Variables influencing the origins of diverse abnormal behaviors in a large sample of captive chimpanzees (Pan troglodytes)

The developmental origin of abnormal behaviors is generally associated with early rearing environments that lack sufficient physical and sensory stimulation. However, other factors should also be considered. A large sample of captive chimpanzees (128 males and 140 females) was surveyed for the presence or absence of 18 abnormal behaviors. Origin variables included the subject's source (zoo, pet, performer, or laboratory), rearing (mother‐ or hand‐reared), and sex. Animals were assessed while held at the Primate Foundation of Arizona, University of Texas M. D. Anderson Cancer Center, or White Sands Research Center. There was a confound among origin variables; more hand‐reared animals than expected were from laboratories. Logistic regression tested the relationship of rearing and source, with sex as a secondary predictor variable, to each of the abnormal behaviors. There was no clear association between any abnormal behavior and source. However, for coprophagy, relative to animals from the laboratory, zoo animals tended to show a higher prevalence, while performers tended to show a lower prevalence (when rearing and sex were controlled). Rocking and self‐sucking were significantly more likely in hand‐reared animals. Coprophagy and depilation of self were significantly more likely in mother‐reared animals. When rearing and source were statistically controlled, the only significant sex difference was a higher prevalence of coprophagy in females and a higher prevalence of rocking in males. In a second, smaller sample of 25 males and 33 females from Southwest Foundation for Biomedical Research, no significant sex association was found for coprophagy, urophagy, rocking, or self‐depilation. In this second sample, coprophagy was also significantly more likely in mother‐reared than hand‐reared subjects. The association of some abnormal behaviors with mother‐rearing suggests that some form of social learning may be involved in the origin of some of these behavior patterns. This indicates that some abnormal behaviors may not be always be indicative of reduced psychological well‐being in captive chimpanzees. Am. J. Primatol. 48:15–29, 1999. © 1999 Wiley‐Liss, Inc.     

Peer separation in infant chimpanzees,a pilot study

Seven nursery reared chimpanzees (Pan troglodytes), 7.5 to 10.5 months of age, were studied to determine the effects of a short period of separation from their peers on behavior and heart rate. The chimpanzees were separated from their mothers at birth, and reared in the nursery in a group living environment. The experiment encompassed a 13-day period, including 4 days of normative baseline, 5 days during which three of the infants were separated and housed in isolation while the other four controls remained together, and 4 days in which all of the animals were reunited. Six quantified behavioral observations and five heart rate measurements were obtained daily. Following separation, the isolated infants were behaviorally agitated, and exhibited increases in vocalizations, rocking and self-clasp behaviors, as well as changes in facial expression including cry face, whimper face and pout face. Time spent locomoting decreased in all seven animals during the separation period. Agitated behavior in the separated and isolated infants alternated with stationary withdrawn behavior. Individual differences were prominent. Heart rate was notable by the generally poorly developed circadian rhythmicity throughout the 13 day period; significant HR changes did not appear otherwise associated with separation. Day three of separation appeared to represent a point of transition with stereotyped motor behaviors developing in the three isolated infants and in one control infant.     

Housing conditions and breeding success of chimpanzees at the primate center TNO

Results of rearing and breeding chimpanzees at the Primate Center TNO are presented. The colony was built up from 1964 to 1971 by the acquisition of mostly young chimpanzees; thereafter, it was increased by local breeding. The ages at which the animals became reproductive were between 6 and 11 years for the males and between 7 and 15 years for the females. Seventy-six percent of the pregnancies (N = 132) were carried to full term and 87% of these were live births. Fifty-five percent of the babies were nursed by their mothers for 2–10 months. The next pregnancy after an abortion occurred on the average after 7 months; after a carriage to term, this occurred after 11.9 months. The difference was not influenced by the duration of the weaning period. Animals of 2 years or more that had been weaned within a month were more likely to show body rocking than animals weaned later. Cases of disturbed social or reproductive behavior were rare; the first locally bred animals have become reproductively active.     

