Food-Sharing Behaviour of the Ants Formica Sanguinea and Formica Fusca

[1. The basic distinction in food-sharing is between donor and acceptor responses, which are mutually inhibitory. 2. Whether the donor or acceptor initiates food-sharing depends on the relative strengths of the motivation of the two potential participants. A similar factor determines whether the donor or the acceptor will terminate food-sharing. 3. Food-sharing may be shown in widely different circumstances. It is not possible to locate normally essential sign stimuli specific to these responses, but various stimuli may be facilitatory. 4. Visual stimuli are not important as cues or releasers and blinding does not depress the amount of food-sharing shown. Removal of one antenna does not impede food-sharing, but removal of both (a) depresses the total food-sharing shown and (b) renders ants markedly less successful in attempts to feed. But, even the antennae are not essential. 5. The stimuli which facilitate food-sharing may be divided into those which: (a) Facilitate food-sharing in general, but are not specific to either donor or acceptor behaviour, e.g. the palpating movements, movement itself, colony odour, etc. (b) Facilitate either donor or acceptor responses in particular, e.g. internal stimuli from the crop and chemoreceptors, etc. Some external stimuli, e.g. licking by the other ant, play a minor role. 6. The two forms of palpation may be shown by either donors or acceptors. The hypothesis was advanced that the palpating movements reflect the relative strength of either tendency to donate or tendency to accept food. Antennal palpation is shown at lower levels of motivation than foreleg plus antennal palpation. 7. Experiments were designed to test the hypothesis using both Formica sanguinea and F. fusca. These included study of situations where a high tendency to feed was induced by a period of desiccation and of returned foragers, where the tendency to regurgitate was high. Evidence from behaviour sequences was also used. 8. It was found that the amount of feeding with foreleg palpation increases with increase in the tendency to feed. Antennal palpation accompanying feeding shows a peak at a lower level of this tendency, and is shown at a time when feeding with no palpation or even regurgitation may be shown. Analysis of sequential behaviour in general gives support to the hypothesis. Scrutiny of results for fusca brings out further points of interest and suggests that differences exist in the relations between regurgitation, regurgitation with antennal palpation, and regurgitation with foreleg plus antennal palpation in the two species. Circumstantial evidence is, thus, fairly strong in support of the hypothesis. The expected sequence, moving from a high tendency to feed to a high tendency to regurgitate, would be:- FP →FA → F → R → RA →RF ∥ ←OFFER→ When: FP = foreleg plus antennal palpation associated with feeding FA = antennal palpation associated with feeding F = feeding with no palpation R = regurgitation with no palpation RA = antennal palpation associated with regurgitation RF = foreleg plus antennal palpation associated with regurgitation Offer = offering. There is good evidence to associate offering with regurgitation motivated at the RA level. 9. The function of palpation as a form of facilitatory behaviour is discussed, and the importance of the two types of palpation in feeding and regurgitation is compared. A diagram attempts to summarize the conclusions relating motivation to the different forms of palpation, etc., 1. The basic distinction in food-sharing is between donor and acceptor responses, which are mutually inhibitory. 2. Whether the donor or acceptor initiates food-sharing depends on the relative strengths of the motivation of the two potential participants. A similar factor determines whether the donor or the acceptor will terminate food-sharing. 3. Food-sharing may be shown in widely different circumstances. It is not possible to locate normally essential sign stimuli specific to these responses, but various stimuli may be facilitatory. 4. Visual stimuli are not important as cues or releasers and blinding does not depress the amount of food-sharing shown. Removal of one antenna does not impede food-sharing, but removal of both (a) depresses the total food-sharing shown and (b) renders ants markedly less successful in attempts to feed. But, even the antennae are not essential. 5. The stimuli which facilitate food-sharing may be divided into those which: (a) Facilitate food-sharing in general, but are not specific to either donor or acceptor behaviour, e.g. the palpating movements, movement itself, colony odour, etc. (b) Facilitate either donor or acceptor responses in particular, e.g. internal stimuli from the crop and chemoreceptors, etc. Some external stimuli, e.g. licking by the other ant, play a minor role. 6. The two forms of palpation may be shown by either donors or acceptors. The hypothesis was advanced that the palpating movements reflect the relative strength of either tendency to donate or tendency to accept food. Antennal palpation is shown at lower levels of motivation than foreleg plus antennal palpation. 7. Experiments were designed to test the hypothesis using both Formica sanguinea and F. fusca. These included study of situations where a high tendency to feed was induced by a period of desiccation and of returned foragers, where the tendency to regurgitate was high. Evidence from behaviour sequences was also used. 8. It was found that the amount of feeding with foreleg palpation increases with increase in the tendency to feed. Antennal palpation accompanying feeding shows a peak at a lower level of this tendency, and is shown at a time when feeding with no palpation or even regurgitation may be shown. Analysis of sequential behaviour in general gives support to the hypothesis. Scrutiny of results for fusca brings out further points of interest and suggests that differences exist in the relations between regurgitation, regurgitation with antennal palpation, and regurgitation with foreleg plus antennal palpation in the two species. Circumstantial evidence is, thus, fairly strong in support of the hypothesis. The expected sequence, moving from a high tendency to feed to a high tendency to regurgitate, would be:- FP →FA → F → R → RA →RF ∥ ←OFFER→ When: FP = foreleg plus antennal palpation associated with feeding FA = antennal palpation associated with feeding F = feeding with no palpation R = regurgitation with no palpation RA = antennal palpation associated with regurgitation RF = foreleg plus antennal palpation associated with regurgitation Offer = offering. There is good evidence to associate offering with regurgitation motivated at the RA level. 9. The function of palpation as a form of facilitatory behaviour is discussed, and the importance of the two types of palpation in feeding and regurgitation is compared. A diagram attempts to summarize the conclusions relating motivation to the different forms of palpation, etc.]