Gérard Coureaud

Scramble competition in newborn domestic rabbits for an unusually restricted milk supply

Rabbit pups, Oryctolagus cuniculus, are nursed only for about 3xa0min once every 24xa0h, and we have previously reported indirect evidence of strong competition among littermates for the mothers milk. In the present study, we examined the nature of this competition more closely. In experiment 1, we investigated the temporal pattern of milk intake during nursing and found that pups obtain almost all milk available to them each day during the second minute of a 3-min nursing event. In experiment 2, we investigated the availability of milk across the eight nipples and found a tendency for more milk to be available from the two middle pairs. In experiment 3, we observed the behaviour of pups beneath the mother during nursing and found no evidence of a fixed ‘teat order,’ of overt aggression, or of pups displacing one another from nipples. However, the results confirmed previous findings of a positive correlation between milk intake and pups birth weight. In experiment 4, the attempt to increase competition among pups by covering half of the mothers nipples did not lead to the expression of overtly aggressive behaviour or to recognizable displacements from nipples. We conclude that in the rabbit, littermates compete for milk by scramble rather than by contest competition, in which the heaviest pups have a clear advantage. It is a strategy presumably well suited to a situation in which milk is effectively available only for 1xa0min every 24xa0h, leaving little time for aggressive tussles.

Human awareness and uses of odor cues in everyday life: Results from a questionnaire study in children

The Childrens Olfactory Behavior in Everyday Life questionnaire was developed to assess attention to, and uses of, odors in real-life situations, and to evaluate individual variations. The tool comprises 16 items prompting self-reports of active seeking, awareness and affective reactivity to odors of food, people and the environment. Children (102 girls, 113 boys) aged 6–10 years participated in the study. The results revealed that girls were significantly more olfaction-oriented than boys, especially towards the odors of people, self and the environment. An increasing ability of children to describe the odor facets of their perceptual world was found between 6 and 10 years, partly due to ameliorating verbal skills. Finally, owning an “attachment object” was linked to olfactory reactivity to odors, especially in social and affective contexts. Overall, this research contributes to expand our understanding of the behavioral importance of odors in children and its individual variations, and it brings additional arguments against the prevalent concept of functional microsmaty applied to the human species.

Rabbit pup response to the mammary pheromone: From automatism to prandial control

Rabbit pups display nipple-search behavior in response to maternal odor cues such as the Mammary Pheromone (MP). Here, we assessed in 3 steps whether the activity of the MP is influenced by prandial and/or rhythmic factors during early development. To address this point, the activity of the MP was tested in 690 pups varying in age (day 0, 2, 5 or 10), prandial state (sucked or un-nursed) and period of their 24-h cycle (-6 to +12 h after the daily sucking). In Experiment 1, the responsiveness of d0 pups was high and stable during the whole day, whether they are nursed or deprived of sucking. The MP activity was thus unaffected by colostrum ingestion. Experiment 2 revealed that some differences appear the next days: whereas the responsiveness of d2 pups was also very high during the 24-h cycle (>94%), it decreased in d5-d10 pups immediately after sucking (<48%), with a rapid recuperation in d5 pups. Experiment 3 showed that this postprandial drop in response to the MP disappeared in d5-d10 pups that missed the daily nursing, suggesting that it resulted from post-ingestive/post-absorptive events rather than from rhythm activity-related factors. Taken together, the results show a progressive change in the circadian dynamics of the MP-induced orocephalic response as a function of age modulated by prandial state. This indicates a transition from an automatic response to the MP to a response regulated by physiological factors associated with satiation.

Attraction of newborn rabbits to abdominal odors of adult conspecifics differing in sex and physiological state.

