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Social variables and divergent selection for mating behaviour of male chickens (Gallus domesticus)
Anim. Behav.,1974,22, 390-396 SOCIAL
VARIABLES
BEHAVIOUR
AND
OF MALE
DIVERGENT CHICKENS
SELECTION
FOR
MATING
(CALLUS DOMESTICUS)
BY W. T. COOK* & P. B. SIEGEL
Poultry Science Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 Abstract. Heterosexual or unisexual contact of juvenile males from two lines divergently selected for male mating frequency, and a control line had little, if any influence on their subsequent mating behaviour. The interaction of lines • social environments for mating behaviour was not significant, showing that lines responded in a similar manner to the environments. It is hypothetized that selection for low cumulative number of completed matings (CNCM) was primarily for higher neural thresholds, whereas selection for high CNCM affected loci operative after neural thresholds are attained. The magnitude of the sexual component of a court was found to be dependent on the genetic background of the population, being less in the low mating than in the high mating line. of the high mating (HM), low mating (LM) and control (AC) lines. The sole selection criterion in the HM and LM lines was the cumulative number of completed matings (CNCM) by a male in eight 10-rain observation periods. Details of selection procedures and responses were given for the HM and LM lines by Siegel (1965, 1972), and the control population was described by Hess (1962). Chicks were hatched 31 March 1970, sexed and reared in heterosexual flocks until 42 days of age. At this age males were randomly assigned to one of the following social environments: (A) Reared with females of the same three lines and age to 206 days of age; (B) Reared in all-male flocks of eight to ten individuals to 196 days of age, then placed with females of a comparable age until 206 days of age, i.e. 10 days with females after the first 42 days; (C) Reared in all-male flocks of eight to ten individuals to 210 days of age, i.e. 0 days with females after the first 42 days. Males in environments A and B were maintained in unisexual flocks of five to eight males each between 206 and 210 days of age. Females were obtained from the same lines as the males, and lines were intermingled in both unisexual and heterosexual flocks. Forty-two days was chosen as the age to randomize males into environmental groups because cockerels separated from females at 58 days of age and maintained in individual cages, mated significantly less than those separated at later ages (Siegel & Siegel 1964). It was thus assumed that mating experiences of males are quite limited during the first 42 days posthatching. Five sexing errors (pullets erroneously
The role of the social environment of juvenile cockerels on subsequent mating behaviour has been studied by several investigators. WoodGush (1958) and Kruijt (1971) reported that males reared either in isolation or in unisexual flocks successfully mated with females as adults. Guiton (1966), however, observed that cockerels maintained in isolation during the first 46 days post-hatching preferred the gloved hand of the experimenter to a female model. The study of mating behaviour should include consideration of both genetic and environmental variables, and possible interactions between them. Artificial selection to change the mating behaviour of male chickens was used by Wood-Gush (1960) and Tindell & Arze (1965) who observed differences between selected lines in the S 2 generation. The design used by Wood-Gush permitted prior heterosexual experiences, whereas the males used by Tindell & Arze were limited to visual and auditory contact with females. Siegel (1965, I972) conducted a divergent selection experiment for mating ability in which he utilized a random bred control as the base population for the selected lines. Selection was made from males reared in unisexual flocks from 8 weeks of age until tested with females at 31 weeks. Each of the selected lines was significantly different from the unselected control by the S 5 generation. Reported here is an experiment designed to evaluate the influence of prior heterosexual contact on the subsequent mating behaviour of males from the selected and control lines. Methods Subjects were obtained from the S 12 generation *Present address: Allied Mills Industries Poultry Ltd., SummerHill, N.S.W. 2130. 390
COOK & SIEGEL: MATING BEHAVIOUR. IN MALE CHICKENS classified as cockerels) were noted between 42 and 105 days of age. When found in an all-male flock, the pullet was immediately removed from the pen. The unisexual male flocks were maintained in visual and tactile isolation from the heterosexual flocks (A and B), each of which consisted o f two males that were randomly assigned to a group of seven to ten females. Measurements
The signal-response sequence of mating behaviour in chickens was outlined by Guhl (1969). The first component of the sequence is the court of the female by the male. The female either crouches or attempts to avoid the court. Crouching may be followed by a mounting, treading, and a completion of the mating, in that order. At any stage during the sequence either the male or female may terminate the process. The mating behaviour of all males was measured during a 16-day interval commencing at 210 days of age. The procedure used followed that of Siegel (1965). Cockerels were tested singly with flocks of six to eight pullets (from environment A) of the same age. Traits measured included the selection criterion, cumulative number of completed matings (CNCM), plus courts (C), mounts (M), treads (T), and crouches received (CR) during seven 10-rain observation periods. Besides these behaviours, additional criteria included CR/C (percentage of courts eliciting a crouch), M/CR, M/C, T/M, CNCM/T, CNCM/ M, C N C M / C R and CNCM/C. All ratios were expressed as percentages which were then converted to Freeman-Tukey arc sines as recommended by Mosteller & Youtz (1961) when there are less than fifty observations per experimental
391
unit. Square roots transformations were made for M, T, CNCM, and CR to alleviate the problem of heterogeneous variances. Aualyses
Correlated chi-square analyses (Jensen, Beus & Storm 1968) were used to compare the number of males completing and not completing at least one mating. Since comparisons were made between environments within lines and between lines within environments, the number of correlated tests ~- was two. Males from environments A and B were combined into one group to obtain adequate sample sizes for analyses. The results of the chi-square analyses suggested that the quantitative data be summarized in two ways: first, with all males included in the analysis (method I) and, second, with only those males completing at least one mating (method II). Both analyses were least squares, multivariates w i t h fixed effects for a 3 • 3 factorial plan (Kramer & Jensen 1970) modified for unequal sample sizes. The model for a completely randomized design was: Y~jk = Ix + Mi Jr Ss + (MS)~j -[- eijk where, Y~jk is the kth observation of the ith male line and jth social environment. Simultaneous confidence limits were used to isolate significant differences among means for each trait (Morrison 1967). Only courts, mounts, treads, CNCM, crouches CNCM/C, CR/C, and M/C were included in the first analysis (method I) which involved all males. The other characters which were percentages (e.g. CNCM/T), were not analysed by method I because, with the exception of four individuals, cockerels that did not complete at
Table I, Comparisons* Between and Within Lines for Proportions of Males Completing and Not Completing at Least One Mating
Lines Social environment
(flock)
Unisexual
Mating activityt
CM no CM
Heterosexual P
CM
no CM
HM
AC
LM
P
22 0
24 11
12 16
0.025
19 1
32 3
15 8
0.025
no test
0.05
NS
*Between-line comparisons are across rows within social environments and within-line comparisons are in columns between social environment. tCM and no CM denotes the number of males completing and not completing at least one mating in seven 10-min test periods.
