- Email: [email protected]
Ventral marking in black and agouti gerbils (Meriones unguiculatus)
BEHAVIORAL BIOLOGY 24, 545--548 (1978)
BRIEF REPORT Ventral Marking in Black and Agouti Gerbils
(Meriones unguiculatus) GERARD DIZINNO 1 AND A N D R E W N . CLANCY
Department of Psychology, The University of Texas at Austin, Austin, Texas 78712 Male and female Mongolian gerbils (Meriones unguiculatus) of both agouti and black coat color variations were tested for ventral marking in an open field. Males marked more than females and black gerbils marked more than the agouti animals. Black females marked at levels equal to those of agouti males, and thus they may be useful in future investigations of neural and hormonal factors affecting ventral marking in females. Such research was difficult in the past because of the extremely low levels of marking normally exhibited by agouti females.
A coat color variation has recently been described in the Monogolian gerbil (Meriones unguiculatus) (Cramlett et al. 1974). These animals, originally derived from a single breeding pair of agouti gerbils (guard hairs of yellow-brown with black tips, undercoat and ventral surface white to grey), are predominantly black in coat color, except for small patches of white hair on the chest and paws. Black gerbils otherwise appear to be similar to the more familiar agouti gerbils in other physical characteristics and are becoming generally available as laboratory animals. Behavioral effects of the coat color variation have not yet been objectively assessed, although observations in our laboratory suggested that black males ventral mark at higher rates than agouti males (B. Gregg, personal communication). In this preliminary investigation, ventral marking was compared between black and agouti gerbils of both sexes. Ventral marking is an important social behavior of the gerbil. The response occurs when the gerbil presses a midventral sebaceous gland over objects in the environment (Thiessen, 1968; Thiessen et aI. 1969; Thiessen et al. 1970; Thiessen, 1 This investigation was supported in part by National Institute of Mental Health Grant MH 14076-11. We thank Dr. D. D. Thiessen for providing the gerbils, facilities, and advice necessary for the successful completion of this investigation. In addition, we thank Steve Scott and Melissa Young for their help in data collection. 545
0091-6773/78/0244-0545502.00/0 Copyright© •978 by Academicth'ess.Inc. All rightsof reproductionin any formreserved.
546
DIZINNO AND CLANCY
1973). The behavior is sexually dimorphic: males mark more frequently than females (Thiessen, 1968; Thiessen et al., 1969). Also, ventral marking and scent gland morphology are testosterone dependent in the male (Thiessen et al. 1969; Blum and Thiessen, 1971). Marking behavior among females is elevated during pregnancy and lactation (Wallace et al. 1973) and may be influenced by estrogen (Yahr and Thiessen, 1975). We viewed ventral marking as a potentially sensitive measure to discriminate genetic influences on the behavior of black as opposed to agouti gerbils. Testing was conducted using the apparatus and procedure of Thiessen (1968). Individual animals were placed for 5 min in a wooden, grey, 1-m-square open field. The floor of the open field was divided by intersecting lines into 16 quadrants. Nine plastic markibg pegs protruded from the floor, one at each point where the dividing lines intersected. The number of ventral marks applied to the pegs and to the floor were combined to give a "total marks" score. Each gerbil was tested a total of three times, with tests occurring at weekly intervals. The floors and walls of the open field were thoroughly cleaned before every test. A total of 41 agouti gerbils (18 males and 23 females) and 42 black gerbils (18 males and 24 females) between 200 and 300 days of age were tested. The gerbils were individually housed and maintained on a 12/12 light/dark cycle with food and water available ad lib. during the course of the experiment. The mean number of marks for all four groups across trials is presented in Fig. 1. Data were first analyzed by means of a 2 x 2 x 3 repeated measures analysis of variance (coat color x sex x trials), and all sub-
15
BM
u') v r't"
< 10 rr" W
.....
BF AM
Z
Ix
1
2
3
TRIALS
F1o. 1. Mean (_+ SEM) number of ventral marks in an open field during three 5-min tests for four groups of gerbils: agouti males (AM), agouti females (AF), black males (BM), and black females (BF).
