Testosterone, testis size, seasonality, and behavior in group-living stumptail macaques (Macaca arctoides)

HORMONES

AND

BEHAVIOR

21, 153-169 (1987)

Testosterone, Testis Size, Seasonality, and Behavior in Group-Living Stumptail Macaques (Macaca arcfoides) KEES NIEUWENHUUSEN, KAREL J. DE NEEF,* JACOB TEN Boscri, AND A. bOS SLOB

J. VAN

DER WERFF

Department of Endocrinology, Growth and Reproduction, Faculty of Medicine, Erasmus University, Rotterdam, The Netherlands, and *Scient$c Development Group, Organon International BY, Oss, The Netherlands During a 2%month period, data were collected on physiological parameters and sociosexual behavior of 13 adult male members of a large mixed-sex group of stumptail macaques living in an outdoor cage. Monthly measurements of plasma testosterone, testis size, and body weight revealed no systematic seasonahty. Seasonal variations did occur in branch shaking and grooming (both with low rates in winter), but not in other behaviors studied (copulation, masturbation, aggression). Dominance ranks were stable throughout the study period and were not sign&antly correlated with mean testosterone levels. Temporal fluctuations in behavioral frequencies did not parallel testosterone fluctuations. Interindividual differences in behavioral frequencies were often correlated with dominance rank, but not with testosterone levels. o 1987ACIUI~~~C PESS. I~C.

Seasonalfluctuations in various physiological parameters occur in adult males of several macaque species. In rhesus (Mucaca mulatfu), Japanese (M. fuscutu), and bonnet macaques (M. rudiutu), plasma testosterone levels and testis size reach maximum values during the fall and early winter (Gordon, Rose, and Bernstein, 1976; Sade, 1964; Glick, 1979; Nigi, Tiba, Yamamoto, Floescheim, and Ohsawa, 1980; Wickings and Nieschlag, 1980; Matsubayashi and Enomoto, 1983). Copulatory activity is restricted to the same period of the year, and’ there is significantly more aggression at this time than during other seasons(Eaton, Modahl, and Johnson, 1981; Gordon et al., 1976;Teas, Taylor, and Richie, 1978; Glick, 1979). The synchrony between endocrine and behavioral parameters suggests that increases in testosterone levels may be the cause of increases in copulatory and aggressiveactivity. It has been hypothesizedthat individual endogenous testosterone levels might be correlated with dominance rank and individual behavioral frequencies. However, studies on such interindividual correlations in group-living primates have yielded conflicting 153 Copyri.&t0 All ri#bts

001&506x/87 $1.50

1987 by Academic F’ress, Inc. of reproduction in my form rewed.

154

NIEUWENHUIJSEN ET AL.

results (review: Dixson, 1980). In many studies, only one or a few blood samples per individual were obtained, or groups of unnatural age/sex composition were studied. To our knowledge, there is only one exception: Gordon et al. (1976) conducted a 3-year study of a captive group of rhesus monkeys that consisted of 7 adult males, 40 adult females, and their offspring. Blood samples were taken monthly from each adult male. Mean levels of testosterone, aggression, and copulations showed similar seasonal changes, but individual differences in testosterone levels did not correlate with dominance rank or copulatory activity. This paper reports on behavioral and physiological parameters of adult male members of a large group of stumptail macaques (M. arcroides). In this species, female reproductive parameters (ovulations, conceptions, births) do not show seasonality (Nieuwenhuijsen, Lammers, de Neef, and Slob, 1985). In order to investigate whether or not a seasonal pattern exists for male reproductive parameters, monthly measurements were made of testosterone, testis size, and body weight. Changes in these measures were correlated with changes in various sociosexual behaviors. MATERIALS AND METHODS Subjects At the start of the study (March 1, 1980), the group (together for at least 6 months) consisted of 45 adults (18 males and 27 females, aged 4 to about 12 years) and 25 immature animals. The group lived in an outdoor cage (15.4 x 9.4 x 4.5 m) with an adjacent heated indoor cage (5 x 5.5 x 2 m). During the day, all animals stayed in the outdoor cage; during the night most animals moved indoors. The group was housed in Oss, The Netherlands (latitude 52” N). Diet (monkey chow with additional fruit and vegetables) and feeding time (8:30 AM; a few hours later on blood-sampling days) did not change over the year. Details on formation of the group, housing, and maintainance are given by Nieuwenhuijsen et al. (1985). Physiological Measurements and Blood Sampling To obtain physiological data and blood samples, the animals were chased into the indoor cage, where each male was captured either by hand or by placing a transfer cage over his body. Once a month, 13 adult males were weighed and the length of each testis was measured with calipers. Testis volume was estimated by palpating each testis and comparing the impression with a set of 23 plastic testis models ranging in size from 1 to 40 ml. Measuring testis volume was complicated by the fact that testes were sometimes larger than the largest model (40 ml). In such cases, a value of 42 ml was used for analyses. All testis measures were taken by two investigators independently. If

