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Differences in patterns of pup care in Mus musculus domesticus I—Comparisons between eleven inbred strains
BEHAVIORAL AND NEURALB1OLOGY35, 205--210 (1982)
BRIEF REPORT Differences in Patterns of Pup Care in Mus Musculus Domesticus ImComparisons between Eleven Inbred Strains1 M . CARLIER,* P. ROUBERTOUX,t AND CH. COHEN-SALMONt *Universitds de Paris X Nanterre et de Paris V, and ?Universit~ de Paris V, Paris, France A comparison of 11 inbred strains of Mus musculus domesticus was carried out for pup care behavior in a retrieving test. Data relating to retrieval of the first pup show differences between strains for all variables except the variable "First Pup Carrying." The strains CBA/H, C3H/Ico, C57BL/6, and CBA/J are better retrievers than the strains BALB/C, NZB, DBA/2, XLII, A/J, AKR, and C57Br. The validity of three retrieving variables is demonstrated by the rankorder correlations between the strain medians in these three variables and the death rate of the pups. The data relating to the kinetics of retrieval behavior show that the time between one retrieval and the following one decreases linearly. The differences between strains relating to the variable first retrieval are interpreted in terms of ease of putting the retrieving process into operation. This hypothesis is discussed in relation to studies on the neurophysiology of motor behavior.
The study of pup care behavior concerns the geneticist for several reasons. First, the survival of individuals in a species depends partly on the care that they have received. In this way observed differences between care behavioral patterns contribute toward modifying the genetics structure of the population to come if the differences in care are related to heritable attributes of the care receivers. Second, care patterns are a source of variation in the postnatal environment. It is possible that the differences in pup care may lead the offspring to benefit from the same nonmaternal environment in different ways and that frequent care may compensate for a deficient nonmaternal environment. Third, on a more technical level, female care behavior patterns must be known before undertaking adoptions (Roubertoux & Carlier, in press). Moreover, when a strain hierarchy is known, a judicious choice can be made before to This research was supported by ERA 79 (CNRS), EPHE (Laboratoire de Psychologie Diff6rentielle), INSERM, Universit6 de Paris V, and Universit6 de Paris X Nanterre. Requests for reprints should be sent to Dr. M. Carlier, Laboratoire de Psychologie Diff6rentielle, Universit6 de Paris V, 28 rue Serpente, France, 75006 Paris. 205 0163 - 1047/82/060205 -06502.00/0 Copyright© 1982by AcademicPress, Inc. All rightsof reproductionin any form reserved.
206
CARLIER, ROUBERTOUX, AND COHEN-SALMON
undertake a genetic analysis and the regression to the mean--which may bias the results of the biometrical genetics analysis--can be avoided. The performances of three inbred strains (A/J, DBA/2, and C57BL/6) have been published for retrieving tests that differ in procedure (Hennessy, Li, Lowe, & Levine, 1980; Wainwright, 1981). As the aim of our team was to study genetic determination and interactions with the maternal environment, observation of the greatest feasible number of strains was a necessary preliminary stage. Eleven inbred strains were compared: CBA/H (CH), CBA/J, C3H, C57BL/6 (B6), C57Br/cd, BALB/C, NZB (N), DBA/2, XLII (L), A/J, and AKR. The breeders identified were supplied by C S E A L - C N R S and IFACREDO. One hundred fifty-four females--all born in the test room--were observed with their first litter. The matings were undertaken at 8 weeks with a male of the same strain. When they appeared to be visibly close to parturition, the females were isolated in a cage 29 × 42 × 18 cm containing 1 1 sawdust and 1 g cotton. Food and water were provided ad libitum. Observations were made 24_+ 10 hr after parturition, with the different strains observed at random between 10 AM and 4 Pi. All females having at least one living offspring were observed in order to avoid selective bias. Moreover, the females were observed with their entire litter so that the effect of litter size could be estimated a posteriori. While the female was isolated outside the parturition cage, the pups were removed and placed in a heap 20 cm from the nest. Observation began when the female was placed on the nest by the experimenter. The data analyzed in Tables 2 and 3 were collected within the 900 sec following the placing of the female on the nest by the experimenter. The following measurements were taken. (1) Mean number of living pups the day of test (Table 1). (2) Duration TABLE 1 Living Pups the Day of the Test Variable 1: Number of pups Strains
N
X
cr
Range
CBA/H CBA/J C3H/Ico C57BL/6 BALB/C NZB DBA/2 XLII A/J C57Br A K R
15 15 10 11 16 15 14 14 12 20 12
4.7 5.5 6.8 5.7 5.3 5.7 3.6 5.4 3.9 6.5 7.5
1.8 1.7 1.5 1.8 1.8 2.0 1.6 1.5 1.9 2.4 1.8
2-8 2-8 3-8 3-8 3-8 2-8 1-6 3-9 1-6 3-11 4-10
Note. F(10, 143) = 4.73, p < .001; N, number of females per strain.