GERBIL VENTRAL MARKING
547
sequent between- and within-group comparisons were performed with Bonferroni t tests (Miller, 1966). Results of the analyses indicate that male gerbils marked significantly more than female gerbils (F = 15.03; df = 1,79; P < 0.001), as expected, given previous reports of a sexual dimorphism for this behavior (Thiessen, 1968; Thiessen et al., 1969). In addition, black gerbils marked significantly more than agouti gerbils (F = 10.52; df = 1.79; P < 0.001). A significant trials effect (F = 15.41; df = 2,158; P < 0.001) was subsequently analyzed, and it was found that gerbils marked significantly less on trial 1 than on trials 2 and 3 (P < 0.01 in both cases) and that the average marks on trials 2 and 3 were equivalent. The interaction of coat color by trials was also significant (F = 6.88; df = 2,158; P < 0.001). Analysis of this interaction showed that there were no significant differences between the mean number of marks across trials for agouti gerbils, but that the black gerbils marked significantly less on trial 1 than on trials 2 or 3 (P < 0.01 in both cases), and that their average marking frequencies on the last two trials were similar (P = ns). Therefore, it appears that the overall trials effect can be primarily accounted for by the marking scores of the black gerbils. It appears that the sexual dimorphism in marking is consistent within the coat color variations, as evidenced by the lack of a significant coat color by sex interaction (F = 0.07; df = 1,79; P = ns), but that this dimorphism occurs at a higher average level in black gerbils. This can be illustrated even more clearly by comparing the average marking scores of all four groups on the third trial. At that time, black males marked significantly more than any other group (P < 0.01 in all cases) and agouti females marked less than any other group (P < 0.01 in all cases). However, the marking scores of agouti males and black females were intermediate to the black males and agouti females and not significantly different from one another. These results are of interest for two reasons. First, since investigators may be supplied with black gerbils in the future, they should be aware of the fact that there are important behavioral and, quite possibly, physiological differences between those animals and the more familiar agouti gerbils. Second, the findings that black gerbils mark significantly more than agouti gerbils and that black females mark at levels similar to those of agouti males are interesting in their own right, because they suggest that the black animals may prove to be useful tools in investigations of the neural and hormonal bases of sexually dimorphic behavior and morphology in this species. Particularly significant is the possibility that the physiological factors controlling ventral marking in the female may now be studied in great detail. The very low levels of marking exhibited by agouti females have made research of this kind difficult until now.
548
DIZINNO AND CLANCY
REFERENCES Blum, S. L., and Thiessen, D. D. (1971). The effect of different amounts of androgen on scent marking in the male Mongolian gerbil. Horm. Behav. 2, 93-105. Cramlett, S. H., Toft, J. D., and Olsen, N. W. (1974). Malignant melanoma in the black gerbil (Meriones unguiculatus). Lab. Anim. Sci. 24, 545-547. Miller, R. G., Jr. (1966). "Simultaneous Statistical Inference." New York: McGraw-Hill. Thiessen, D. D. (1973). Footholds for survival. Amer. Sci. 61, 346-351. Thiessen, D. D. (1968). The roots of marking in the Mongolian gerbil: A problem of species-common topography. Behav. Res. Methods Instrum. 1, 70-76. Thiessen, D. D., Blum, S. L., and Lindzey, G. (1969). A scent marking response associated with the ventral sebaceous gland of the Mongolian gerbil (Meriones unguiculatus). Anita. Behav. 18, 26-30. Thiessen, D. D., Friend, H. C., and Lindzey, G. (1968). Androgen control of territorial marking in the Mongolian gerbil. Science 160, 432-434. Thiessen, D. D., Lindzey, G., Blum, S. L., and Wallace, P. (1970), Social interactions and scent marking in the Mongolian gerbil (Meriones unguiculatus). Anim. Behav. 19, 505-513. Wallace, P., Owen, K., and Thiessen, D. D. (1973). The control and function of maternal scent marking in the Mongolian gerbil (Meriones unguiculatus). Physiol. Behav. 10, 463-466. Yahr, P., and Thiessen, D. D. (1975). Estrogen control of scent marking in female Mongolian gerbils (Meriones unguiculatus). Behav. Biol. 13, 95-101.
