- Email: [email protected]
Do vocalizations of the male rat elicit calling from the female?
BEHAVIORALAND NEURALBIOLOGY59, 76--78 (1993)
BRIEF REPORT Do Vocalizations of the Male Rat Elicit Calling from the Female? NICHOLAS R. WHITE, REYNALDO N. GONZALES, AND RONALD J . BARFIELD1
Department of Biological Sciences, Busch Campus, Rutgers University, Piscataway,New Jersey 08855-1059 when the female was unable to call, she increased her rate of darting. In an attempt to analyze the sensory regulation of female calling, White, Colona, and Barfield (1991) found t h a t male odor cues stimulated calling in the female. Cues from sexually mature, gonadally intact males were more effective t h a n cues from castrates, juveniles, or females. Male calls were presented to the females, but the calls did not come from the same location as a nearby devocalized male. The present study was u n d e r t a k e n to determine whether male vocalizations elicit calling in female rats.
Female rats emit calls during copulation that appear to be associated with their own proceptive behavior. In an earlier study, we had determined that females emit calls when presented with odor cues from a sexually competent adult male. Two experiments were undertaken to determine whether females would vocalize when presented with tape recorded male ultrasonic vocalizations. In the first females were presented with no calls, male mating calls or male preejaculatory calls. They received one test in each sound condition with a devocalized male in the immediate vicinity and one test with no male present. Females tested alone called at a lower level than those tested in the presence of a devocalized male. The presence of male calls did not significantly increase the frequency of calling in females tested in the presence of a male. When females were tested alone, however, calling did increase significantly when male mating calls were presented, but not when preejaculatory calls were presented. In a second experiment, it was confirmed that male mating vocalizations elicited more calls from the female. Thus, male mating calls may elicit vocalizations from the female, but are less effective than male odor cues. © 1993Academic Press, Inc.
Experiment 1. Female rats were presented both with male odor cues and with two different male vocalizations to determine whether male calling elicits vocalization from the female. Twelve female rats and four males were used as subjects in this study. All were purchased from Blue Spruce, Inc. (Altamont, NY). The rats were housed singly in our colony, which was on a reverse 12:12 light cycle with lights out at 1000 h. They had constant access to food and water in their home cages. The females were ovariectomized under Metofane anesthesia shortly after their arrival in the laboratory. All males were devocalized under Chloropent anesthesia by means of a unilateral section of the inferior laryngeal nerve. Both males and females were allowed to copulate through one ejaculatory series at least three times before the experiment began. Testing took place in a 30 x 30 x 39-cm wood and Plexiglas cage. A wire mesh cage (18 x 18 x 21 cm) was positioned against one of the wooden walls of the test cage. An electrostatic speaker was put into a hole in the wall of the test cage, at the back of the wire mesh cage. Male vocalizations were tape recorded on a Lock-
Thomas and Barfield (1985) first reported t h a t female rats emitted ultrasonic vocalizations during copulation. These calls generally had the spectral characteristics of calls produced by males. White and Barfield (1987, 1989) found t h a t calling in females appeared to be related to proceptive behavior; This research was supported by grants from NIH and NSF to Ronald J. Barfield. Reynaldo Gonzales performed this research for his Senior Project in Biology at Rutgers University. He is now at the University of Medicine and Dentistry of New Jersey in Newark. This project was presented at the Conference on Reproductive Behavior in 1990 at Atlanta, GA. Address correspondence and reprint requests to Dr. Ronald J. Barfield, Department of Biological Sciences, Busch Campus, Rutgers University, Piscataway, NJ 08855-1059. 76 0163-1047/93 $5.00 Copyright © 1993 by Academic Press, Inc. All rights of reproduction in any form reserved.