ANIMAL
392
BEHAVIOUR,
22,
2
LM line. This relationship between the H M and LM lines existed regardless of the length o f time the males spent in heterosexual flocks. Within the AC line, significantly more of the males reared in heterosexual flocks completed at least one mating than did those maintained in unisexual flocks. However, for the LM line the proportion of males completing and not completing a mating, was not significantly different for those reared with or without pullets. The contrasting results of the A C and LM lines suggest a line • social environment interaction. Analyses were not possible within the H M line since all males, except one, completed at least one mating. Although the experimental designs were not the same, the results for our unselected AC controls were somewhat different from those of Wood-Gush (1958) and Kruijt (1971). They found that the proportion of leghorn and jungle fowl males reared in isolation that successfully copulated was similar to the proportion for males
least one mating did not elicit a crouch. Thus, it was impossible to calculate CNCM/T, CNCM/M, C N C M / C R , M/C, and T/M for males that did not mate. All traits were analysed by method II which involved males completing at least one mating. All possible phenotypic correlations between courts, mounts, treads, CNCM, and crouches were calculated within each line. Correlations of C N C M with CNCM/C, CR/C, M/CR, M/C, CNCM/M, C N C M / T and C N C M / C R were also calculated. The F statistic was used to determine if each correlation coefficient was significantly different from zero. Results and Discussion Qualitative Data
Chi-square comparisons between and within lines for proportions of males completing and not completing at least one mating are shown in Table I. There were significant differences among lines with an excess of H M males completing at least one mating compared to those from the
Table H. Numbers, Means, and Standard Errors of Behaviours for the Social Envirormtents(0,10 and 168 Days with Females) by Methods I and H
Method I Behaviour*
Method II
0
10
168
0
10
168
85
25
53
59
20
48
Courts (C)
69.1 4- 4"0
88.0 4- 7.4
65.7 4- 5.1
74.5 4- 4-7
102.24- 8.0
70.3 4- 5.2
Mounts(M)
9.8 • 0.9
11.4 4- 1.6
10.7 4- 1.1
11.2 :~ 1.2
14.0 4- 2-0
11.7 4- 1-3
Treads (T)
8.0 4- 0,7
8-8 4- 1.3
9-3 4- 0-9
9.3 • 1.0
10.8 4- 1.6
10.1 -4- 1.1
CNCM
7.0 5:0.6
8.0 4- 1.2
8.5 • 0.8
8.1 4- 0.8
9.8 • 1.5
9-2 4- 0"9
Crouches (CR)
10.2 4- 0.9
12.1 4- 1'7
10.9 4- 1.2
11.7 ~ 1.2
14.6 d: 2.1
11.9 t 1-4
CR/C
11.4 :k 1.4
10.8 t 2.1
12.5 4- 1"5
22.4 4- 1.5
14.3 4- 2"3
14.0 4- 1.5
M/C
10.8 d: 1-4
10.0 d: 2.7
12.3 d: 1,4
15-1 ~: 1.4
14.0 d: 3.1
13.8 ~ 1.4
7.5 4- 1.0
7-4 ~ 1.6
9.8 4- 1.6
10-6 • 1.0
9.8 -4- 1-8
11.0 4- 1-7
M/CR
89.6 ~ 3"0
92.3 d: 4-5
96.5 q- 1.5
TIM
81.7 ~ 3.2
81.1 -b 4-9
87.1 4- 3.2
CNCM/T
81.9 • 3-7
94.6 4- 2.0
90.6 4- 3.0
CNCM/M
73.2 4- 3"6
77.3 d: 5.3
83.0 4- 3"4
CNCM/CR
67.1 4- 3"9
71-9 4- 6'2
82.2 ~ 2-8
Nt
CNCM/C
*All ratios expressed as percentages. No significant differences(P<0.05) were found among social environments by either method of analysis. tNo. of males.
COOK & SIEGEL: MATING BEHAVIOUR IN MALE CHICKENS reared in all-male flocks. It is interesting to n o t e that a l t h o u g h stocks used in the three studies were diverse, the absolute percentage for males reared in unisexual flocks c o m p l e t i n g at least one m a t i n g was similar (65 per cent in ours, 75 to 100 p er cent in Kruijt's a n d 70 p e r cent in Wood-Gush's).
393
o f male m a t i n g b e h a v i o u r during the test periods. Line effects, method L There were significant differences a m o n g lines for m o u n t s, treads, C N C M an d crouches. M e a n s were largest for the H M line an d smallest for the L M line. Values for the r a n d o m bred co n t r o l were intermediate a n d significantly different f r o m those o f the selected lines (Table III). T h e selected lines, while significantly different f r o m each other for courts a n d M / C , did n o t differ significantly f r o m the A C controls. M e a n s f o r C R / C and C N C M / C were significantly larger in the H M line t h a n in the L M a n d A C lines. Th e means f o r these t w o b e h a v i o u r patterns in the A C line, while intermediate to t h o se for the selected lines, were n o t significantly different f r o m those o f the L M line.