MACAQUE TESTOSTERONE

AND BEHAVIOR

155

values differed by more than 2 mm or 2 ml, measurementswere repeated until consensus was reached. Mean values ([left + right]/2) were used for analysis. Furthermore, blood samples (5 ml) were obtained from the femoral vein or artery using heparinized syringes. Physical measuresand blood samples were taken between 8:30 and 10:00AM, before the animals had been fed and while they were lightly anesthetized with ketamineHCl (10 mg/kg). It is unlikely that this anesthesia affected testosterone levels (Puri, Puri, and Kumar, 1981; Zaidi, Wickings, and Nieschlag, 1982). Catching the males is a stressful event, which may affect testosterone levels (Rose, Gordon, and Bernstein, 1972; Sapolsky, 1986). Therefore, the adult males were captured and placed in individual cages 24 hr before blood sampling began. One male (M140) plucked his fur when placed in an individual cage. Therefore, he was left in the group and not captured until blood-sampling time. Hormone Assays

Blood was centrifuged within 1 hr after sampling and plasma was stored at -20°C prior to hormone determination. Testosterone was estimated using the radioimmunoassay described by Vejans, Cooke, de Jong, de Jong, and van der Molen (1973) with the modification: in the present study, an antiserum against 1lo-OH-testosterone 11-succinyl-BSA(R5225, provided by Organon International BV) was used. The only major crossreaction was with 17@OH-5a androstan3-one (DHT; 60%). This elevated testosterone data by approximately lO-25%, assumingthat in stumptails, as in other macaques, peripheral plasma levels of DHT are 20-40% of the testosterone levels (Robinson, Scheffler, Eisele, and Goy, 1975;Phoe, nix, 1980; Wickings and Nieschlag, 1980; Meusy-Dessolle and Dang, 1985). Average intraassay and interassay coefficients of variance were 6 and lO%, respectively. Samplescollected before October 1981were assayedlongitudinally (all samples for one male were in one assay). From January 1982, assays were programmed transversally (all samples for one month were in one assay). From October through December 1981, mixed assays were performed. Interindividual differencesin testosteronelevels may have occurred that actually represented interassay differences. Only the transversal assaysprovided reliable indications of interindividual differences.Individual averagesbased on these latter assays correlated well with averagesfrom other assays (7 = 0.833, N = 13, P < 0.0001). Therefore, interassay differences did not bias interindividual differences. In order to investigate the effects of the 24 hr of isolation, blood samples were taken twice in February, March, and May 1982:each male was bled within 10 min after capturing (direct) and again 24 hr later (morning after).

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ET AL.

Behavioral Observations

Between March 1, 1980and July 1, 1982,932hr of systematicbehavioral observations were conducted. They were equally distributed over the months and the hours of the day (9 AM-~ PM, or, in winter, 9 AM-~ PM). No systematic observations were scheduled on “capturing” or “blood sampling” days. Observations were made by one experienced person at a time, with the complete group present in the outdoor cage. The first author did about 90% of all observations and trained students did the remaining 10%. The wire mesh walls of the cage and the ability to walk around the cage ensured excellent observability. Behaviors were recorded verbally on a portable tape recorder and were later transcribed. For most behaviors the “all occurrences” method was used, except for grooming, for which “scan samples” were taken every 5 mm (definitions of observation techniques follow Altmann, 1974). Aggression

