Precopulatory behaviour in male rats: ethological analysis and functional considerations

Ethologically derived procedure was used to determine the appearance of precopulatory behavioural elements in adult male rats in the course of interaction with a behaviourally strictly defined female partner, the so-called Presenting female. The data obtained were tabulated in sequence tables of elements. Two versions were used with the aim to analyze an expected value for each cell and comparing this with the observed value. Flow diagrams were constructed to depict the appearance of the individual precopulatory elements as well as transitions among them. The results can be summarized as follows. The appearance of precopulatory elements in males interacted with Presenting female proceeds in a certain sequence. After the partners are close together, the typical sequence of short body-sniffing, anogenital exploration and touching the flank was found. The other elements - climbing over, circling around, manipulation, standing on - lack a similar regularity; the relations among them are rather complicated. If the male is not able to pass from the precopulatory to the copulatory phase, he reverts very often to the exhibition of the two out of three formerly exhibited elements, i.e. anogenital exploration and touching the flank. However, there are considerable interindividual as well as intraindividual differences in total frequencies of precopulatory elements. The results are discussed from a point of view of the optimum goal-directness of sexual interaction and compared with those achieved in the previous studies in which different stimulus females were used. Further, the function of the individual precopulatory elements of male rats in sexual interaction is reviewed. Finally, the precopulatory interaction is considered to be a communicative process by means of which the sex partners are approaching the transition into the copulatory phase.     

Precopulatory behaviour and the evolutionary relationships of Discoglossidae

The phylogenetic relationships among primitive anurans remain controversial, even when several morphological and molecular approaches have been used in an attempt to resolve them. Nevertheless, very little effort has been made to study these relationships with behavioural data. We studied the relation between some precopulatory behaviour characters (male call characteristics and call recognition by females) and the different proposed phylogenies among the anuran genera Alytes, Discoglossus and Bombina . Different acoustic variables were analysed from male calls of different species of these genera; Alytes cisternasii females were used in recognition tests with calls from those species. A phenetic tree generated from male call characteristics grouped Bombina with Discoglossu s and separated these two genera from Alytes, although the tree generated from female response data did not show such a clear result. A. cisternasii females are mostly using some features that are absent in Alytes calls in order to recognize male calls. The two characters, mapped onto the three alternative phylogenetic proposals, did not resolve the trichotomy among the three genera, but suggested that the studied behavioural characters have a clear phylogenetic load.     

Transition from precopulatory to copulatory behaviour in male rats with lesions in medial preoptic area: dependence on precopulatory pattern of female

In the present study, both the precopulatory behaviour and the copulatory readiness of male rats following the bilateral medial preoptic area lesions was compared with their intact states. In behavioural testing, the intensity of female precopulatory behaviour was used as an experimental variable. The results showed that the natural threshold of copulatory readiness of males was increased in the lesioned state, the animals were more dependent on the soliciting patterns of the female. However, all the males exhibited conspicuous precopulatory behaviour towards the stimulus females used. Apparently, further brain structures participate in the regulation of sexual behaviour of males, above all, in activation or maintenance of precopulatory activity.     

Precopulatory and mating behaviour in the tasmanian bettongBettongia gaimardi desmarest (Marsupialia: Potoroidae)

Intersexual interactions in Tasmanian bettongs (Bettongia gaimardi) were observed in dyadic combinations. Several behaviours were associated with agonistic confrontations and occurred in predictable response sequences. There was no evidence of a consort period between males and pre-oestrous females. Overt sexual interactions occurred only on the night of oestrus, coincidentally with the maintenance of close spatial proximity. During copulation, multiple intromissions were regularly achieved but the intervals between successive bouts of these acts generally increased. Males were also observed to engage in regular attempts at social (urogenital) investigation and were apparently able to detect the reproductive state of all resident females, presumably utilising olfactory cues. The brevity of sexual interactions occurring between individuals contrasts with the more complex repertoire of the gregarious large macropodoid marsupials.     

Influence of sildenafil on central dopamine-mediated behaviour in male rats

Two experiments were performed to evaluate the effects of sildenafil on spontaneous or dopamine agonist-induced behaviour in male rats. Data obtained in experiment 1 show that oral administration of the drug, at 1 mg/kg, significantly increased the occurrence of penile erections, anogenital self-grooming and homosexual mounting in grouped sexually-experienced, but not inexperienced, animals. In experiment 2, pre-treatment with sildenafil (0.5, 1 or 10 mg/kg) dose-dependently modified several behavioural signs, centrally evoked by the D2/D3 dopamine agonists, 7-OH-DPAT or B-HT 920 (both at 0.1 mg/kg), in experimentally naive male rats. While sildenafil at 1 mg/kg significantly increased the number of penile erection and stretching-yawning episodes induced by 7-OH-DPAT or B-HT 920, at 10 mg/kg it elicited low stereotyped behaviour, antagonizing stretching-yawning and sedation in 7-OH-DPAT treated rats. Discussion centres on the modulatory activity of sildenafil on central dopaminergic pathways and, possibly, on nitric oxide production.     