77
MATING CALLS OF FEMALE RATS
heed Store 4 tape recorder and played through a driver amplifier to the electrostatic speaker. Playback was controlled by an electronic switch that produced no extraneous noise. Calling by the females was monitored with a QMC heterodyne receiver (bat detector) that converts ultrasounds into the humanly audible range. The bat detector was set to "broadband," enabling it to monitor calls from 20 to 150 kHz. The output of the bat detector was monitored through headphones. Tape recordings of both male mating calls and male preejaculatory calls were used in this experiment, white, Cagiano, Moises, and Barfield (1990) found that calling patterns of male rats changed as the ejaculatory series progressed. Mating calls with higher frequency and shorter duration occurred ubiquitously throughout the series. Preejaculatory calls occurred later in the series; they were of lower frequency, longer duration, and higher intensity than the mating calls. The preejaculatory call taped in this experiment was of the "low-long" category. Calls were tape recorded from one of three males copulating individually with a devocalized female. These rats came from the same shipment as the other rats used in the experiment, but were not used in the tests themselves. Using a Uniscan 2 fast Fourier analyzer, a suitable example of a mating call and a preejaculatory call was found and played into a Kay digital Sonagraph. One side of a tape was filled with each of the calls. Sonagrams from the "stimulus tape" were compared with Sonagrams from the original tape and were found to be identical. In selecting the call to be used in the experiment, the clarity of the call and the absence of background noise was given priority. White et al. (1990) found that there was very little variability among calls of either type in terms of spectral frequency or duration. During the tests, mating calls were played at 70 dB (SPL) and preejaculatory calls at 80 dB, as determined by a measuring amplifier; these are consistent with the intensities of calls emitted by copulating rats reported by White et al. (1990). Each of 12 females was tested individually 6 times. In 3 of the tests, a devocalized male was present in the wire mesh cage; in the other 3 tests, there was no male in the mesh cage. Each of the three types of sound stimulus were presented to the females twice, once when the devocalized female was present and once when she was absent. The three sound stimuli consisted of mating calls, preejaculatory calls, and tape hiss produced by playing a blank tape; the latter was used for control purposes. Only one sound stimulus was presented in
PLAYBACK STIMULUS
40
T
u~
o
I'-
30
[]
NO CALL
[]
MATING CALL
[]
PREJ. CALL
N
...% O O
20"
m
10
:i
Z
MALE PRESENT
I
NO MALE PRESENT
FIG. 1. The m e a n n u m b e r (and S t a n d a r d Error) of vocalizations emitted by the female in each of the playback conditions, both when a devocalized male was present and when no male was present.
each test. The order of all tests was determined at random. There was an interval of at least 4 days between each test. Females were brought into estrus by injections of 8 t~g estradiol benzoate (sc) and 500/~g progesterone, 48 and 4 h prior to testing, respectively. Before each test, the cages were washed with soapy water. In tests requiring the presence of a male, the male was first checked to verify devocalization by shaking him twice under the microphone of the bat detector, and then allowing him to explore the cage for 3 rain. Males were rotated after each test. After the male was positioned in the wire mesh cage, the female was put into the test cage for 5 min. During this time, ultrasonic calls were monitored with the bat detector. After each test, the female was paired with a male to determine that she was receptive. The number of vocalizations emitted in each test is shown in Fig. 1. Log-transformed data were subjected to a factorial ANOVA. There was a significant interaction between the male stimulus condition and the type of call (F(2, 22) = 7.42; p < .01). Overall, female calling was higher when the devocalized male was present than when no male was present (orthogonal contrast F(1, 22) = 92.5; p < .001). When the male was present, there was no difference in female calling across the sound stimulus conditions. When no male was present, however, the female emitted more calls when mating calls were presented than when either tape hiss or preejaculatory calls were presented. The present studies show that females call at a high rate when tested in the vicinity of a sexually competent male. Presentation of male vocalizations does not affect the level of calling when the male
78
WHITE, GONZALES,AND BARFIELD