Aggressionincluded threats, mild physical attacks (threats in combination with push, hit, etc.), lunges, pursuits, and severe attacks (fierce hair pulling and/or biting). Only aggressive initiation, and not retaliation, were considered. If an animal aggressed the same partner more than once, with intervals not longer than 2 min, this was scored as one aggressive act. Winner/loser outcomes of dyadic agonistic interactions, without interference by a third animal, were used to construct a dominance matrix. The animal that performed submissive gestures (withdraw, shrink, flee, bared teeth) at the end of the interaction was considered the loser. Sexual Behavior Present. Standingon all fours, perineum directed at partner, tail deviated. Four types: female towards previously inactive male (spontaneous),female in response to approach or’ contact by male (induced), female to male while one or both are involved in a conflict (agonistic), and male to male (isosexual). Mount, Typical macaque double-foot-clasp mount. Several mounts by the same pair, not more than 2 min apart, were scored as one mount. Two types: male on female (heterosexual) and male on male (isosexual). The latter never included intromission or ejaculation. Copulation. One or more heterosexual mounts, not more than 2 min apart and including at least one intromission (recognized by deep pelvic thrusting). Ejaculation was easily recognizedby cessationof pelvic thrusts, body rigidity, and a specific facial expression in the male (“frowning round-mouthed look,” Chevalier-Skolnikoff, 1974; “ejaculation face,” Goldfoot, Westerborg-van Loon, Groeneveld, and Slob, 1980).

MACAQUE TESTOSTERONE

AND BEHAVIOR

157

Masturbation. Manipulation of erect penis, resulting in ejaculation (recognized by the appearance of semen). Other Behaviors Branch shaking. Shaking vigorously the branch of a tree or the wire

netting of the cage. ~ Grooming. Gently manipulating another monkey’s fur or skin. Data Analyses

For the analysis of seasonal patterns, data were used from 2 complete years: July 1, 1980 until July 1, 1982. This period was chosen because the youngest adult males had relatively small testes at the start of the study: in March 1980 their volumes were < 30 ml. Their testes grew rapidly during the next few months and were within the range of older males (> 8 years old, 3 34 ml) from June 1980. A similar but less distinctive pattern occurred in testes lengths of young males. Testosterone levels of the youngest males were within the range of the older males from the start of the study. Seasonalchanges in grooming were analyzed from March 1, 1980until March 1, 1982, the only period for which data were available. Individual scores per month (physiological data) or per 2 months (behavior) were subjected to a two-way ANOVA (Kirk, 1968). July data were excludedfrom the testosteroneanalysisbecauseno data were available for July 1980.Data from M403 were excluded from the testis-size analyses because this male had only one well-developed testis: the other was either absent or atrophied. In the analysis of body weights, the two youngest adult males (< 6 years old in March 1980) were excluded because their weights gradually increased throughout the study period. ANOVA of the behavioral data included only the 13 males for which physiological data were available. Excluded from these analyses were copulation data of M300 (alpha male, extremely high scores) and of M239, M7, and MS02 (no or very few copulations), and branch shaking data of M300 (extremely high scores) and of MS02 (no branch shaking performed). Thus, the number of individuals per analysis varied (see Table 2).

It was assumed that a seasonal pattern existed if two-way ANOVA yielded no significant interaction between months and years (thus, when the same pattern occurred in both years) and if there was a significant effect of months. If a seasonal pattern was present, differences between months were further analyzed using the least significant difference method (Kirk, 1968). Calculations of rank cotrelation coefficients(Kendall’s 7) followed Siegel (1956). Two-tailed tests of significance were used, and the 0.05 level of probability was adopted as the level of statistical significance.

158

NIELJWENHUIJSEN

ET AL.

RESULTS Reliability of Testosterone Data

Some of the individual “direct” versus “morning after” comparisons revealed major differences in testosterone levels, but on the whole no systematic rise or fall occurred (see Table 1). Individual averagesbased on the three direct samples correlated well with those based on the three morning-after samples (7 = 0.462, N = 13, P < 0.05). Seasonal Fluctuations

Table 2 summarizesthe resultsof the ANOVA’s. No seasonalityoccurred in testis length, testis volume, or body weight (see also Fig. 1). A weak effect of months occurred in testosterone levels: April and May values tended to be higher than August and December values (Fig. 2). In Fig. 1, it can be seen that during the first 4 months of the study (not included in the ANOVA), average testis volumes increased sharply. This was due to the growth occurring in the four youngest males. Testis volumes continued to increase slowly during the following 2 years. This latter trend occurred in all individuals, including the oldest. Frequencies of copulation, masturbation, and aggressionof adult males showed no seasonality (Table 2, Fig. 3). Branch shaking by the alpha male remained rather stable throughout the study period (Fig. 3) but in other males a seasonal pattern occurred, winter scores being relatively TABLE 1 Testosterone Levels (q/ml) in Blood Samples Taken Immediately after Removing Male Stumptails from Their Group (A), and after 24 hr of Isolation (B) March

