Social rank, stress, fitness, and life expectancy in wild rabbits

Low 25-hydroxyvitamin D concentrations in wild rabbits (Oryctolagus cuniculus) in southern Finland

BACKGROUND

Diet and endogenous vitamin D synthesis are possible sources of vitamin D in wild rabbits. Higher 25-hydroxyvitamin D (25(OH)D) concentrations have been reported in rabbits after artificial UVB light exposure than in rabbits without this exposure, suggesting that endogenous vitamin D synthesis occurs in the former group. In Finnish pet rabbits, diet was reported as main source of vitamin D, while outdoor access was not. Finland's northern location only enables endogenous synthesis from mid-March to mid-October in people with light skin type. Living conditions during winter are challenging for Finnish wild rabbits. This study aimed to measure serum 25(OH)D concentrations and possible natural seasonal variation of vitamin D concentrations in Finnish wild rabbits.

RESULTS

Post-mortem blood samples (n = 78) were collected between 2013 and 2021 from wild rabbits hunted for reduction of the wild rabbit population. Separated sera were stored at - 80 °C until 25(OH)D concentrations were measured by enzyme immunoassay. Data regarding sex were available from 50 rabbits, 29 (58%) of which were females. Mean 25(OH)D concentration was 3.3 (range 0.3-7.1) ng/ml. 25(OH)D concentration was statistically similar between season (autumn, winter, summer), month or year of sample collection, and sex.

CONCLUSIONS

Wild rabbits living in Finland have very low serum 25(OH)D concentrations. This is far below the previously suggested threshold of vitamin D deficiency in rabbits (17 ng/mL) or the mean 25(OH)D concentration reported in Finnish pet rabbits (26.0 ng/mL). Seasonal variation was not observed in 25(OH)D concentrations between winter and summer months. Even though rabbits are crepuscular animals and may spend the mid-day in underground burrows, the very low observed 25(OH)D concentrations raise doubt about whether vitamin D synthesis occurs efficiently in the skin of rabbits and whether the diet of wild rabbits provides adequate amounts of vitamin D. Cutaneous vitamin D synthesis, possible long-term consequences of low 25(OH)D concentrations, and the association of low vitamin D status with other health disorders warrant further investigations in rabbits.

Pregnancy Complications and Feto-Maternal Monitoring in Rabbits

Rabbit production holds significant relevance in modern agriculture due to its potential as a sustainable source of high-quality protein and efficient feed conversion, contributing to food security and economic diversification. Nevertheless, studies incorporating feto-maternal monitoring in this species are uncommon. This review gathers research on the monitoring and evaluation of factors affecting rabbit gestation, providing a better understanding of the causes of prenatal development abnormalities. These include studies regarding how chronic maternal hypertension, gestational diabetes, maternal stress, ectopic gestation, maternal uterine ischemia and fetal hypoxia, intrauterine growth restriction, superfetation, maternal age, maternal nutritional status, maternal physical condition, maternal and embryonic genotype, and the intrauterine location of rabbit fetuses can potentially impact rabbits' reproduction and maternal and fetal health. Among other monitoring techniques, ultrasonography, considered one of the best tools for diagnosing pregnancy and conducting follow-up, is also reviewed. Details on measurable fetal-development parameters in rabbits and precautions to be considered before and during the examination are also provided. Additional studies are required to understand why some events occur and their consequences throughout gestation, allowing the determination of new biomarkers or cut-offs that can be helpful for early diagnosis and improve reproductive efficiency.

Aspects of social behaviour and reproduction in the wild rabbit – Implications for rabbit breeding?

