Relationships between fluctuating asymmetry and sexual maturity, social aggressiveness and comb size in chickens

Transcription

1 Arch.Geflügelk., 73 (3). S , 2009, ISSN Verlag Eugen Ulmer, Stuttgart Relationships between fluctuating asymmetry and sexual maturity, social aggressiveness and comb size in chickens Beziehungen zwischen wechselnder Asymmetrie und Geschlechtsreife, sozialer Auseinandersetzung und Kammgröße bei Hühnern J.L. Campo, María Teresa Prieto and Sara García Dávila Manuskript eingegangen am 19. Juni 2008, angenommen am 21. September 2008 Introduction Departamento de Genética Animal, Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria, Madrid, Spain The behavioural and physiological changes associated with sexual maturity are yet not well understood. These changes manifest themselves through various physical attributes that can be quantified. Age at first egg is commonly used in defining female sexual maturity in hens. Comb and wattle size can be used as indicators of reproductive function and to characterize the progression of a flock toward sexual maturity, because their growth is related to the androgen levels in hens as well as roosters (ETCHES, 1996). Changes in stress-related traits accompanying sexual maturity have been very little studied. CAMPO et al. (1999) compared tonic immobility duration and heterophil to lymphocyte ratio in mature and immature pullets and cockerels from two breeds of chickens (Black Castellana and White Leghorn). They found significant differences between groups of females, mature hens showing shorter tonic immobility and higher heterophil to lymphocyte ratio than immature hens; the duration of tonic immobility was significantly longer in the mature group of males, and the heterophil to lymphocyte ratio was not significantly different between groups of males. It may be interesting to indicate that FORKMAN and CORR (1996) found that hens mated with symmetrical wattle males laid more eggs, whereas no effect was found for wattle asymmetry of hens on egg production. On the other hand, chickens use aggression to establish a dominance hierarchy within social groups, and behaviours such as increased aggression have been associated with stress in poultry and other animals. MARSTELLER et al. (1980) found that the correlations between behavioural (agonistic encounters, social rank) and physiological (plasma corticosterone level, antibody response to red blood cell antigen) variables were low. JONES (1996) indicated that animals with short duration of tonic immobility or low plasma corticosterone level adopt an active fighting strategy when challenged. CAMPO et al. (2005), did not find significant relationships between social aggressiveness of cocks, based on dominant-subordinate paired encounters, and heterophil to lymphocyte ratio or tonic immobility. MOLLER (1992), and SWADDLE and WITTER (1994), have investigated the relationship between social dominance rank and asymmetry in swallows and starlings, respectively. As alternatives to dominance relationships, birds use comb and body sizes (indicators of the amount of male hormone present and strength, respectively) as signal of status or fighting ability in the formation of dominance orders, avoiding costly contests (CLOUTIER et al., 1996; PAGEL and DAWKINS, 1997). The objectives of the current study were to analyse the relationships between the fluctuating asymmetry, a criterion for measuring levels of stress and welfare of animals (PARSONS, 1990), and onset of sexual maturity, social aggressiveness, or comb size (an indicator of male quality) in chickens. It would be hypothesized that birds with early sexual maturity, high social aggressiveness, and large comb size would show less asymmetrical morphological traits than birds with late sexual maturity, low social aggressiveness, and small comb size. As far as the authors know, these relationships have not been studied yet. Materials and Methods General procedure Different Spanish breeds of chickens (Black-Barred Andaluza, Black-Red Andaluza, Blue Andaluza, Black Castellana, Buff Prat, White Prat, Red-Barred Vasca, Red Villafranquina, Black Menorca, White-Faced Spanish, and Birchen Leonesa), a synthetic breed (Quail Castellana), a White Leghorn population (CAMPO and JURADO, 1982), and the e y tester line (SMYTH, 1976) were used in the current study. Andaluza and Castellana