PUP CARE IN MOUSE INBRED STRAINS
207
between the moment when the female is placed on the nest and the moment when her snout contacted one of her pups (first contact). (3) Duration between the first contact and the taking into the mouth of the first pup (first retrieval). The maximum value of 900 sec was given when this behavior did not occur. (4) The duration between the first retrieval and placing of the first offspring in the nest (first pup carrying). A score of 900 was given when one pup was taken but placed outside the nest. (5) The time spent in the nest after placing of the first pup in the nest (nest with first pup). (6) The number of times the female drew away from one of her pups, situated outside the nest, without their being transported (move away). For Variables 2 to 6, taking into account the shape of distributions, the significance of the differences was tested by the Kruskall-Wallis one-way analysis of variance by ranks (Table 2). (7) Percentage of females remaining in the nest with all their pups 2 consecutive rain in the 15 min of observation (nest with all pups) (Table 3). (8) The intervals between the retrieval of the first and second pups, the second and third pups, and the third and fourth pups were recorded for females having retrieved at least four pups. Seven females per strain were considered. The scores were logarithmically transformed in order to normalize the distributions and homogenize the variances. A two-way analysis of variance involving strains and intervals between retrievals was computed, with interval treated as a repeated measure. The rank of the interval considered has a significant effect (F(2, 132) = 34.28, p < .005). The time between one retrieval and the following one decreases linearly (linear tendency, F(1, 66) = 70.0, p < .001, quadratic tendency ns). The effect of strain approaches significance (F(10, 66) = 1.79, p < .10) like that of the interaction between these two factors (F(20, 132) = 1.48, p < .10). It is possible to bring forward four complementary observations. (1) Number of days of isolation had no observable effect on any measure; rank-order correlations between strain means on number of days of isolation and strain medians on retrieving variables were nonsignificant (p > . 10). (2) The differences between the mean number of offspring per strain cannot account for differences observed here between strains; indeed, rank-order correlations between strain means on number of pups and strain medians on retrieving variables are nonsignificant (p > . 10). Moreover, the females of four strains were observed with their first litter born of crossing with males of another strain (CH with pups CHNF1; N with N C H F I ; B6 with B6LF1; L with LB6F1). The size of the first litter of heterozygotes is significantly higher than the size of the first litter of homozygotes, but the median scores of the females of these strains in the retrieving test variables do not differ significantly from those of Tables 1 and 2. (3) Rank-order intercorrelations between strain medians on three variables--first retrieval, move away, and nest with
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TABLE 3 In the Nest with All Pups during 120 sec. Variable 7: Nest with all pups Strains
N
Percent
CBA/H CBA/J C3H/Ico C57BL/6 BALB/C NZB DBA/2 XLII A/J C57B4 AKR
14 15 9 10 10 8 9 8 11 16 6
93.33 100 90 90.9 62.5 53.3 64.3 57.1 92.7 80 54.6
Note.
X2
=
23.67, p < .01; N, number of
females.