Further knowledge on aspects of social behaviour in the wild rabbit (Oryctolagus cuniculus), including the link to reproduction, could possibly point to new ways to improve housing and breeding conditions in rabbit farming. In this review, I present some results of our long-term study on a 2-hectare field enclosure population of wild rabbits (University of Bayreuth, Germany), exploring group-level and individual-level differences in agonistic behaviour of females and their potential associations with reproductive traits, including offspring survival. The frequency of agonistic behaviour in which females were involved, increased with increasing group size, and was lower in groups with a more heterogeneous age structure. At the individual level, reproducing females were involved in more agonistic interactions when groupmates gave birth and thus built their burrows and nests at around the same time, and higher-ranking mothers were particularly aggressive when other females approached close to their nursery burrows. Associations between females’ social environment and reproduction were evident, as the numbers of litters and offspring per female were lower at higher female densities, high-ranking females produced more offspring and had a lower offspring mortality than low-ranking ones, and cases of infanticide were lower in more stable groups, which we quantified by the more heterogeneous age structure of the females’ rank hierarchy in such groups. Furthermore, perinatal offspring mortality was increased in females with a delayed burrow and nest building activity, i.e. does that dug their nursery burrow and built their nest only during the last 24 h pre-partum, possibly driven by the more unfavourable social environment experienced by such females. Most importantly, our studies highlight the importance of the presence of litter siblings in improving an individual’s social environment, which resulted in an earlier onset of breeding in such females. Higher levels of positive social interactions with litter siblings were also associated with lower stress hormone (corticosterone) levels and with a better health status in terms of lower loads with an intestinal nematode. These findings on ameliorating effects of litter sibling presence in growing rabbits as well as in reproducing females may be a promising starting point worth further exploration in the context of group housing of domestic rabbits.

Agonism and grooming behaviour explain social status effects on physiology and gene regulation in rhesus macaques

Variation in social status predicts molecular, physiological and life-history outcomes across a broad range of species, including our own. Experimental studies indicate that some of these relationships persist even when the physical environment is held constant. Here, we draw on datasets from one such study-experimental manipulation of dominance rank in captive female rhesus macaques-to investigate how social status shapes the lived experience of these animals to alter gene regulation, glucocorticoid physiology and mitochondrial DNA phenotypes. We focus specifically on dominance rank-associated dimensions of the social environment, including both competitive and affiliative interactions. Our results show that simple summaries of rank-associated behavioural interactions are often better predictors of molecular and physiological outcomes than dominance rank itself. However, while measures of immune function are best explained by agonism rates, glucocorticoid-related phenotypes tend to be more closely linked to affiliative behaviour. We conclude that dominance rank serves as a useful summary for investigating social environmental effects on downstream outcomes. Nevertheless, the behavioural interactions that define an individual's daily experiences reveal the proximate drivers of social status-related differences and are especially relevant for understanding why individuals who share the same social status sometimes appear physiologically distinct. This article is part of the theme issue 'The centennial of the pecking order: current state and future prospects for the study of dominance hierarchies'.

The benefits of being dominant: health correlates of male social rank and age in a marmot

The benefits of dominance may not come without costs, particularly for males. For example, the “immunocompetence handicap hypothesis” states that males with enhanced mating success allocate resources to enhance reproductive output at a cost to their current health, whereas the “resource quality hypothesis” predicts that high-ranking males may benefit from increased reproduction and good health. Whereas the predictions from each have been well tested in captive animals and in a variety of highly social primates, fewer studies have been carried out in free-living, facultatively social animals. Using adult male yellow-bellied marmots (Marmota flaviventer), we evaluated predictions of these hypotheses by examining the relationship between social rank and 2 health indicators—fecal glucocorticoid metabolite (FCM) levels, and neutrophil/lymphocyte (N/L) ratios—after accounting for variation explained by age, body mass, and seasonality. We found that higher-ranking males tended to have a lower N/L ratio (reflecting good health) than lower-ranking individuals, whereas FCM levels were not significantly related to rank. In addition, heavier male marmots had lower N/L ratios, whereas body mass was not associated with FCM levels. We also found that older adult males had lower FCM levels (reflecting less physiological stress) but higher N/L ratios than younger adults. Finally, we found that FCM levels decreased as the active season progressed and FCM levels were associated with the time of the day. Overall, our results suggest that socially-dominant male marmots enjoyed better, not worse health in terms of lower N/L ratios.

Aggression, glucocorticoids, and the chronic costs of status competition for wild male chimpanzees