are white shell egg layers, whereas Prat is a tinted shell egg layer and Vasca and Villafranquina are brown and dark brown shell egg layers. Menorca and White-Faced Spanish are two classical ornamental breeds, and Leonesa is used to produce hackles and saddles for the fishermen. The synthetic breed originated from an F 2 cross between Black Castellana and Buff Prat (CAMPO and OROZCO, 1986; CAMPO, 1991). All these 14 breeds are maintained at the Experimental Station of El Encín (Madrid, Spain) in a conservation program of genetic resources started in 1975 (CAMPO and OROZCO, 1982) and have been described by CAMPO (1998). In each experiment, birds from all the breeds were reared together in an all-litter floor pen (9 20 m) at a density of 10 birds/m 2 until 8 wk of age (mixed sexes). Artificial light was only provided during the first week of age (23L:1D). Temperature was controlled with gas heaters (33 35 C at the chick level during the first week fol-

2 194 Campo et al.: Fluctuating asymmetry, sexual maturity, aggressiveness and comb size lowed by a reduction of 3 C each week until the temperature reached C at the sixth week of age). Birds were reared in another all-litter floor pen (13 20m) at a density of 6 birds/m 2 from 8 to 18 wk of age. The lighting regime was 8L:16D. Birds were fed standard rearing diets, containing 19% CP, 2,800 kcal ME/kg, 1% Ca, and 0.5% available P, until 8 wk, and 15% CP, 2,700 kcal ME/kg, 0.9% Ca, and 0.4% available P, until 18 wk. Feed and water were supplied for ad libitum consumption. At 18 wk of age, cocks from each breed were housed separately in pens with a raised (30 cm from the ground) slatted floor covering a dropping pit and straw litter on the rest of the floor; the slatted area occupied approximately one-third of the floor. The number of cocks was 50 in each breed, bird density being 4 birds/m 2. In experiment 1, hens from each breed were housed separately in pens with perches and nest boxes (one nest per five hens) at 18 wk of age; the number of females was 100 from each breed. The pens had a raised slatted floor covering a dropping pit and straw litter on the rest of the floor; the slatted area occupied approximately one-third of the floor. Bird density was 4 birds/m 2. The lighting regime was 14 h light:10 h darkness (light from 7.00 to 21.00) and room temperature was C. Birds were fed standard laying diet, containing 16% CP, 2700 kcal ME/kg, 3.5% Ca, and 0.5% available P. Feed and water were supplied for ad libitum consumption. Feeders, drinkers, and nest boxes were in the slatted floor area. The measured morphological traits were both right (R) and left (L) middle toe length, leg (metatarsus) length, wing (radius) length, wattle length, and leg width. Right and left values of an animal were taken during the same session. All four lengths and leg width were measured in millimetres using a digital calliper. Trait size was the mean of the right and left traits [(R+L)/2]. All traits showed normal frequency distributions. The fluctuating asymmetry for a trait was defined by the absolute difference between sides [ R L ]. A series of steps (PALMER, 1994; KNIERIM et al., 2007) was followed before identifying exhibited asymmetry as fluctuating asymmetry (FA; normal distribution of signed right minus left differences with a mean of zero), because there are several confounding factors that complicate the analysis of asymmetry (details can be found in CAMPO et al., 2008). First, the presence of directional asymmetry (DA; normal distribution with a non-zero mean) and antisymmetry (AS; non-normal distribution with a mean of zero) were tested by inspecting the distribution of (R L). The presence of DA was tested by using a t-test: significant value of the mean (R L) divided by its standard error. Departures from normality (e.g., AS) were assessed using skewness and kurtosis measures; AS is characterized by bimodal (or broad-peaked) distributions, tending to be platykurtic (more intermediate values than the normal distribution). Second, FA and measurement error are normally distributed over a mean of zero. Thus, it is essential to show that the variance in asymmetry observed between individuals is greater than the variance due to measurement error; the FA is often small and sometimes of the same magnitude as measurement error. The effect of measurement error was calculated from