Quantitative Data Line x social environment interaction. Multivariate analyses revealed that the in te r a c ti o n o f lines by social e n v i r o n m e n t s was n o t significant for each behaviour. Results were the same f o r b o t h m e t h o d s I and II, showing t h a t the influence o f the three social e n v i r o n m e n t s on the quantitative behaviours was similar f o r all lines. Effects of social environment. T h e r e were no significant differences a m o n g social environments for an y o f the behaviours measured. This was consistent for b o t h m e th o d s o f analysis (Table II) a n d implies that the time spent as juveniles in heterosexual or unisexual flocks h a d little influence on the quantitative expression
Line effects, method IL A l t h o u g h the n u m e r i c a l ranks o f the lines were the same f o r m e t h o d s I and II, the significance o f differences between lines changed f o r m o s t traits (Table III). T h e differences in courts between the H M an d L M
Table HI. Numbers, Means, and Standard Errors of Behaviours for the HM, AC, and LM Lines by Methods I and II Method I Behaviour*
Method II
HM
AC
LM
HM
AC
LM
nt
42
70
51
41
56
30
Courts (C)
93"8 • 6"4b
75"8 4- 5"0ab
53.1 • 5"6a
99'3 4- 6"3a
80"7 • 5.0a
66"9 4- 6"9a
Mounts (M)
19.5 Jz 1"4e
8-4 • 1.1 b
3-9 4- 1"3a
20"6 q- 1"6b
9"9 4- 1.2b
6-4 4- 1"8a
Treads (T)
15'8 t 1"2c
7"2 • 0'9 b
3"1 4- 1'0 a
16.6 4- 1"2b
8'4 4- 1"0b
5"2 -4- 1.4a
CNCM
14-1 4- 1"0e
6.6 • 0"8b
2.8 4- 0"9a
14"8 4- 1.1 b
7.7 • 0"9ab
4-7 4- 1"2a
Crouches (CR)
20"3 4- 1-5c
8-8 4- 1"Ib
4"0 4- 1"3a
21.5 4- 1"6a
10"1 4- 1"2a
6"6 4- 1-8a
CR/C
22.6 • 1.3b
9"4 4- 0"4a
5.6 4- 1"4a
23"I • 1"3a
11"4 4- 0"5a
10"6 4- 2-2a
M/C
21.6 • 1"4b
9.2 4- 0"5ab
5"4 4- 1.4a
22"2 4- 1"3a
10.8 4- 0"5a
10-2 4- 2"2a
CNCM/C
15"1 4- 1"1b
6"8 4- 0"8a
4.1 4- 0"9a
16-3 4- 1"1a
8"1 4- 1"Ia
7.7 4- 1"5a
M]CR
95"7 4- 1"3a
88"9 4- 3-5a
79.4 + 2"2a
T/M
82"9 • 2-3a
81.1 4- 3.8a
90"7 4- 3"7a
CNCM/T
89"6 4- 1"9a
83"1 4- 3"9a
92'5 4- 3"9a
CNCM/M
75"4 4- 2"8a
76"0 4- 4"0a
84"3 4- 5"0a
CNCM/CR
72"7 4- 3"0a
70"7 4- 4"2a
81"4 4- 5"4a
*All ratios are expressed as percentages. Lines within a method of analysis with the same superscript are not significantly different (P<0"05). tNo. of males.
394
ANIMAL BEHAVIOUR,
lines were no longer significant when the analysis was based on only those males that completed at least one mating (method II). Males of the LM line mounted and treaded significantly less than those from the AC and HM lines which were not different from each other. Although the AC controls were no longer significantly different from both the HM and LM lines for the selected trait, CNCM, the latter two lines remained significantly different. This indicates that elimination of non-maters raised proportionally the level of CNCM in both the AC and LM lines, but not in the HM line. This is congruent with the excess of nonmaters found in the AC controls relative to the HM line and the excess of non-maters found in the LM line relative to the AC controls. Interpretation of line effects. McCollom, Siegel & Van Krey (1971) proposed that bidirectional selection for CNCM modified both the neural and endocrine influences on mating behaviour. They suggested that the neural system may be primary to the behaviour and that endocrine responses are only observable after the neural threshold is reached. Further support for this hypothesis was presented by Cook, Siegel & Hinkelmann (1972). The results of the present experiment provide additional support for this hypothesis, and also suggest that selection for low CNCM has elevated neural thresholds to a level that prevents a sizable proportion of males from completing at least one mating. The CNCM for the LM line was still significantly lower than that for the HM line even after the removal of non-maters, suggesting that selection for low CNCM has also influenced loci other than those which modify neural thresholds. The evidence suggests that selection for low CNCM has acted primarily upon a set of loci that alter neural thresholds such that males are not likely to mate, and secondarily upon a set of loci that lowers CNCM in those that do mate. This does not, however, imply that the two sets of loci are independent of each other. It can also be hypothesized that selection for high CNCM was initially for those males with low neural thresholds, since there was a greater proportion of non-maters in the AC controls than in the HM line. An extension of the hypothesis of McCollom et al. (1971) would suggest that selection in the HM line has primarily affected alleles that are operative once the neural threshold has been attained and simultaneously altered the frequency of alleles at loci which lower the neural thresholds for CNCM.
22, 2
Natural selection might be expected to have aided the second set of loci, and, thus, artificial selection for high CNCM may have primarily influenced the first set. This is consistent with the crossing experiment by Cook et al. (1972) who observed that alleles of the loci affected by selection for low CNCM (i.e. those raising neural thresholds) were dominant to those influencing the response to selection for high CNCM. Alleles at the latter loci were relatively more additive in effect. These relationships suggest that selection for high CNCM may have primarily affected those loci whose effects are phenotypically expressed only after the neural thresholds are attained, and secondarily, influenced neural thresholds. Although the pattern was the same, the significance of differences among lines for courts was not consistent with that found for the selected trait, CNCM. This concurs with the hypothesis of GuM (1969) and Kruijt (1966) that courtship behaviour in chickens has a dual role, that is, both agonistic and sexual. Cook et al. (1972) have indicated that the inheritance of courts is different from that for CNCM, and Siegel (1972) obtained a genetic correlation of 0.45 between them. Mounting and treading, in contrast to courting, are integral components of the signal-response sequence that leads to a completed mating. The close association of these with CNCM is evident in Table II by the high percentage of CNCM/M and CNCM/T. The low percentage of CNCM/C relative to those for CNCM/M and CNCM/T also demonstrates the closer association of both mounting and treading to CNCM than to that between courting and CNCM. The significantly lower CNCM/C for LM males in comparison to HM males by method I and the absence of differences by method II suggest that courts by LM males were either ineffectual sexual stimuli or were used to assert their dominance over the females. Although qualitative data were not available, the waltz was the more frequent display during courtship in the LM line. Wood-Gush (1956) suggested that the waltz display represents a conflict within the cock between aggressive and sexual tendencies and shows that the sex drive is temporarily weak or inhibited. The absence of significant differences between lines for CNCM/M and CNCM/T (Table II) conflicts with the results of McCollom et al. (1971) and may be due to the method of analysis. They used a univariate analysis which considers