Across vertebrates, high social status affords preferential access to resources, and is expected to correlate positively with health and longevity. Increasing evidence, however, suggests that although dominant females generally enjoy reduced exposure to physiological and psychosocial stressors, dominant males do not. Here we test the hypothesis that costly mating competition by high-ranking males results in chronic, potentially harmful elevations in glucocorticoid production. We examined urinary glucocorticoids (n = 8029 samples) in a 20-year longitudinal study of wild male chimpanzees (n = 20 adults) in the Kanyawara community of Kibale National Park, Uganda. We tested whether glucocorticoid production was associated with dominance rank in the long term, and with mating competition and dominance instability in the short term. Using mixed models, we found that both male aggression and glucocorticoid excretion increased when the dominance hierarchy was unstable, and when parous females were sexually available. Glucocorticoid excretion was positively associated with male rank in stable and unstable hierarchies, and in mating and non-mating contexts. Glucorticoids increased with both giving and receiving aggression, but giving aggression was the primary mechanism linking elevated glucocorticoids with high rank. Glucocorticoids also increased with age. Together these results show that investment in male-male competition increases cumulative exposure to glucocorticoids, suggesting a long-term tradeoff with health that may constrain the ability to maintain high status across the life course. Our data suggest that the relationship between social rank and glucocorticoid production often differs in males and females owing to sex differences in the operation of sexual selection.

Enhancement of synaptic responses in ascending interneurones following acquisition of social dominance in crayfish

When crayfish have attained dominant status after agonistic bouts, their avoidance reaction to mechanical stimulation of the tailfan changes from a dart to a turn response. Ascending interneurones originating in the terminal ganglion receive sensory inputs from the tailfan and they affect spike activity of both uropod and abdominal postural motor neurones, which coordinates the uropod and abdominal postural movements. Despite the varying output effects of ascending interneurones, the synaptic responses of all interneurones to sensory stimulation were enhanced when they acquired a dominant state. The number of spikes increased as did a sustained membrane depolarizations. Regardless of social status, the output effects on the uropod motor neurones of all interneurones except VE-1 remained unchanged. VE-1 mainly inhibited the uropod opener motor neurones in naive animals, but tended to excite them in dominant animals. Synaptic enhancement of the sensory response of ascending interneurones was also observed in naive animals treated with bath-applied serotonin. However, subordinate animals or naive animals treated with octopamine had no noticeable effect on the synaptic response of their ascending interneurones to sensory stimulation. Thus, enhancement of the synaptic response is a specific neural event that occurs when crayfish attain social dominance and it is mediated by serotonin.

Life expectancy, family constellation and stress in giant mole-rats (Fukomys mechowii)

Giant mole-rats (Fukomys mechowii) are remarkably long-lived subterranean rodents (maximum recorded lifespan as reported here greater than 26 years) that live in families with one reproductive pair (breeders) and their non-reproductive offspring (non-breeders). Previous studies have shown that breeders live on average approximately twice as long as non-breeders, a finding contradicting the classic trade-off between reproduction and lifespan. Because recent evidence points to the hypothalamic-pituitary-adrenal axis as playing an important role in shaping the pace of ageing in mole-rats, we analysed the influence of the social environment of giant mole-rats on intrafamilial aggression levels, indicators of long-term stress, and, ultimately, mortality. Behavioural data indicated that family constellation, especially the presence or the absence of parents, influences agonistic behaviour. As a measure of long-term stress, we established a non-invasive method of extracting and measuring cortisol from hair of giant mole-rats. Interestingly, orphaned non-breeders exhibited significantly lower levels of cortisol and lower mortality rates than did non-breeders living with both parents. Because hypercortisolism is harmful in the long-term, intrafamilial stress could help explain the earlier onset of senescence in non-breeders, resulting in a shorter lifespan. Our findings suggest that the social environment should be considered as a further factor in ageing studies involving group-living animals. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Social bonds, social status and survival in wild baboons: a tale of two sexes

People who are more socially integrated or have higher socio-economic status live longer. Recent studies in non-human primates show striking convergences with this human pattern: female primates with more social partners, stronger social bonds or higher dominance rank all lead longer lives. However, it remains unclear whether social environments also predict survival in male non-human primates, as it does in men. This gap persists because, in most primates, males disperse among social groups, resulting in many males who disappear with unknown fate and have unknown dates of birth. We present a Bayesian model to estimate the effects of time-varying social covariates on age-specific adult mortality in both sexes of wild baboons. We compare how the survival trajectories of both sexes are linked to social bonds and social status over the life. We find that, parallel to females, male baboons who are more strongly bonded to females have longer lifespans. However, males with higher dominance rank for their age appear to have shorter lifespans. This finding brings new understanding to the adaptive significance of heterosexual social bonds for male baboons: in addition to protecting the male's offspring from infanticide, these bonds may have direct benefits to males themselves. This article is part of the theme issue 'Evolution of the primate ageing process'.