a sub-sample of 20 birds randomly selected and measured three times on three different days. These repeated measurements were analysed using a two-way analysis of variance (LEAMY, 1984) with side (fixed) and bird (random) as main factors (1 and 19 df), their interaction (19 df), and the measurement error (80 df). Significant variation between sides indicates variation in DA, whereas a significant interaction indicates significant FA (in the absence of AS). Finally, the product-moment correlation between FA and trait value was used to determine if they were independent. If a positive relationship was found between the mean value and the asymmetry of a trait, this effect would be removed by dividing the absolute asymmetry score by the trait mean, defined as the relative FA: [2 R L /(R+L)]. Relative fluctuating asymmetry for all traits had distributions that were not normal and were transformed to arc-sin square root prior to analysis. Mean relative asymmetry was defined as the mean of the relative asymmetries of the different traits. Experiment 1 (fluctuating asymmetry and sexual maturity) Cockerels from six different breeds (Black-Barred Andaluza, Black-Red Andaluza, Black Castellana, Buff Prat, White Prat, and White Leghorn) were used. Pullets were sampled from the Black Castellana, Black-barred Andaluza, and Blue Andaluza breeds, and the e y tester line. A total of 122 cockerels and 126 pullets from two different replicates (hatches) separated by 14 days were used to study the association of sexual maturity and fluctuating asymmetry at 20 weeks of age. Group 1 (mature birds) consisted of the 61 cockerels (31 and 30 in each replicate, respectively) and 63 pullets (32 and 31 in each replicate, respectively) which showed early sexual maturity, as indicated by the presence of comb and wattles with large size in males and by the lay of the first egg in females. The number of cockerels was 20, 15, 9, 7, 5, and 5 in the Black Castellana (11 and 9 in each replicate), Black-Barred Andaluza (7 and 8 in each replicate), Black-Red Andaluza (5 and 4 in each replicate), Buff Prat (2 and 5 in each replicate), White Prat (3 and 2 in each replicate), and White Leghorn (3 and 2 in each replicate) breeds, respectively. The number of pullets was 31, 20, 7, and 5 in the e y (14 and 17 in each replicate), Black-Red Andaluza (11 and 9 in each replicate), Black Castellana (5 and 2 in each replicate), and Blue Andaluza (2 and 3 in each replicate) breeds, respectively. Group 2 (immature birds) consisted of 61 additional cockerels and 63 additional pullets (randomly selected) with late sexual maturity, as indicated by comb and wattles with small size in males and the lack of laying in females. The number of sampled birds was equal to that of Group 1: 20, 15, 9, 7, 5, and 5 cockerels in the Black Castellana (11 and 9 in each replicate), Black-barred Andaluza (7 and 8 in each replicate), Black-red Andaluza (5 and 4 in each replicate), Buff Prat (2 and 5 in each replicate), White Prat (3 and 2 in each replicate), and White Leghorn (3 and 2 in each replicate) breeds, respectively, and 31, 20, 7, and 5 pullets in the e y (14 and 17 in each replicate), Black-red Andaluza (11 and 9 in each replicate), Black Castellana (5 and 2 in each replicate), and Blue Andaluza (2 and 3 in each replicate) breeds, respectively. The data for each sex were analyzed separately. Experiment 2 (fluctuating asymmetry and social aggressiveness) Nine breeds (Black-Barred Andaluza, Black-Red Andaluza, Black Castellana, Buff Prat, Black Menorca, White-faced Spanish, Birchen Leonesa, Red Villafranquina, and White Leghorn) were used. We used a total of 81 cocks to study the association of social aggressiveness and fluctuating asymmetry at 36 weeks of age. Cocks were sampled on nine different days (blocks), with each block including nine different cocks (one for every breed). Relative social aggressiveness, based on dominant-subordinate relationships, was determined by observing each male in each block in eight randomly paired encounters in a neutral cage (36 encounters per block), and expressed as a percentage of encounters won (fighting ability). Arc sin square root transformation was used for analysis. Prior to

