Raquel Monclús

Behavioural and physiological responses of naïve European rabbits to predator odour

Animals show a variety of antipredator strategies in response to the presence of chemical cues from mammalian predators. Nevertheless, there is no general agreement as to whether recognition of predator odours is dependent upon experience. We conducted an experiment on European rabbits Oryctolagus cuniculus naive to any contact with predators and we investigated (1) whether they possessed a mechanism for the recognition of the odour of a predator, and (2) how they responded behaviourally and physiologically to that odour. We used fox Vulpes vulpes faeces as the source of the predator odour and sheep Ovis aries faeces as a nonpredator control odour. The experiments were conducted in small outdoor enclosures where the animals were kept singly. We recorded patterns of vigilance, activity and feeding, and changes in glucocorticoids and body mass. The rabbits showed a clear antipredator response to the presence of fox faeces, whereas they behaved neutrally in response to sheep odour. The response consisted of increased avoidance and vigilance while feeding and more investigation before feeding. Furthermore, the rabbits showed a physiological alarm response, that is, an increased responsiveness of their adrenocortical system and weight loss. However, the total activity budget, measured as time spent outside the burrow, the time spent feeding, and the amount of food ingested remained largely stable during the experiment. We conclude that rabbits recognised predator odours and that this recognition was independent of experience.

Testing the threat-sensitive predator avoidance hypothesis: physiological responses and predator pressure in wild rabbits

Predation is a strong selective force with both direct and indirect effects on an animal’s fitness. In order to increase the chances of survival, animals have developed different antipredator strategies. However, these strategies have associated costs, so animals should assess their actual risk of predation and shape their antipredator effort accordingly. Under a stressful situation, such as the presence of predators, animals display a physiological stress response that might be proportional to the risk perceived. We tested this hypothesis in wild European rabbits (Oryctolagus cuniculus), subjected to different predator pressures, in Doñana National Park (Spain). We measured the concentrations of fecal corticosterone metabolites (FCM) in 20 rabbit populations. By means of track censuses we obtained indexes of mammalian predator presence for each rabbit population. Other factors that could modify the physiological stress response, such as breeding status, food availability and rabbit density, were also considered. Model selection based on information theory showed that predator pressure was the main factor triggering the glucocorticoid release and that the physiological stress response was positively correlated with the indexes of the presence of mammalian carnivore predators. Other factors, such as food availability and density of rabbits, were considerably less important. We conclude that rabbits are able to assess their actual risk of predation and show a threat-sensitive physiological response.

Non-invasive measurement of the physiological stress response of wild rabbits to the odour of a predator

Summary.Stress has been widely studied in different mammals, but the physiological stress reaction that the odour of a predator could induce in preys has not received much attention. Besides, not all the animals would respond to the same extent to a known stressor.We developed an experimental procedure with eleven naïve European rabbits (Oryctolagus cuniculus) in order to determine the individual physiological response to the olfactory detection of a potential predator. The rabbits were housed singly in small enclosures with a concrete burrow system and food and water were available ad libitum. The animals followed a control trial, without odour, and an experimental trial where we confronted the rabbits with fox (Vulpes vulpes) odour. Furthermore, another sample of eleven rabbits followed a control procedure subjected to the same housing and handling procedures but without facing the predator odour. In order to assess the physiological response we analysed the concentration of glucocorticoid metabolites in the faeces of the rabbits. Therefore, everyday faecal samples were collected and analysed with an enzyme immunoassay in order to measure the corticosterone metabolites (CM), particularly, those metabolites with a 5α-3β, 11β-diol structure.After validating the assay for wild rabbits, we found that the simulated presence of a predator (fox odour) in the enclosure resulted in an increase in faecal CM concentrations. However, the stressor did not affect all the animals in the same way. We found a general increase in the individual differences. In particular, males experienced a higher increase than females, though the overall response was similar for both sexes.To our knowledge this is one of the first attempts to analyse the assessment of the risk of predation by means of non-invasive methods.

Litter sex composition affects life-history traits in yellow-bellied marmots

1. The presence of siblings might have long-lasting fitness consequences because they influence the early environment in which an animal develops. Several studies under laboratory conditions have shown long-lasting consequences from the presence of male siblings in utero on morphology and life-history traits. However, in wild animals, such effects of litter sex composition are unexplored. 2. We capitalized on a long-term study of individually marked yellow-bellied marmots (Marmota flaviventris) and documented the effects of weaned litter sex composition and anogenital distance on several life-history and fitness traits. 3. First, we demonstrated that the number of males in a litter influenced anogenital distance. Then, we found that masculinized females, those with larger anogenital distances, were less likely to survive their first hibernation, were more likely to disperse and were less likely to become pregnant and wean young. Males from male-biased litters had lower growth rates, but we failed to detect longer-term consequences. 4. Taken together, our results show profound sex-dependent effects of litter sex composition, probably due to differential prenatal exposure to androgens, in free-living animals. We conclude that masculinization might constitute an alternative mechanism explaining variation in different demographic traits. This finding highlights the importance of studying these maternal effects, and they enhance our concern over the widespread use of endocrine disrupting compounds.

Red foxes (Vulpes vulpes) use rabbit (Oryctolagus cuniculus) scent marks as territorial marking sites

One of the functions of chemical communication is territorial signalling. To achieve this, animals should mark their territories in a manner that increases the detectability of the marks, thereby maximising the probability that other animals detect the scent marks. In this study, we focused on the scent-marking behaviour of red foxes in relation to the abundance of their main prey, the European rabbit, in a suburban forest in Madrid, Spain. Our results reveal that foxes scent-marked more and increased the detectability of their marks in areas of higher rabbit density. It would appear that foxes defend food resources from competitors by increasing the number and the detectability of their scent marks.