Maternal influence on the development of nut‐cracking skills in the chimpanzees of the Taï forest,Côte d'Ivoire (Pan troglodytes verus)

Chimpanzees’ (Pan troglodytes) nut‐cracking behavior represents one of the most complex forms of tool‐use known among nonhuman animals. Given the close phylogenetic relationship between these apes and humans, investigating how such complex behavior develops in immatures can reveal the evolutionary roots of the cognitive processes that enabled the evolution of outstanding technological skills in our lineage. In this study, we investigated whether maternal behavior directly enhanced nut‐cracking skills in immature individuals. We analyzed the behavior of 11 immatures and their mothers (N = 8) during nut‐cracking activity, spanning over three consecutive nut‐cracking seasons in the Taï National Park, Côte d'Ivoire. We used generalized linear mixed models to (a) obtain values of maternal scaffolding (defined as provision of learning opportunities) and active nut‐sharing behavior of each mother according to the age of their offspring, and their average nut‐cracking efficiency; (b) to test whether these variables enhanced immatures’ nut‐cracking skills; and (c) to test whether immatures’ features (age, sex, and begging behavior) influenced maternal behavior as observed in our videos. Although the predicted values of maternal scaffolding and active nut‐sharing did not obviously affect immatures’ skills, they were positively influenced by the average maternal efficiency and by sharing hammers with their mothers. In addition, our observations showed that mothers were more likely to share nuts with their sons than with their daughters, and the more their offspring begged. Concurrently, male immatures were also found to beg more often than females. Our results add evidence on the ontogenetic pathway leading to the full acquisition of nut‐cracking in wild chimpanzees and on the effect that maternal behavior can have in promoting the acquisition of this complex tool‐use behavior. Moreover, our study strengthens the importance of naturalistic observations to understand complex skill acquisition. Finally, we suggest future avenues for investigating the maternal influence on learning.     

Uprooted trees facilitate the psychological well-being of captive chimpanzees

After the introduction of uprooted trees to their environment, the behavior of 28 socially housed, laboratory chimpanzees (Pan troglodytes) was studied for five months. Subjects used the tree during 41.9% of the data points collected during the first day trees were introduced. Thereafter, the mean for tree use dropped to 3.5% and remained fairly consistent. Immature subjects used the trees significantly more than did adult subjects, as measured by the Mann-Whitney U-test. No sex difference was detected. The trees elicited a variety of species-appropriate behaviors. Increasing the similarity between the behavior of captive and wild chimpanzees can be viewed as promoting the psychological well-being of the captive animals.     

Copulatory behaviors and body condition predict post-mating female hormone concentrations, fertilization success, and primary sex ratios in Japanese quail

Environmental cues and social interactions are known to influence reproductive physiology and behavior in vertebrates. In female birds, male courtship displays can result in the growth of ovarian follicles, the production of reproductive hormones, and stimulation of oviduct development, all of which have the potential to influence maternal investment. Male Japanese quail follow a typical sequence of copulatory behaviors during a mating interaction and often force copulations with unreceptive females. We hypothesized that female Japanese quail could adjust maternal investment in response to male copulatory behaviors during a single mating interaction. We investigated the relationships between 1) male copulatory behaviors and post-mating concentrations of steroids in the female, 2) female steroid concentrations and fertilization success of inseminations and 3) female steroid concentrations and the offspring sex ratio. We found that male condition and copulatory behaviors predicted female steroid concentrations and maternal investment in eggs laid after a mating trial. The body condition of one or both mates was a significant predictor of the changes in female corticosterone and testosterone concentrations after mating, whereas specific male copulatory behaviors significantly predicted changes in female progesterone concentrations. Male and female body condition, male neck grabs and post-mating concentrations of female corticosterone, progesterone, and testosterone were all significant predictors of egg fertilization rates. Female body condition, male copulation efficiency, and female testosterone concentrations were significant predictors of offspring sex ratios. Our results show that phenotypic and behavioral characteristics of male Japanese quail modulate female steroid concentrations and result in changes in maternal investment.     