3 Campo et al.: Fluctuating asymmetry, sexual maturity, aggressiveness and comb size 195 the encounters, cocks were kept in individual cages. In a typical situation, one individual initiated or threatened an attack and the other fought back, ran away, or signalled submission. The birds were scored over a 5-minute period for latency to start of fighting and whether if they initiated the fight or not. Fights, once decided were not allowed to continue. Experiment 3 (fluctuating asymmetry and comb size) Six breeds (Black Castellana, Buff Prat, Red-Barred Vasca, Red Villafranquina, Quail Castellana, and White Leghorn), were included in this experiment. A total of 120 cocks from two different replicates (hatches) separated by 14 days were used to study the association of comb size and fluctuating asymmetry at 36 weeks of age. Group 1 consisted of 60 cocks (30 in each replicate), randomly selected, showing large comb size (10 cocks of each breed, 5 of them in each replicate). Group 2 consisted of 60 additional cocks (30 in each replicate), randomly selected, with small comb size (10 cocks of each breed, 5 of them in each replicate). Statistical analysis To test the differences in fluctuating asymmetry between groups (experiments 1 and 3), a 3-way analysis of variance (SOKAL and ROHLF, 1981) was used with the statistical model x ijkl = µ + G i + B j + GB ij + r k + Gr ik + Br jk + GBr ijk + ijkl, where x ijkl is the analyzed measurement (fluctuating asymmetry), µ is the overall mean, G i is the effect of group (mature vs. immature in experiment 1, and large vs. small comb size in experiment 3), B j is the effect of breed (j = 1 4 in females and j = 1 6 in males in experiment 1; j = 1 6 in experiment 3), r k is the effect of replicate (k = 1 2), GB ij, Gr ik, Br jk, and GBr ijk are the interactions, and ijkl is the residual (the number of birds in the individual subclasses was unequal in experiment 1, l ranging from 2 to 17; l = 1 5 in experiment 3). Group and breed were considered fixed effects and replicates were assumed to be a random effect. There were no significant differences among replicates or their interactions, and they were pooled with the residual to give a 2-way factorial model of group and breed effects (x ijk = µ + G i + B j + GB ij + ijk ). Significant differences among breeds were estimated using the Student-Newman-Keuls multiple-range test (SNEDECOR and COCHRAN, 1980). A randomized-block design was used to analyze the effect of breed in experiment 2, according to the following model for a 2-way analysis of variance with one replicate per breed per block: x ij = µ + B j + b j + ij, where x ij is the analyzed measurement (fluctuating asymmetry or relative social aggressiveness), µ is the overall mean, B i is the effect of breed (j = 1 9), b j = the effect of block (day of sampling; j = 1 9), and ij is the residual. Correlations between relative social aggressiveness (x) and fluctuating asymmetry (x ) of each cock (r x x ) were calculated from the residual variances (var x and var x ) and covariances (cov x x ): r x x = cov x x /(var x var x ) 0.5. The SAS statistical package, GLM procedure, was used for data analysis. Results Fluctuating asymmetry and sexual maturity (experiment 1) Mean values indicating the effect of sexual maturity on fluctuating asymmetry for males and females are summarized in Table 1 and 2, respectively. Group effect was significant (P < 0.05) for the relative asymmetry of wattle length and the combined relative asymmetry of the five traits in males and females, the relative asymmetry of immature birds being larger than that of mature birds. In males, there was no significant group by breed interaction for any relative asymmetry, indicating consistent differences between mature and immature birds. Breed effect was significant (P < 0.01) for the relative asymmetry of leg width, the mean value being larger in the Black-Barred Andaluza than in the other breeds, and for the combined relative asymmetry of the five traits, the mean value being larger in the Black-Barred Andaluza than in the Black-Red Andaluza breed. In females, there was no significant breed effect or group by breed interaction. Wattle length was significantly different (P <0.001) between the mature group and the immature group of males Table 1. Mean relative asymmetry (x 100) of various morphological traits in mature and immature males from six breeds (experiment 1; n = 122) Mittlere relative Asymmetrie (x 100) verschiedener morphologischer Merkmale bei geschlechtsreifen und nicht geschlechtsreifen Hähnen aus sechs Rassen (Versuch 1; n = 122) Effect Toe length Leg length Wing length Wattle length Leg width Combined Sexual maturity Mature b b Immature a a Breed White Leghorn b 2.54 ab Black Castellana b 2.60 ab Black-Barred Andaluza a 3.22 a Buff Prat b 2.66 ab White Prat b 2.39 ab Black-Red Andaluza b 1.93 b Error mean square

