Martin al., 1997a

This study simultaneously varied experiences of recent victory or defeat, 2-hour familiarity with the meeting place, and hen weight in order to understand their combined effects on the establishment of dyadic dominance relationships between hens not previously acquainted with each other. Three kinds of encounters were arranged: (i) a previous winner unfamiliar with the meeting place met a previous loser familiar with the meeting place (n =28 dyads); (ii) a previous winner met a previous loser, both unfamiliar with the meeting place (n=27); (iii) a previous winner familiar with the meeting place encountered a previous loser unfamiliar with the meeting place (n=28). The weight asymmetry was combined with these three types of encounters by selecting hens showing various weight differences, in favour of the recent loser in 54 dyads and of the recent winner in 29 dyads. Results indicate that recent victory or defeat experience significantly affected the outcome. Even an important weight asymmetry, or familiarity with the meeting place were not sufficient for a hen recently defeated to overcome an opponent that was previously victorious. A 2-hour period of familiarization with the meeting place did not provide any significant advantage over unfamiliarity. Although a significant relationship was found to exist between comb and wattles areas and the initial and final statuses, examination of partial correlations indicates that the influence was from initial status to final status, rather than from comb and wattles to final status. These results suggest that more importance should be attributed to recent social experience in comparison to intrinsic factors in determining dyadic dominance in the hen. Martin al., 1997a file:///C|/Documents and Settings/Administrator/My ...ments/publications/Martin-Beaugrand-Lague-1997a.htm (1 of 17) [12/2/2001 14:24:06] Key-words: Dominance; Agonistic conflict; Weight; Size of comb and wattles; Recent experience of victory and defeat; Site familiarity; Individual differences; Hen; Gallus domesticus. Introduction In the hen, many factors have been reported to influence dominance: the acquisition of sexual maturity (Schjelderup-Ebbe, 1935; Rushen, 1982), success in previous encounters (McBride, 1958; Zayan, 1987), prior residency (Zayan et al., 1983), presence of known individuals (Schjelderup-Ebbe, 1935), and tendency and latency in engaging in conflict (Collias, 1943; Huntington Potter, 1949; Wood-Gush, 1957; Ligon et al., 1990). These factors seem to favour a hen facing an unfamiliar rival. However, severe moulting (Collias, 1943) or defeat in a previous encounter (McBride, 1958; Ratner, 1961; Zayan, 1987) may reduce the chances of a hen being dominant. Comb size and colour attributes may also be important factors in the organization of a dominance hierarchy (Allee and Collias, 1938; Guhl and Ortman, 1953; Ligon et al., 1990; Siegel and Hurst, 1962). Within a breed, comb size and colour reflect the hens' relative blood androgen concentrations (Allee et al., 1939; Collias, 1943; Ligon et al., 1990). Hens displaying a small comb frequently find themselves at the lower end of the hierarchy even if they are heavier than their conspecifics. Body size is most often identified as the best cue for gauging resource holding potential in animal conflicts (RHP; Parker, 1974; Maynard Smith, 1982). Size correlates with strength; it is presumed to be an important factor in conflict outcome. In fish, it has been shown that the larger individuals usually won (Myrberg, 1971; Jakobsson et al., 1979; Francis, 1983; Turner and Huntingford, 1986; Noble, 1939; Braddock, 1945). In hens, the importance of weight has also been studied. However, the picture which emerges is less clear. Murchison (1935) and Guhl and Allee (1944) reported that heavier subjects were more likely to adopt aggressive behaviour and to hold a higher position in the social hierarchy. These findings were later confirmed by Ligon et al. (1990). There is also evidence that body weight correlates with social rank in cocks (Graves et al., 1985). However, Huntington Potter (1949) compared dominance relations in many chicken breeds and concluded that weight differences were not a deciding factor of dominance. These results were more recently confirmed by Bradshaw (1992) who did not find any significant correlation between dominance and body weight in laying hens. The situation is sometimes further complicated by the fact that weight has a tendency to correlate with comb size (Graves et al., 1985; Bradshaw, 1992), which in turn correlates with dominance, thus confounding their respective contribution to dominance. Once the factors which may contribute to dominance have been clearly identified, their relative contribution and possible interactions in affecting RHP merit further consideration. This can be achieved in experiments which seek to vary the factors suspected of affecting dominance in dyadic encounters. Varying previous experiences of victory or defeat as initial individual attributes in a dyadic situation can reasonably be assumed to approximate carry-over effects that may occur in a polyadic situation and which may be due to successive victories or defeats. Numerous studies in fish have sought to simultaneously manipulate experimentally a number of factors. Frey and Miller (1972), Beaugrand and Zayan (1985), Beacham (1988), and Beaugrand et al. (1991, 1996) simultaneously varied many parameters to establish their combined effects. Experiments by Beaugrand and Zayan (1985) and Beaugrand et al. (1991, 1996) have investigated in Xiphophorus helleri the interactions of several factors in dyadic dominance encounters. Previous experiences of victory or defeat, 3-hour familiarity with the meeting place, and size differences were found to predict the dominant Martin al., 1997a file:///C|/Documents and Settings/Administrator/My ...ments/publications/Martin-Beaugrand-Lague-1997a.htm (2 of 17) [12/2/2001 14:24:06] subjects in unacquainted pairs. Moreover, results obtained by Beaugrand et al. (1991, 1996) clearly suggest that previous victory or defeat experience and size can either add or cancel out each other. Though Xiphophorus fish and Gallus are phylogenetically distant, it may be hypothesised that they share not only a common basic dominance mechanism, but also some determining factors as well, namely recent experience, familiarity with the surrounding, and size or weight. In contrast to studies carried out on Xiphophorus, most research in hens has focused on the effects of single characteristics in studies which have precluded the study of their possible interactions. Only a few researchers have investigated the relationship between several factors, mostly in a purely descriptive, non-experimental way (e.g., Collias, 1943; Bradshaw, 1992). The aim of the present study was, therefore, to evaluate the effects of recent victory or defeat experience, with that of familiarity with the meeting site in hen dyads where asymmetries defined by these factors were combined or opposed. Methods Subjects and material