Patrick Gouat

Seasonal reproduction and delayed sexual maturity in mound-building mice Mus spicilegus

In the mound-building mouse, Mus spicilegus, which is found from Central to Eastern Europe, reproduction is seasonal and limited to spring and summer. In autumn, the mice build voluminous mounds composed of vegetable matter covered with earth, where juvenile animals (autumnal individuals) over-winter in groups without reproducing. Autumnal animals delay reproduction until the next spring when they are 6 months old. The influence and interactions of environmental (short light period and cold temperature (C conditions) compared with long light period and temperate temperature (T conditions)) and social factors (lack of odours from breeding adults (NB conditions) compared with presence of odours from breeding adults (B conditions)) on reproduction and sexual maturation were studied. Forty groups of three autumnal individuals (two males and a female or two females and a male) were placed in four experimental conditions (CB, CNB, TB and TNB), corresponding to interactions between environmental and social factors (n = 10 groups for each condition). Of the 40 groups only one initiated reproduction during the 18 weeks of cohabitation. Subsequently, animals were separated and isolated for 1 month and then paired with unfamiliar partners. Reproduction was monitored for an additional month, and 24 out of 39 females reproduced. In addition, of eight reproducing pairs placed in C conditions and 10 reproducing pairs maintained in T conditions, all but one pair continued reproduction. It was concluded that the delay in reproduction observed in autumnal individuals was the result of the social effects of living in groups as opposed to the environmental conditions of winter.

Paternal care in the mound-building mouse reduces inter-litter intervals

In many rodent species males display paternal behaviour. The primary reported effect of this paternal care is to increase pup survival. In mammal females, pregnancy and lactation are energetically demanding, especially when they are concurrent in post-partum reproduction. To face this energy requirement, females generally lengthen the duration of their post-partum pregnancy. In the present study we tested whether paternal care could affect this duration in the monogamous mound building mouse Mus spicilegus. In this species, females have a short reproductive life that does not exceed 4 months. Reduction of inter-delivery latencies would then be an efficient way to increase reproductive success. In a male removal experiment, we showed that inter-delivery latency was shortened by male presence. Moreover, behavioural estimations of paternal involvement were correlated with inter-delivery latency. The longer the male spent inside the nest the shorter the inter-delivery latency. In the mound-building mouse, the female might be able to monopolise the parental care of a single male, which could be important for the evolution of monogamy. The characteristics of first reproduction as compared to post-partum reproduction suggest that it may contribute to the formation of a strong and exclusive social bond between the reproductive partners.

Deficit in reproduction in polygynously mated females of the monogamous mound-building mouse Mus spicilegus

In monogamous mound-building mice Mus spicilegus, facultative polygyny was observed in April, at the beginning of the reproductive season. In order to evaluate the cost of polygyny, we compared, under laboratory conditions, the reproductive success of trios and pairs composed of sister females mated with unrelated brother males. Females in trios were able to tolerate each other during the reproductive period and to reproduce with the same male under spatial constraints. Nevertheless, polygyny had a strong negative effect on the reproductive success of the females. The average number of young per litter was smaller in trio females than in paired females, whereas the interval between two successive litters was higher. As a result, the number of litters and the number of young per time unit were smaller in each of the trio females compared with paired females. Agonistic behaviour being absent in trios, our results strongly suggest that living in trios led to pheromonal production that affected the female physiological state and reproduction. Males of trios did not obtain a better reproductive success than males in pairs.

Conspecific and heterospecific behavioural discrimination of individual odours by mound-building mice.

We have tested the ability of male mound-building mice, Mus spicilegus, to discriminate on the basis of their social odours a) two males of their own species; and b) two males of the house mouse, Mus musculus domesticus. An habituation-dishabituation procedure was used. An experimental animal was presented with the scent from the same stimulus animal for four trials; on the fifth trial, scent from a second stimulus animal was presented. Male Mus spicilegus were able to discriminate the olfactory signatures of two mound-building mouse males but did not discriminate between the olfactory signatures of two house mouse males. The lack of inter-specific individual recognition is discussed in terms of specificity and attractive value of odour cues.

Male and female mound-building mice, Mus spicilegus, discriminate dietary and individual odours of conspecifics

Individual body odour is known to provide information to conspecifics about both the identity of the donor and its biological state (e.g. reproductive condition, age, diet). It is not clear whether information related to individuality and biological state is evaluated collectively or separately. To gain insight into this subject, we examined the effect of a change in diet on conspecific recognition of individual chemical signatures in mound-building mice, Mus spicilegus . The diet change consisted of the addition of an aromatic concentrate to the drinking water. We used two different procedures based on spontaneous responses of mice to the presentation of odorous stimuli: the habituation–dishabituation procedure and the habituation–generalization procedure. Mice of both sexes were able to perceive the two types of information contained in the modified chemical signature of the donor, that is, they were able both to perceive the change in diet and to identify the chemical signature of the donor.

Short-term contact elicits heterospecific behavioral discrimination of individual odors in mound-building mice (Mus spicilegus).