Time limitation affects offspring traits and female's fitness through maternal oviposition behaviour

Plasticity of various life‐history traits has evoked continuing interest among biologists. For example, the plasticity of offspring characteristics as well as maternal effects may be affected by time limitation and by limitation caused by changing environmental conditions. However, it is difficult to tell apart the effect of a time constraint, experienced by the mother, from food limitation, which is experienced by the offspring at the end of the season. In this study, we controlled for food limitation and simulated a time constraint for the mother. We tested how the seed beetle, Coccotrypes dactyliperda, adapts its reproductive investment after encountering a period of low availability of seeds as oviposition sites, as compared with females that encountered a seed at an early adult stage, while maintaining a similar food supply for offspring of both groups. We show that time limitation has a significant effect on the reproductive investment patterns of females. Females that were prevented from ovipositing, but provided with abundant food and later given oviposition sites, produced more, but smaller offspring than control females. Although the number of offspring increased, there was no indication of competition for food between offspring. We propose that, in order to compensate for the loss of time, mothers that experienced a shortage of oviposition sites influence their offspring to mature faster at the cost of a smaller than average body size. This study emphasizes the importance of considering more than one offspring generation in order to correctly estimate female fitness. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 728–736.     

Precopulatory mate guarding and mating behaviour in the rotifer Epiphanes senta (Monogononta: Rotifera)

Epiphanes senta is a littoral rotifer species that occurs in temporary waters and displays a mating behaviour which has not, to my knowledge, so far been described for monogonont rotifers. Monogonont rotifers show distinctive periods within their life cycle during which mictic females appear. Mictic females produce haploid eggs that develop into males or into diapausing eggs if fertilized. The females of E. senta are mostly stationary on the substrate while males are more active swimmers. If they encounter eggs with female embryos of their own species, they attend them and mate with the hatching female. Experiments showed that males are able to discriminate between male, female and diapausing eggs. They exhibit a strong preference for female eggs that are only a few hours away from hatching compared with eggs in early developmental stages. Further experiments did not show any significant differences in male attendance of mictic and amictic eggs. It is hypothesized that males judge the age of a female egg by sensing a chemical that is produced by the growing embryo and diffuses through the egg shell. The male mating behaviour is similar to precopulatory mate guarding known from arthropods but it lacks the monopolization of the female by the male.     

Sexual interaction in adult laboratory rats: importance of female's stimuli and of male's experience

Precopulatory behaviour of adult male rats towards the passively receptive and towards the ovariectomized females was observed in dyadic interaction, first, at the time when the males were sexually inexperienced and later on after they had gained small and uniform copulatory experience (with a darting female). It was found that precopulatory activity of the sexually inexperienced males towards the ovariectomized female was "higher and richer" than that of males exposed to the passively receptive female. When the males were sexually experienced the frequency of precopulatory behavior increased and the patterns changed only in the animals exposed to the passively receptive female. Precopulatory activity of males weakened during the interaction under all experimental conditions. It is remarkable, however, that the weakening of precopulatory activity of sexually inexperienced males exposed to the ovariectomized female was reinforced again after the female temporarily exhibited behaviour typical of the male. We concluded that both the quality of the female's precopulatory behaviour and the quantity of previous male's experience are the decisive factors in successful interaction.     

Intracerebral oxytocin modulates sleep-wake behaviour in male rats

Oxytocin released within the brain under basal conditions and in response to stress is differentially involved in the regulation of the hypothalamo-pituitary-adrenal (HPA) axis. Because the HPA axis plays an important role in the regulation of wakefulness, central oxytocin may modulate sleep-wake behaviour. In the present vehicle-controlled study, we assessed the influence of a selective oxytocin receptor antagonist (des-Gly-NH2d(CH2)5 [Tyr(Me)2,Thr4] OVT; 0.75 microg/5 microl) or of synthetic oxytocin (0.1 microg and 1 microg/5 microl), infused into the lateral ventricle (i.c.v.), on the sleep pattern in male Wistar rats (n=7). Compared to vehicle, the oxytocin antagonist slightly but persistently increased wakefulness at the expense of all sleep states. This finding indicates that endogenous brain oxytocin promotes sleep. However, acute icv infusion of oxytocin delayed sleep onset latency, which resulted in a transient reduction of non-REMS and REMS, and augmented high-frequency activity in the electroencephalogram (EEG) within non-REMS. These observations agree with previous reports that icv oxytocin induces a state of arousal. Based on these findings, we postulate that oxytocin has a dual mechanism of action in dependence of the physiological state. Under basal, stress-free conditions, endogenous oxytocin may promote sleep. Conversely, the high brain levels of oxytocin after central oxytocin infusion may reflect a condition of stress accompanied by behavioural arousal and, possibly via an excitatory action on the CRH system, increase vigilance.     