February

x

May

Male (ID)

A

B

A

B

A

B

A

B

300 303 410 416 253 239 403 378 15 4 2 7 502

8.1 8.5 12.1 14.6 9.9 6.8 26.8 8.2 11.7 7.1 13.4 10.3 4.0

5.8 8.0 12.1 22.7 15.1 11.1 17.4 4.5 12.2 23.9 21.4 23.6 2.4

16.9 10.4 21.2 15.2 26.9 19.0 31.5 17.3 30.7 25.6 30.3 29.3 17.7

10.6 11.4 25.3 27.4 30.1 14.1 10.0 8.0 11.9 24.4 32.2 21.1 4.7

18.5 23.2 22.9 28.1 32.5 22.2 20.2 25.6 24.1 19.4 24.7 31.5 20.7

7.3 20.3 15.4 21.6 42.6 13.1 6.4 28.8 35.6 8.6 30.6 9.4 10.2

14.5 14.0 18.7 19.3 23.1 16.0 26.2 17.0 22.2 17.4 22.8 23.7 14.1

1.9 13.2 17.6 23.9 29.3 12.8 11.3 13.8 19.9 19.0 28.1 18.0 5.8

x

10.9

13.9

22.5

17.8

24.1

19.2

19.2

17.0

a Difference between ?A and %:

t = 1.28, df = 12, P > 0.10.

MACAQUE TESTOSTERONE

159

AND BEHAVIOR

TABLE 2 Seasonality in Physiological and Behavioral Measures, July 1980 through June 1982 (Grooming, March 1980 through February 1982) Month x year interaction Parameter

N8c3

Testosterone Testis length Testis volume Body weight Copulation Masturbation Aggression Branch shaking Grooming

13 12 12 11 9 13 13 11 13

df

101252 111253 111253 111230 S/88 S/l32 S/l32 5/110 51132

F

P

1.44 9.65 1.85 1.14 1.72 0.97 5.38 1.14 0.86

NS
Effect of months F 1.85 1.00 1.67 0.37 7.18 20.89

P

Seasonality

weak no no no NS no NS no NS no co.01 yes
’ Results of 2-way ANOVA; physiological measures per month; behaviors per block of 2 months. Effect of months is presented only if no signitlcant month x year interaction existed. NS: P > 0.10; NC?6: number of individuals included in analysis, see Materials and Methods.

low. A seasonal pattern was obvious in grooming by adult males: spring and summer scores were 3-5 times higher than winter scores (Fig. 3). This difference occurred both in male-to-male and in male-to-female grooming. No seasonal pattern was detected in presents or mounts. Adult females showed the same seasonality in grooming as adult males. Branch shaking by females occurred rarely, but seemed to be seasonal: only 1 of the 30 instances recorded occurred in winter (November through February). Female aggression was not seasonal. Differences

between Individuals

Two-way ANOVA yielded highly significant individual differences for the physiological and behavioral measures presented in Table 2 (grooming, P < 0.01; other parameters, P < O.OOl), even though some males with extremely high or low behavioral scores were excluded from the analyses. Average scores over 2 years are presented in Table 3. Testis length and testis volume were correlated (7 = 0.879, N = 12, P c 0.001). Other correlations between various physiological parameters were not statistically significant (see Table 3); for example, relatively heavy males did not necessarily have large testes or high testosterone levels. Dominance relationships among adult males were strictly linear and remained stable throughout the study period. Rank correlations between dominance positions and behavioral frequencies were significant for most of the behaviors listed in Table 3, with the exceptions of masturbation

160

NIEUWENHUIJSEN

ET AL.

25 .w

plasma testosterone

ng tml 20 -

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FIG. I. Plasma testost+one (IV = 13), testis size (IV = 12), and body w&.&t (N = 11) per cakndar month: X f SEM.