BRIEF REPORT Ventral Marking in Black and Agouti Gerbils
(Meriones unguiculatus) GERARD DIZINNO 1 AND A N D R E W N . CLANCY
Department of Psychology, The University of Texas at Austin, Austin, Texas 78712 Male and female Mongolian gerbils (Meriones unguiculatus) of both agouti and black coat color variations were tested for ventral marking in an open field. Males marked more than females and black gerbils marked more than the agouti animals. Black females marked at levels equal to those of agouti males, and thus they may be useful in future investigations of neural and hormonal factors affecting ventral marking in females. Such research was difficult in the past because of the extremely low levels of marking normally exhibited by agouti females.
A coat color variation has recently been described in the Monogolian gerbil (Meriones unguiculatus) (Cramlett et al. 1974). These animals, originally derived from a single breeding pair of agouti gerbils (guard hairs of yellow-brown with black tips, undercoat and ventral surface white to grey), are predominantly black in coat color, except for small patches of white hair on the chest and paws. Black gerbils otherwise appear to be similar to the more familiar agouti gerbils in other physical characteristics and are becoming generally available as laboratory animals. Behavioral effects of the coat color variation have not yet been objectively assessed, although observations in our laboratory suggested that black males ventral mark at higher rates than agouti males (B. Gregg, personal communication). In this preliminary investigation, ventral marking was compared between black and agouti gerbils of both sexes. Ventral marking is an important social behavior of the gerbil. The response occurs when the gerbil presses a midventral sebaceous gland over objects in the environment (Thiessen, 1968; Thiessen et aI. 1969; Thiessen et al. 1970; Thiessen, 1 This investigation was supported in part by National Institute of Mental Health Grant MH 14076-11. We thank Dr. D. D. Thiessen for providing the gerbils, facilities, and advice necessary for the successful completion of this investigation. In addition, we thank Steve Scott and Melissa Young for their help in data collection. 545
0091-6773/78/0244-0545502.00/0 Copyright© •978 by Academicth'ess.Inc. All rightsof reproductionin any formreserved.
546
DIZINNO AND CLANCY
1973). The behavior is sexually dimorphic: males mark more frequently than females (Thiessen, 1968; Thiessen et al., 1969). Also, ventral marking and scent gland morphology are testosterone dependent in the male (Thiessen et al. 1969; Blum and Thiessen, 1971). Marking behavior among females is elevated during pregnancy and lactation (Wallace et al. 1973) and may be influenced by estrogen (Yahr and Thiessen, 1975). We viewed ventral marking as a potentially sensitive measure to discriminate genetic influences on the behavior of black as opposed to agouti gerbils. Testing was conducted using the apparatus and procedure of Thiessen (1968). Individual animals were placed for 5 min in a wooden, grey, 1-m-square open field. The floor of the open field was divided by intersecting lines into 16 quadrants. Nine plastic markibg pegs protruded from the floor, one at each point where the dividing lines intersected. The number of ventral marks applied to the pegs and to the floor were combined to give a "total marks" score. Each gerbil was tested a total of three times, with tests occurring at weekly intervals. The floors and walls of the open field were thoroughly cleaned before every test. A total of 41 agouti gerbils (18 males and 23 females) and 42 black gerbils (18 males and 24 females) between 200 and 300 days of age were tested. The gerbils were individually housed and maintained on a 12/12 light/dark cycle with food and water available ad lib. during the course of the experiment. The mean number of marks for all four groups across trials is presented in Fig. 1. Data were first analyzed by means of a 2 x 2 x 3 repeated measures analysis of variance (coat color x sex x trials), and all sub-
15
BM
u') v r't"
< 10 rr" W
.....
BF AM
Z
Ix
1
2
3
TRIALS
F1o. 1. Mean (_+ SEM) number of ventral marks in an open field during three 5-min tests for four groups of gerbils: agouti males (AM), agouti females (AF), black males (BM), and black females (BF).
