Comparison of the Impact between Classical and Novel Strains of Rabbit Haemorrhagic Disease on Wild Rabbit Populations in Spain

The outbreaks of two strains of rabbit haemorrhagic disease (RHD) (GI.1 and GI.2) in the Iberian Peninsula have caused substantial economic losses in commercial rabbitries and have affected the conservation of rabbit-sensitive predators due to the dramatic decline of their natural populations. However, the assessment of the impact of both RHD strains on wild rabbit populations has been limited to a few small-scale studies. Little is known about the overall impact within its native range. In this study, we described and compared the effects of GI.1 and GI.2 countrywide by using time series of hunting bag data widely available across the country and compared their trend during the first eight years after the first outbreak of GI.1 (i.e., 1998) and GI.2 (i.e., 2011), respectively. We used Gaussian generalised additive models (GAM) with the number of hunted rabbits as the response variable and year as the predictor to evaluate the non-linear temporal dynamics of the population at the national and regional community levels. The first GI.1 caused a population decline of around 53%, affecting most Spanish regional communities where the disease occurred. The positive trend observed after GI.1 in Spain ended with the initial outbreak of GI.2, which did not appear to cause a national population decline. In contrast, we found significant variability in the rabbit population trend among regional communities, where some increased, and others decreased. Such a disparity is unlikely to be explained by a single factor; rather, it appears to result from several factors, such as climatic conditions, host resistance improvement, virulence attenuation, or population density. Our study suggests that a national comprehensive hunting bag series could aid in elucidating the differences in the impact of emerging diseases on a large scale. Future research should focus on national longitudinal serological studies to shed light on the immunological status of rabbit populations in different regions to better understand the evolution of RHD strains and the resistance gained by the wild populations.

Population genetics of the European rabbit along a rural-to-urban gradient

The European rabbit (Oryctolagus cuniculus) is declining in large parts of Europe but populations in some German cities remained so far unaffected by this decline. The question arises of how urbanization affects patterns of population genetic variation and differentiation in German rabbit populations, as urban habitat fragmentation may result in altered meta-population dynamics. To address this question, we used microsatellite markers to genotype rabbit populations occurring along a rural-to-urban gradient in and around the city of Frankfurt, Germany. We found no effect of urbanization on allelic richness. However, the observed heterozygosity was significantly higher in urban than rural populations and also the inbreeding coefficients were lower, most likely reflecting the small population sizes and possibly on-going loss of genetic diversity in structurally impoverished rural areas. Global FST and G'ST-values suggest moderate but significant differentiation between populations. Multiple matrix regression with randomization ascribed this differentiation to isolation-by-environment rather than isolation-by-distance. Analyses of migration rates revealed asymmetrical gene flow, which was higher from rural into urban populations than vice versa and may again reflect intensified agricultural land-use practices in rural areas. We discuss that populations inhabiting urban areas will likely play an important role in the future distribution of European rabbits.

Does wild rabbit population size affect connectivity?

<p>Wild rabbit is a relevant species in the Iberian Peninsula due to its ecological  and economic roles. Conservationists and game managers therefore have a shared interest in assuring the existence of resilient and sustainable populations. Although management principles and guidelines are  mostly known and understood, often the results are not as good as expected. Local abundance can vary significantly even in short periods, while the colonisation of adjacent territories is uncommon, probably due to the territorial behaviour of the species. Aware that the foundation of nuclei requires interaction among individuals, we hypothesised that rabbit abundance plays a significant part in population connectivity. In order to find out whether the population size affects nuclei connectivity, we conducted a graph theory-based connectivity analysis. The results confirm that connectivity grows with rabbit abundance, but only to a certain degree, and there is a spatial separation of the nuclei regardless of the population size. These outcomes suggest that a comprehensive wild rabbit population increment plan should address both the abundance and spatial distribution, but should not aim at achieving a continuous distribution of wild rabbit with constant or similar abundance. Regarding specific management actions, we argue that in restocking operations new nuclei should be located within dispersal range from the existing ones to promote inter-nuclei connectivity, but not too close, as the nuclei segregation tendency is likely to persist due to the species’ territoriality.</p>