MACAQUE TESTOSTERONE 20 nglml 15 10 5 0 J

F

M

A

M

J

* rrr

161

AND BEHAVIOR

J

A

S

0

-

N

FIG. 2. Annual pattern of mean plasma testosterone levels of 13 adult males. Based on 2 years of monthly measurements (August 1980 through July 1982). July (no data in 1980)not included. Significant differences: *lower than April and May (P < 0.05); **lower than April and May (P < 0.01) and than February (P < 0.05).

and grooming performed. Furthermore, significant positive correlations with dominance rank existed for presents received (all four types) and mounts performed (both heterosexual and isosexual). Testosterone and Behavior

Neither dominance rank nor any of the behaviors studied correlated with average individual testosterone levels (Table 3). Also, temporal fluctuations in individual testosterone levels did not significantly coincide with temporal fluctuations in individual behavioral frequencies. DISCUSSION

Plasma testosterone levels and sociosexual behavior were studied in group-living stumptail monkeys. Blood samples were obtained in males that had been isolated for 24 hr. If rhesus males are removed from their group and placed in individual cages, their testosterone levels may drop. In one study, decreasesoccurred after isolation for 1 hr (Hemdon, Turner, and Collins, 1981), but in another study decreases occurred only after several weeks (Phoenix, 1980). No effects of isolation (lasting 1 week) on testosterone levels have been found in pigtail macaques (Bernstein, Rose, Gordon, and Grady, 1979b). In the present study no systematic changes in testosterone were seen between samples taken immediately following capturing and samples taken after isolation. Thus, testosterone levels obtained through the 24-hour isolation procedure seemed to be stable. Whether or not monthly samples provided a valid estimate of an indvidual’s testosterone output remains unknown. Testosterone levels in male stumptail macaques were found to show weak fluctuations, with relatively low values in August and December and high values in April and May. An earlier study of stumptail macaques in a laboratory yielded peak values in June (Slob, Ooms, and Vreeburg,

162

I

NIEUWENHUIJSEN

.lO

ET AL. -1

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JF M

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FIG. 3. Mean behavioral frequencies per 2-month block. For copulations and branch shaking, the alpha mate’s scores (a---a) have been depicted separately from the means of other males (O--O). Non responders were not included; number of individuals, top to bottom: 9 + 1, 13, 13, 11 + 1, and 13. Right hand side: mean annual patterns, based on O-O curves, July 1980 through June 1982(grooming, March 1980through February 1982). Sign&ant differences: *lower than SO (P < 0.001) and lower than MA, MJ, and JA (P < 0.05); Vower than MJ (P < 0.05); ***lower than MA through SO (P < 0.001).

1979). Although these differences were statistically significant, close examination of the data (Fig. 1 in the present study and Fig. 1C in Slob et al., 1979)reveals that both relatively high and relatively low averages could occur in all seasons. Thus, plasma testosterone levels in stumptail males showed no strict seasonality. There was also no seasonalityin testis size, body weight, and copulation frequencies.This is in line with earlier observationson stumptail macaques (Smith, 1984: copulations) and pigtail macaques (Bernstein, 1972: cop-

circa circa before circa circa circa circa circa Nov. Sept. Nov. Feb. Apr. June July Aug. Jan. Before

1972 1974 1974 1974 1970

1975 1973

1975

1968 1970 1970 1975 1975

I%9

1970 1970

I%7

1968

BDb

NS

12.2 14.8 19.8 23.8 26.1 9.6 10.5 8.3 24.8 17.8 24.3 20.5 5.4 16.8 13 0.026

T

NS

-0.333

NS

48.5 47.4 50.0 46.4 50.2 48.5 (53.0) 50.6 45.0 47.0 49.0 46.2 50.2 48.2 12 0.000

TL

NS

-0.333

0.061 NS

40.8 38.7 40.3 37.8 41.6 39.9 (42.0) 41.8 36.5 38.1 40.5 37.6 41.1 39.6 12

TV

NS

0.141

NS

12.6 11.0 11.6 11.7 9.9 11.4 9.6 9.8 10.3 12.4 9.1 10.7 10.5 11.9 11.4 10.8 10.3 12.3 11.0 18 0.046

BW

0.001 0.231 NS

48 18 0.739

1 0 0 0

35 0. 16 22 14 22 14 13 3 5

101 162

42

409

C

NS

346 20 68 112 18 0 5 14 9 14 2 8 1 4 0 0 0 0 34 18 0.680 0.001 0.205

E

NS

-0.256

NS

30 543 8 7 24 124 454 74 18 26 5 24 42 131 96 37 20 64 % 18 -0.026

M

0.001 -0.090 NS

85 '86 138 143 45 29 23 34 55 74 35 20 17 7 79 18 0.667

190 181

181 87

AP

0.001 -0.051 NS

7 19 22 107 31 84 74 44 57 60 123 76 123 80 137 60 18 -0.7%

1 13 18

AR

0.001 - 0.128 NS

1508 391 254 32 47 54 511 151 18 17 61 18 6 33 5 2 18 0 174 18 0.654

BS

NS

0.2bs

NS

63 46 20 25 90 32 8 52 39 46 38 47 48 41 8 25 13 6 36 18 0.294

GP

performed.