The present study aimed at assessing the ability of newborn rabbits (1-3 days) to detect and discriminate abdominal odors emitted by adult conspecifics varying in sex and physiological state. Pups were submitted to a two-choice test exclusively based on olfaction, which permitted exposure to conspecifics either during successive or simultaneous presentations. Their orientation toward either of the two stimuli was timed. These behavioral assays revealed that (a) pups display attraction to odors of the abdomen of nonlactating, nonpregnant females and males when pitted against a control stimulus; (b) pups preferred the odor of nonlactating, nonpregnant females when simultaneously presented with the odor of a male; (c) all sexually mature females (virgin, pregnant, or lactating) were attractive to pups; (d) the odor of lactating females was preferred to the odor of either nonlactating, nonpregnant or pregnant females. Thus, from the first day after birth, newborn rabbits are able to olfactorily discriminate conspecifics from cues emitted at the abdominal level and display the strongest attraction to lactating females.

Perception of odor blending mixtures in the newborn rabbit

In adult mammals, the processing of complex odor mixtures is elemental or configural. Here, we challenged these processes in newborn rabbits, in evaluating their perception of a binary odor mixture for which perceptual blending occurs in humans. This model of newborn animal was interesting since general questions remain on how odor cues are processed in immature organisms, and since rabbit pups present abilities of rapid odor learning. In the present study, we first demonstrated (Exp. 1) that rabbit pups rapidly acquired the odor of the binary mixture through associative conditioning (when the mammary pheromone was used as unconditioned stimulus). Then, we compared how they responded to the mixture, its components and the mammary pheromone, after they had learned the mixture or one of its constituents. After they had learned the odor of the mixture, they responded to its odor and the odor of its constituents (Exp. 2). However, after they had learned one constituents odor, they responded to this odor but not to the mixtures odor (Exp. 3). The response to the mixture appeared nevertheless when pups successively acquired the odor of the two components (Exp. 4). Therefore, both elemental and configural processing of the mixture seem to be displayed by rabbit pups, suggesting that neonatal perception of a simple odor mixture may involve more than the perception of its constituents.

Elemental and configural processing of odour mixtures in the newborn rabbit.

SUMMARY The processing of odour mixtures by young organisms is poorly understood. Recently, the perception of an AB mixture, known to engage configural perception in adult humans, was suggested also to be partially configural in newborn rabbits. In particular, pups did not respond to AB after they had learned A or B. However, two alternative hypotheses might be suggested to explain this result: the presence in the mixture of a novel odorant that inhibits the response to the learned stimulus, and the unevenness of the sensory and cognitive processes engaged during the conditioning and the behavioural testing. We conducted four experiments to explore these alternative hypotheses. In experiment 1, the learning of A or B ended in responses to mixtures including a novel odorant (AC or BC). Experiment 2 pointed to the absence of overshadowing. Therefore, a novelty effect cannot explain the non-response to AB after the learning of A or B. In experiment 3, pups having learned A or B in AC or BC did not respond to AB. However, they generalized odour information acquired in AB to AC or BC in experiment 4. Thus, the balancing of the perceptual tasks between the conditioning and retention test does not enhance the response to the AB mixture. To sum up, the present experiments give concrete support to the partially configural perception of specific odour mixtures by newborn rabbits.

A single key-odorant accounts for the pheromonal effect of rabbit milk: further test of the mammary pheromone's activity against a wide sample of volatiles from milk

Summary.In the rabbit, lactating females emit a volatilencompound in milk, the mammary pheromone (MP), thatntriggers rooting for the nipple and its grasping in pups.nPrevious studies have shown that the MP seems to act selectively,nin terms both of intensity and quality. Here, we aimednto add new evidence to these properties of the MP. Newbornnrabbits (n=825) were submitted to an oral activation testnallowing to measure their searching/grasping responsesntowards different stimuli. In Experiment 1 we assessednwhether pups respond to the MP in an intensity-dependentnmanner. In Experiment 2 we assessed the activity of 20nvolatiles previously identified in rabbit milk, other than thenMP, which were never systematically tested for intensitydependence.nThe assays showed that a) neonatal responsesnare released by the MP only for a limited range of concentrations;nb) the 20 other odorants from milk are inactive atnany concentration. Thus, the MP appears to be the singlenvolatile from rabbit milk that releases searching/graspingnbehaviour in pups.n

Convergent changes in the maternal emission and pup reception of the rabbit mammary pheromone