4 196 Campo et al.: Fluctuating asymmetry, sexual maturity, aggressiveness and comb size Table 2. Mean relative asymmetry (x 100) of various morphological traits in mature and immature females from four breeds (experiment 1; n = 126) Mittlere relative Asymmetrie (x 100) verschiedener morphologischer Merkmale bei geschlechtsreifen und nicht geschlechtsreifen Hennen aus vier Rassen (Versuch 1; n = 126) Effect Toe length Leg length Wing length Wattle length Leg width Combined Sexual maturity Mature b b Immature a a Breed Black Castellana Blue Andaluza e y Black-Red Andaluza Error mean square Table 3. Mean values (mm) of various morphological traits in mature and immature males and females (experiment 1; n = 122 and n = 126) Mittelwerte (mm) verschiedener morphologischer Merkmale bei geschlechtsreifen und nicht geschlechtsreifen Hähnen und Hennen (Versuch 1; n = 122 und n = 126) Sex Toe length Leg length Wing length Wattle length Leg width Males Mature a a a a a Immature b b b b b Error mean square Females Mature a Immature b Error mean square (Table 3), mature males showing greater length than immature males. Additionally, toe length, leg length, wing length, and leg width differed significantly (P <0.001) between the mature group and the immature group of males. Only wattle length was significantly different (P <0.01) between the mature group and the immature group of females, mature females having greater length than immature females. Fluctuating asymmetry and social aggressiveness (experiment 2) Male relative aggressiveness was negatively and significantly (P < 0.05) correlated with relative fluctuating asymmetry of leg length (r = 0.27) and the combined relative asymmetry of the five traits (r = 0.24). Correlation between relative aggressiveness and relative fluctuating asymmetry of toe, wing, and wattle lengths, and leg width was not significantly different from zero ( 0.20, 0.03, 0.14, and 0.08, respectively). There were significant differences (P < 0.05) among breeds for relative social aggressiveness (Table 4), whereas the effect of block (sampling day) was not significant. Cocks from the Black Castellana breed were the most aggressive, with more than 1/3 of the encounters won. They differed significantly from cocks of the Red Villafranquina and Buff Prat breeds, which were the least aggressive (those from the Prat breed lost all their encounters). Cocks of the Black-Red Andaluza breed showed significant greater (P < 0.05) relative fluctuating asymmetry of leg length than those of the Buff Prat breed. No significant differences were found among breeds for relative fluctuating asymmetry of toe length, leg width, wing length, wattle length, and the combined relative fluctuating asymmetry of the five traits. Fluctuating asymmetry and comb size (experiment 3) Males with large comb size had significantly (P <0.01) greater relative asymmetry than males with small comb size for leg width (Table 5). There was no significant group

5 Campo et al.: Fluctuating asymmetry, sexual maturity, aggressiveness and comb size 197 Table 4. Relative social dominance (percentage of paired encounters won) and relative fluctuating asymmetry of various morphological traits in males from nine breeds (experiment 2; n = 81) Relative soziale Dominanz (Anteil gewonnener Begegnungen) und relative wechselnde Asymmetrie verschiedener morphologischer Merkmale bei Hähnen und Hennen aus neun Rassen (Versuch 2; n = 81) Breed Relative dominance Toe length Leg width Leg length Wing length Wattle length Combined Black Castellana a ab White-Faced Spanish ab ab Black-Barred Andaluza ab ab White Leghorn ab ab Black Menorca ab ab Birchen Leonesa 8.33 ab ab Black-Red Andaluza 6.94 ab a Red Villafranquina 5.55 b ab Buff Prat 0.00 b b SEM Table 5. Mean relative asymmetry (x 100) of various morphological traits in males with large and small comb size from six breeds (experiment 3; n = 120) Mittlere relative Asymmetrie (x 100) verschiedener morphologischer Merkmale bei Hähnen mit großen und kleinen Kämmen