Prenatal stress and maternal behavior in intact virgin rats: response latencies are decreased in males and increased in females

The repeated findings that levels of various male-typical behaviors (e.g., copulatory behavior and intermale aggression) are reduced in prenatally stressed (P-S) males, coupled with reports of effects on female physiology and behavior, prompted us to examine the maternal behaviors of P-S animals toward young. Sprague-Dawley female rats were timed-mated (+ sperm = Day 1). From Gestation Days 15 to 22 experimental females were subjected to heat and restraint stress. Control females remained undisturbed throughout pregnancy. The offspring, as adults, were assessed for maternal behavior. P-S males exhibited a significantly shorter latency (in days) to show full maternal behavior (FMB) than Control males, median = 5.0 vs 8.0, respectively. P-S females, on the other hand, exhibited a significantly longer latency than Control females to show FMB (7.0 vs 3.0, respectively). as well as longer latencies to retrieve one, two, or three pups, to begin to crouch over pups, and to build nests in response to young. Sex differences were apparent between Control males and Control females (females were more responsive to young). In contrast, P-S males and Control females exhibited similar latencies to show components of FMB (3-5 days), as did P-S females and Control males (7-9 days). These data demonstrate, therefore, that prenatal stress eliminates the sex difference normally observed in pup-induced maternal behavior. Moreover, the data suggest that prenatal stress renders the male's responsiveness to young more "female-like," while conversely rendering the response of the female more "male-like."     

Observations on reproduction,hormones, copulatory behavior,and neonatal mortality in captive Lemur mongoz (Mongoose lemur)

This study examines correlates of reproduction in Lemur mongoz, an endangered prosimian primate with a history of poor captive reproduction. Male testicular growth and regression were quantified via testicular indices (TI). Although TIs could be used to predict male breeding condition, they were not indicators of ability to sire offspring. Serum estradiol (E₂) and progesterone (P) concentrations, along with vaginal cytology, were used to monitor female reproductive cyclicity. E₂ and P profiles showed no abnormalities. An elevation of E₂ with low P, approximately one estrous cycle length (31.4 days) prior to the onset of fertile cycles, was consistent with the phenomenon of ‘pseudoestrus’ observed in other lemur species. The copulatory pattern, consisting of thrusting, multiple intromissions, single or multiple ejaculations, and no copulatory lock, was more complex than expected for an animal with a supposedly monogamous mating system. The preference for natural arboreal substrata during copulation suggests that enclosure furnishings may influence copulatory behavior. A 30% neonatal mortality rate tempered recent success in breeding L. mongoz at the Duke University Primate Center (DUPC). Although infant sex and parity of the mother were not predictive of neonatal mortality, mother's natal status was, with captive-born females having a 67% infant mortality rate, compared with 15% in wild-caught females. Based on these observations, a number of factors, including housing, behavior, and photoperiod, may be relevant to successful captive propagation of L. mongoz. © 1992 Wiley-Liss, Inc.     

Catarrhine juvenile mortality in captivity,under seminatural conditions,and in the wild