Grouping of breeding rabbit does at different time points: effects on fertility, mortality and weight

<p>Semi-group housing in breeding does has been shown to reduce production and breeding success in comparison to single-housed animals. One reason for this reduction could be stress and aggression when grouping does only 2 d after artificial insemination. The aim of this study was to test different time points of grouping on fertility of does, body weight of both kits and does, and mortality rates. Hence, does were separated and housed individually one day before giving birth to their kits. The does were then artificially inseminated on day 10 postpartum (dpp) and regrouped according to the treatment (time point) on 12 (TG12), 18 (TG18), or 22 (TG22) dpp, respectively. In total, five trials with three groups pertaining to the three treatments (eight does per treatment group) were conducted. Non-pregnant does were replaced with pregnant does before each new trial (57 different does needed). Data were analysed with (generalised) linear mixed effect models and survival analysis. There were no significant differences in fertility, body weight<br />or mortality of does among the treatments. The average fertility rate (number of kindling events/number of artificial inseminations×100) was low (40.92%) and seasonal effects may have partially masked treatment effects, as most trials took place during winter. Likewise, the survival rate of kits was not influenced by the treatment (survival test: χ²=2.3, df = 2, <em>P</em> = 0.3). Body weight of the kits was also not affected by the time point of grouping (average weight: 447.70±46.42 g (TG12), 452.20±55.30 g (TG18) and 460.06±89.23 g (TG22); <em>P</em> = 0.33). In conclusion, grouping does at a later time point in the reproductive cycle did not show any significant improvement in the breeding or productive success in a Swiss semi-group housing system. An elongated separation from conspecifics did not enhance the welfare of semi-group housed rabbits.</p>

Social determinants of health and survival in humans and other animals

The social environment, both in early life and adulthood, is one of the strongest predictors of morbidity and mortality risk in humans. Evidence from long-term studies of other social mammals indicates that this relationship is similar across many species. In addition, experimental studies show that social interactions can causally alter animal physiology, disease risk, and life span itself. These findings highlight the importance of the social environment to health and mortality as well as Darwinian fitness-outcomes of interest to social scientists and biologists alike. They thus emphasize the utility of cross-species analysis for understanding the predictors of, and mechanisms underlying, social gradients in health.

Housing Rabbit Does in a Combi System with Removable Walls: Effect on Behaviour and Reproductive Performance

We evaluated the effects of two types of colony cages, in which rabbit does were always in a group (C1), and where they were in combi cages furnished with removable internal walls to allow both individual and grouphousing (C2), in addition to the control group (C: conventional individual cage), on welfare, reproductive performance, and global efficiency. Forty-eight New Zealand White nulliparous rabbit does underwent artificially insemination (AI) and were divided into three groups, and reared in the different systems for about 1 year. The reproductive rhythm provides AIs at weaning (30d). In the C1 system, does were continuously grouped, while in C2, walls were inserted four days before kindling and removed 1week after it (60% of the timesheet in group). Reproductive traits and behaviour were evaluated during the entire year. The behavioural observations were performed around days 7, 36, and 44, corresponding to the inclusion of the does in the maternal cages, the insertion of walls four days before kindling, and the removal of the walls 1week after parturition in the C2 group, respectively. The percentages of does with severe skin injuries and the distribution of the injuries on different parts of body were also registered. Does reared in conventional cages showed the greatest presence of stereotype behaviours, while the C1 group showed the highest (p < 0.05) incidence of aggressiveness after regrouping (attack, dominance features, and lower allo-grooming) in comparison to the C2 group (17% and 22%, in C2 and C1 does, respectively).Individually caged does achieved the best productive performance (sexual receptivity, fertility, kindling rate, and number of kits born alive and at weaning). The C1 group showed the lowest performance (p < 0.05), whereas C2 showed an intermediate one. Does housed in the combi cage (C2) had higher (p < 0.05) receptivity and fertility rates and higher numbers of kits born alive and at weaning (79.2% and 76.2%; 7.95 and 7.20, respectively) than the C1 group, but lower values (p < 0.05) than does that were individually housed.