all pups--are significant, the third variable being negatively correlated with the two others (rho values between 1.611 and 1.821, p < .05). It may be noted here that the variables are not independent by construction. For example, when one female draws away from one of her pups (move away variable), she often can take more time to transport the first pup (first retrieval variable). However, because behaviors were recorded for 15 min after the first retrieval, in the case where the female did not stay 2 consecutive min in the nest with all the pups, it was possible to measure the variables move away and nest with all pups by taking the first retrieval as origin. In this case the variables remain intercorrelated (p < .05). (4) The validity of the measurements first retrieval, move away, and nest with all pups is demonstrated by their association with the probability of pup survival. This latter was measured 24 hr after the test using the ratio pups living at 48 hr/pups living at 24 hr. Rank-order correlations between strain medians on first retrieval, move away, nest with all pups, and this criterion are, respectively, - . 6 1 , - . 6 5 , and .58 (p < .05). Several factors might account for the ordering of strains in this test. The role of production by the pups and the mother's processing of ultrasonic data are discussed by Roubertoux, Carlier, Cohen-Salmon, and Jouhaneau (1982). Differences between the strains do not appear for all the variables. For example, first pup carrying does not differ from one strain to another--what differs is the latency of retrieval that allows this conduct (similar results have been reported on biparous females from eight inbred strains by Cohen-Salmon, Carlier, & Roubertoux, in press). Thus, for
210
CARLIER, ROUBERTOUX, AND COHEN-SALMON
the retrieval laying down sequence the hypothesis is made (Roubertoux, 1981)--by analogy with neurophysiology of motor behavior (H6can & Jeannerod, 1978)--that there is a kind of preprogramed or selected loop whose starting requires a stimulus of variable intensity. In subjects requiring a high stimulus level, the latency of first retrieval is longer than in those that require a low stimulus level. Moreover, once activated, this loop could demand a stimulus level increasingly weak from one trial to another. This hypothesis could be compatible with decrease of intervals between retrievals, as is revealed by the kinetics analysis. REFERENCES Cohen-Salmon, Ch., Carlier, M., & Roubertoux, P. (1982). Differences in pattern of pup care in Mus musculus domesticus. II Effects of parity on eight inbred strains. Biology of Behavior, in press. H6can, H., & Jeannerod, M. (1978). Du Contr6le Moteur it l'Organisation du Geste, p. 443. Paris: Masson. Hennessy, M. B., Li, J., Lowe, E. L., & Levine, S. (1980). Maternal behavior, pup vocalizations, and pup temperature changes following handling in mice of 2 inbred strains. Developmental Psychobiology, 13,(6), 573-584. Roubertoux, P. (1981). R61e des comportements dans les m6canismes 6volutifs: Ethologie g6n~tique et diff6rentielle. In Apprentissage, M~moire et l~volution. Hommage it M. Rosenzweig, Paris: Publications de la Sorbonne. Roubertoux, P., & Cartier, M. (1982). Analyse g6n6tique et d6veloppement pr6coce. In Le Ddveloppement. Paris, P.U.F.: Association de Psychologie Scientifique de Langue Francaise, in press. Roubertoux, P., Carlier, M., Cohen-Salmon, Ch., & Jouhaneau, J. (1982). Developmental study of pup vocalizations in 8 inbred strains of Mice. Helsinki: Third International Theriological Congress, 15-20 August. Wainwright, P. E. (1981). Maternal performance of inbred & hybrid laboratory mice (Mus musculus). Journal of Comparative and Physiological Psychology, 95, 694-707.
BRIEF REPORT Differences in Patterns of Pup Care in Mus Musculus Domesticus ImComparisons between Eleven Inbred Strains1 M . CARLIER,* P. ROUBERTOUX,t AND CH. COHEN-SALMONt *Universitds de Paris X Nanterre et de Paris V, and ?Universit~ de Paris V, Paris, France A comparison of 11 inbred strains of Mus musculus domesticus was carried out for pup care behavior in a retrieving test. Data relating to retrieval of the first pup show differences between strains for all variables except the variable "First Pup Carrying." The strains CBA/H, C3H/Ico, C57BL/6, and CBA/J are better retrievers than the strains BALB/C, NZB, DBA/2, XLII, A/J, AKR, and C57Br. The validity of three retrieving variables is demonstrated by the rankorder correlations between the strain medians in these three variables and the death rate of the pups. The data relating to the kinetics of retrieval behavior show that the time between one retrieval and the following one decreases linearly. The differences between strains relating to the variable first retrieval are interpreted in terms of ease of putting the retrieving process into operation. This hypothesis is discussed in relation to studies on the neurophysiology of motor behavior.
The study of pup care behavior concerns the geneticist for several reasons. First, the survival of individuals in a species depends partly on the care that they have received. In this way observed differences between care behavioral patterns contribute toward modifying the genetics structure of the population to come if the differences in care are related to heritable attributes of the care receivers. Second, care patterns are a source of variation in the postnatal environment. It is possible that the differences in pup care may lead the offspring to benefit from the same nonmaternal environment in different ways and that frequent care may compensate for a deficient nonmaternal environment. Third, on a more technical level, female care behavior patterns must be known before undertaking adoptions (Roubertoux & Carlier, in press). Moreover, when a strain hierarchy is known, a judicious choice can be made before to This research was supported by ERA 79 (CNRS), EPHE (Laboratoire de Psychologie Diff6rentielle), INSERM, Universit6 de Paris V, and Universit6 de Paris X Nanterre. Requests for reprints should be sent to Dr. M. Carlier, Laboratoire de Psychologie Diff6rentielle, Universit6 de Paris V, 28 rue Serpente, France, 75006 Paris. 205 0163 - 1047/82/060205 -06502.00/0 Copyright© 1982by AcademicPress, Inc. All rightsof reproductionin any form reserved.