COOK & SIEGEL: MATING BEHAVIOUR IN MALE CHICKENS
395
Table IV. Phenotypie Correlations for Mating Behaviours by Lines* HM M C M T CNCM
0-66
T
CNCM CR
0 " 6 0 0 " 6 0 0"65 0.95 0'88 0.99 0.97 0"92 0"85
AC M 0.52
T
CNCM
LM CR
0 " 5 2 0"55 0"56 0-97 0 . 9 5 0.99 0"99 0'96 0"94
M 0"28
T
CNCM
CR
0"29 0 " 3 0 0"29 0.99 0.98 0"99 0"99 0"99 0.98
*dffor HM, AC, and LM lines were 1 and 40, 1 and 70 and 1 and 51, respectivelyfor the F statistic. All correlations were highly significant (P<0'01), except for those involving courts in the LM line which were not significant(P<0"05). each trait independently; whereas, we employed a multivariate analysis which considers the lack of independence of the traits, thus providing a more rigorus test of differences among lines. Interrelationship of Qualitative and Quantitative Data The qualitative data for AC controls may be interpreted to suggest that, had juvenile males of the base population been reared in heterosexual flocks, a different group of individuals may have been selected to initiate the LM line. This would have occurred had selection for low CNCM initially involved timidity during the first experiences of adult males with females. It does not, however, imply that rearing methods would have altered the responses to divergent selection for high and low CNCM. Evidence that responses would not be altered is the absence of significant differences between social environments for CNCM and the lack of a significant line by social environment interaction for CNCM in the multivariate analysis. Relationships Among Behaviours Phenotypic correlations were computed to measure the association between traits. Since the lines were distinct populations, correlations were obtained within each line. All males were used in the analyses. H M line. The correlations of courts with mounts, treads, CNCM, and crouches were highly significant (Table IV), indicating that in this line courting had an important sexual aspect. All possible correlations between mounts, treads, CNCM, and crouches were large and highly significant, showing a considerable association among these behaviours. Although not presented in tabular form, the correlations between the selected trait, CNCM, with CR/C, with M/CR, M/C and CNCM/C were 0.32,
0.37, 0.37 and 0.73 respectively. Since these correlations were significant, it may be concluded that males that courted most often were the most effective in eliciting crouches and most likely to complete matings. This does not imply that selection for high CNCM was primarily for courts, since males that complete a large number o f matings must court. Correlations between CNCM and the other percentages were not significant. AC controls. All correlations involving courts, mounts, treads, CNCM and crouches were highly significant. Although the degree of significance was not altered (Table IV), the correlations between courts and the other behaviours tended to be consistently lower than those in the H M line. Additional traits that were significantly correlated with C N C M included CR/C, M/CR, C N C M / T and CNCM/C. The respective values for these were 0.61, 0.48, 0.36, 0.33 and 0.74. L M line. The correlations of numbers of courts with mounts, treads, CNCM and crouches were not significant, while those among mounts, treads, and CNCM were highly significant (Table IV). Also highly significant were the correlations of CNCM with CR/C, M/CR, M/C, and CNCM/C (0.84, 0.56, 0.84 and 0.84, respectively). The lack of a significant correlation between courts and CNCM in the LM line contrasts with the highly significant correlation of the same two traits in the H M and AC lines. This suggests that the sexual element of a court in the LM line is considerably less than that in the H M and AC lines. Furthermore, the correlations of courts, with crouches, mounts, treads, and CNCM in the AC controls were intermediate in magnitude to those in the H M and LM lines. The function of the court thus appears to be dependent on the genetic background of the population.
396
ANIMAL
BEHAVIOUR,
The high correlation between crouches per court (CR/C) a n d C N C M in all three lines m a y reflect that males whose courts were primarily sexual in i n t e n t effectively elicit a larger prop o r t i o n of crouches per court. Similarly, the large a n d highly significant correlations o f crouches, m o u n t s , a n d treads with C N C M emphasize the close association of these traits in the signal-response sequence of m a t i n g beh a v i o u r in the fowl. REFERENCES Cook, W. T., Siegel, P. B. & Kinkelmann, K. (1972). Genetic analyses for male mating behavior in chickens. 2. Crosses among selected and control lines. Behav. Genet., (in press). Guhl, A. M. (1969). The behavior of chickens. In: The Behavior of Domestic Animals (Ed. by E. S. E. Hale ). Baltimore: Williams and Wilkins. Guiton, P. (1966). Early experience and sexual objectchoice in the Brown Leghorn. Anita. Behav., 14, 534-539. Hess, C. W. (1962). Randombred population of the Southern Regional Poultry Breeding Project. Wld's Poult. Sci., J., 18, 147-152. Jensen, D. R., Beus, G. B. & Storm, G. (1968). Simultaneous statistical tests on categorical data. J. exp. Educ., 36, 47-56. Kramer, C. u & Jensen, D. R. (1970). Fundamentals of multivariate analysis. IV. Analyses of variance for balanced experiments. J. Qual. Tech., 2, 32--40. Kruijt, J. P. (1966). The development of ritualized displays in Junglefowl. Phil. Trans. R. Soc. (B), 251, 479-484.
