The paradox of endangered European rabbits regarded as pests on the Iberian Peninsula: trends in subspecies matter

The European rabbit Oryctolagus cuniculus faces a paradoxical situation in its native range on the Iberian Peninsula. While many populations have declined sharply due to a new variant of the rabbit haemorrhagic disease virus (RHDV-b), others remain healthy. The latter populations, which flourish mostly on farmland, cause significant crop damage. We explored if this difference could be related to the existence of the 2 rabbit subspecies (O. c. algirus and O. c. cuniculus) that coexist allopatrically on the Iberian Peninsula. Potential differences in population trends between rabbit subspecies may also be relevant in assisting the conservation of endangered rabbit-dependent predators which mainly occur in the distribution area of O. c. algirus. To test this, we assessed rabbit trends after the outbreak of RHDV-b by an online questionnaire to the senior administrative officers of all provincial official game departments throughout peninsular Spain (n = 47). A generalized negative trend was reported by officers in the distribution area of O. c. algirus, while a more stable or even positive trend was reported in the distribution area of O. c. cuniculus. We point to the need for establishing a long-term rabbit population monitoring programme on the Iberian Peninsula to further confirm the observed patterns, but also to contribute to evidence-based management decision-making. Our results suggest a need to apply different management systems for each rabbit subspecies.

Cerebral bioenergetic differences measured by phosphorus-31 magnetic resonance spectroscopy between bipolar disorder and healthy subjects living in two different regions suggesting possible effects of altitude

AIM

Increased oxidative stress in cerebral mitochondria may follow exposure to the systemic hypobaric hypoxia associated with residing at higher altitudes. Because mitochondrial dysfunction is implicated in bipolar disorder (BD) pathophysiology, this may impact the cerebral bioenergetics in BD. In this study, we evaluated the cerebral bioenergetics of BD and healthy control (HC) subjects at two sites, located at sea level and at moderate altitude.

METHODS

Forty-three veterans with BD and 33 HC veterans were recruited in Boston (n = 22) and Salt Lake City (SLC; n = 54). Levels of phosphocreatine, β nucleoside triphosphate (βNTP), inorganic phosphate, and pH over total phosphate (TP) were measured using phosphorus-31 magnetic resonance spectroscopy in the following brain regions: anterior cingulate cortex and posterior occipital cortex, as well as bilateral prefrontal and occipitoparietal (OP) white matter (WM).

RESULTS

A significant main effect of site was found in βNTP/TP (Boston > SLC) and phosphocreatine/TP (Boston < SLC) in most cortical and WM regions, and inorganic phosphate/TP (Boston < SLC) in OP regions. A main effect analysis of BD diagnosis demonstrated a lower pH in posterior occipital cortex and right OP WM and a lower βNTP/TP in right prefrontal WM in BD subjects, compared to HC subjects.

CONCLUSION

The study showed that there were cerebral bioenergetic differences in both BD and HC veteran participants at two different sites, which may be partly explained by altitude difference. Future studies are needed to replicate these results in order to elucidate the dysfunctional mitochondrial changes that occur in response to hypobaric hypoxia.

Nicotine Increases Activation to Anticipatory Valence Cues in Anterior Insula and Striatum

Introduction

Smoking is associated with significant morbidity and mortality. Understanding the neurobiology of the rewarding effects of nicotine promises to aid treatment development for nicotine dependence. Through its actions on mesolimbic dopaminergic systems, nicotine engenders enhanced responses to drug-related cues signaling rewards, a mechanism hypothesized to underlie the development and maintenance of nicotine addiction.

Methods

We evaluated the effects of acute nicotine on neural responses to anticipatory cues signaling (nondrug) monetary reward or loss among 11 nonsmokers who had no prior history of tobacco smoking. In a double-blind, crossover design, participants completed study procedures while wearing nicotine or placebo patches at least 1 week apart. In each drug condition, participants underwent functional magnetic resonance imaging while performing the monetary incentive delay task and performed a probabilistic monetary reward task, probing reward responsiveness as measured by response bias toward a more frequently rewarded stimulus.

Results

Nicotine administration was associated with enhanced activation, compared with placebo, of right fronto-anterior insular cortex and striatal regions in response to cues predicting possible rewards or losses and to dorsal anterior cingulate for rewards. Response bias toward rewarded stimuli correlated positively with insular activation to anticipatory cues.

Conclusion

Nicotinic enhancement of monetary reward-related brain activation in the insula and striatum in nonsmokers dissociated acute effects of nicotine from effects on reward processing due to chronic smoking. Reward responsiveness predicted a greater nicotinic effect on insular activation to salient stimuli.