aus sechs Rassen (Versuch 3; n = 120) Effect Toe length Wing length Wattle length Leg width Combined Comb size Large a 2.42 Small b 2.35 SEM Breed Black Castellana 2.75 a ab 2.44 b 2.22 b Red-Barred Vasca 2.38 ab b 3.79 ab 2.12 b White Leghorn 2.29 ab ab 3.23 ab 2.33 b Red Villafranquina 2.27 ab ab 2.86 b 2.40 b Quail Castellana 1.93 ab a 5.08 a 3.03 a Buff Prat 1.34 b ab 4.29 ab 2.22 b SEM by breed interaction, and breed effect was significant (P < 0.05) for the relative asymmetry of toe length and the combined relative asymmetry of the five traits, and for wattle length and leg width (P < 0.01). The relative asymmetry of toe length was larger in the Black Castellana than in the Buff Prat breed, whereas the Quail Castellana had larger relative asymmetry than the Red-Barred Vasca breed for wattle length, the Red Villafranquina and Black Castellana breeds for leg width, and the other breeds for the combined mean value of the five traits. Since group by breed interaction was significant for the relative asymmetry of leg length (P < 0.05), subclass means are summarized in Table 6. The effect of comb size varied from breed to breed, differences between comb sizes being significant in 3 breeds. In 2 of these breeds (Black Castellana and Buff Prat), relative asymmetry of leg length was significantly greater in males with large comb size and smaller in males with small comb size, the opposite being true in the other breed (Red-Barred Vasca). In the large comb size group of males, there were no significant differences among breeds in terms of relative asymmetry, although the Red-Barred Vasca had significant greater relative asymmetry than the Black Castellana breed in the small comb size group of males. Discussion There were significant differences in relative fluctuating asymmetry of wattle length and the combined relative fluctuating asymmetry of the five traits between mature and immature males (experiment 1), the immature group

6 198 Campo et al.: Fluctuating asymmetry, sexual maturity, aggressiveness and comb size Table 6. Mean relative asymmetry (x 100) of leg length in males with large and small comb size from six breeds (experiment 3; n = 120) Mittlere relative Asymmetrie (x 100) der Beinlänge bei Hähnen mit großen und kleinen Kämmen aus sechs Rassen (Versuch 3; n = 120) Comb size Breed Large Small Black Castellana 0.74 a 0.27 b,y Red-Barred Vasca 0.57 b 0.96 a,x White Leghorn xy Red Villafranquina xy Quail Castellana xy Buff Prat 0.88 a 0.57 b,xy a-b Means within the same breed with no common superscript differ (P < 0.05). x-y Means within the same comb size with no common superscript differ (P <0.05). having 36% and 12% greater relative fluctuating asymmetries than the mature group of males, respectively. Similarly, the difference in relative fluctuating asymmetry of wattle length and the combined relative fluctuating asymmetry between mature and immature females was significant, relative values being 60% and 26% greater in the females with late sexual maturity than in the females with early sexual maturity. This fact agrees with the changes in the tonic immobility reaction and the heterophil to lymphocyte ratio, another two stress-related indicators, reported by CAMPO et al. (1999). In this way, birds with symmetrical wattles had early sexual maturity, and females might have a better egg production, although FORKMAN and CORR (1996) did not find significant effect for wattle asymmetry of hens on egg production. Similarly, MOLLER (1994) found that swallow females with more asymmetric tails started laying later than symmetric females. The fluctuating asymmetry for wattle length was estimated confidently, and it was not confounded with measurement error (CAMPO et al., 2008). As expected, toe length, leg length, wing length, wattle length and leg width were significantly greater in the mature group than in the immature group of males (42% approximately the wattle length and ranging from 4 to 7% the other traits), whereas wattle length was the only trait significantly greater (27% approximately) in the mature females compared with the immature females, suggesting that the morphological changes associated with the sexual maturity are bigger in cockerels than in pullets, and confirming that wattle size can be used to characterize the progression toward sexual maturity in both sexes (ETCHES, 1996). A significant but