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Kruijt, J. P. (1971). Early experience and the development of social behavior in Junglefowl. Psychiat. Neurol., Neurochir., 74, 7-20. McCollom, R. E., Siegel, P. B. & Van Krey, H. P. (1971). Responses to androgen in lines of chickens selected for mating behavior. Horm. & Behav., 2, 31-42. Morrison, D. F. (1967). Multivariate Statistical Methods. New York: McGraw-Hill. Mosteller, F. & Youtz, C. (1961). Tables of the FreemanTukey transformations for binomial and Poisson distributions. Biometrika, 48, 433-440. Siegel, P. B. (1965). Genetics of behavior" Selection for mating ability in chickens. Genetics, 52, 1269-1277. Siegel, P. B. (1972). Genetic analyses of male mating behaviour in chickens. 1. Artificial selection. Anim. Behav., 20, 564--570. Siegel, P. B. & Siegel, H. S. (1964). Rearing methods and subsequent sexual behaviours of male chickens. Anim. Behav., 12, 270-271. Tindell, D. & Arze, C. G. (1965). Sexual maturity of male chickens selected for mating ability. Poult. Sci., 44, 70-72. Wood-Gush, D. G. M. (1956). The agonistic and courtship behaviour of the Brown Leghorn cock. Br. J. Anita. Behav., 4, 133-142. Wood-Gush, D. G. M. (1958). The effect of prior experience on the mating behaviour of the domestic cock. Anita. Behav., 6, 68-71. Wood-Gush, D. G. M. (1960). A study of sex drive of two strains of cockerels through three generations. Anim. Behav., 8, 43-53. (Received 7 April 1972; revised 11 July 1972; MS. number: A1316)
VARIABLES
BEHAVIOUR
AND
OF MALE
DIVERGENT CHICKENS
SELECTION
FOR
MATING
(CALLUS DOMESTICUS)
BY W. T. COOK* & P. B. SIEGEL
Poultry Science Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061 Abstract. Heterosexual or unisexual contact of juvenile males from two lines divergently selected for male mating frequency, and a control line had little, if any influence on their subsequent mating behaviour. The interaction of lines • social environments for mating behaviour was not significant, showing that lines responded in a similar manner to the environments. It is hypothetized that selection for low cumulative number of completed matings (CNCM) was primarily for higher neural thresholds, whereas selection for high CNCM affected loci operative after neural thresholds are attained. The magnitude of the sexual component of a court was found to be dependent on the genetic background of the population, being less in the low mating than in the high mating line. of the high mating (HM), low mating (LM) and control (AC) lines. The sole selection criterion in the HM and LM lines was the cumulative number of completed matings (CNCM) by a male in eight 10-rain observation periods. Details of selection procedures and responses were given for the HM and LM lines by Siegel (1965, 1972), and the control population was described by Hess (1962). Chicks were hatched 31 March 1970, sexed and reared in heterosexual flocks until 42 days of age. At this age males were randomly assigned to one of the following social environments: (A) Reared with females of the same three lines and age to 206 days of age; (B) Reared in all-male flocks of eight to ten individuals to 196 days of age, then placed with females of a comparable age until 206 days of age, i.e. 10 days with females after the first 42 days; (C) Reared in all-male flocks of eight to ten individuals to 210 days of age, i.e. 0 days with females after the first 42 days. Males in environments A and B were maintained in unisexual flocks of five to eight males each between 206 and 210 days of age. Females were obtained from the same lines as the males, and lines were intermingled in both unisexual and heterosexual flocks. Forty-two days was chosen as the age to randomize males into environmental groups because cockerels separated from females at 58 days of age and maintained in individual cages, mated significantly less than those separated at later ages (Siegel & Siegel 1964). It was thus assumed that mating experiences of males are quite limited during the first 42 days posthatching. Five sexing errors (pullets erroneously
The role of the social environment of juvenile cockerels on subsequent mating behaviour has been studied by several investigators. WoodGush (1958) and Kruijt (1971) reported that males reared either in isolation or in unisexual flocks successfully mated with females as adults. Guiton (1966), however, observed that cockerels maintained in isolation during the first 46 days post-hatching preferred the gloved hand of the experimenter to a female model. The study of mating behaviour should include consideration of both genetic and environmental variables, and possible interactions between them. Artificial selection to change the mating behaviour of male chickens was used by Wood-Gush (1960) and Tindell & Arze (1965) who observed differences between selected lines in the S 2 generation. The design used by Wood-Gush permitted prior heterosexual experiences, whereas the males used by Tindell & Arze were limited to visual and auditory contact with females. Siegel (1965, I972) conducted a divergent selection experiment for mating ability in which he utilized a random bred control as the base population for the selected lines. Selection was made from males reared in unisexual flocks from 8 weeks of age until tested with females at 31 weeks. Each of the selected lines was significantly different from the unselected control by the S 5 generation. Reported here is an experiment designed to evaluate the influence of prior heterosexual contact on the subsequent mating behaviour of males from the selected and control lines. Methods Subjects were obtained from the S 12 generation *Present address: Allied Mills Industries Poultry Ltd., SummerHill, N.S.W. 2130. 390
COOK & SIEGEL: MATING BEHAVIOUR. IN MALE CHICKENS classified as cockerels) were noted between 42 and 105 days of age. When found in an all-male flock, the pullet was immediately removed from the pen. The unisexual male flocks were maintained in visual and tactile isolation from the heterosexual flocks (A and B), each of which consisted o f two males that were randomly assigned to a group of seven to ten females. Measurements
The signal-response sequence of mating behaviour in chickens was outlined by Guhl (1969). The first component of the sequence is the court of the female by the male. The female either crouches or attempts to avoid the court. Crouching may be followed by a mounting, treading, and a completion of the mating, in that order. At any stage during the sequence either the male or female may terminate the process. The mating behaviour of all males was measured during a 16-day interval commencing at 210 days of age. The procedure used followed that of Siegel (1965). Cockerels were tested singly with flocks of six to eight pullets (from environment A) of the same age. Traits measured included the selection criterion, cumulative number of completed matings (CNCM), plus courts (C), mounts (M), treads (T), and crouches received (CR) during seven 10-rain observation periods. Besides these behaviours, additional criteria included CR/C (percentage of courts eliciting a crouch), M/CR, M/C, T/M, CNCM/T, CNCM/ M, C N C M / C R and CNCM/C. All ratios were expressed as percentages which were then converted to Freeman-Tukey arc sines as recommended by Mosteller & Youtz (1961) when there are less than fifty observations per experimental
391
unit. Square roots transformations were made for M, T, CNCM, and CR to alleviate the problem of heterogeneous variances. Aualyses
Correlated chi-square analyses (Jensen, Beus & Storm 1968) were used to compare the number of males completing and not completing at least one mating. Since comparisons were made between environments within lines and between lines within environments, the number of correlated tests ~- was two. Males from environments A and B were combined into one group to obtain adequate sample sizes for analyses. The results of the chi-square analyses suggested that the quantitative data be summarized in two ways: first, with all males included in the analysis (method I) and, second, with only those males completing at least one mating (method II). Both analyses were least squares, multivariates w i t h fixed effects for a 3 • 3 factorial plan (Kramer & Jensen 1970) modified for unequal sample sizes. The model for a completely randomized design was: Y~jk = Ix + Mi Jr Ss + (MS)~j -[- eijk where, Y~jk is the kth observation of the ith male line and jth social environment. Simultaneous confidence limits were used to isolate significant differences among means for each trait (Morrison 1967). Only courts, mounts, treads, CNCM, crouches CNCM/C, CR/C, and M/C were included in the first analysis (method I) which involved all males. The other characters which were percentages (e.g. CNCM/T), were not analysed by method I because, with the exception of four individuals, cockerels that did not complete at
Table I, Comparisons* Between and Within Lines for Proportions of Males Completing and Not Completing at Least One Mating
Lines Social environment
(flock)
Unisexual
Mating activityt
CM no CM
Heterosexual P
CM
no CM
HM
AC
LM
P
22 0
24 11
12 16
0.025
19 1
32 3
15 8
0.025
no test
0.05
NS
*Between-line comparisons are across rows within social environments and within-line comparisons are in columns between social environment. tCM and no CM denotes the number of males completing and not completing at least one mating in seven 10-min test periods.