Juvenile mortality is an important problem in the development of captive populations. I compiled data from published literature on abortion, premature mortality, stillbirth, and death of unweaned young. Cumulative mortality incidences (CMI) during the first month in captive populations (CP) of Cercopithecoidea range between 13 and 51%, and CMI in the first year between 28 and 56%. Mortality rate during the first year ranges between <4 and 48% in free- ranging populations (FRP) and between 10 and 60% in wild populations (WP). Much of the juvenile mortality in CP appears to occur in the first month, whereas in FRP and WP mortality is more scattered throughout the juvenile period. High mortality rates occur in both CP and WP of nonhuman Hominoidea. Mortality rate during the first month in CP is between 12 and 36% for the Hylobatidae and between 18 and 31% for the Pongidae. If the entire juvenile period is considered, gorilla CP and WP have comparable CMI, while CMI is higher in WP than CP for chimpanzees. Most of the juvenile mortality in CP of chimpanzees occurs before the age of 1 year. Trauma, including infanticide and maternal inadequacy, seems to be a more important factor in infant mortality of Cercopithecoidea than infectious disease is. Relatively frequent reports of congenital, hereditary, and/or genetically determined malformations in the Cercopithecoidea may be related to the long use of animals in this group for laboratory purposes. Infectious disease is the most important cause of nonhuman hominoid juvenile mortality, followed by trauma and maternal disorders, particularly related aberrant maternal behavior. Cercopithecoid juvenile mortality risk factors most frequently mentioned in the literature are sex of the infant and rank of the mother: dominant females produce more female offspring, and juvenile males suffer higher mortality than females do. The female skewed sex ratio at birth in gorillas and chimpanzees could be explained by the local resource competition theory. Higher male mortality rates occur in nonhuman Hominoidea, except in two Hylobatesspp. and Pan paniscus,which have higher female mortality. Parity and rearing history of the mother are very important risk factors in nonhuman hominoid infant mortality.     

Procedures for improving maternal behavior in captive chimpanzees

Captive female chimpanzees who have had no opportunity to observe mothers with infants or to interact with infants often show inappropriate maternal behavior, particularly with their first-born infant, and this usually results in the removal of the infant to be human-reared. The present study used two techniques to encourage appropriate maternal behavior in ten pregnant female chimpanzees. These females were housed together with unrelated infant chimpanzees to adopt, or with lactating female chimpanzees and infants to observe. In five cases both techniques were used, in two cases only the first technique was used, and in three cases only the second technique was used. All ten female chimpanzees showed appropriate maternal behavior when their infants were born, in contrast to a group of eight female chimpanzees who had no such experience whose infants had to be removed for human-rearing. It is suggested that these techniques, or adaptations of them, could be applied to many other captive female chimpanzees with similar results.     

Effects of age,lactation, and repeated cycles on rhesus monkey copulatory intervals

Young, sexually mature female rhesus monkeys copulate on more days prior to conception than do older females, and this prolonged discrete mating period is associated with an earlier rise in serum estradiol prior to the first ovulation of the breeding season. The influence of repeated ovulatory cycles and the presence of a suckling infant on the copulatory patterns were examined in two separate analyses. Extending previous work, young, nulliparous females copulated on more days at the first ovulation of the breeding season than did older, multiparous females. However, the duration of the copulatory period at the second ovulation of the breeding season was similar and significantly shorter for both age groups. Furthermore, the presence of a suckling infant did not influence the duration of the mating periods in adult, multiparous females. The onset of copulatory behavior for all females was associated with serum estradiol concentrations of approximately 90 pg/ml, indicating that the age and cycle differences in the duration of the copulatory periods are due to the time course of serum estradiol prior to ovulation. A separate, longitudinal analysis of the duration of the mating period associated with the first ovulation of three successive breeding seasons indicated that females copulated on more days during their first ovulatory cycle of their first breeding season. These data indicate that the copulatory interval is longer for females during the first ovulation of the breeding season, and this pattern is accentuated in young, sexually mature animals.     

Maternal and offspring methylenetetrahydrofolate‐reductase genotypes interact in a mouse model to induce autism spectrum disorder‐like behavior