The authors used a habituation-dishabituation procedure to test the ability of male mound-building mice (Mus spicilegus) to discriminate individual odors from males of another species of mouse. Male mound-building mice failed to spontaneously discriminate individual odors from Mus musculus musculus males, a natural competitor. After 24-hr contact with a male of one of the M. musculus subspecies (M. m. musculus or M. m. domesticus), experienced M. spicilegus males discriminated the individual odors of unfamiliar males of the same subspecies. These results confirm that discrimination of individual chemosignals is not confined to olfactory cues of a single species and provide new information about the effect of short-term contact on discrimination of individual odors across species.

Behavioral differentiation during collective building in wild mice Mus spicilegus

Although well documented in social insects, the possibility of behavioral differentiation during collective building has been poorly studied in mammals. In this context, the mound-building mouse Mus spicilegus is an interesting model. Under natural conditions, juveniles from different litters gather vegetal material and build a sophisticated structure, the mound, under which the mice will spend winter. The first steps of this complex building process may be elicited under laboratory conditions by offering cotton balls as building material. Spatio-temporal distribution of both animals and cotton balls was automatically recorded by RFID (Radio-Frequency Identification Device) technique. Our results revealed a behavioral differentiation during a collective building task. In a group of six individuals, only two mice (called carriers) transported 80% of the building material whereas the contribution of the remaining mice was weak or even non-existent. The proportion of carriers was constant in all of the six groups studied. This behavioral differentiation was implemented immediately after the building material was made available and remained stable during the 4 days of experiment. The high contribution level of carriers did not result from resource monopolization, nor did it depend on the gender or parental origin of the mice.

Specialization in building tasks in the mound-building mouse, Mus spicilegus

Specialization can be defined as when specific individuals perform a specific task for a relatively long period of time. The mound-building mouse is a suitable species to study specialization during a collective construction task, as juveniles build imposing mounds in which to overwinter. The process includes several successive phases involving the transport and piling up of different kinds of materials along with covering up the mound with dirt and digging galleries. Laboratory studies revealed that within a group of six individuals, two individuals transported most of the material provided for building. We tested whether this behavioural differentiation corresponded to a real specialization. Mice were given two different transport tasks corresponding to different phases of the building process. Experimental groups received two different building materials in two consecutive periods while control groups received the same building material for both periods. As predicted, in experimental groups, carriers of one material were not the same individuals as the carriers of the second material. This shift in the identity of the carrier according to the material we provided indicates a specialization for a different transport task. By contrast, in control groups, mice tended to keep their carrier status during the two periods. We concluded that, at least under controlled laboratory conditions, a task-related specialization occurred during the collective construction of the mound. This specialization could be explained as part of a division of labour in the mound-building mouse.

A laboratory study of social behaviour of pairs of females during the reproductive season in Spermophilus spilosoma and Spermophilus mexicanus

Spermophilus spilosoma and Spermophilus mexicanus are closely related species with a low degree of sociality. They are sympatric in the Bolson de Mapimi (Chihuahua Desert, Mexico), where they occupy similar ecological niches. In Sciurid rodents, advanced social structures may have evolved through the formation of sedentary female groups. The purpose of this study is to compare the ability of S. spilosoma and S. mexicanus females to cohabit with another conspecific female under space constraints during the mating period. The stability of the female relationships was tested by introducing a male of the same species. In both species, females managed to cohabit under space constraints with a low level of agonism. Nevertheless, an increase of defensive behaviour and a decrease of amicable behaviour were observed during female cohabitation in S. spilosoma. Moreover, female S. mexicanus had a higher tolerance index than S. spilosoma during this same period. The introduction of a male induced an increase of the level of agonism of S. mexicanus females while no reaction was detected in S. spilosoma. These differences were discussed in terms of mechanisms which could preclude the formation of sedentary social groups of females.

Transmission of food preference between unfamiliar house mice (Mus musculus domesticus) is dependent on social context.

Rodents obtain information about a new food source through olfactory cues of conspecifics and consequently develop an attraction for this diet. Generally, physical contact between an observer and a demonstrator that has recently consumed a novel food item is required to allow the social transmission of food preference (STFP). However, in natural populations of house mice, social encounters between unfamiliar individuals usually turn into a fight. Thus, social intolerance between the individuals involved could prevent STFP. It has been shown that the feces of rodents can act as a social stimulus and promote STFP in mice, which could reduce the social constraints associated with an encounter. Here, we examined the acquisition of the STFP in female house mice of wild origin (Mus musculus domesticus) after a direct encounter with a familiar and unfamiliar female, and after the presentation of olfactory marks of an unfamiliar female. Unlike in encounters between familiar females, our results did not provide significant support for the existence of STFP after encounters between two unfamiliar females, independently of the occurrence or absence of offensive agonistic behavior. However, STFP through olfactory marks of an unfamiliar female was effective. We suggest that the social context might strongly impair direct STFP, not necessarily via the unfamiliarity of the information provider but rather via its physical presence.