* Individual averages of monthly measurements (physical measures), and frequencies per 100 scan samples (grooming), per 100 hr (aggression) or per 1tkXt hr (other behaviors). Based on’ 2 years of data collection (July 1980 through June 1982; except for grooming, March 1980 through February 1982). Individuals are in dominance rank order (300 is alpha male). Kendall’s T: rank order correlation with dominance rank and with testosterone level; NS = P > 0.10. Parentheses, sizes of one well-developed testis of male 403 were not included in calculations of x and 7. ’ BD = Birthdate; T = plasma testosterone (rig/ml); TL = testis length (mm); TV = testis volume; BW = body weight; C = copulations; E = ejaculatory copulations; M = masturbations; AP = aggression performed; AR = aggression received; BS = branch shaking; GP = grooming

P

r-testosterone

P

N r-dominance

983 970 4 2 7 8 6 502 F

15

300 303 410 416 253 239 403 378 16

Male (ID)

TABLE 3 Mean Physiological and Behavioral Measures of Adult Male Stumptails”

164

NIEUWENHUIJSEN

ET AL.

ulations; Bernstein, Gordon, Rose, and Peterson, 1978:testosterone). In both species, births occur during all months of the year (references: Nieuwenhuijsen et al., 1985). Stumptails and pigtails can therefore be considered as nonseasonal breeders. In contrast to this, rhesus monkeys, bonnet macaques, and Japanese macaques are strictly seasonal breeders. Copulations in these species are restricted to the autumn and early winter (Kaufmann, 1965;Rahaman and Parthasarathy, 1969; Hanby, Robertson, and Phoenix, 1971, Vandenberghand Drickamer, 1974;Gordon et al., 1976;Glick, 1979;Takahata, 1980),and births are restricted to the spring and early summer(references: Nieuwenhuijsen et al., 1985). During the mating season, testosterone level and testis size show marked increases (Sade, 1964; Gordon et al., 1976; Glick, 1979; Nigi et al., 1980; Wickings and Nieschlag, 1980; Matsubayashi and Enomoto, 1983), while body weights are slightly elevated (Glick, 1979; Matsubayashi and Enomoto, 1983). An intermediate pattern occurs in crab-eating macaques (Mucucu fusciculuris): testosterone levels are highest in autumn but fluctuate less dramatically than in strictly seasonalspecies (Dang and Meusy-Dessolle, 1981);copulations occur all year round (Dang and Meusy-Dessolle, 1981; Wheatley, 1982) and births may or may not be seasonal (references: Nieuwenhuijsen et al., 1985). Semenproduction and spermatogenesisin rhesus monkeys and Japanese macaques are greatest in autumn and early winter and may come to a complete stop in spring (Conaway and Sade, 1965; Zamboni, Conaway, and van Pelt, 1974; Nigi et al., 1980; Wickings and Nieschlag, 1980; Matsubayashi and Enomoto, 1983).Although not studied systematically, adult males in the present study produced semen during all months of the year. Conceptions and births occurred all year round, indicating that spermatogenesiscould not be seasonal Individual differencesin sexualactivity did not correlate with testosterone levels in the present study. This corroborates many earlier studies on primates in heterosexual groups (Gordon et al., 1976;Eberhart, Keveme, and Meller, 1980;Glick, 1980;Phoenix, 1980;Sapolsky, 1982;Loy, Loy, Keifer, and Conaway, 1984)and in laboratory pair tests (Goldfoot, Slob, Schemer, Robinson, Wiegand, and Cords, 1975; Robinson et al., 1975; Phoenix, 1977; Slob et al., 1979;Dang and Meusy-Dessolle, 1981;Chambers, Resko, and Phoenix, 1982). Chambers et al. (1982) suggested that in intact adult male primates, testosterone levels are present in suprathreshold quantities with respect to sexual behavior. The present data indicate that this suggestion also applies to the stumptail monkey. In the present study, testosterone levels of adult males were not correlated with dominance rank. This is in line with many previous findings in groups of primates which comprised both males and females (Eaton and Resko, 1974; Gordon et al., 1976; Bernstein, Gordon and Petersen,