Individuals with autism constitute a variable population whose members are spread along the autism spectrum. Subpopulations within that spectrum exhibit other conditions, such as anxiety, intellectual disabilities, hyperactivity and epilepsy, with different severities and co‐occurrences. Among the genes associated with the increased risk for autism is the methylenetetrahydrofolate‐reductase (MTHFR) 677C>T polymorphism, which impairs one‐carbon (C1) metabolic pathway efficiency. The frequency of the MTHFR677TT homozygote is markedly higher among autism patients and their mothers than in the general population. Here, we report on the Mthfr heterozygous knockout (KO) mouse as a rodent model of autism that shows the contributions of maternal and offspring genotypes to the development of autistic‐like behaviors. Maternal Mthfr‐deficiency was associated with developmental delays in morphogenic features and sensory‐motor reflexes in offspring. In the adult male mouse, behaviors representing core autism symptoms, such as repetitive behavior and restricted interest, were affected by maternal genotype while social behaviors were affected by both maternal and offspring genotypes. In females and males, behaviors associated with autism such as memory impairment, social aggression and anxiety were affected by both the maternal and offspring Mthfr genotypes, with sex‐dependent differences. Mthfr‐deficient male mice with observable impacts on behavior presented a particular laminar disturbance in parvalbumin interneuron density and innervation in superficial and deep layers of the cingulate cortex. This mouse model of autism will help to elucidate the molecular mechanisms that predispose a significant subgroup of autistic patients to abnormal development and to distinguish between the in‐utero and autonomous factors involved in autism.     

Birth sex ratios and maternal social rank in a captive colony of rhesus monkeys (Macaca mulatta)

Data from a 35-year study of rhesus macaques (Macaca mulatta) at Madingley, Cambridge, were used to investigate sex ratio biases associated with maternal rank. Data were available from two colonies, the Old colony (1960–81) and New colony (1982–93). Overall, top-ranking mothers gave birth to 30.9% sons, while non-top mothers gave birth to 58.4% sons. Among non-top mothers, middle- and bottom-ranking ones had 59.0 and 55.0% sons, respectively. Top mothers' daughter biases were strongest in matrilines with two adult females in the year the infants were conceived (15.4 sons and 14.3% sons in Old and New colonies). Non-top mothers' son biases (88.9 and 71.0% in Old and New colonies) were strongest in matrilines with 3 females. The findings are discussed in relation to the colonies' small matriline sizes and data on breeding performance and infant survival, which indicate the costs to mothers of different rank of having different sex infants. Overall, top-ranking mothers were more likely to breed in two successive years (78.6%) than non-top mothers (56.7%). Infant survival to 7 days was significantly higher in the New colony (89.0%) than the Old colony (75.3%), with daughters born to Old colony mothers doing especially poorly. We point out that between-group and between-species comparisons of sex ratio effects depend critically on how females are assigned to rank categories, and require information about divergences of sex ratios from 50:50 in each category. © 1996 Wiley-Liss, Inc.     

Decline of sexual behavior in castrated male rats: Effects of female precopulatory behavior

From the population of 89 adult sexually inexperienced Wistar male rats 20 animals that initiated copulatory behavior with females exhibiting low intensity of precopulatory behavior (presenting females) were preselected. Prior to castration all 20 males had the same sexual experience: three ejaculatory series in four weekly sessions with females exhibiting high intensity of precopulatory behavior (darting females). Following castration, the decline of copulatory behavior was much slower for the nine males tested with darting females as compared to the 11 males tested with presenting females. Male precopulatory behaviors (anogenital sniffing, touching flanks, etc) outlasted the loss of copulatory behavior and seem to be less dependent on both external and internal determinants. It is concluded that intensive external sexual stimuli can function to compensate, and therefore mask, the subnormal operation of androgen-dependent mechanisms in initiating the copulatory behavior.     

Sexual differentiation of brain and behavior in quail and zebra finches: Studies with a new aromatase inhibitor, R76713