Adaptive diversification between the classic rabbit hemorrhagic disease virus (RHDV) and the RHDVa isolates: A genome-wide perspective

Rabbit haemorrhagic disease virus (RHDV) is a highly infectious pathogen that causes high mortality in wild and domestic rabbits. RHDV could be divided into two subtypes, classic RHDV and RHDVa, which present clear genetic, antigenic, and epidemiological differences. To further understand the nature of the diversity, we performed a genome-wide evolutionary study on the classic RHDV and RHDVa isolates. The results show that RHDV had experienced adaptive diversification with the dividing process of these subtypes. Furthermore, amino acid changes relevant to the adaptive diversification mainly cluster in viral capsid protein VP60. These results might be beneficial for a further understanding the function of VP60 and provide helpful hints for the genetic basis of RHDV emergence and re-emergence.

Experimental transmission of rabbit haemorrhagic disease virus (RHDV) from rabbit to wild mice (Mus spretus and Apodemus sylvaticus) under laboratory conditions

Rabbit haemorrhagic disease (RHD) is a highly lethal and contagious viral disease that produces haemorrhagic lesions in liver and lungs of domestic and wild rabbits (Oryctolagus cuniculus). This study investigates the transmission of RHDV from infected rabbits to mice, based on the detection of viral RNA. Sixteen wild mice (Mus spretus, n=12 and Apodemus sylvaticus, n=4) were put in contact with nine rabbits inoculated with RHDV. No mice died following exposure to RHDV-infected rabbits or developed macroscopic haemorrhagic lesions. On the fourth day of contact, RHDV was detected by RT-PCR in the faeces of three of the four mice killed and in the livers of two of them. Three days after contact period with the inoculated rabbits (7th day of the experiment), RHDV was detected by RT-PCR in 100% (n=4) of the faeces and 50% (n=2) of the livers of euthanized animals. Ten days after contact period (14th day of the experiment), RHDV was not detected in the faeces or liver from any of the mice euthanized. However, 64days after contact period, RHDV was detected in the faeces of one mouse (1 of 4). We demonstrate cross-species transmission of RHDV-RNA from rabbit to rodent and the capability of RHDV-RNA to persist in mice for at least 10days after contact, and potentially up to two months, although viral replication within the rodent and/or infectivity was not evaluated in the present study.

Disease-mediated bottom-up regulation: An emergent virus affects a keystone prey, and alters the dynamics of trophic webs

Emergent diseases may alter the structure and functioning of ecosystems by creating new biotic interactions and modifying existing ones, producing cascading processes along trophic webs. Recently, a new variant of the rabbit haemorrhagic disease virus (RHDV2 or RHDVb) arguably caused widespread declines in a keystone prey in Mediterranean ecosystems - the European rabbit (Oryctolagus cuniculus). We quantitatively assess the impact of RHDV2 on natural rabbit populations and in two endangered apex predator populations: the Iberian lynx (Lynx pardinus) and the Spanish Imperial eagle (Aquila adalberti). We found 60–70% declines in rabbit populations, followed by decreases of 65.7% in Iberian lynx and 45.5% in Spanish Imperial eagle fecundities. A revision of the web of trophic interactions among rabbits and their dependent predators suggests that RHDV2 acts as a keystone species, and may steer Mediterranean ecosystems to management-dependent alternative states, dominated by simplified mesopredator communities. This model system stresses the importance of diseases as functional players in the dynamics of trophic webs.