ANIMAL
392
BEHAVIOUR,
22,
2
LM line. This relationship between the H M and LM lines existed regardless of the length o f time the males spent in heterosexual flocks. Within the AC line, significantly more of the males reared in heterosexual flocks completed at least one mating than did those maintained in unisexual flocks. However, for the LM line the proportion of males completing and not completing a mating, was not significantly different for those reared with or without pullets. The contrasting results of the A C and LM lines suggest a line • social environment interaction. Analyses were not possible within the H M line since all males, except one, completed at least one mating. Although the experimental designs were not the same, the results for our unselected AC controls were somewhat different from those of Wood-Gush (1958) and Kruijt (1971). They found that the proportion of leghorn and jungle fowl males reared in isolation that successfully copulated was similar to the proportion for males
least one mating did not elicit a crouch. Thus, it was impossible to calculate CNCM/T, CNCM/M, C N C M / C R , M/C, and T/M for males that did not mate. All traits were analysed by method II which involved males completing at least one mating. All possible phenotypic correlations between courts, mounts, treads, CNCM, and crouches were calculated within each line. Correlations of C N C M with CNCM/C, CR/C, M/CR, M/C, CNCM/M, C N C M / T and C N C M / C R were also calculated. The F statistic was used to determine if each correlation coefficient was significantly different from zero. Results and Discussion Qualitative Data
Chi-square comparisons between and within lines for proportions of males completing and not completing at least one mating are shown in Table I. There were significant differences among lines with an excess of H M males completing at least one mating compared to those from the
Table H. Numbers, Means, and Standard Errors of Behaviours for the Social Envirormtents(0,10 and 168 Days with Females) by Methods I and H
Method I Behaviour*
Method II
0
10
168
0
10
168
85
25
53
59
20
48
Courts (C)
69.1 4- 4"0
88.0 4- 7.4
65.7 4- 5.1
74.5 4- 4-7
102.24- 8.0
70.3 4- 5.2
Mounts(M)
9.8 • 0.9
11.4 4- 1.6
10.7 4- 1.1
11.2 :~ 1.2
14.0 4- 2-0
11.7 4- 1-3
Treads (T)
8.0 4- 0,7
8-8 4- 1.3
9-3 4- 0-9
9.3 • 1.0
10.8 4- 1.6
10.1 -4- 1.1
CNCM
7.0 5:0.6
8.0 4- 1.2
8.5 • 0.8
8.1 4- 0.8
9.8 • 1.5
9-2 4- 0"9
Crouches (CR)
10.2 4- 0.9
12.1 4- 1'7
10.9 4- 1.2
11.7 ~ 1.2
14.6 d: 2.1
11.9 t 1-4
CR/C
11.4 :k 1.4
10.8 t 2.1
12.5 4- 1"5
22.4 4- 1.5
14.3 4- 2"3
14.0 4- 1.5
M/C
10.8 d: 1-4
10.0 d: 2.7
12.3 d: 1,4
15-1 ~: 1.4
14.0 d: 3.1
13.8 ~ 1.4
7.5 4- 1.0
7-4 ~ 1.6
9.8 4- 1.6
10-6 • 1.0
9.8 -4- 1-8
11.0 4- 1-7
M/CR
89.6 ~ 3"0
92.3 d: 4-5
96.5 q- 1.5
TIM
81.7 ~ 3.2
81.1 -b 4-9
87.1 4- 3.2
CNCM/T
81.9 • 3-7
94.6 4- 2.0
90.6 4- 3.0
CNCM/M
73.2 4- 3"6
77.3 d: 5.3
83.0 4- 3"4
CNCM/CR
67.1 4- 3"9
71-9 4- 6'2
82.2 ~ 2-8
Nt
CNCM/C
*All ratios expressed as percentages. No significant differences(P<0.05) were found among social environments by either method of analysis. tNo. of males.
COOK & SIEGEL: MATING BEHAVIOUR IN MALE CHICKENS reared in all-male flocks. It is interesting to n o t e that a l t h o u g h stocks used in the three studies were diverse, the absolute percentage for males reared in unisexual flocks c o m p l e t i n g at least one m a t i n g was similar (65 per cent in ours, 75 to 100 p er cent in Kruijt's a n d 70 p e r cent in Wood-Gush's).
393
o f male m a t i n g b e h a v i o u r during the test periods. Line effects, method L There were significant differences a m o n g lines for m o u n t s, treads, C N C M an d crouches. M e a n s were largest for the H M line an d smallest for the L M line. Values for the r a n d o m bred co n t r o l were intermediate a n d significantly different f r o m those o f the selected lines (Table III). T h e selected lines, while significantly different f r o m each other for courts a n d M / C , did n o t differ significantly f r o m the A C controls. M e a n s f o r C R / C and C N C M / C were significantly larger in the H M line t h a n in the L M a n d A C lines. Th e means f o r these t w o b e h a v i o u r patterns in the A C line, while intermediate to t h o se for the selected lines, were n o t significantly different f r o m those o f the L M line.