relative small negative correlation was found between cock relative social aggressiveness and relative fluctuating asymmetry of leg length and the combined relative fluctuating asymmetry of the five traits (experiment 2), indicating that aggression is associated with stress, and that levels of aggression are more pronounced among males with less asymmetrical legs. On the contrary, MARSTELLER et al. (1988) and CAMPO et al. (2005) reported that birds were not significantly stressed by social rank, using three different stress indicators (plasma corticosterone level, and tonic immobility reaction and heterophil to lymphocyte ratio, respectively). SWADDLE and WITTER (1994) found a positive relationship between social dominance rank and asymmetry of wing feathers in starlings, the most asymmetric birds being the most dominant, although MOLLER (1992) reported no relationship between social dominance and asymmetry of tail feathers in swallows. The fluctuating asymmetry for leg length was estimated confidently, and it was not confounded with measurement error (CAMPO et al., 2008). There was no significant association between relative aggressiveness and wattle size, one of the better indicators of male hormone output (the correlation coefficient between relative aggressiveness and wattle length was r = 0.09). This fact might suggest that birds do not use wattle size as signal of status or fighting ability in the formation of dominance orders, as indicated by CLOUTIER et al. (1996), and PAGEL and DAWKINS (1997) for comb and body sizes. In the current study, the associations between relative aggressiveness and leg length or wing length were not either significant (r = 0.01 and 0.15, respectively). Cocks from the Buff Prat and Red Villafranquina were less aggressive than cocks from the other breeds, and significantly from those of the Black Castellana. This finding suggests that birds from Spanish breeds which lay tinted or brown eggs might be more placid and have a decrease in their levels of aggression than those from Spanish breeds laying white eggs. There was significant difference in relative fluctuating asymmetry of leg width between males with large and small comb size (experiment 3), the former having greater relative fluctuating asymmetry than the latter. However, fluctuating asymmetries of toe length, wing length, and wattle length were not associated with comb size. In addition, fluctuating asymmetry of leg length was positively associated with comb size in two breeds (Black Castellana and Buff Prat) and negatively in one breed (Red-Barred Vasca). These results do not support the use of fluctuating asymmetry to predict adult male quality (as indicated by the comb size), as suggested by MOLLER (1990). This author found a negative relationship between asymmetry and mating success in swallows. Since the Red-Barred Vasca is the only dual purpose breed (brown eggs and meat) in the study, it might be suggested that in this genetic background the asymmetry in leg length is an useful indicator of the cock quality. In conclusion, results of the current study show that fluctuating asymmetry of wattle length and the combined relative fluctuating asymmetry of the five traits indicates male and female reproductive quality at the onset of sexual maturity, and that this association is consistent (there was no significant group by breed interaction). Success in male to male competition appears to be associated with by fluctuating asymmetry of leg length and the combined relative fluctuating asymmetry of the five traits. On the contrary, fluctuating asymmetry does not indicate adult male reproductive quality (only fluctuating asymmetry of leg width was significant and consistent, that of leg length being an useful indicator of cock quality in the Red-Barred Vasca breed). Summary The purpose of the present study was to analyse the relationship between fluctuating asymmetry of several traits (middle toe length, leg length, wing length, wattle length, and leg width), sexual maturity, social aggressiveness, and comb size in chickens (experiments 1, 2, and 3, respectively). In experiment 1, cockerels (n = 122; 20-week-old) from five Spanish breeds and a White Leghorn population,

