Major histocompatibility complex variation and age-specific endoparasite load in subadult European rabbits.

Genes of the major histocompatibility complex (MHC) play a fundamental role in the vertebrate immune response and are amongst the most polymorphic genes in vertebrate genomes. It is generally agreed that the highly polymorphic nature of the MHC is maintained through host-parasite co-evolution. Two nonexclusive mechanisms of selection are supposed to act on MHC genes: superiority of MHC heterozygous individuals (overdominance) and an advantage for rare MHC alleles. However, the precise mechanisms and their relative importance are still unknown. Here, we examined MHC dependent parasite load in European rabbits (Oryctolagus cuniculus) from a distinct population with low MHC diversity (three alleles, six genotypes). Using a multivariate approach, we tested for associations of individual MHC class II DRB constitution and the rabbits' intestinal burden with nematodes and coccidia. Rabbits having a particular allele showed lower infestations with hepatic coccidia (E. stiedai). However, a comparison of all six genotypes in the population revealed that carriers of this allele only benefit when they are heterozygous, and furthermore, MHC heterozygosity in general did not affect individual parasite load. In conclusion, this study suggests an immunogenetic basis of European rabbit resistance to hepatic coccidiosis, which can strongly limit survival to maturity in this species. Our study gives a complex picture of MHC-parasite correlations, unveiling the limits of the classical hypotheses of how MHC polymorphism is maintained in natural systems.

Characterisation of MHC class II DRB genes in the northern tree shrew (Tupaia belangeri).

Genes of the major histocompatibility complex (MHC) mainly code for proteins of the immune system of jawed vertebrates. In particular, MHC class I and II cell surface proteins are crucial for the self/non-self discrimination of the adaptive immune system and are the most polymorphic genes in vertebrates. Positive selection, gene duplications and pseudogenes shape the face of the MHC and reflect a highly dynamic evolution. Here, we present for the first time data of the highly polymorphic MHC class II DRB exon 2 of a representative of the mammalian order scandentia, the northern tree shrew Tupaia belangeri. We found up to eight different alleles per individual and determined haplotype constitution by intensively studying their inheritance. The alleles were assigned to four putative loci, all of which were polymorphic. Only the most polymorphic locus was subject to positive selection within the antigen binding sites and only alleles of this locus were transcribed.

Features of the early juvenile development predict competitive performance in male European rabbits.

The outcome of an intra-specific aggressive encounter between two competitors is frequently influenced by differences in individual characteristics. Apart from differences in adult body condition, aspects of the early juvenile development, which are commonly found to influence traits during later life, may be of particular importance. In an observational study on individually marked European rabbit males (Oryctolagus cuniculus L.) from a field enclosure, we investigated short-term and long-term consequences of different features of the early development on measures of competitive performance during later life. Males from smaller litters, which consequently had a higher nestling body mass, showed more escalated offensive behavior (chasing) against other juveniles during juvenile life. Furthermore, such males were more offensive and successful fighters in intra-sexual conflicts during their first breeding season. Interestingly, when comparing the effects of different measures of body mass during different life stages, the nestling mass was the best predictor for male competitive performance after maturity. The body mass measured during the late juvenile stage in autumn was also significantly, but more weakly correlated with the males' offensive behavior after maturity, whereas the adult body mass did not show significant effects. In conclusion our study points out, that parameters of the early development are involved in shaping the competitive performance during later life via other mechanisms than just by promoting a high adult body mass.

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.

Chronic intake of fermented floral nectar by wild treeshrews.

For humans alcohol consumption often has devastating consequences. Wild mammals may also be behaviorally and physiologically challenged by alcohol in their food. Here, we provide a detailed account of chronic alcohol intake by mammals as part of a coevolved relationship with a plant. We discovered that seven mammalian species in a West Malaysian rainforest consume alcoholic nectar daily from flower buds of the bertam palm (Eugeissona tristis), which they pollinate. The 3.8% maximum alcohol concentration (mean: 0.6%; median: 0.5%) that we recorded is among the highest ever reported in a natural food. Nectar high in alcohol is facilitated by specialized flower buds that harbor a fermenting yeast community, including several species new to science. Pentailed treeshrews (Ptilocercus lowii) frequently consume alcohol doses from the inflorescences that would intoxicate humans. Yet, the flower-visiting mammals showed no signs of intoxication. Analysis of an alcohol metabolite (ethyl glucuronide) in their hair yielded concentrations higher than those in humans with similarly high alcohol intake. The pentailed treeshrew is considered a living model for extinct mammals representing the stock from which all extinct and living treeshrews and primates radiated. Therefore, we hypothesize that moderate to high alcohol intake was present early on in the evolution of these closely related lineages. It is yet unclear to what extent treeshrews benefit from ingested alcohol per se and how they mitigate the risk of continuous high blood alcohol concentrations.