Morphological diversity of wild rabbit populations: implications for archaeology and palaeontology

Morphometric characteristics of the European rabbit (Oryctolagus cuniculus) are regularly used in archaeological and palaeontological studies to explore aspects of prehistoric human hunting behaviour, to reconstruct past environments or to define new species. However, the variability of these characteristics is still both poorly understood and under-documented due to a lack of population-level data that are essential for reliably interpreting the fossil record of this species. Here we address the morphometric diversity of wild rabbits in seven current populations from south-western Europe. Size variations in different skeletal parts were analysed to explore the potential impact of sexual dimorphism. A geometric morphometric analysis of the third lower premolar (p3) – a tooth commonly used to distinguish leporid species – was used to evaluate the relative effects of size, phylogeny, geographical location and climate on shape variation. The results show a negligible impact of sexual dimorphism, contradicting previous studies. We also demonstrate geography and climate to be the main factors driving variation in p3 shape, potentially calling into question criteria typically used to identify rabbit species. These results are valuable not only for palaeobiologists studying the taxonomy and the evolutionary history of the leporid family but also for archaeologists interested in the socio-economic and behavioural aspects of Palaeolithic human groups.

A review of recent research outcomes on the housing of farmed domestic rabbits: reproducing does

<p>The housing of farmed animals is increasingly scrutinised by society and thereby subject to a change towards more animal-friendly systems. For rabbits, also kept as pets, there are no EC regulations regarding their housing under farming conditions. In many countries, studies have been carried out to improve their welfare and health under current and alternative housing systems. This paper reviews and integrates the research efforts made since the EFSA report in 2005 on reproducing rabbit does and provides some conclusions, where possible, with special emphasis on animal welfare according to the principles stated by the Welfare Quality® project, i.e. good housing, good health and appropriate behaviour. The use of an elevated platform provides greater opportunities for does and their kits to move, jumping up and down. Management and housing systems (especially flooring) must guarantee good hygienic conditions (all-in, all-out) and separation of the rabbits from their excreta for proper resting places, hygiene and health. Plastic floors and footrests and environmental enrichments (e.g. gnawing material) are also recommended. Continuous group housing systems for reproducing females have been definitively proven to challenge animal welfare by increased aggression and injuries among does and to kits. Part-time group housing systems have proven to have potential, but cannot yet be recommended in farms until major problems of aggression and injuries among animals are solved.</p>

The relationship between social rank and spatial learning in pheasants, Phasianus colchicus: cause or consequence?

Individual differences in performances on cognitive tasks have been found to differ according to social rank across multiple species. However, it is not clear whether an individual’s cognitive performance is flexible and the result of their current social rank, modulated by social interactions (social state dependent hypothesis), or if it is determined prior to the formation of the social hierarchy and indeed influences an individual’s rank (prior attributes hypothesis). We separated these two hypotheses by measuring learning performance of male pheasants, Phasianus colchicus, on a spatial discrimination task as chicks and again as adults. We inferred adult male social rank from observing agonistic interactions while housed in captive multi-male multi-female groups. Learning performance of adult males was assayed after social rank had been standardised; by housing single males with two or four females. We predicted that if cognitive abilities determine social rank formation we would observe: consistency between chick and adult performances on the cognitive task and chick performance would predict adult social rank. We found that learning performances were consistent from chicks to adults for task accuracy, but not for speed of learning and chick learning performances were not related to adult social rank. Therefore, we could not support the prior attributes hypothesis of cognitive abilities aiding social rank formation. Instead, we found that individual differences in learning performances of adults were predicted by the number of females a male was housed with; males housed with four females had higher levels of learning performance than males housed with two females; and their most recent recording of captive social rank, even though learning performance was assayed while males were in a standardized, non-competitive environment. This does not support the hypothesis that direct social pressures are causing the inter-individual variation in learning performances that we observe. Instead, our results suggest that there may be carry-over effects of aggressive social interactions on learning performance. Consequently, whether early life spatial learning performances influence social rank is unclear but these performances are modulated by the current social environment and a male’s most recent social rank.

Alternative and enriched housing systems for breeding does: a review

The main results and observations on group and individually housed rabbit does were reviewed by Szendrő and McNitt in 2012, but in recent years several new papers in this field have been published. This provides a new opportunity to summarise the current knowledge on alternative housing systems for breeding does. In Switzerland, rabbit does are generally housed in group systems. The recently legislated Belgian and Dutch housing systems will be converted step by step into group housing systems. Recent research demonstrated that with semi-group housing systems much better performance levels are possible than with the Swiss group housing system. However, solutions to eliminate aggression, stress and injuries which are common among rabbit does in group housing systems have yet to be found. Some authors are of the opinion that individual cages are too small and allow limited possibilities for movement and social contact. Positive results were seen when platforms were inserted into the cages and the possibility for movement increased. The does and their kits could jump up and down using the platforms. Using footrests, the incidence of sore hocks declined. Several environmental enrichments which increase the well-being of rabbit does can also be used. These enriched cages (equipped with platforms, footrests, gnawing sticks, etc.) are fully in line with animal welfare requirements. Increasing the size of cages and enriching them increases the production cost and the meat will be more expensive.

