Selecting dominants and subordinates at conflict outcome can confound the effects of prior dominance or subordination experience

Abstract

Individuals with a previous experience of dominance are likely to be dominants in further encounters. To test this effect, individuals with a previous experience of dominance are used for the experiments. One way to obtain such individuals is to let opponents «self-select»: encounters between pairs of more or less equivalent opponents are staged and one selects ex post facto the dominant and subordinate from the ensuing conflict. This paper formally shows that the selection of dominant and subordinate animals modifies the dominance probability functions of the two corresponding sub-samples of animals. As a result, the propensity of previous winners to win again and of previous losers to repeat their loss can be attributed to this artefact rather than to prior social experience. A simulation confirms the results of the theoretical analysis. This result has serious methodological implications. When one relies solely on selection to obtain winners and losers, equiprobability is no longer the appropriate null hypothesis against which prior social experience effects have to be tested. To clearly demonstrate the effect of dominance experience, one must show that prior winners defeat neutral opponents in at least of all cases; reciprocally, to show that prior subordinate experience plays a role, prior losers must win in less than of all fights against neutral opponents; finally, to conclude that a combined effect of the two kinds of prior experience is in operation, one must obtain that prior winners defeat prior losers in more than 83% of all planned conflicts. The present result does not imply that experience effects are not at work when the selection procedure is used, but that the procedure used to show their effects is inadequate because effects of experience on a subsequent encounter are confounded with those introduced by statistical selection.

The role of hen's weight and recent experience on dyadic conflict outcome

“…Bégin et al (1996) have demonstrated that in experiments allowing winners and losers to self-select, what appears to be the result of recent experience may actually be caused by uncontrolled differences between individuals on attributes associated with dominance ability. They suggest that by imposing victory or defeat (by retaining only winners and losers that were predicted to win or lose in experimentally rigged contests), such a confounding is most probably reduced.…”

“…This happened in only 24.4% (60/246) of all planned cases, indicating that size superiority combined with residency provided a highly significant advantage at this step of the research (p=q=½, x=60, N=246, P<.001 to a binomial test). This approach ensured that social experience and statistical selection were not confounded effects (Bégin et al, 1996).…”

The role of recent experience and weight on hen's agonistic behaviour during dyadic conflict resolution

“…Nonetheless, comb and wattles size was co-selected with the repartition of the birds into victorious and defeated ones at the issue of rigged contests in which victory and defeat had been correctly forecast. This raises serious questions either about the effectiveness of the control procedure suggested by Bégin et al (1996), or about the generality of co/self-selection in the present domain.…”

“…Its mutual assessment when there is a conflict between two unfamiliar hens is surely influential upon which bird will first attack the other. Bégin et al (1996) have demonstrated that , in experiments allowing winners and losers to self-select, what appears to be the result of recent experience may actually be caused by uncontrolled differences between individuals on attributes associated with dominance ability. They suggest that by imposing victory or defeat by retaining only winners and losers that were predicted to win or lose in experimentally rigged contests, such a confounding is most probably reduced.…”

“…This happened in only 24.4% (60/246) of all planned cases, indicating that size superiority combined with familiarity and absence of handling were a highly significant advantage at this step of the research (p=q=½, x=60, N=246, P<.001 to a binomial test). This approach was followed to ensure that, in the present research, recent victory/defeat experience and statistical selection would not be confounded effects (Bégin et al, 1996).…”