Implications

Previous research demonstrates that nicotine enhances anticipatory responses to rewards in regions targeted by midbrain dopaminergic systems. The current study provides evidence that nicotine also enhances responses to rewards and losses in the anterior insula. A previous study found enhanced insular activation to rewards and losses in smokers and ex-smokers, a finding that could be due to nicotine sensitization or factors related to current or past smoking. Our finding of enhanced anterior insula response after acute administration of nicotine in nonsmokers provides support for nicotine-induced sensitization of insular response to rewards and losses.

Nicotine-induced activation of caudate and anterior cingulate cortex in response to errors in schizophrenia

BACKGROUND

Nicotine improves attention and processing speed in individuals with schizophrenia. Few studies have investigated the effects of nicotine on cognitive control. Prior functional magnetic resonance imaging (fMRI) research demonstrates blunted activation of dorsal anterior cingulate cortex (dACC) and rostral anterior cingulate cortex (rACC) in response to error and decreased post-error slowing in schizophrenia.

METHODS

Participants with schizophrenia (n = 13) and healthy controls (n = 12) participated in a randomized, placebo-controlled, crossover study of the effects of transdermal nicotine on cognitive control. For each drug condition, participants underwent fMRI while performing the stop signal task where participants attempt to inhibit prepotent responses to "go (motor activation)" signals when an occasional "stop (motor inhibition)" signal appears. Error processing was evaluated by comparing "stop error" trials (failed response inhibition) to "go" trials. Resting-state fMRI data were collected prior to the task.

RESULTS

Participants with schizophrenia had increased nicotine-induced activation of right caudate in response to errors compared to controls (DRUG × GROUP effect: p _corrected < 0.05). Both groups had significant nicotine-induced activation of dACC and rACC in response to errors. Using right caudate activation to errors as a seed for resting-state functional connectivity analysis, relative to controls, participants with schizophrenia had significantly decreased connectivity between the right caudate and dACC/bilateral dorsolateral prefrontal cortices.

CONCLUSIONS

In sum, we replicated prior findings of decreased post-error slowing in schizophrenia and found that nicotine was associated with more adaptive (i.e., increased) post-error reaction time (RT). This proof-of-concept pilot study suggests a role for nicotinic agents in targeting cognitive control deficits in schizophrenia.

First assessment of the potential introduction by hunters of eastern cottontail rabbits (Sylvilagus floridanus) in Spain

Context Humans have introduced lagomorph species in areas outside their native ranges for their meat, fur or value as game species. Assessing the rate of success of lagomorph introductions is vital to address the ecological damage they may cause. Cases of failed lagomorph introductions in apparently suitable areas may also shed light on mechanisms that may deter invasion, which are useful in developing strategies for population control. In Spain, it has been suggested that hunters introduced the non-native eastern cottontail (Sylvilagus floridanus) to compensate for the recent drastic declines of the native European rabbit (Oryctolagus cuniculus). Aims Our main goals were to investigate (1) whether Sylvilagus rabbits have indeed been introduced by hunters across Spain, and (2) whether the species has become established in Spanish ecosystems. Methods We interviewed 311 hunters or naturalists across Spain. The questionnaires inquired about the characteristics of game management in each locality, including the frequency of rabbit restocking, and particularly whether Sylvilagus rabbits had been released in the surveyed localities. In addition, we sampled 192 rabbit populations (n=3974 individuals) across Spain by using molecular analysis to determine whether Sylvilagus rabbits were present in these areas. Key results Our interview results suggest that Sylvilagus rabbits may have been released in 6% of the 311 localities surveyed. However, molecular analyses failed to confirm their persistence, because all samples belonged to O. cuniculus. Conclusions We infer that Sylvilagus rabbits failed to establish themselves in Spain, although interviewees reported their introduction. Several reasons may explain the unsuccessful establishment of this species, such as a low propagule pressure, competition with native species, predation, inability to cope with local pathogens and unsuitable climatic conditions. Implications The risk of future introductions of non-native game species can be reduced through the implementation of stricter regulations of animal releases into the wild. Long-term monitoring networks should be developed to help identify non-native game species before they become established and spread to neighbouring areas, thereby preventing any ecological or economic impacts these species may cause.

Does fox control improve red–legged partridge (Alectoris rufa) survival? An experimental study in Northern Spain

This work evaluates the effectiveness of fox control as a method to improve the survival of red–legged partridge (Alectoris rufa). We radio–tracked 89 adult partridges and their chicks (62 few days old chicks and 46 over one–month–old chicks) and monitored their nests (N = 45) on two hunting estates in northern Spain over two years. Generalist predators (red fox, Vulpes vulpes, and magpie, Pica pica) were selectively controlled on one half of each estate during the first year, and on the other half in the second year. We estimated the effect of predator control on survival rates. Predator control did not improve survival rates for adult partridges and nests, but it improved chick survival, especially for chicks over one–month old.