Context-dependent responses to neighbours and strangers in wild European rabbits (Oryctolagus cuniculus).

Territorial animals defend their territories against intruders. The level of aggression directed to intruders depends on the familiarity and/or the relative threat they pose, and it could be modified by the context of the interaction. We explored in a wild social mammal, the European rabbit (Oryctolagus cuniculus), whether residents responded more aggressively to strangers or to neighbours (dear enemy or nasty neighbour effects, respectively). We simulated the intrusion of neighbours or strangers in different parts of the territory of wild European rabbits in a suburban area in central Spain. For that, we placed faecal pellets of neighbouring or stranger rabbits in the territory of 5 rabbit colonies. Resident rabbits counter-marked preferably the odour stations with stranger odour, compared to the ones with neighbour odour, and they did not make a difference between neighbour and a non-odour control stimuli. The results suggest that rabbits show a dear enemy effect. However, repeated intrusions escalated the responses of rabbits towards neighbours. The location within the territory or the sex of the stranger did not affect the level of response. We conclude that in rabbits the relative threat posed by the intruder triggers the intensity of the interaction.

Masculinized female yellow-bellied marmots initiate more social interactions

The presence of male siblings in utero influences female morphology and life-history traits because testosterone transferred among foetuses may masculinize females. Similarly, litter sex composition might alter the display of sexually dimorphic behaviour, such as play and allogrooming, since they are modulated by androgens. We explored whether masculinization alters the frequency of play and sociopositive behaviour in female yellow-bellied marmots (Marmota flaviventris). We found that masculinized juvenile females were more likely to initiate play and allogrooming, but yearling females exhibited higher levels of oestrogen-modulated sociopositive behaviours. Additionally, the more they interacted, the greater number of different partners they interacted with. Our results suggest that masculinization increases the rate of age-dependent social behaviour. This probably works by increasing exploration that predisposes individuals to higher encounter rates. Further support comes from previous findings showing that masculinized females were more likely to disperse. Our study stresses the importance of considering litter sex composition as a fitness modulator.

Long-term effects of litter sex ratio on female reproduction in two iteroparous mammals

Summary 1. Female mammals that develop in male-biased litters show signs of masculinization because they are exposed to the testosterone produced by their male siblings in utero. The early exposure to testosterone can affect female morphology, physiology, behaviour and life-history traits. 2. Masculinization is commonly seen as the collateral effect of developing in a male-biased litter. However, when resources are limiting, masculinization might be adaptive because androgenized females could monopolize resources. 3. We investigated whether females from male-biased litters, and therefore likely to be masculinized, showed adaptive advantages under different competing scenarios. For that, we used data from two long-term field projects studying yellow-bellied marmots (Marmota flaviventris Audubon and Bachman, 1841) and European rabbits (Oryctolagus cuniculus Linnaeus, 1758). We explored whether litter sex composition affected fitness-related reproductive traits: the onset of breeding, offspring production and the probability of reproduction in a given year. 4. Our study shows long-term consequences of litter sex composition on reproduction in European rabbits and yellow-bellied marmots. Females from male-biased litters from both species delayed the onset of breeding, suggesting the maladaptive nature of masculinization. However, in European rabbits, this effect was density-dependent. Under higher-density conditions, female rabbits from male-biased litters brought forward the onset of breeding, which might increase the probability of offspring overwinter survival and therefore their fitness. These females under limiting conditions might have a higher resource holding potential. 5. We conclude that prenatal maternal effects in natural populations should be taken into account when studying life-history variation. Moreover, it is notable that small variations in naturally occurring prenatal exposure to androgens have profound impacts on individuals, social groups and the population structure.

Maternal Effects on Anogenital Distance in a Wild Marmot Population

In mammals, prenatal exposure to sex steroid hormones may have profound effects on later behavior and fitness and have been reported under both laboratory and field conditions. Anogenital distance is a non-invasive measure of prenatal exposure to sex steroid hormones. While we know that intra-uterine position and litter sex ratio influence anogenital distance, there are other, heretofore unstudied, factors that could influence anogenital distance, including maternal effects. We capitalized on a long-term study of wild yellow-bellied marmots (Marmota flaviventris) to study the importance of maternal effects on explaining variation in anogenital distance and found significant effects. The strength of these effects varied annually. Taken together, our data highlights the strong variability due to environmental effects, and illustrates the importance of additive genetic and maternal genetic effects on neonatal anogenital distance. We suspect that, as others apply recently popularised quantitative genetic techniques to study free-living populations, such effects will be identified in other systems.

Yellow-bellied marmots do not compensate for a late start: the role of maternal allocation in shaping life-history trajectories

Yellow-bellied marmots, Marmota flaviventris, are obligate hibernators with a relatively short active season. Animals born earlier in the season have higher chances of fulfilling the energetic requirements to survive the long winter. Therefore, the onset of breeding should have a profound impact on juvenile survival. However, there are different ways to compensate for a late start. Late breeders might allocate more resources to late born offspring, making up for the bad start, or juveniles might show compensatory growth. They are not exclusive hypotheses and both can lead to juveniles entering hibernation with a similar body condition. We used data from a long term study in and around the Rocky Mountain Biological Laboratory in Colorado to test these two hypotheses. Animals are individually marked and trapped regularly. We compared mass at weaning, mass at the end of the season, growth rates and survival between animals born earlier and later in the season. We found no evidence of increased maternal input: late breeders had lighter offspring at weaning than early breeders, and late born juveniles did not increase their growth rates. Therefore, late born individuals ended the season with lower body mass, and were thus, less likely to survive the winter. In conclusion, life-history trajectories of juvenile yellow-bellied marmots were determined by maternal allocation, whereas post-weaning decisions did not modify their fate.