Multi-event capture-recapture modeling of host-pathogen dynamics among European rabbit populations exposed to myxoma and Rabbit Hemorrhagic Disease Viruses: common and heterogeneous patterns

Host-pathogen epidemiological processes are often unclear due both to their complexity and over-simplistic approaches used to quantify them. We applied a multi-event capture-recapture procedure on two years of data from three rabbit populations to test hypotheses about the effects on survival of, and the dynamics of host immunity to, both myxoma virus and Rabbit Hemorrhagic Disease Virus (MV and RHDV). Although the populations shared the same climatic and management conditions, MV and RHDV dynamics varied greatly among them; MV and RHDV seroprevalences were positively related to density in one population, but RHDV seroprevalence was negatively related to density in another. In addition, (i) juvenile survival was most often negatively related to seropositivity, (ii) RHDV seropositives never had considerably higher survival, and (iii) seroconversion to seropositivity was more likely than the reverse. We suggest seropositivity affects survival depending on trade-offs among antibody protection, immunosuppression and virus lethality. Negative effects of seropositivity might be greater on juveniles due to their immature immune system. Also, while RHDV directly affects survival through the hemorrhagic syndrome, MV lack of direct lethal effects means that interactions influencing survival are likely to be more complex. Multi-event modeling allowed us to quantify patterns of host-pathogen dynamics otherwise difficult to discern. Such an approach offers a promising tool to shed light on causative mechanisms.

A rapid survey method for estimating population density of European rabbits living in native vegetation

European rabbits are severe environmental pests in Australia but reporting of density-damage relationships has been hindered by a lack of simple methods to estimate the density of rabbit populations in native vegetation. A methodology for quantifying rabbit densities suitable for use in sparse populations of rabbits in conjunction with surveys of the condition of native vegetation is proposed. Dung pellets were counted in 11 629 regularly-spaced quadrats of 0.1 m2 in semiarid, coastal and cool-temperate areas of southern Australia. Mean pellet counts in latrines and the relationship between dung counts outside of latrines and the proportion of quadrats falling on latrines were quantified. This allowed density of dung pellets to be estimated by using a correction factor for latrines instead of attempting to count all pellets within quadrats that included parts of latrines. Rabbit density was calculated from pellet density based on mean pellet size, pellet breakdown rate and estimates of rabbits’ dry matter intake and digestive efficiency. Results were validated against estimates of rabbit density from long-term studies using a combination of spotlight transect counts and burrow entrance counts. The proposed methodology allows estimates of rabbit density in native vegetation to be obtained from just a few hours work and can be used in conjunction with surveys of the condition of native vegetation to quantify rabbit impacts. This methodology is seen as particularly useful in providing a tool to allow rabbit densities to be estimated and then compared with the thresholds, determined separately, at which damage occurs for given ecosystems.

The usefulness of field data and hunting statistics in the assessment of wild rabbit (Oryctolagus cuniculus) conservation status in Portugal

Context. The wild rabbit (Oryctolagus cuniculus) is a keystone species from the Iberian Peninsula that has suffered a strong decline in Spain during the past decades. Data on historical and current population trends in Portugal are virtually non-existent. Aims. To investigate changes in rabbit abundance at the national level so as to inform conservation status assessments, and to evaluate the usefulness of hunting bags as a rabbit abundance index. Methods. Field surveys based on latrine counts in linear transects were performed in two periods (1995 and 2002) to assess variation in population abundance. Hunting bags were also analysed for the same period to verify whether these data showed the same trends. General trends of rabbit abundance were estimated using TRIM software. Key results. Field data revealed that most of the sampling units across Portugal have low abundances, despite the observation of local high-density spots. A population reduction of 27% was estimated. Although some fluctuations were observed in hunting bags, global results obtained from these data suggest a slightly increasing trend in rabbit abundance. Conclusions. A discrepancy between field data and hunting statistics was observed. Because hunting bags may be influenced by sporadic management operations undertaken by hunters and the lack of systematic procedures in data collection, we believe that hunting statistics are not representative of real changes in rabbit populations. Thus, observed reduction in rabbit abundance estimated by field data, combined with the high initial morbidity due to rabbit haemorrhagic disease (RHD) after 1988 and the potential for continuing decline in population trends because of other factors, led to an inference of a reduction of >30% in rabbit abundance in Portugal during the past decade. Implications. Taking into account the estimated reduction, the species’ biology and socioeconomic implications, wild rabbit in Portugal was listed in 2005 in the Near Threatened category under IUCN criteria. Because of its ecological and economic importance, this classification prompted the definition of several conservation actions aimed at the recovery of the species in Portugal.