206
CARLIER, ROUBERTOUX, AND COHEN-SALMON
undertake a genetic analysis and the regression to the mean--which may bias the results of the biometrical genetics analysis--can be avoided. The performances of three inbred strains (A/J, DBA/2, and C57BL/6) have been published for retrieving tests that differ in procedure (Hennessy, Li, Lowe, & Levine, 1980; Wainwright, 1981). As the aim of our team was to study genetic determination and interactions with the maternal environment, observation of the greatest feasible number of strains was a necessary preliminary stage. Eleven inbred strains were compared: CBA/H (CH), CBA/J, C3H, C57BL/6 (B6), C57Br/cd, BALB/C, NZB (N), DBA/2, XLII (L), A/J, and AKR. The breeders identified were supplied by C S E A L - C N R S and IFACREDO. One hundred fifty-four females--all born in the test room--were observed with their first litter. The matings were undertaken at 8 weeks with a male of the same strain. When they appeared to be visibly close to parturition, the females were isolated in a cage 29 × 42 × 18 cm containing 1 1 sawdust and 1 g cotton. Food and water were provided ad libitum. Observations were made 24_+ 10 hr after parturition, with the different strains observed at random between 10 AM and 4 Pi. All females having at least one living offspring were observed in order to avoid selective bias. Moreover, the females were observed with their entire litter so that the effect of litter size could be estimated a posteriori. While the female was isolated outside the parturition cage, the pups were removed and placed in a heap 20 cm from the nest. Observation began when the female was placed on the nest by the experimenter. The data analyzed in Tables 2 and 3 were collected within the 900 sec following the placing of the female on the nest by the experimenter. The following measurements were taken. (1) Mean number of living pups the day of test (Table 1). (2) Duration TABLE 1 Living Pups the Day of the Test Variable 1: Number of pups Strains
N
X
cr
Range
CBA/H CBA/J C3H/Ico C57BL/6 BALB/C NZB DBA/2 XLII A/J C57Br A K R
15 15 10 11 16 15 14 14 12 20 12
4.7 5.5 6.8 5.7 5.3 5.7 3.6 5.4 3.9 6.5 7.5
1.8 1.7 1.5 1.8 1.8 2.0 1.6 1.5 1.9 2.4 1.8
2-8 2-8 3-8 3-8 3-8 2-8 1-6 3-9 1-6 3-11 4-10
Note. F(10, 143) = 4.73, p < .001; N, number of females per strain.
PUP CARE IN MOUSE INBRED STRAINS
207
between the moment when the female is placed on the nest and the moment when her snout contacted one of her pups (first contact). (3) Duration between the first contact and the taking into the mouth of the first pup (first retrieval). The maximum value of 900 sec was given when this behavior did not occur. (4) The duration between the first retrieval and placing of the first offspring in the nest (first pup carrying). A score of 900 was given when one pup was taken but placed outside the nest. (5) The time spent in the nest after placing of the first pup in the nest (nest with first pup). (6) The number of times the female drew away from one of her pups, situated outside the nest, without their being transported (move away). For Variables 2 to 6, taking into account the shape of distributions, the significance of the differences was tested by the Kruskall-Wallis one-way analysis of variance by ranks (Table 2). (7) Percentage of females remaining in the nest with all their pups 2 consecutive rain in the 15 min of observation (nest with all pups) (Table 3). (8) The intervals between the retrieval of the first and second pups, the second and third pups, and the third and fourth pups were recorded for females having retrieved at least four pups. Seven females per strain were considered. The scores were logarithmically transformed in order to normalize the distributions and homogenize the variances. A two-way analysis of variance involving strains and intervals between retrievals was computed, with interval treated as a repeated measure. The rank of the interval considered has a significant effect (F(2, 132) = 34.28, p < .005). The time between one retrieval and the following one decreases linearly (linear tendency, F(1, 66) = 70.0, p < .001, quadratic tendency ns). The effect of strain approaches significance (F(10, 66) = 1.79, p < .10) like that of the interaction between these two factors (F(20, 132) = 1.48, p < .10). It is possible to bring forward four complementary observations. (1) Number of days of isolation had no observable effect on any measure; rank-order correlations between strain means on number of days of isolation and strain medians on retrieving variables were nonsignificant (p > . 10). (2) The differences between the mean number of offspring per strain cannot account for differences observed here between strains; indeed, rank-order correlations between strain means on number of pups and strain medians on retrieving variables are nonsignificant (p > . 10). Moreover, the females of four strains were observed with their first litter born of crossing with males of another strain (CH with pups CHNF1; N with N C H F I ; B6 with B6LF1; L with LB6F1). The size of the first litter of heterozygotes is significantly higher than the size of the first litter of homozygotes, but the median scores of the females of these strains in the retrieving test variables do not differ significantly from those of Tables 1 and 2. (3) Rank-order intercorrelations between strain medians on three variables--first retrieval, move away, and nest with
208
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PUP CARE IN MOUSE INBRED STRAINS
209
TABLE 3 In the Nest with All Pups during 120 sec. Variable 7: Nest with all pups Strains
N
Percent
CBA/H CBA/J C3H/Ico C57BL/6 BALB/C NZB DBA/2 XLII A/J C57B4 AKR
14 15 9 10 10 8 9 8 11 16 6
93.33 100 90 90.9 62.5 53.3 64.3 57.1 92.7 80 54.6
Note.