Social environment and reproduction in female European rabbits (Oryctolagus cuniculus): benefits of the presence of litter sisters.

The authors investigated in an observational study the consequences of the presence of litter sisters on the social interactions and on reproductive performance of young female European rabbits (Oryctolagus cuniculus) from a population living under seminatural conditions. In early winter, when all young females were settled in a social group, they were characterized by the presence or absence of litter sisters in their groups. Females with litter sisters in their groups displayed significantly more positive social interaction with females of their social group compared to females without sisters, whereas this difference was mainly due to the high frequency of positive social interactions among the respective sisters. Such differences between the females of both categories were already apparent during the animals' juvenile phase, before the females integrated into a particular group: females which later had litter sisters in their group showed more positive social behavior than females which later no longer had litter sisters. During their first breeding season, females with litter sisters present generally started to breed earlier by an average of 14 days. A more favorable social environment might have possibly facilitated the earlier onset of breeding in females with present litter sisters by attenuating the negative consequences of stress.

Separating maternal and litter-size effects on early postnatal growth in two species of altricial small mammals.

Growth during an animal's early ontogeny can have important consequences for its health, reproduction and survival during later life. We studied pre-weaning growth rates of two species of small altricial mammals, and assessed the impact and compared the importance of two main aspects of the animals' early environment: maternal characteristics and the number of litter siblings (i.e. litter size). Study animals were wild-type European rabbits living in a field enclosure and laboratory rats kept under standardized housing conditions. Growth of rabbit pups was best explained (to 47%) by the combined effects of litter size, maternal age and whether females had given birth to another litter shortly before. Similarly, growth in rat pups was best explained (to 75%) by the combined effects of litter size, maternal body mass and whether mothers had previously given birth. In both species, litter size correlated negatively with pup growth. In rabbits, growth was greatest in litters of middle-aged females. In rats, pup growth correlated positively with maternal mass. Pups of both species showed higher growth rates when the mother had not given birth to a previous litter. Despite major differences in maternal behaviour and study conditions between the two species, the findings point to a similar ranking in the importance of the different parameters tested: Litter size, i.e. sibling number, was the most important factor, followed by maternal mass or age, and then by mothers' history of previous reproductive activity. We therefore think it likely that these findings will be valid for other mammalian species giving birth to large litters of altricial young.

Behavioral styles in European rabbits: social interactions and responses to experimental stressors.

The existence and consistency of individual behavioral types in response to challenging situations is of increasing interest in behavioral biology. In our study on European rabbits (Oryctolagus cuniculus), we (1) investigated correlations between social behavior during early development and responses to experimental stressors during later life, and (2) tested for consistencies in these responses across different situations. For this, we observed juveniles living in field enclosures in early summer and recorded agonistic and positive social interactions. In autumn, the animals were (a) introduced singly into a novel environment and were (b) confronted with predator (red fox Vulpes vulpes) odor. We recorded behavioral and physiological stress responses. In addition, we evaluated the predator odor test with an independent sample of animals. These latter results showed a correlation between the animals' behavioral and physiological response: Individuals, which reacted to the presence of fox odor by low scanning rates showed a high increase in serum corticosterone challenge concentrations, whilst the levels in high scanners remained stable. Overall, we found correlations among social behavior displayed during early development and behavioral responses in the two experimental tests, however the correlations between the different traits of social behavior and the responses during the two different experimental tests were not consistent. Animals which were involved in more agonistic interactions during their early development started to explore faster when entered into the novel environment. During the second test we found that rabbits which previously showed a higher frequency of positive social behavior responded to the presence of predator odor by more scanning. Moreover, the behavioral responses during both experimental tests were not correlated: fast explorers in the novel environment test did not show a more active response during the predator odor test. Due to this lack of consistent behavioral styles across both tests we conclude that the study fails to support the existence of domain-general behavioral phenotypes in European rabbits.