7 Campo et al.: Fluctuating asymmetry, sexual maturity, aggressiveness and comb size 199 and pullets (n = 126; 20-wk-old) from three Spanish breeds and the e y tester line, which show early or late sexual maturity, were used. There was a significant difference between mature and immature birds on the relative fluctuating asymmetry of wattle length and the combined relative fluctuating asymmetry of the five traits (P < 0.05), the relative fluctuating asymmetry of immature birds being larger. In experiment 2, we measured the fluctuating asymmetry and the relative social aggressiveness in 36-week-old cocks (n = 81) from eight Spanish breeds and the White Leghorn population. There was a significant negative correlation between cock relative social aggressiveness and relative fluctuating asymmetry of leg length and the combined relative fluctuating asymmetry of the five traits (P < 0.05). In experiment 3, cocks (n = 120; 36-week-old) from four Spanish breeds, the White Leghorn population and a synthetic breed, which showed large or small comb size, were used. There was a significant difference between large and small comb size birds on the relative fluctuating asymmetry of leg width (P <0.05), the relative fluctuating asymmetry of large comb size birds being larger. In addition, relative fluctuating asymmetry of leg length was positively associated with comb size in two breeds (Black Castellana and Buff Prat) and negatively in one breed (Red-Barred Vasca). Results show that fluctuating asymmetry indicates male and female reproductive quality at the onset of sexual maturity, and that success in male to male competition appears to be associated with fluctuating asymmetry. On the contrary, fluctuating asymmetry does not indicate adult male reproductive quality. Key words Chicken, fluctuating asymmetry, sexual maturity, social aggressiveness, comb size Zusammenfassung Beziehungen zwischen wechselnder Asymmetrie und Geschlechtsreife, sozialer Auseinandersetzung und Kammgröße bei Hühnern Das Ziel der Studie war die Untersuchung der Beziehungen zwischen wechselnder Asymmetrie verschiedener Merkmale (Länge der Mittelzehe, Beinlänge, Flügellänge, Länge der Kehllappen, Beindurchmesser) und der Geschlechtsreife, der sozialen Auseinandersetzung sowie der Kammgröße bei Hühnern (Versuche 1, 2 und 3). In Versuch 1 wurden Hähne (n = 122; Alter 20 Wochen) von fünf spanischen Rassen und eine Population Weiße Leghorn sowie Junghennen (n = 126; Alter 20 Wochen) von drei spanischen Rassen und einer e y Testlinie, die entweder frühe oder späte Geschlechtsreife aufwies, verwendet. Die relative wechselnde Asymmetrie der Kehllappenlänge und die kombinierte wechselnde Asymmetrie der anderen fünf Merkmale waren zwischen den geschlechtsreifen und den nicht geschlechtsreifen Tieren signifikant unterschiedlich (P < 0,05), wobei die wechselnde Asymmetrie bei den nicht geschlechtsreifen Tieren höher war. In Versuch 2 wurde die wechselnde Asymmetrie und die relative soziale Auseinandersetzung bei 36 Wochen alten (n = 81) Hähnen aus acht spanischen Rassen und einer Population Weiße Leghorn untersucht. Zwischen der relativen sozialen Auseinandersetzung und der relativen wechselnden Asymmetrie der Beinlänge sowie der kombinierten relativen wechselnden Asymmetrie der anderen fünf Merkmale wurde eine signifikant negative Korrelation geschätzt (P < 0,05). Im dritten Versuch wurden Hähne (n = 120; Alter 36 Wochen) aus vier spanischen Rassen, einer Population Weiße Leghorn und aus einer synthetischen Linie, die entweder große oder kleine Kämme besaß, verwendet. Hier konnte ein signifikanter Unterschied zwischen den Hähnen mit kleinen und mit großen Kämmen im Hinblick auf die relative wechselnde Asymmetrie des Beindurchmessers ermittelt werden (P < 0,05), wobei die relative wechselnde Asymmetrie bei den Hähnen mir großen Kämmen ausgeprägter war. Ferner stand die relative wechselnde Asymmetrie der Beinlänge bei zwei Rassen (Schwarze Kastilianer, Buff Prat) in einem positiven Zusammenhang und bei einer Rasse (Rot-Gestreifte Vasca) in einem negativen Zusammenhang zur Kammgröße. Die Ergebnisse belegen, dass die wechselnde Asymmetrie bei Hähnen und Hennen die Reproduktionsleistung beim Eintritt der Geschlechtsreife vorhersagen kann. Ferner scheint der Erfolg bei einer Auseinandersetzung zwischen Hähnen mit der wechselnden Asymmetrie in Zusammenhang zu stehen. Allerdings ermöglicht die wechselnde Asymmetrie keine Aussagen über die Reproduktionsleistung der Hähne. 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