X2
=
23.67, p < .01; N, number of
females.
all pups--are significant, the third variable being negatively correlated with the two others (rho values between 1.611 and 1.821, p < .05). It may be noted here that the variables are not independent by construction. For example, when one female draws away from one of her pups (move away variable), she often can take more time to transport the first pup (first retrieval variable). However, because behaviors were recorded for 15 min after the first retrieval, in the case where the female did not stay 2 consecutive min in the nest with all the pups, it was possible to measure the variables move away and nest with all pups by taking the first retrieval as origin. In this case the variables remain intercorrelated (p < .05). (4) The validity of the measurements first retrieval, move away, and nest with all pups is demonstrated by their association with the probability of pup survival. This latter was measured 24 hr after the test using the ratio pups living at 48 hr/pups living at 24 hr. Rank-order correlations between strain medians on first retrieval, move away, nest with all pups, and this criterion are, respectively, - . 6 1 , - . 6 5 , and .58 (p < .05). Several factors might account for the ordering of strains in this test. The role of production by the pups and the mother's processing of ultrasonic data are discussed by Roubertoux, Carlier, Cohen-Salmon, and Jouhaneau (1982). Differences between the strains do not appear for all the variables. For example, first pup carrying does not differ from one strain to another--what differs is the latency of retrieval that allows this conduct (similar results have been reported on biparous females from eight inbred strains by Cohen-Salmon, Carlier, & Roubertoux, in press). Thus, for
210
CARLIER, ROUBERTOUX, AND COHEN-SALMON
the retrieval laying down sequence the hypothesis is made (Roubertoux, 1981)--by analogy with neurophysiology of motor behavior (H6can & Jeannerod, 1978)--that there is a kind of preprogramed or selected loop whose starting requires a stimulus of variable intensity. In subjects requiring a high stimulus level, the latency of first retrieval is longer than in those that require a low stimulus level. Moreover, once activated, this loop could demand a stimulus level increasingly weak from one trial to another. This hypothesis could be compatible with decrease of intervals between retrievals, as is revealed by the kinetics analysis. REFERENCES Cohen-Salmon, Ch., Carlier, M., & Roubertoux, P. (1982). Differences in pattern of pup care in Mus musculus domesticus. II Effects of parity on eight inbred strains. Biology of Behavior, in press. H6can, H., & Jeannerod, M. (1978). Du Contr6le Moteur it l'Organisation du Geste, p. 443. Paris: Masson. Hennessy, M. B., Li, J., Lowe, E. L., & Levine, S. (1980). Maternal behavior, pup vocalizations, and pup temperature changes following handling in mice of 2 inbred strains. Developmental Psychobiology, 13,(6), 573-584. Roubertoux, P. (1981). R61e des comportements dans les m6canismes 6volutifs: Ethologie g6n~tique et diff6rentielle. In Apprentissage, M~moire et l~volution. Hommage it M. Rosenzweig, Paris: Publications de la Sorbonne. Roubertoux, P., & Cartier, M. (1982). Analyse g6n6tique et d6veloppement pr6coce. In Le Ddveloppement. Paris, P.U.F.: Association de Psychologie Scientifique de Langue Francaise, in press. Roubertoux, P., Carlier, M., Cohen-Salmon, Ch., & Jouhaneau, J. (1982). Developmental study of pup vocalizations in 8 inbred strains of Mice. Helsinki: Third International Theriological Congress, 15-20 August. Wainwright, P. E. (1981). Maternal performance of inbred & hybrid laboratory mice (Mus musculus). Journal of Comparative and Physiological Psychology, 95, 694-707.