Contrasting effects of climate change on rabbit populations through reproduction

BACKGROUND

Climate change is affecting many physical and biological processes worldwide. Anticipating its effects at the level of populations and species is imperative, especially for organisms of conservation or management concern. Previous studies have focused on estimating future species distributions and extinction probabilities directly from current climatic conditions within their geographical ranges. However, relationships between climate and population parameters may be so complex that to make these high-level predictions we need first to understand the underlying biological processes driving population size, as well as their individual response to climatic alterations. Therefore, the objective of this study is to investigate the influence that climate change may have on species population dynamics through altering breeding season.

METHODOLOGY/PRINCIPAL FINDINGS

We used a mechanistic model based on drivers of rabbit reproductive physiology together with demographic simulations to show how future climate-driven changes in breeding season result in contrasting rabbit population trends across Europe. In the Iberian Peninsula, where rabbits are a native species of high ecological and economic value, breeding seasons will shorten and become more variable leading to population declines, higher extinction risk, and lower resilience to perturbations. Whereas towards north-eastern countries, rabbit numbers are expected to increase through longer and more stable reproductive periods, which augment the probability of new rabbit invasions in those areas.

CONCLUSIONS/SIGNIFICANCE

Our study reveals the type of mechanisms through which climate will cause alterations at the species level and emphasizes the need to focus on them in order to better foresee large-scale complex population trends. This is especially important in species like the European rabbit whose future responses may aggravate even further its dual keystone/pest problematic. Moreover, this approach allows us to predict not only distribution shifts but also future population status and growth, and to identify the demographic parameters on which to focus to mitigate global change effects.

Comparison of performance and welfare of single-caged and group-housed rabbit does

Although rabbit does are generally single housed on rabbit farms worldwide, it has been suggested by some specialists and recommendation of organic rabbit production systems that group housing of does is more comfortable and similar to the living conditions of the European wild rabbits. The aim of this experiment was to compare production of single-caged (S) and group-housed does (G). The S does were housed in commercial rabbit cages (floor area 0.32 m(2) and 0.3 m high). In treatment G, four does and one buck were housed in four pens measuring 7.7 m(2) (half of the floor was deep litter and the other half was plastic slat), with four nest boxes in each pen (n = 16). In treatment S, approximately half of the does (n = 18) were inseminated 2 days after kindling (S-33), whereas in the remaining does (n = 16) AI was done 11 days after kindling (S-42). A single-batch system (all of the does in the group were inseminated on the same day) was used in both S treatments. Kindling rates were 77.6%, 85.2% and 45.6% in treatments S-33, S-42 and G, respectively (P < 0.05). During the experiment, the percentage of does that kindled 0, 1, 2, 3, 4 and 5 times were 17%, 25%, 17%, 25%, 17% and 0% (G); 0%, 0%, 0%, 8%, 69% and 23% (S-33); and 0%, 0%, 17%, 58% and 25% (S-42, in this treatment does had a maximum of four kindlings). There were no significant differences among treatments for litter size. In treatments S-33, S-42 and G, suckling mortality was 14.0%, 15.2% and 38.5%, respectively (P < 0.001); survival of does was 71%, 81% and 50% (P = 0.084); and faecal corticosterone concentrations were 61, 54 and 175 nmol/g (P < 0.001). The high mortality of kits was associated with stress and aggressive behaviour of does, including scratching, biting or killing the kits, which resulted in the high rates of mortality and culling, as well as shorter lifespan of does. Because of high stress, increased mortality and morbidity, and low productivity, group housing of rabbit does resulted in poorer animal welfare and increased production costs, and therefore is not recommended.