is present. Both these results confirm the findings of Colona et al. (1991). When a stimulus male is not present, however, females call more only when presented with male mating calls. E x p e r i m e n t 2. The second experiment was performed to confirm that females emit more calls when presented with male mating calls with no male present. In order to see if this result would generalize to a larger test cage, we used cages of two different sizes. Twelve female rats were maintained in the same manner as the females in Experiment 1. No males were used in this study as stimulus animals. Each female was tested four times in a cage in which the length could be varied by moving a wooden partition. In two of the tests, the cage was 30 cm long (small cage), as in the first experiment. In the other two tests, it was 89 cm long (large test). The other dimensions of the cage were 30 cm wide and 39 cm high. In one of the tests in each cage condition, male mating calls were presented. In the other test, tape hiss was presented for control purposes. Male preejaculatory calls were not presented in this experiment. In other respects, the procedure of this experiment was the same as the previous
study. The overall frequency of calls was lower in Experiment 2 than that in Experiment 1. Since assumptions of normality were violated, the results were analyzed with nonparametric Wilcoxon tests, comparing the mating call and control tests in both the short-cage and long-cage conditions. When tested in the short cage, females emitted more calls when mating calls were played than when mating calls were not played (medians and (SIQR's): mating calls 2.5 (2.0), control 1.5 (1.0); Wilcoxon test p = .05). Similarly, there was a significant difference in calling in the large test (mating calls 4.5 (2.5), control 0.5 (0.0); p < .02). The results of this experiment follow the same pattern as the previous experiment: females are likely to call more if presented with tape-recorded male mating calls than with a control sound. Overall, however, the females emitted m a n y fewer vocalizations than in the earlier study. Such discrepancies are not unusual; there are differences in call parameters of various kinds among rat cohorts (e.g., White et al., 1990). Informally, we have often been aware of considerable variability in the n u m b e r of calls emitted by rats in different cohorts; perhaps the difference is seasonal. Nonetheless, there is generally a high level of consistency in the w a y in which
the calls affect copulatory behavior across experiments. Male mating calls can elicit small amounts of ultrasonic vocalization from females in induced estrus. This finding suggests that the female will respond with a call of her own to a vocal cue that indicates that a male is in the area. The females are more responsive to the mating calls that the male emits throughout copulation rather than the preejaculatory calls that occur late in the series. If the female attracted a male that was about to ejaculate, it is unlikely that he would be able to provide her with enough intromissive stimulation to induce a progestational state, at least not immediately. It is possible that the female m a y emit vocalizations to attract a relatively fresh male to her immediate vicinity. Females call more if there is a male nearby. It is likely that she is responding to his odor cues, although she m a y also respond to visual or tactile cues. When the male was positioned in such a w a y that the likelihood of visual or tactile contact was greatly reduced, females still vocalized at high levels (White et al., 1991; Experiment 4). Female calls probably function as a proceptive cue to the male when he is in the immediate vicinity of the female rather than as a means to attract him from a distance. Female calling was highest when the male was present nearby; less calling occurred when more distal cues were available, either in the form of vocalizations (this study) or odor cues left in bedding (White et al., 1991; Experiment 1). Taken together with earlier studies that demonstrated that darting increases when the female was unable to call, the results suggest that female vocalizations function as a proceptive cue to solicit sexual behavior from the male. REFERENCES Thomas, D. A., & Barfield, R. J. (1985). Ultrasonic vocalizations of the female rat (Rattus norvegicus) during mating. Animal Behaviour, 33, 720-725. White, N. R., & Barfield, R. J. (1987). Role of the ultrasonic vocalization of the female rat (Rattus norvegicus) in sexual behavior. Journal of Comparative Psychology, 101, 83-91. White, N. R., & Barfield, R. J. (1989). Playback of female ultrasonic vocalizations during sexual behavior. Physiology and Behavior, 45, 229-233. White, N. R., Cagiano, R., Moises, A. U., & Barfield, R. J. (1990). Changes in mating vocalizations over the ejaculatory series in rats (Rattus norvegicus). Journal of Comparative Psychology, 104, 255-262. White, N. R., Colona, L. C., & Barfield, R. J. (1991). Sensory cues that elicit ultrasonic vocalizations in female rats. (Rattus norvegicus). Behavioral and Neural Biology, 55, 154-165.