In many species of vertebrates, major sex differences affect reproductive behavior and endocrinology. Most of these differences do not result from a direct genomic action but develop following early exposure to a sexually differentiated endocrine milieu. In rodents, the female reproductive phenotype mostly develops in the absence of early steroid influence and male differentiation is imposed by the early action of testosterone, acting at least in part through its central conversion into estrogens or aromatization. This pattern of differentiation does not seem to be applicable to avian species. In Japanese quail (Coturnix japonica), injection of estrogens into male embryos causes a permanent loss of the capacity to display male-type copulatory behavior when exposed to testosterone in adulthood. Based on this experimental result, it was proposed that the male reproductive phenotype is “neutral” in birds (i.e. develops in the absence of endocrine influence) and that endogenous estradiol secreted by the ovary of the female embryo is responsible for the physiological demasculinization of females. This model could be recently confirmed. Females indeed display a higher level of circulating estrogens that males during the second part of their embryonic life. In addition, treatment of female embryos with the potent aromatase inhibitor, R76713 or racemic vorozole™ which suppresses the endogenous secretion of estrogens maintains in females the capacity to display the full range of male copulatory behaviors. The brain mechanisms that control this sexually differentiated behavior have not been identified so far but recent data suggest that they should primarily concern a sub-population of aromatase-immunoreactive neurons located in the lateral parts of the sexually dimorphic preoptic nucleus. The zebra finch (Taeniopygia guttata) exhibits a more complex, still partly unexplained, differentiation pattern. In this species, early treatment with exogenous estrogens produces a masculinization of singing behavior in females and a demasculinization of copulatory behavior in males. Since normal untreated males sing and copulate, while females never show these behaviors even when treated with testosterone, it is difficult to understand under which endocrine conditions these behaviors differentiate. In an attempt to resolve this paradox, we recently treated young zebra finches with R76713 in order to inhibit their endogenous estrogens secretion during ontogeny and we subsequently tested their behavior in adulthood. As expected, the aromatase inhibitor decreased the singing frequency in treated males but it did not affect the male-type copulatory behavior in females nor in males. In addition, the sexuality differentiated brain song control nuclei which are also masculinized in females by early treatment with estrogens, were not affected in either sex by the aromatase inhibitor. In conclusion, available data clearly show that sexual differentiation of reproductive behaviors in birds follows a pattern that is almost opposite to that of mammals. This difference may be related to the different mechanisms of sex determination in the two taxa. In quail, the ontogeny of behavioral differentiation is now well understood but we only have a very crude notion of the brain structures that are concerned. By contrast, in zebra finches, the brain mechanisms controlling the sexually differentiated singing behavior in adulthood have been well identified but we do not understand how these structures become sexually dimorphic during ontogeny.     

The Influence of Maternal Quality on Brood Sex Allocation in the Small Carpenter Bee,Ceratina calcarata

In the twig‐nesting carpenter bee, Ceratina calcarata, body size is an important component of maternal quality, smaller mothers producing significantly fewer and smaller offspring than larger mothers. As mothers precisely control the sex and size of each offspring, smaller mothers might compensate by preferentially allocating their investment towards sons. We investigated whether variation in maternal quality leads to variation in sex allocation patterns. At the population level, the numerical sex ratio was 57% male‐biased (1.31 M/F), but the investment between the sexes was balanced (1.02 M/F), because females are 38% larger than males (1.28 F/M). Maternal body size explained both sex allocation pattern and size variation among offspring: larger mothers invested more in individual progeny and produced more female offspring than smaller mothers. Maternal investment in offspring of both sexes decreased throughout the season, probably as a result of increasing maternal wear and age. The exception to this pattern was the curious production of dwarf females in the first two brood cell positions. We suggest that the sex ratio distribution reflects the maternal body size distribution and a constraint on small mothers to produce small broods. This leads to male‐biased allocation by small females, to which large mothers respond by biasing their allocation towards daughters.     

