underlying genetic behaviour is probably more complex than Rothenbuhler suspected, 'the genetic control of hygenic behaviour in honey bees' has become a standard text book example. It is rather unfortunate that the "unhygenic" strain could not be maintained and studied further because this was an excellent example of the genetic control of fairly complex behaviour. The situation has now been remedied with the discovery, once again in the honey bee Apis mellifera, of the genetic basis of an even more complex behavioural phenomenon namely "Polyethism" or division of labour. It is well known that honey bee workers share amongst themselves a variety of complex tasks such as nest-building, nursing brood, food, 4
storage, foraging etc. Sharing of work or division of labour is achieved by two means.
Workers change their behavioural roles as they grow older and even within a given age class some. workers are more likely to perform certain tasks than other workers. How is such division of labour brought about? Untill recently behavioural variation among workers was thought to be exclusively environmentally induced. That such behavioural variability among worker honey bees has a genetic basis is the message of two recent pa..,ers published in Nature in May 1988 (G.E. Robinson and R.E. Page Jr., Vol. 333, pp. 356-358 and P. C. Frumhoff and J. Bdker. Vol. 333, pp. 358-361).
Robinson and Page established experimental honey bee colonies by artificially inseminating queen bees such that she produced electrophoretically distinguishable patrilines of daughter.
Then they collected three samples of about 40 bees each from such colonies : the first sample consisted of 'control' bees picked randomly irrespective of what behaviour they were performing;
the second sample consisted of bees which were g:.iarding the nest entrance; and the third sample of bees that were performing the task of clearing the nest of dead bees. By electrophoresing all of these bees, they determined the genetic composition of bees in each group. Repeating his experiment ten times, they came up with the surprising result that the worker bees fathered by some males were more likely to guard the nest while those fathered by a different male were more likely to remove dead bees.
Frumhoff and Baker also set up colonies by artificially inseminating queen bees, but this time the drones used would produce daughters not only distinguishable by electrophoresis but by body colour itself. This made their task simpler and they found that bees of one patriline are significantly more likely to specialise in the task of grooming nest-mates, but such very common behaviours as feeding nest-mates are performed almost equally by both patrilines.
This evidence of the genetic determination of, or atleast genetic pre-disposition for certain behaviours once again makes honey bees an ideal model system for studies on behaviour genetics. More importantly these results might help explain an otherwise perplexing aspect of honey bee biology. The queen bee is known to mate with several males, sometimes as manY as 17 before she returns to the colony and begins her career of egg-laying. Why should the queen create such genetic heterogeneity among her. daughters ? Intuitively on~ might have thought that genetically similar daughters might be more likely to co-operate with each other and make colony life harmonious. If it is true, however, that different genotypes of bees have different propensities for performing different behaviours, then such multiple mating by the queen may be a better way of ensuring efficient colony organisation.
RAGHAVENDRA GADAGKAR Centre for Ecological Science·s. Indian Institute of Science Bangalore-560 012
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