Del Thiessen

The harderian gland and thermoregulation in the gerbil (Meriones unguiculatus)

Abstract Seven experiments with Meriones unguiculatus assessed the thermoregulatory consequence of Harderian secretion and fur anointment with lipids by autogrooming. Harderianectomy reduced the animals capability to withstand cold (3–5°C) and wetness. During a 9 to 15 min exposure to cold-wet stress glandless animals lost an average of 4.6°C core body temperature, compared to an average loss of 1.6°C among intact animals. A comparable loss in body temperature occurred in animals whose fur lipids were removed with shampooing. Shaved animals coated with petroleum jelly withstood the cold-wet stress with a lesser decrease in body temperature than animals without the exogenous coat of jelly. The in vitro insulating qualities of fur lipids were demonstrated by blocking a cold air stream with various layers of lipids. The degree of insulation was related to the thickness of the lipid layers. Fur lipids were extracted from Harderianectomized and shampooed animals. Relative to controls, both procedures resulted in approximately 40–50% loss of fur lipds. The loss seen in gerbils following Harderianectomy was not found in the rat, golden hamster or C57 and DBA strains of inbred mice. Thus, in the gerbil the behavioral spread of Harderian lipids during a thermoregulatory groom insulated the gerbil from cold and wetness. The use of insulating lipids may be related to the gerbils ecology in the cold deserts of Mongolia and Northeast China.

The roots of territorial marking in the Mongolian gerbil: A problem of species-common topography

The Mongolian gerbil (Meriones unguiculatus) has recently been introduced into behavioral research. Many features make it an ideal laboratory animal. It is docile, highly exploratory, a good learner, virtually odorless and can be maintained without water; other than that it metabolizes from its food. General characteristics of the gerbil are described, and a brief review of behavioral research is given. The gerbil also possesses unique attributes that can only be studied by matching experimental methodology with species-common responses. Territorial marking is used as example. The gerbil regularly marks objects in an open field by skimming the object with a midventral sebaceous scent gland. The marking and gland are dimorphic, with the male marking about twice as frequently as the female and possessing a gland roughly twice the size. The configuration of the field (object quality) modifies the frequency of the response, as does the time of day the animals are exposed to the field. Androgen levels control the level of marking in the male and female, and the correlations between testis weight, size of the sebaceous gland, secretory output and marking frequency are significant. When a gerbil is introduced into an open field recently contaminated by another gerbil, or when objects are smeared with sebum and placed in the field, the male tends to be more hesitant in several types of behavior. The laboratory measures are internally consistent and congruous with the notion that natural selection has acted to reinforce a hormone-behavior relation of social significance to the gerbil.

Mate assortment in dating and married couples

Abstract Dating and married couples show comparable levels of assortment for physical traits. Married couples, however, are more assorted on psychological traits. It is argued that both dating and married couples initially assort on physical similarity, but that couples who are similar on psychological traits are more likely to marry. Physical traits are apparently critical in initial partner selection; psychological traits are more important for long-term relationships. There is little evidence that couples become more similar in psychological traits over time, implying that existing similarities are due to initial assortment.

Harderian gland exudates in the male Meriones unguiculatus regulate female proceptive behavior, aggression, and investigation.

Harderian gland secretions exit from the nose of Meriones unguiculatus during an autogroom (Thiessen, 1977). The exudates act as an attractant pheromone and as a thermoregulatory barrier when spread throughout the pelage. A recent study demonstrated that Harderian exudates in the male guide proceptive behavior in the female (Harriman & Thiessen, 1985). The present study replicated this finding by showing that estrous females direct fewer proceptive acts toward males lacking Harderian glands. In addition, it was found that females are more defensively aggressive toward Harderianectomized males and prefer to spend more time in the vicinity of intact males. It is speculated that Harderian spread allows the female to assess the reproductive competence of the male.

Social pressures for assortative mating

Two experiments explored the degree to which dating couples assort on physical and psychological traits. Experiment I demonstrates that 59 couples show similarities on a number of physical and non-physical (psychological) traits. Correlations are significantly different from randomized pairs and from zero when individuals rate the degree to which their partner shares similar traits. Correlations range from 0.35 to 0.66 for traits related to reproduction (i.e. interest in sex, marriage, and reproduction). Approximately equal levels of assortment occur for physical and psychological traits, and in short- and long-term relationships. Experiment II shows that subjects can reassort individual photographs of 12 dating couples presented in a random array significantly better than chance. The frequency with which the 50 subjects reassort couples is significantly correlated with the rated degree of similarity for those couples (r = 0.50). Moreover, attributions of reproductive potential are significantly related to judgments of couple similarity (r = 0.78 to 0.99).