GERBIL VENTRAL MARKING
547
sequent between- and within-group comparisons were performed with Bonferroni t tests (Miller, 1966). Results of the analyses indicate that male gerbils marked significantly more than female gerbils (F = 15.03; df = 1,79; P < 0.001), as expected, given previous reports of a sexual dimorphism for this behavior (Thiessen, 1968; Thiessen et al., 1969). In addition, black gerbils marked significantly more than agouti gerbils (F = 10.52; df = 1.79; P < 0.001). A significant trials effect (F = 15.41; df = 2,158; P < 0.001) was subsequently analyzed, and it was found that gerbils marked significantly less on trial 1 than on trials 2 and 3 (P < 0.01 in both cases) and that the average marks on trials 2 and 3 were equivalent. The interaction of coat color by trials was also significant (F = 6.88; df = 2,158; P < 0.001). Analysis of this interaction showed that there were no significant differences between the mean number of marks across trials for agouti gerbils, but that the black gerbils marked significantly less on trial 1 than on trials 2 or 3 (P < 0.01 in both cases), and that their average marking frequencies on the last two trials were similar (P = ns). Therefore, it appears that the overall trials effect can be primarily accounted for by the marking scores of the black gerbils. It appears that the sexual dimorphism in marking is consistent within the coat color variations, as evidenced by the lack of a significant coat color by sex interaction (F = 0.07; df = 1,79; P = ns), but that this dimorphism occurs at a higher average level in black gerbils. This can be illustrated even more clearly by comparing the average marking scores of all four groups on the third trial. At that time, black males marked significantly more than any other group (P < 0.01 in all cases) and agouti females marked less than any other group (P < 0.01 in all cases). However, the marking scores of agouti males and black females were intermediate to the black males and agouti females and not significantly different from one another. These results are of interest for two reasons. First, since investigators may be supplied with black gerbils in the future, they should be aware of the fact that there are important behavioral and, quite possibly, physiological differences between those animals and the more familiar agouti gerbils. Second, the findings that black gerbils mark significantly more than agouti gerbils and that black females mark at levels similar to those of agouti males are interesting in their own right, because they suggest that the black animals may prove to be useful tools in investigations of the neural and hormonal bases of sexually dimorphic behavior and morphology in this species. Particularly significant is the possibility that the physiological factors controlling ventral marking in the female may now be studied in great detail. The very low levels of marking exhibited by agouti females have made research of this kind difficult until now.
548
DIZINNO AND CLANCY
REFERENCES Blum, S. L., and Thiessen, D. D. (1971). The effect of different amounts of androgen on scent marking in the male Mongolian gerbil. Horm. Behav. 2, 93-105. Cramlett, S. H., Toft, J. D., and Olsen, N. W. (1974). Malignant melanoma in the black gerbil (Meriones unguiculatus). Lab. Anim. Sci. 24, 545-547. Miller, R. G., Jr. (1966). "Simultaneous Statistical Inference." New York: McGraw-Hill. Thiessen, D. D. (1973). Footholds for survival. Amer. Sci. 61, 346-351. Thiessen, D. D. (1968). The roots of marking in the Mongolian gerbil: A problem of species-common topography. Behav. Res. Methods Instrum. 1, 70-76. Thiessen, D. D., Blum, S. L., and Lindzey, G. (1969). A scent marking response associated with the ventral sebaceous gland of the Mongolian gerbil (Meriones unguiculatus). Anita. Behav. 18, 26-30. Thiessen, D. D., Friend, H. C., and Lindzey, G. (1968). Androgen control of territorial marking in the Mongolian gerbil. Science 160, 432-434. Thiessen, D. D., Lindzey, G., Blum, S. L., and Wallace, P. (1970), Social interactions and scent marking in the Mongolian gerbil (Meriones unguiculatus). Anim. Behav. 19, 505-513. Wallace, P., Owen, K., and Thiessen, D. D. (1973). The control and function of maternal scent marking in the Mongolian gerbil (Meriones unguiculatus). Physiol. Behav. 10, 463-466. Yahr, P., and Thiessen, D. D. (1975). Estrogen control of scent marking in female Mongolian gerbils (Meriones unguiculatus). Behav. Biol. 13, 95-101.