Summary.Lactating rabbit females emit volatile odour cues that trigger specialized motor actions leading to sucking. But the activity of these cues may change with advancing lactation. Here, we tested this possibility in three experiments. In Exp. 1, we assessed whether 2-day-old pups respond differently to the odour of milk from females in early (day 2) as compared to late (day 23) lactation. In Exp. 2, a compound bearing pheromonal properties, the Mammary Pheromone (MP), was dosed in these milks to assess whether its concentration is correlated with behavioural activity. In Exp. 3, the responsiveness to a constant level of MP was compared in d2 versus d23-pups. Run on 240 pups, the assays showed that a) the milk activity declines between d2 and d23 of lactation; b) during this same period, the concentration of the MP decreases in milk; c) the MP itself becomes less active to elicit oral grasping in pre-weaning pups than in newborns. These results indicate that the MP is active during the period when pups are exclusively dependent on milk. The convergent changes in emission and reception of this pheromone may sequentially warrant that pups are first attracted to the mammae, and then that they progressively disinvest the mother as they begin to eat solid food and to be attracted by other conspecifics.

Experience influences elemental and configural perception of certain binary odour mixtures in newborn rabbits

SUMMARY Elemental and configural olfactory perception allows interaction with the environment from very early in life. To evaluate how newborn rabbits can extract and respond to information from the highly complex chemical surroundings, and how experience acts on this sensory, cognitive and behavioural capability, we ran a study in four steps including a total of eight experiments. We mainly used a binary AB mixture comprising ethyl isobutyrate (component A) and ethyl maltol (component B), previously shown as a bearer of blending properties; in rabbit pups (as in human adults), the mixture elicits a weak configural perception, i.e. the perception of a configural odour different from the odours of the components. First, a repeated exposure to one component of AB led to a more elemental perception of this mixture; conversely, a repeated exposure to AB facilitated its configural processing. Second, similar impact of experience did not appear with a non-blending AC mixture (ethyl isobutyrate-guaïacol). Third, repeated exposure to AB impacted not only the perception of AB, but also and in the same way the perception of the AC mixture sharing one component, and reciprocally. However, facilitation to perceive one mixture in one mode (configural/elemental) was not generalized to a mixture sharing no components with the experienced mixture [AB versus DE (damascenone and vanillin)]. Thus, experience contributes to the neonatal perception of odour mixtures and adds plasticity to the perceptual system. However, this impact remains dependent on the chemical composition of the mixtures.

The reactivity of neonatal rabbits to the mammary pheromone as a probe for viability

Newborn rabbits depend on a daily nursing interaction with the mother to gain milk and to survive. During this interaction, they localise and seize the nipples displaying a typical behaviour triggered by maternal odour cues. The mammary pheromone constitutes such a signal in domestic rabbits: it elicits sucking-related movements in more than 90% of the pups. However, some newborns remain unresponsive to the presentation of the pheromone, even pups apparently healthy and highly motivated to suck. The main goal of the present study was therefore to explore the link between the unresponsiveness of rabbit pups to the mammary pheromone and their growth and survival in breeding conditions. To that end, 293 newborns from 30 litters were tested for their head searching-oral grasping responses to the mammary pheromone on days 1 and 3, and their milk intake and mortality were followed up from days 1 to 21. It was hypothesised that unresponsive newborns would have subsequent difficulties in finding nipples, sucking and surviving. Early weight and success in milk intake were further considered as mediating factors in growth and viability. The results showed that pups that were unresponsive to the mammary pheromone on day 1 were less successful in gaining milk and had a higher rate of mortality than the responsive pups. However, this impact was modulated by the weight of pups: it appeared only in the lightest newborns. Moreover, this impact vanished on day 3. On the other hand, the pup weight and sucking success on days 1 to 3 strongly influenced viability and growth during the period extending from days 1 to 21. Taken together, the results show that the day-1 responsiveness of rabbit pups to the mammary pheromone can be considered as an indicator of individual viability in pups having a small weight (<48 g on day 1). The predictive validity of the pups pheromonal reactivity seems however time-limited as it works only during the first, but crucial, postnatal days.