A simple method of olfactory discrimination of urines for the Mongolian gerbil, Meriones unguiculatus

Abstract Olfactory discrimination in gerbils can be reliably assessed by measuring changes in rearing toward an odor. After the frequency of rearing stabilizes during a non-odor period, the introduction of a urinary odor through a ceiling aperture quickly produced an increase in rearing frequency and duration. Rearing then habituated during the odor presentation period but recurred at high levels if a new urinary odor was introduced. This pattern of rearing was robust enough to allow for the testing of three urinary odors during a single 24-min test period. Preliminary work suggests that the procedure is equally sensitive with different odors, can be adapted for use with other rodents, and may provide additional information about differential investigation of urinary odors. The simplicity, reliability, and brevity of this method makes it a potentially important tool for olfactory research.

Environmental tracking by females

Human females are generally reserved in their sexuality, in keeping with their heavy investment in reproduction. Males tend to be less reserved. Relative to males, however, females demonstrate more variability in sexuality and are more likely to inhibit or express high levels of sexuality. The heightened variability may in part originate with genetic mechanisms that predispose females toward greater variability (the Lyon hypothesis). Menarche, menstrual cycles, menopause, food reactions, responses to living conditions, reactions to cultural factors, and responses to sexual stimuli and potential mates are unique to or are more variable among females than males. There is a correlation between the variation expressed and female reproductive potential—females tend to shift dramatically from sexual inhibition to sexual expression. Females apparently track the quality of the environment and link their sexuality to reproductive opportunities. Successful male reproduction depends less on quality environments and more on the availability of females. In short, females track the environment; males track the females.

Harderian letdown in male mongolian gerbils (Meriones unguiculatus) contributes to proceptive behavior.

Adult female gerbils in estrus, like other female rodents, tend to engage in proceptive displays toward conspecific males. The displays, which may be interspersed with the more usual female agonistic activity, if the males are strangers, are preceded by female olfactory investigation of those head areas in the male gerbil where Harderian letdown accumulates most densely. This study explored the possibility that the male Harderian glands are a source of olfactory signals which promote proceptive behavior but suppress female agonistic behavior. Female gerbils in estrus were found to display significantly less than normal rates of proceptive behavior toward Harderianectomized males. The proceptive activity which was observed appeared to be slowed, but the typical pattern was retained. Female aggression, however, was not affected by their estrous condition or by the Harderian state of the males. Possibly Harderian letdown in male gerbils may inform females as to the reproductive competence of the males.

Haloperidol and clonidine increase, and apomorphine decreases ultrasonic vocalizations by gerbils

Ten psychotropic drugs that have putative effects on central brain neurotransmitters were assessed for influences on ultrasonic signaling relative to general activity in male Mongolian gerbils. Haloperidol (1 mg/kg IP), a dopamine antagonist, and clonidine (0.1 mg/kg IP), a norepinephrine agonist, increased ultrasonic signaling, and apomorphine (5 mg/kg IP), a dopamine agonist, decreased ultrasonic signaling. Catecholamines may modulate ultrasonic signaling in the gerbil. Body temperature changes were positively with ultrasonic emission in tests after saline, haloperidol, apomorphine, and 5-hydroxytryptophan (30 mg/kg IP).

Biomechanics of ultrasound emissions in the Mongolian gerbil, Meriones unguiculatus.

Mechanisms of ultrasonic emissions were studied in adult male pairs of Meriones unguiculatus. Preventing the mouth from opening did not change the frequency of emissions, suggesting that the sounds are conveyed through the nasal passages. Laryngeal nerve sectioning diminished or eliminated ultrasonic emission, depending on which nerves were cut. The return of functioning appeared to be related to nerve regeneration. Animals did not orient their heads or bodies in any particular direction relative to each other when producing ultrasounds. Nevertheless there was a strong correlation between locomotion, body movements, lung compression, and the generation of ultrasounds.