Stimulatory effect of a maize diet on sexual behaviour of male rats

Feeding rats for 4 days with a diet of maize, a staple which is deficient in tryptophan (TP), caused a depletion of brain 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) without affectin noradrenaline and dopamine content.Addition of TP (2 g/kg of diet) to the TP deficient diet resulted in increased brain 5-HT and 5-HIAA content.Isolated male rats consuming the maize diet, when brought together, showed markedly increased mounting activity, while rats on the maize diet supplemented with TP did not display such a behaviour.These data provide further evidence for the role of the 5-HT system in regulating the sexual behaviour of male rats.     

Pre-copulatory behaviour in the male Mongolian gerbil: I. Differences in dependence on androgen of component patterns

Male behaviour patterns, including ultrasonics, olfactory investigation, grooming and sequences of following of oestrous females during the pre-copulatory period, were described for the Mongolian gerbil. Differences in dependence of these patterns on gonadal hormones were examined by measuring the rates of decline after castration and the degree of restoration following the subcutaneous injection of testosterone propionate (20 μg/2 days/animal). Castration and androgen therapy did not influence the performance of male genital grooming, allogrooming and the olfactory investigation of both female secretory products and the female's body, excluding the posterio-dorsal area. The other male patterns differed in the extent to which they were affected. Thus ventral gland marking, foot-stomping and sequences of follow/dart interactions declined rapidly and were not restored to pre-castration levels by androgen; whereas the upsweep ultrasonic vocalization and olfactory investigation of the female's perineal area declined more gradually, and were completely restored. These consistent differences in both decline and restoration suggest that mechanisms underlying some pre-copulatory patterns are influenced by androgen to a greater degree than others.     

Effect of rapid eye movement sleep deprivation on sexual behaviour of male rats

Rapid eye movement sleep deprivation for 3 to 4 days by the platform pedestal procedure produced an increase in sexual behaviour of male rats. The possible factors contributing towards the increase in sexual behaviour are discussed.     

Dominance status of adult male Japanese macaques: Relationship to female dominance status,male mating behaviour,seasonal changes,and developmental changes

Aggressive dominance orders of all adults in a confined troop of Japanese macaques (Macaca fuscata) were determined each mating and birth season during a 4-year interval. Males outranked more females in the mating than in the birth season, and some males shifted back and forth from ranks lower than female ranks in the birth season to ranks higher than female ranks in the mating season. Mating behaviour (number of female partners in mount and ejaculation series and ejaculation frequency) did not differ among males with ranks higher than, as high as, or lower than those of most females, nor did individual males mate more in years, when they were high-ranking than in years when they were not. There was a correlation, however, between ejaculation frequency and the number of females defeated by males. A pattern of increasing male rank with age was found.     

Sexual behaviour and reproductive competition in male wild and domestic Norway rats

The copulatory behaviour of male wild Norway rats (Rattus norvegicus) exposed individually to females in hormone-induced oestrus is characterized by fewer mounts and intromissions per ejaculatory series, shorter ejaculation latencies, and longer ejaculatory clasps than the copulatory behaviour of domestic males. Competition between wild and domestic males tested simultaneously in pairs produced only minor changes in copulatory behaviour. The reproductive success of wild and domestic male pairs simultaneously exposed to naturally cycling females was nearly equal in both the laboratory and an outdoor enclosure. Genotype of the female had little effect on male copulatory behaviour. The copulatory behaviour of sexually naive and experienced domestic rats did not differ. However, most sexually naive wild males failed to exhibit copulatory behaviour under the test conditions employed.     

Seoul virus infection increases aggressive behaviour in male Norway rats

In natural populations of rodents, males are more likely to engage in aggression and be infected with hantaviruses than females. Whether the relationship between hantavirus infection and aggression is due to host- or parasite-mediated mechanisms is unknown. The aim of this study was to determine whether hantavirus infection causes an increase in aggression in male rats and whether these behavioural changes are due to infection of the central nervous system or peripheral tissues. Male laboratory rats were infected with Seoul virus and tested for aggression in a resident-intruder paradigm 15 and 30 days postinoculation (p.i.). Males tested 30 days p.i. (i.e. during the persistent phase of infection) spent more time engaged in aggression than either uninfected males or males tested during the acute phase of infection (i.e. 15 days p.i.). Males that engaged in aggression for a longer duration had more virus present in lung, kidney and testis than males that spent less time engaged in aggression. Infected males shed virus in saliva, faeces, and urine; virus shedding, however, was not correlated with aggression and neither wounding nor transmission of virus to intruder males occurred during behavioural tests. Infection with Seoul virus did not alter either testosterone or corticosterone concentrations. Seoul virus antigens were not detected in the brains of infected rats. These data suggest that hantavirus infection leads to elevated aggression in infected males and may be a by-product of increased virus replication in peripheral tissues.