Widespread exposure to Sarcoptes scabiei in wild European rabbits (Oryctolagus cuniculus) in Spain

Sarcoptic mange was recently described in the wild European rabbit (Oryctolagus cuniculus) in north-eastern Mediterranean Spain, the first such infection reported in this species anywhere in the world. This finding has created concern in conservationists and game managers given that an outbreak of mange after a translocation would have catastrophic consequences for naïve rabbit populations in other parts of Spain. A retrospective serosurvey using an 'in house' ELISA test based on the use of a recombinant antigen aimed at determining the rates of contact with Sarcoptes scabiei was carried out on sera from 966 rabbits collected between 1993 and 2010 in Spain. Antibodies were found in 13% of wild rabbits in 60% of the 53 areas surveyed, as well as in 16 of the 17 Spanish provinces and islands studied. Seropositive rabbits were found amongst the oldest samples analyzed and in all studied years. Antibodies were also detected in 36% of rabbits from the protected island of Dragonera, where rabbits have probably not been released since the 1970s. On Mallorca, where 89 rabbits were inspected for both lesions and antibodies, the prevalence of lesions (5.6%) was much lower than the seroprevalence (22.5%), indicating that rabbits often survive infection or that ELISA detects infected rabbits before they develop visible lesions. Seroprevalence was higher in areas with medium levels of rabbit abundance, no restocking and high rainfall. The results show that mange is widespread in rabbits and that the mite is not a recent introduction. Thus, sarcoptic mange could be considered as an enzootic disease in the wild rabbit and so prophylactic measures implemented during rabbit translocations are to be encouraged to avoid local outbreaks in naïve populations.

Harbouring pests: rabbit warrens in agricultural landscapes

Context Warrens are central to rabbit biology and available warren space can set a limit to the number of rabbits living in an area. Therefore, quantifying and analysing the distribution of rabbit warrens is a key step towards the management of the species in agricultural lands where it causes significant damage to crops. Aims The present study investigates the distribution and spatial pattern of wild rabbit (Oryctolagus cuniculus) warrens in an intensively managed agricultural landscape within the rabbit’s native range in semiarid southern Spain, where rabbits constitute an emerging pest problem. Methods All natural rabbit warrens within two sites were mapped, and information on their size, use and protection was recorded. The effects of environmental variables (e.g. habitat features and distances to key resources) in determining warren occurrence were evaluated using binomial generalised linear models (GLM). Key results The main variable explaining warren occurrence was the distance to the nearest neighbouring warren. Habitat variables and the distances to key resources played only a secondary role, and were mainly related to frequent ploughing linked to agricultural practices that prevent warren construction. Conclusions Habitat instability resulting from agricultural practices (i.e. frequent ploughing and intensive human disturbance) promotes warren construction on stable grounds only and partly explains the clumped spatial pattern found. However, warren occurrence in intensively managed agricultural areas seems to be more constrained by the proximity of neighbouring warrens that would facilitate rabbit recolonisation from patches nearby. Despite becoming increasingly scarce as a result of agricultural intensification, these unploughed remnants may act as safe islands for digging warrens. Implications The management of unploughed patches and the connectivity among them in semiarid agroecosystems of southern Spain is therefore of utmost importance to the management of rabbits as an agricultural pest.

Reduced introgression of the Y chromosome between subspecies of the European rabbit (Oryctolagus cuniculus) in the Iberian Peninsula

The role of the Y chromosome in speciation is unclear. Hybrid zones provide natural arenas for studying speciation, as differential introgression of markers may reveal selection acting against incompatibilities. Two subspecies of the European rabbit (Oryctolagus cuniculus) form a hybrid zone in the Iberian Peninsula. Previous work on mitochondrial DNA (mtDNA), Y- and X-linked loci revealed the existence of two divergent lineages in the rabbit genome and that these lineages are largely subspecies-specific for mtDNA and two X-linked loci. Here we investigated the geographic distribution of the two Y chromosome lineages by genotyping two diagnostic single nucleotide polymorphisms in a sample of 353 male rabbits representing both subspecies, and found that Y chromosome lineages are also largely subspecies-specific. We then sequenced three autosomal loci and discovered considerable variation in levels of differentiation at these loci. Finally, we compared estimates of population differentiation between rabbit subspecies at 26 markers and found a surprising bimodal distribution of F(ST)values. The vast majority of loci showed little or no differentiation between rabbit subspecies while a few loci, including the SRY gene, showed little or no introgression across the hybrid zone. Estimates of population differentiation for the Y chromosome were surprisingly high given that there is male-biased dispersal in rabbits. Taken together, these data indicate that there is a clear dichotomy in the rabbit genome and that some loci remain highly differentiated despite extensive gene flow following secondary contact.