BRIEF REPORT Do Vocalizations of the Male Rat Elicit Calling from the Female? NICHOLAS R. WHITE, REYNALDO N. GONZALES, AND RONALD J . BARFIELD1
Department of Biological Sciences, Busch Campus, Rutgers University, Piscataway,New Jersey 08855-1059 when the female was unable to call, she increased her rate of darting. In an attempt to analyze the sensory regulation of female calling, White, Colona, and Barfield (1991) found t h a t male odor cues stimulated calling in the female. Cues from sexually mature, gonadally intact males were more effective t h a n cues from castrates, juveniles, or females. Male calls were presented to the females, but the calls did not come from the same location as a nearby devocalized male. The present study was u n d e r t a k e n to determine whether male vocalizations elicit calling in female rats.
Female rats emit calls during copulation that appear to be associated with their own proceptive behavior. In an earlier study, we had determined that females emit calls when presented with odor cues from a sexually competent adult male. Two experiments were undertaken to determine whether females would vocalize when presented with tape recorded male ultrasonic vocalizations. In the first females were presented with no calls, male mating calls or male preejaculatory calls. They received one test in each sound condition with a devocalized male in the immediate vicinity and one test with no male present. Females tested alone called at a lower level than those tested in the presence of a devocalized male. The presence of male calls did not significantly increase the frequency of calling in females tested in the presence of a male. When females were tested alone, however, calling did increase significantly when male mating calls were presented, but not when preejaculatory calls were presented. In a second experiment, it was confirmed that male mating vocalizations elicited more calls from the female. Thus, male mating calls may elicit vocalizations from the female, but are less effective than male odor cues. © 1993Academic Press, Inc.
Experiment 1. Female rats were presented both with male odor cues and with two different male vocalizations to determine whether male calling elicits vocalization from the female. Twelve female rats and four males were used as subjects in this study. All were purchased from Blue Spruce, Inc. (Altamont, NY). The rats were housed singly in our colony, which was on a reverse 12:12 light cycle with lights out at 1000 h. They had constant access to food and water in their home cages. The females were ovariectomized under Metofane anesthesia shortly after their arrival in the laboratory. All males were devocalized under Chloropent anesthesia by means of a unilateral section of the inferior laryngeal nerve. Both males and females were allowed to copulate through one ejaculatory series at least three times before the experiment began. Testing took place in a 30 x 30 x 39-cm wood and Plexiglas cage. A wire mesh cage (18 x 18 x 21 cm) was positioned against one of the wooden walls of the test cage. An electrostatic speaker was put into a hole in the wall of the test cage, at the back of the wire mesh cage. Male vocalizations were tape recorded on a Lock-
Thomas and Barfield (1985) first reported t h a t female rats emitted ultrasonic vocalizations during copulation. These calls generally had the spectral characteristics of calls produced by males. White and Barfield (1987, 1989) found t h a t calling in females appeared to be related to proceptive behavior; This research was supported by grants from NIH and NSF to Ronald J. Barfield. Reynaldo Gonzales performed this research for his Senior Project in Biology at Rutgers University. He is now at the University of Medicine and Dentistry of New Jersey in Newark. This project was presented at the Conference on Reproductive Behavior in 1990 at Atlanta, GA. Address correspondence and reprint requests to Dr. Ronald J. Barfield, Department of Biological Sciences, Busch Campus, Rutgers University, Piscataway, NJ 08855-1059. 76 0163-1047/93 $5.00 Copyright © 1993 by Academic Press, Inc. All rights of reproduction in any form reserved.