Anogenital distance as a predictor of attractiveness, litter size and sex ratio of rabbit does

In the case of some mammalian species, females with larger anogenital distance (AGD) have smaller litters, where the sex ratio is male-biased. The first aim of the present study was to test whether this phenomenon exists in the Lagomorph group, especially in rabbits. The results revealed that does with large AGD have significantly smaller and lighter litters with a male biased sex ratio; with fewer females but not more males. The second aim of the present study was to test whether males differentiate between females differing in their AGD and are thus capable of choosing the more fertile and fecund does. Males showed a stronger response to the chin marks of females with small AGD than to the marks of females with large AGD. Our results suggest that variation in the prenatal hormonal environment, reflected through variation in AGD, could have long-term consequences on mate choice and population dynamics.

Social status-dependent modulation of LG-flip habituation in the crayfish

Strong stimuli applied to tailfan of the crayfish Procambarus clarkii (Girard) evoked lateral giant (LG) mediated tailflips. When the sensory stimulus was applied repeatedly, the response of LG habituated until it failed to give rise to a spike. We found that this LG-flip habituation was dependent on social-status. With a short interstimulus interval of 5 s, the rate of habituation of the LG in both socially dominant and subordinate crayfish was less than in socially isolated animals. By contrast, with a long interstimulus interval of 60 s, the rate of habituation of subordinate animals was less than both socially isolated and dominant animals. The excitability of the LGs following habituation was also dependent on social status. Following habituation the spike response of LGs recovered within several minutes, however they showed significant depression with a decrease in excitability. With a 5 s or 60 s interstimulus interval, subordinate animals showed longer delays of depression compared to dominant animals. A decrease in the rate of habituation and a delay of depression in subordinate crayfish would be advantageous to maintain an active escape response to evade repeated attacks of dominant animals and a reduced learning ability to adapt to social status.

Dying like rabbits: general determinants of spatio-temporal variability in survival

1. Identifying general patterns of how and why survival rates vary across space and time is necessary to truly understand population dynamics of a species. However, this is not an easy task given the complexity and interactions of processes involved, and the interpopulation differences in main survival determinants. 2. Here, using European rabbits (Oryctolagus cuniculus) as a model and information from local studies, we investigated whether we could make inferences about trends and drivers of survival of a species that are generalizable to large spatio-temporal scales. To do this, we first focused on overall survival and then examined cause-specific mortalities, mainly predation and diseases, which may lead to those patterns. 3. Our results show that within the large-scale variability in rabbit survival, there exist general patterns that are explained by the integration of factors previously known to be important at the local level (i.e. age, climate, diseases, predation or density dependence). We found that both inter- and intrastudy survival rates increased in magnitude and decreased in variability as rabbits grow old, although this tendency was less pronounced in populations with epidemic diseases. Some causes leading to these higher mortalities in young rabbits could be the stronger effect of rainfall at those ages, as well as, other death sources like malnutrition or infanticide. 4. Predation is also greater for newborns and juveniles, especially in population without diseases. Apart from the effect of diseases, predation patterns also depended on factors, such as, density, season, and type and density of predators. Finally, we observed that infectious diseases also showed general relationships with climate, breeding (i.e. new susceptible rabbits) and age, although the association type varied between myxomatosis and rabbit haemorrhagic disease. 5. In conclusion, large-scale patterns of spatio-temporal variability in rabbit survival emerge from the combination of different factors that interrelate both directly and through density dependence. This highlights the importance of performing more comprehensive studies to reveal combined effects and complex relationships that help us to better understand the mechanisms underlying population dynamics.

No deleterious effect of low dose methotrexate on titanium implant osseointegration in a rabbit model

OBJECTIVE

To evaluate the effect of low dose methotrexate alone or in combination with glucocorticoid treatment on titanium implant osseointegration.

METHODS

Groups of 6-8 adult New Zealand White rabbits were treated for 18 weeks with saline (control), methotrexate, glucocorticoid, or methotrexate plus glucocorticoid. The animals received a titanium implant in the tibia at week 6. Lumbar spine and tibia bone mineral densities were analyzed before and after treatment. Histomorphometric analysis of bone cortical thickness, total bone area around the implant, and % of bone to implant contact was performed.