MACAQUE TESTOSTERONE

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1979a; Bernstein et al., 1979b; Glick, 1980; Phoenix, 1980; Sapolsky, 1982; Loy et al., 1984; Steklis, Brammer, Raleigh, and McGuire, 1985). The present data showed no sign&ant correlation between aggression frequencies (performed or received) and testosterone levels. It was of interest, however, that the lowest ranking adult male had consistently lower testosterone levels than any other adult male. He was also most frequently and most severely attacked, especially by other adult males: he received about one-fifth of all intermale aggression. This may have caused the low testosterone levels, as was earlier suggestedby Rose et al. (1972), Bernstein et al. (1979b), and Eberhart et al. (1980). There were no significant intraindividual correlations between testosterone and any of the other behavioral measures:masturbation,presenting (both performed and received), mounting (both heterosexualand isosexual), branch shaking, and social grooming. With regard to masturbation, this result is in line with earlier findings on intact rhesus monkeys (Loy et al., 1984).Rhesus males that had been castrated prepubertally, frequently manipulated their penes, but never ejaculated(Loy et al., 1984).In adult rhesusmales,castration and androgen replacement had no consistent effect on masturbation scores (Michael and Wilson, 1974). Previous studies on isosexual behavior also failed to show significant correlations with testosterone levels (interindividual differences in intact rhesus males: Gordon, Bernstein and Rose, 1978; Loy et al., 1984). The annual patterns of isosexual activity may vary between groups and seem to depend on social variables rather than on fluctuations in testosterone levels (Hanby, 1974; Gordon et al., 1978; Loy et al., 1984). Branch shaking occurred least frequently during the winter months in the present study. In Japanese macaques, branch shaking or “display behavior” may be most common during the autumn mating season(Modahl and Eaton, 1977; Wolfe, 1981), or may occur about equally frequently throughout the year (Enomoto, 1981). In rhesus monkeys, peaks were reported in January and June, the, transition months between the mating and the birth season (Hausfater, 1972). Thus, no synchronism exists between, branch shaking and testosterone levels. Still, androgens may be involved in this behavior, since it is almost exclusively performed by males(studiescited above), and occurs infrequently before puberty (present study). Furthermore, “cage shaking” in laboratory stumptails was significantly depressed after castration (Schenck and Slob, 1986). Maybe some minimal amount of testosterone is required for the expression of display behavior (Modahl and Eaton, 1977), as was earlier mentioned for the expression of sexual behavior. However, the presence of such a minimal amount of testosterone does not always result in high branchshaking scores: in the present study, this dependedon a male’s dominance rank (as was the case with sexual behavior).

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Male-to-female grooming has been seen most frequently in the mating season in rhesus monkeys (Vandenbergh and Drickamer, 1974), which could suggest that testosterone enhances grooming behavior. However, laboratory studies on stumptails (Slob and Schenck, 1981; Schenck and Slob, 1986) and crab-eating macaques (Zumpe and Michael, 1985) suggest the opposite. The present data did not indicate any relationship between social grooming and testosterone levels. Instead, this behavior seemed to depend on the outside temperature: in both years of the study, the monthly scores of grooming activity and temperature during observation hours were highly correlated (P < 0.001). This correlation occurred both in males and in females. Bernstein (1980) found a similar relationship between temperature and grooming in stumptail macaques. In conclusion, the present study revealed no seasonality in any reproductive parameter (physiological or behavioral) in adult male stumptail macaques. Furthermore, interindividual and intraindividual variations in testosterone levels were not found to be correlated with any behavioral variations. For most sociosexual behaviors, individual frequencies depended on dominance rank. ACKNOWLEDGMENTS Gert van Cappellen skillfully performed the testosterone assays. The continuous expert assistance of Wim Hagedoom and his staff of animal caretakers is gratefully acknowledged. We thank Marielle Bonke-Jansen, Els Broekhuyzen, and Bas Drukker for their assistance in collecting behavioral data. Peter Schenck is thanked for his statistical support.

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