Testosterone induction of male‐typical sexual behavior is associated with increased preoptic NADPH diaphorase and citrulline production in female whiptail lizards

In rodents, male‐typical copulatory behavior is generally dependent on gonadal sex steroids such as testosterone, and it is thought that the mechanism by which the hormone gates the behavior involves the gaseous neurotransmitter nitric oxide. According to one model, testosterone induces an up‐regulation of nitric oxide synthase (NOS) in the preoptic area, increasing nitric oxide synthesis following exposure to a sexual stimulus. Nitric oxide in turn, possibly through its effect on catecholamine turnover, influences the way the stimulus is processed and enables the appropriate copulatory behavioral response. In whiptail lizards (genus Cnemidophorus), administration of male‐typical levels of testosterone to females induces the display of male‐like copulatory responses to receptive females, and we hypothesized that this radical change in behavioral phenotype would be accompanied by a large change in the expression of NOS in the preoptic area. As well as comparing NOS expression using NADPH diaphorase histochemistry between testosterone‐treated females and controls, we examined citrulline immunoreactivity (a marker of recent nitric oxide production) in the two groups, following a sexual stimulus and following a nonsexual stimulus. Substantially more NADPH diaphorase‐stained cells were observed in the testosterone‐treated animals. Citrulline immunoreactivity was greater in testosterone‐implanted animals than in blank‐implanted animals, but only following exposure to a sexual stimulus. This is the first demonstration that not only is NOS up‐regulated by testosterone, but NOS thus up‐regulated is activated during male‐typical copulatory behavior. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Advanced age influences chimpanzee behavior in small social groups

Management strategies for captive chimpanzees (Pan troglodytes) must begin to take into account the increasing age of the captive chimpanzee population. This study represents a baseline assessment of the relationship between advancing age and behavior among male and female chimpanzees living in pairs and trios in indoor/outdoor runs. Data collected on 14 old individuals (30–44 years old) and 20 younger adult individuals (11–22 years old) totaled 240 hours. Levels of agonistic and affiliative social behavior, non‐social activity, abnormal behaviors, and behavioral indicators of anxiety were evaluated. In the same captive setting, the behavior of old chimpanzees was significantly different from younger chimpanzees. Old chimpanzees showed less aggression and moved about their enclosures less. Old females behaved submissively more often than younger adult females; the reverse was found among males. However, affiliative social behavior occurred at similar levels in old and younger adult chimpanzees, implying continued need for social housing with advancing age. The effect of enrichment devices may differ for aged female chimpanzees, given their submissiveness and the lower levels of object manipulation found in aged subjects. These results suggest that aging in chimpanzees may be accompanied by altered patterns of social interaction, requiring careful attention to the compatibility of social partners. Zoo Biol 19:111–119, 2000. © 2000 Wiley‐Liss, Inc.     

Ecdysteroids as a component of the genital sex pheromone in two species of hard ticks,Dermacentor variabilis andDermacentor andersoni (Acari: Ixodidae)

Neutering of part-fed females eliminated copulatory behavior inDermacentor variabilis (Say) andD. andersoni Stiles males. Extracts from the anterior reproductive tracts of part-fed (7 days) females partly restored the male copulatory behavior in conspecific neutered females. Similar extracts from unfed females did not restore the behavior, suggesting that the pheromone was produced during feeding. Perception of the genital sex pheromone by sensillae on the male cheliceral digits was confirmed by electrophysiological techniques.Males ofD. variabilis andD. andersoni responsed positively to authentic ecdysone and 20-hydroxyccdysone (20HE) in neutered female bioassays. Responses to sterols were significantly lower than to ecdysteroids. Electrophysiological assays suggest a sensitivity of males to high doses of ecdysteroids. The strongest responses were to 20HE in both species. Ecdysteroids, specifically ecdysone and 20HE were shown to be present in the anterior reproductive tracts in excess of amounts that could be explained by mere hemolymph contamination. Ecdysteroids were also found in washings of the vaginal lumen of these two species.Dermacentor andersoni females contained larger amounts of ecdysteroids thanD. variabilis females. 20-hydroxyecdysone and possibly ecdysone appear to be components of the genital sex pheromone ofD. variabilis andD. andersoni. Species recognition may be facilitated by these components, but the complete mechanism is not yet fully understood.Supported by grant AI10, 986 from the National Institute of Allergy and Infectious Diseases, National Institutes of Health, U.S. Public Health Service, Department of Health and Human Services, Bethesda, Maryland.