Quantitative Data Line x social environment interaction. Multivariate analyses revealed that the in te r a c ti o n o f lines by social e n v i r o n m e n t s was n o t significant for each behaviour. Results were the same f o r b o t h m e t h o d s I and II, showing t h a t the influence o f the three social e n v i r o n m e n t s on the quantitative behaviours was similar f o r all lines. Effects of social environment. T h e r e were no significant differences a m o n g social environments for an y o f the behaviours measured. This was consistent for b o t h m e th o d s o f analysis (Table II) a n d implies that the time spent as juveniles in heterosexual or unisexual flocks h a d little influence on the quantitative expression
Line effects, method IL A l t h o u g h the n u m e r i c a l ranks o f the lines were the same f o r m e t h o d s I and II, the significance o f differences between lines changed f o r m o s t traits (Table III). T h e differences in courts between the H M an d L M
Table HI. Numbers, Means, and Standard Errors of Behaviours for the HM, AC, and LM Lines by Methods I and II Method I Behaviour*
Method II
HM
AC
LM
HM
AC
LM
nt
42
70
51
41
56
30
Courts (C)
93"8 • 6"4b
75"8 4- 5"0ab
53.1 • 5"6a
99'3 4- 6"3a
80"7 • 5.0a
66"9 4- 6"9a
Mounts (M)
19.5 Jz 1"4e
8-4 • 1.1 b
3-9 4- 1"3a
20"6 q- 1"6b
9"9 4- 1.2b
6-4 4- 1"8a
Treads (T)
15'8 t 1"2c
7"2 • 0'9 b
3"1 4- 1'0 a
16.6 4- 1"2b
8'4 4- 1"0b
5"2 -4- 1.4a
CNCM
14-1 4- 1"0e
6.6 • 0"8b
2.8 4- 0"9a
14"8 4- 1.1 b
7.7 • 0"9ab
4-7 4- 1"2a
Crouches (CR)
20"3 4- 1-5c
8-8 4- 1"Ib
4"0 4- 1"3a
21.5 4- 1"6a
10"1 4- 1"2a
6"6 4- 1-8a
CR/C
22.6 • 1.3b
9"4 4- 0"4a
5.6 4- 1"4a
23"I • 1"3a
11"4 4- 0"5a
10"6 4- 2-2a
M/C
21.6 • 1"4b
9.2 4- 0"5ab
5"4 4- 1.4a
22"2 4- 1"3a
10.8 4- 0"5a
10-2 4- 2"2a
CNCM/C
15"1 4- 1"1b
6"8 4- 0"8a
4.1 4- 0"9a
16-3 4- 1"1a
8"1 4- 1"Ia
7.7 4- 1"5a
M]CR
95"7 4- 1"3a
88"9 4- 3-5a
79.4 + 2"2a
T/M
82"9 • 2-3a
81.1 4- 3.8a
90"7 4- 3"7a
CNCM/T
89"6 4- 1"9a
83"1 4- 3"9a
92'5 4- 3"9a
CNCM/M
75"4 4- 2"8a
76"0 4- 4"0a
84"3 4- 5"0a
CNCM/CR
72"7 4- 3"0a
70"7 4- 4"2a
81"4 4- 5"4a
*All ratios are expressed as percentages. Lines within a method of analysis with the same superscript are not significantly different (P<0"05). tNo. of males.
394
ANIMAL BEHAVIOUR,
lines were no longer significant when the analysis was based on only those males that completed at least one mating (method II). Males of the LM line mounted and treaded significantly less than those from the AC and HM lines which were not different from each other. Although the AC controls were no longer significantly different from both the HM and LM lines for the selected trait, CNCM, the latter two lines remained significantly different. This indicates that elimination of non-maters raised proportionally the level of CNCM in both the AC and LM lines, but not in the HM line. This is congruent with the excess of nonmaters found in the AC controls relative to the HM line and the excess of non-maters found in the LM line relative to the AC controls. Interpretation of line effects. McCollom, Siegel & Van Krey (1971) proposed that bidirectional selection for CNCM modified both the neural and endocrine influences on mating behaviour. They suggested that the neural system may be primary to the behaviour and that endocrine responses are only observable after the neural threshold is reached. Further support for this hypothesis was presented by Cook, Siegel & Hinkelmann (1972). The results of the present experiment provide additional support for this hypothesis, and also suggest that selection for low CNCM has elevated neural thresholds to a level that prevents a sizable proportion of males from completing at least one mating. The CNCM for the LM line was still significantly lower than that for the HM line even after the removal of non-maters, suggesting that selection for low CNCM has also influenced loci other than those which modify neural thresholds. The evidence suggests that selection for low CNCM has acted primarily upon a set of loci that alter neural thresholds such that males are not likely to mate, and secondarily upon a set of loci that lowers CNCM in those that do mate. This does not, however, imply that the two sets of loci are independent of each other. It can also be hypothesized that selection for high CNCM was initially for those males with low neural thresholds, since there was a greater proportion of non-maters in the AC controls than in the HM line. An extension of the hypothesis of McCollom et al. (1971) would suggest that selection in the HM line has primarily affected alleles that are operative once the neural threshold has been attained and simultaneously altered the frequency of alleles at loci which lower the neural thresholds for CNCM.
22, 2
Natural selection might be expected to have aided the second set of loci, and, thus, artificial selection for high CNCM may have primarily influenced the first set. This is consistent with the crossing experiment by Cook et al. (1972) who observed that alleles of the loci affected by selection for low CNCM (i.e. those raising neural thresholds) were dominant to those influencing the response to selection for high CNCM. Alleles at the latter loci were relatively more additive in effect. These relationships suggest that selection for high CNCM may have primarily affected those loci whose effects are phenotypically expressed only after the neural thresholds are attained, and secondarily, influenced neural thresholds. Although the pattern was the same, the significance of differences among lines for courts was not consistent with that found for the selected trait, CNCM. This concurs with the hypothesis of GuM (1969) and Kruijt (1966) that courtship behaviour in chickens has a dual role, that is, both agonistic and sexual. Cook et al. (1972) have indicated that the inheritance of courts is different from that for CNCM, and Siegel (1972) obtained a genetic correlation of 0.45 between them. Mounting and treading, in contrast to courting, are integral components of the signal-response sequence that leads to a completed mating. The close association of these with CNCM is evident in Table II by the high percentage of CNCM/M and CNCM/T. The low percentage of CNCM/C relative to those for CNCM/M and CNCM/T also demonstrates the closer association of both mounting and treading to CNCM than to that between courting and CNCM. The significantly lower CNCM/C for LM males in comparison to HM males by method I and the absence of differences by method II suggest that courts by LM males were either ineffectual sexual stimuli or were used to assert their dominance over the females. Although qualitative data were not available, the waltz was the more frequent display during courtship in the LM line. Wood-Gush (1956) suggested that the waltz display represents a conflict within the cock between aggressive and sexual tendencies and shows that the sex drive is temporarily weak or inhibited. The absence of significant differences between lines for CNCM/M and CNCM/T (Table II) conflicts with the results of McCollom et al. (1971) and may be due to the method of analysis. They used a univariate analysis which considers