77
MATING CALLS OF FEMALE RATS
heed Store 4 tape recorder and played through a driver amplifier to the electrostatic speaker. Playback was controlled by an electronic switch that produced no extraneous noise. Calling by the females was monitored with a QMC heterodyne receiver (bat detector) that converts ultrasounds into the humanly audible range. The bat detector was set to "broadband," enabling it to monitor calls from 20 to 150 kHz. The output of the bat detector was monitored through headphones. Tape recordings of both male mating calls and male preejaculatory calls were used in this experiment, white, Cagiano, Moises, and Barfield (1990) found that calling patterns of male rats changed as the ejaculatory series progressed. Mating calls with higher frequency and shorter duration occurred ubiquitously throughout the series. Preejaculatory calls occurred later in the series; they were of lower frequency, longer duration, and higher intensity than the mating calls. The preejaculatory call taped in this experiment was of the "low-long" category. Calls were tape recorded from one of three males copulating individually with a devocalized female. These rats came from the same shipment as the other rats used in the experiment, but were not used in the tests themselves. Using a Uniscan 2 fast Fourier analyzer, a suitable example of a mating call and a preejaculatory call was found and played into a Kay digital Sonagraph. One side of a tape was filled with each of the calls. Sonagrams from the "stimulus tape" were compared with Sonagrams from the original tape and were found to be identical. In selecting the call to be used in the experiment, the clarity of the call and the absence of background noise was given priority. White et al. (1990) found that there was very little variability among calls of either type in terms of spectral frequency or duration. During the tests, mating calls were played at 70 dB (SPL) and preejaculatory calls at 80 dB, as determined by a measuring amplifier; these are consistent with the intensities of calls emitted by copulating rats reported by White et al. (1990). Each of 12 females was tested individually 6 times. In 3 of the tests, a devocalized male was present in the wire mesh cage; in the other 3 tests, there was no male in the mesh cage. Each of the three types of sound stimulus were presented to the females twice, once when the devocalized female was present and once when she was absent. The three sound stimuli consisted of mating calls, preejaculatory calls, and tape hiss produced by playing a blank tape; the latter was used for control purposes. Only one sound stimulus was presented in
PLAYBACK STIMULUS
40
T
u~
o
I'-
30
[]
NO CALL
[]
MATING CALL
[]
PREJ. CALL
N
...% O O
20"
m
10
:i
Z
MALE PRESENT
I
NO MALE PRESENT
FIG. 1. The m e a n n u m b e r (and S t a n d a r d Error) of vocalizations emitted by the female in each of the playback conditions, both when a devocalized male was present and when no male was present.
each test. The order of all tests was determined at random. There was an interval of at least 4 days between each test. Females were brought into estrus by injections of 8 t~g estradiol benzoate (sc) and 500/~g progesterone, 48 and 4 h prior to testing, respectively. Before each test, the cages were washed with soapy water. In tests requiring the presence of a male, the male was first checked to verify devocalization by shaking him twice under the microphone of the bat detector, and then allowing him to explore the cage for 3 rain. Males were rotated after each test. After the male was positioned in the wire mesh cage, the female was put into the test cage for 5 min. During this time, ultrasonic calls were monitored with the bat detector. After each test, the female was paired with a male to determine that she was receptive. The number of vocalizations emitted in each test is shown in Fig. 1. Log-transformed data were subjected to a factorial ANOVA. There was a significant interaction between the male stimulus condition and the type of call (F(2, 22) = 7.42; p < .01). Overall, female calling was higher when the devocalized male was present than when no male was present (orthogonal contrast F(1, 22) = 92.5; p < .001). When the male was present, there was no difference in female calling across the sound stimulus conditions. When no male was present, however, the female emitted more calls when mating calls were presented than when either tape hiss or preejaculatory calls were presented. The present studies show that females call at a high rate when tested in the vicinity of a sexually competent male. Presentation of male vocalizations does not affect the level of calling when the male
78
WHITE, GONZALES,AND BARFIELD