RESULTS

After 18 weeks, the change in the bone mineral density in the lumbar spines and tibias in the methotrexate group was comparable to the control group (0.035 vs. 0.055 g/cm² and 0.021 vs. 0.041 g/cm², respectively). In contrast, both the glucocorticoid group and glucocorticoid plus methotrexate group had significant reductions at both sites. Histomorphometric analysis of the tibia in the control and methotrexate groups revealed no significant changes in cortical thickness (133 vs. 126 μm), total bone area around the implant (33 vs. 30%), or bone to implant contact (40 vs. 38%). In contrast, glucocorticoid group had significant reductions compared to controls in tibia cortical thickness (99 vs. 133 μm), total bone area around the implant (24 vs. 33%), and bone to implant contact (27 vs. 40%). Similar reductions were observed in the glucocorticoid plus methotrexate group.

CONCLUSIONS

Our results demonstrate that low dose methotrexate treatment does not affect titanium implant osseointegration, suggesting that this therapy is safe for surgical procedures requiring a titanium implant.

Suitability of the clonal marbled crayfish for biogerontological research: a review and perspective, with remarks on some further crustaceans

This article examines the suitability of the parthenogenetic marbled crayfish for research on ageing and longevity. The marbled crayfish is an emerging laboratory model for development, epigenetics and toxicology that produces up to 400 genetically identical siblings per batch. It is easily cultured, has an adult size of 4-9 cm, a generation time of 6-7 months and a life span of 2-3 years. Experimental data and biological peculiarities like isogenicity, direct development, indeterminate growth, high regeneration capacity and negligible senescence suggest that the marbled crayfish is particularly suitable to investigate the dependency of ageing and longevity from non-genetic factors such as stochastic developmental variation, allocation of metabolic resources, damage and repair, caloric restriction and social stress. It is also well applicable to examine alterations of the epigenetic code with increasing age and to identify mechanisms that keep stem cells active until old age. As a representative of the sparsely investigated crustaceans and of animals with indeterminate growth and extended brood care the marbled crayfish may even contribute to evolutionary theories of ageing and longevity. Some relatives are recommended as substitutes for investigation of topics, for which the marbled crayfish is less suitable like genetics of ageing and achievement of life spans of decades under conditions of low food and low temperature. Research on ageing in the marbled crayfish and its relatives is of practical relevance for crustacean fisheries and aquaculture and may offer starting points for the development of novel anti-ageing interventions in humans.

Family legacies: short- and long-term fitness consequences of early-life conditions in female European rabbits

1. Environmental conditions during an animal's early life can have profound long-term consequences and affect its fitness. In particular, maternal and sibling effects, which can strongly influence the early growth of altricial mammals may be important. Few studies have investigated the influence of such early-life parameters in small mammals, because in these species the early post-natal stage is difficult to monitor under natural conditions. 2. We quantified the effects of litter size (i.e. number of litter siblings), maternal social rank and age and reproductive history of the mother (i.e. whether or not the mother had given birth to a previous litter during this season), and the individual date of birth and social rank on two fitness components of female European rabbits (Oryctolagus cuniculus L.) from a field enclosure population. Analyses were based on data on survival to maturity of 1836 female pups from 10 annual cohorts, and on lifetime reproductive success (LRS; here: the summed up number of offspring surviving to maturity) of 81 adult females from eight annual cohorts. 3. Both fitness components were correlated with the size of the females' original litter and with the age of their mother. Litter size was related to survival to maturity and to LRS in a nonlinear (quadratic) way being highest in females from medium-sized litters. Maternal age also exerted quadratic effects on LRS, which peaked in females born to 2- to 3-year-old mothers. In contrast, survival to maturity increased with increasing age of the mother. 4. Survival to maturity and LRS were decreased in females born later in the breeding season, likely because of the longer time for growth that early born young enjoy before the winter season. In addition, LRS was lower in females which occupied a higher social rank at the onset of their first breeding season. 5. Our results emphasize that factors during early development, in particular parameters of the early social environment, do not only affect juvenile survival but have the potential to exert long-term fitness consequences throughout life.

Longevity record for a wild European rabbit (Oryctolagus cuniculus) from South Australia

A population of European rabbits (Oryctolagus cuniculus) has been monitored since November 1996 through mark–recapture as part of a longitudinal epidemiological study into two Australian rabbit biocontrol agents, rabbit haemorrhagic disease (RHD) and myxomatosis. A female rabbit, first captured as a subadult in late November 1999, was recaptured 18 times before its final capture at the end of February 2007. The longevity of this rabbit, being from its calculated birth date to the date it was last captured, was 7.6 years. A review of the literature indicates this to be the longest lifespan recorded for a European rabbit in the wild.

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.