COOK & SIEGEL: MATING BEHAVIOUR IN MALE CHICKENS
395
Table IV. Phenotypie Correlations for Mating Behaviours by Lines* HM M C M T CNCM
0-66
T
CNCM CR
0 " 6 0 0 " 6 0 0"65 0.95 0'88 0.99 0.97 0"92 0"85
AC M 0.52
T
CNCM
LM CR
0 " 5 2 0"55 0"56 0-97 0 . 9 5 0.99 0"99 0'96 0"94
M 0"28
T
CNCM
CR
0"29 0 " 3 0 0"29 0.99 0.98 0"99 0"99 0"99 0.98
*dffor HM, AC, and LM lines were 1 and 40, 1 and 70 and 1 and 51, respectivelyfor the F statistic. All correlations were highly significant (P<0'01), except for those involving courts in the LM line which were not significant(P<0"05). each trait independently; whereas, we employed a multivariate analysis which considers the lack of independence of the traits, thus providing a more rigorus test of differences among lines. Interrelationship of Qualitative and Quantitative Data The qualitative data for AC controls may be interpreted to suggest that, had juvenile males of the base population been reared in heterosexual flocks, a different group of individuals may have been selected to initiate the LM line. This would have occurred had selection for low CNCM initially involved timidity during the first experiences of adult males with females. It does not, however, imply that rearing methods would have altered the responses to divergent selection for high and low CNCM. Evidence that responses would not be altered is the absence of significant differences between social environments for CNCM and the lack of a significant line by social environment interaction for CNCM in the multivariate analysis. Relationships Among Behaviours Phenotypic correlations were computed to measure the association between traits. Since the lines were distinct populations, correlations were obtained within each line. All males were used in the analyses. H M line. The correlations of courts with mounts, treads, CNCM, and crouches were highly significant (Table IV), indicating that in this line courting had an important sexual aspect. All possible correlations between mounts, treads, CNCM, and crouches were large and highly significant, showing a considerable association among these behaviours. Although not presented in tabular form, the correlations between the selected trait, CNCM, with CR/C, with M/CR, M/C and CNCM/C were 0.32,
0.37, 0.37 and 0.73 respectively. Since these correlations were significant, it may be concluded that males that courted most often were the most effective in eliciting crouches and most likely to complete matings. This does not imply that selection for high CNCM was primarily for courts, since males that complete a large number o f matings must court. Correlations between CNCM and the other percentages were not significant. AC controls. All correlations involving courts, mounts, treads, CNCM and crouches were highly significant. Although the degree of significance was not altered (Table IV), the correlations between courts and the other behaviours tended to be consistently lower than those in the H M line. Additional traits that were significantly correlated with C N C M included CR/C, M/CR, C N C M / T and CNCM/C. The respective values for these were 0.61, 0.48, 0.36, 0.33 and 0.74. L M line. The correlations of numbers of courts with mounts, treads, CNCM and crouches were not significant, while those among mounts, treads, and CNCM were highly significant (Table IV). Also highly significant were the correlations of CNCM with CR/C, M/CR, M/C, and CNCM/C (0.84, 0.56, 0.84 and 0.84, respectively). The lack of a significant correlation between courts and CNCM in the LM line contrasts with the highly significant correlation of the same two traits in the H M and AC lines. This suggests that the sexual element of a court in the LM line is considerably less than that in the H M and AC lines. Furthermore, the correlations of courts, with crouches, mounts, treads, and CNCM in the AC controls were intermediate in magnitude to those in the H M and LM lines. The function of the court thus appears to be dependent on the genetic background of the population.
396
ANIMAL
BEHAVIOUR,
The high correlation between crouches per court (CR/C) a n d C N C M in all three lines m a y reflect that males whose courts were primarily sexual in i n t e n t effectively elicit a larger prop o r t i o n of crouches per court. Similarly, the large a n d highly significant correlations o f crouches, m o u n t s , a n d treads with C N C M emphasize the close association of these traits in the signal-response sequence of m a t i n g beh a v i o u r in the fowl. REFERENCES Cook, W. T., Siegel, P. B. & Kinkelmann, K. (1972). Genetic analyses for male mating behavior in chickens. 2. Crosses among selected and control lines. Behav. Genet., (in press). Guhl, A. M. (1969). The behavior of chickens. In: The Behavior of Domestic Animals (Ed. by E. S. E. Hale ). Baltimore: Williams and Wilkins. Guiton, P. (1966). Early experience and sexual objectchoice in the Brown Leghorn. Anita. Behav., 14, 534-539. Hess, C. W. (1962). Randombred population of the Southern Regional Poultry Breeding Project. Wld's Poult. Sci., J., 18, 147-152. Jensen, D. R., Beus, G. B. & Storm, G. (1968). Simultaneous statistical tests on categorical data. J. exp. Educ., 36, 47-56. Kramer, C. u & Jensen, D. R. (1970). Fundamentals of multivariate analysis. IV. Analyses of variance for balanced experiments. J. Qual. Tech., 2, 32--40. Kruijt, J. P. (1966). The development of ritualized displays in Junglefowl. Phil. Trans. R. Soc. (B), 251, 479-484.
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Kruijt, J. P. (1971). Early experience and the development of social behavior in Junglefowl. Psychiat. Neurol., Neurochir., 74, 7-20. McCollom, R. E., Siegel, P. B. & Van Krey, H. P. (1971). Responses to androgen in lines of chickens selected for mating behavior. Horm. & Behav., 2, 31-42. Morrison, D. F. (1967). Multivariate Statistical Methods. New York: McGraw-Hill. Mosteller, F. & Youtz, C. (1961). Tables of the FreemanTukey transformations for binomial and Poisson distributions. Biometrika, 48, 433-440. Siegel, P. B. (1965). Genetics of behavior" Selection for mating ability in chickens. Genetics, 52, 1269-1277. Siegel, P. B. (1972). Genetic analyses of male mating behaviour in chickens. 1. Artificial selection. Anim. Behav., 20, 564--570. Siegel, P. B. & Siegel, H. S. (1964). Rearing methods and subsequent sexual behaviours of male chickens. Anim. Behav., 12, 270-271. Tindell, D. & Arze, C. G. (1965). Sexual maturity of male chickens selected for mating ability. Poult. Sci., 44, 70-72. Wood-Gush, D. G. M. (1956). The agonistic and courtship behaviour of the Brown Leghorn cock. Br. J. Anita. Behav., 4, 133-142. Wood-Gush, D. G. M. (1958). The effect of prior experience on the mating behaviour of the domestic cock. Anita. Behav., 6, 68-71. Wood-Gush, D. G. M. (1960). A study of sex drive of two strains of cockerels through three generations. Anim. Behav., 8, 43-53. (Received 7 April 1972; revised 11 July 1972; MS. number: A1316)