is present. Both these results confirm the findings of Colona et al. (1991). When a stimulus male is not present, however, females call more only when presented with male mating calls. E x p e r i m e n t 2. The second experiment was performed to confirm that females emit more calls when presented with male mating calls with no male present. In order to see if this result would generalize to a larger test cage, we used cages of two different sizes. Twelve female rats were maintained in the same manner as the females in Experiment 1. No males were used in this study as stimulus animals. Each female was tested four times in a cage in which the length could be varied by moving a wooden partition. In two of the tests, the cage was 30 cm long (small cage), as in the first experiment. In the other two tests, it was 89 cm long (large test). The other dimensions of the cage were 30 cm wide and 39 cm high. In one of the tests in each cage condition, male mating calls were presented. In the other test, tape hiss was presented for control purposes. Male preejaculatory calls were not presented in this experiment. In other respects, the procedure of this experiment was the same as the previous
study. The overall frequency of calls was lower in Experiment 2 than that in Experiment 1. Since assumptions of normality were violated, the results were analyzed with nonparametric Wilcoxon tests, comparing the mating call and control tests in both the short-cage and long-cage conditions. When tested in the short cage, females emitted more calls when mating calls were played than when mating calls were not played (medians and (SIQR's): mating calls 2.5 (2.0), control 1.5 (1.0); Wilcoxon test p = .05). Similarly, there was a significant difference in calling in the large test (mating calls 4.5 (2.5), control 0.5 (0.0); p < .02). The results of this experiment follow the same pattern as the previous experiment: females are likely to call more if presented with tape-recorded male mating calls than with a control sound. Overall, however, the females emitted m a n y fewer vocalizations than in the earlier study. Such discrepancies are not unusual; there are differences in call parameters of various kinds among rat cohorts (e.g., White et al., 1990). Informally, we have often been aware of considerable variability in the n u m b e r of calls emitted by rats in different cohorts; perhaps the difference is seasonal. Nonetheless, there is generally a high level of consistency in the w a y in which
the calls affect copulatory behavior across experiments. Male mating calls can elicit small amounts of ultrasonic vocalization from females in induced estrus. This finding suggests that the female will respond with a call of her own to a vocal cue that indicates that a male is in the area. The females are more responsive to the mating calls that the male emits throughout copulation rather than the preejaculatory calls that occur late in the series. If the female attracted a male that was about to ejaculate, it is unlikely that he would be able to provide her with enough intromissive stimulation to induce a progestational state, at least not immediately. It is possible that the female m a y emit vocalizations to attract a relatively fresh male to her immediate vicinity. Females call more if there is a male nearby. It is likely that she is responding to his odor cues, although she m a y also respond to visual or tactile cues. When the male was positioned in such a w a y that the likelihood of visual or tactile contact was greatly reduced, females still vocalized at high levels (White et al., 1991; Experiment 4). Female calls probably function as a proceptive cue to the male when he is in the immediate vicinity of the female rather than as a means to attract him from a distance. Female calling was highest when the male was present nearby; less calling occurred when more distal cues were available, either in the form of vocalizations (this study) or odor cues left in bedding (White et al., 1991; Experiment 1). Taken together with earlier studies that demonstrated that darting increases when the female was unable to call, the results suggest that female vocalizations function as a proceptive cue to solicit sexual behavior from the male. REFERENCES Thomas, D. A., & Barfield, R. J. (1985). Ultrasonic vocalizations of the female rat (Rattus norvegicus) during mating. Animal Behaviour, 33, 720-725. White, N. R., & Barfield, R. J. (1987). Role of the ultrasonic vocalization of the female rat (Rattus norvegicus) in sexual behavior. Journal of Comparative Psychology, 101, 83-91. White, N. R., & Barfield, R. J. (1989). Playback of female ultrasonic vocalizations during sexual behavior. Physiology and Behavior, 45, 229-233. White, N. R., Cagiano, R., Moises, A. U., & Barfield, R. J. (1990). Changes in mating vocalizations over the ejaculatory series in rats (Rattus norvegicus). Journal of Comparative Psychology, 104, 255-262. White, N. R., Colona, L. C., & Barfield, R. J. (1991). Sensory cues that elicit ultrasonic vocalizations in female rats. (Rattus norvegicus). Behavioral and Neural Biology, 55, 154-165.