The effect of exclusion of terrestrial predators on short-term survival of translocated European wild rabbits

Many translocation methods have been tested in southern Europe in recent decades to increase the translocation success of the European wild rabbit (Oryctolagus cuniculus L.) for both conservation and game purposes. The main problem experienced during such translocations is the high short-term (7 days) mortality attributed to predation during the days immediately following rabbit release. In this study, we test the effect of the exclusion of terrestrial predators on the survival of translocated rabbits for recovery purposes. Four translocation plots (4 ha with 18 artificial warrens each) were constructed, two of them with a fence to exclude terrestrial predators. In all, 724 rabbits were released to the translocation plots in five batches and forced to remain inside warrens for 7 days. Following liberation, exclusion of predators did not increase rabbit survival in the short term. Contrary to expectations, three months after release, survival of rabbits in the unfenced plot was slightly, but not significantly, higher than in the fenced plot (0.57 and 0.40 respectively). Although predator control is a frequent management practice associated with rabbit translocations, our results suggest that it may not favour rabbit survival rate as much as the adaptation of rabbits to the release site.

Trypanosoma spp. infection in wild rabbits (Oryctolagus cuniculus) during a restocking program in Southern Spain

The effect of parasites on managed rabbit populations may prove crucial to develop sanitary strategies during restocking programs of such key prey species. We investigated natural infection of European wild rabbits (Oryctolagus cuniculus) with Trypanosoma spp. in Spain. By fencing part of the warrens during a rabbit restocking program, we induced host variation in rabbit density across these socio-spatial units. We aimed (i) to compare Trypanosoma spp. infection spread between fenced and open warrens and (ii) to assess the relationship between body condition and infection. Trypanosoma spp. parasitaemia peaked in juveniles and decreased onwards. Adult females showed statistically higher infection rates than males. Rabbits from fenced warrens presented statistically higher infection rates than those from open ones, but did not differ in body condition. Parasite abundance negatively correlated with body condition in adults. Sex differences could resemble increased susceptibility to infection in females as a cost of reproduction and/or a higher exposition inside the warrens. Future studies should clarify whether aggregation caused enhanced exposition to intermediate hosts (fleas) and subsequent transmission of the parasite, and we stress that the study of non-lethal parasites during restocking programs provides valuable information on host contact rates and on factors affecting disease susceptibility.

Effects of vaccination against viral haemorrhagic disease and myxomatosis on long-term mortality rates of European wild rabbits

The effects of vaccination against myxomatosis and viral haemorrhagic disease (VHD) on long-term mortality rates in European rabbits (Oryctolagus cuniculus) were studied from 1993 to 1996 by radiotracking a free-living population of wild rabbits. During the three months after immunisation, unvaccinated young rabbits weighing between 180 and 600 g were 13.6 times more likely to die than vaccinated young rabbits. In adult rabbits, vaccination did not significantly decrease mortality, mainly owing to the high proportion of rabbits which had previously been exposed to the antigens of both diseases. Compared with adult rabbits with natural antibodies to VHD, rabbits without these antibodies were 5.2 times more likely to die of VHD during annual outbreaks.

Spatial variation in helminth community structure in the red-legged partridge (Alectoris rufaL.): effects of definitive host density

Parasite community ecology has recently focused on understanding the forces structuring these communities. There are few surveys, however, designed to study the spatial repeatability and predictability of parasite communities at the local scale in one host. The purpose of our study was to address the relationship between infracommunity and component community richness, and to describe spatial variations on the local scale, of helminth parasite communities in an avian host, the red-legged partridge (Alectoris rufa). We sampled 235 wild partridges from 8 separate localities, with different partridge population densities, in the Ciudad Real and Toledo provinces of central Spain, and we determined their overall and intestinal helminth species. We found that habitat variables (mean temperature and land use) were not significantly associated with any component community. The partridge population abundance index was directly correlated with the prevalence and mean intensity of infection but not with component community species richness. There was a curvilinear relationship between infracommunity and component community species richness, as well as negative interspecific associations, for the helminth species assemblage parasitizing the intestine. A nestedness/anti-nestedness pattern, considered as part of a continuum, was associated with prevalence, mean intensity and partridge population abundance index, but not with component community richness. Increases in the partridge population abundance index and the prevalence and mean intensity of infection were associated with increases in helminth community nestedness. Although negative interactions between helminth species could not be ruled out as forces structuring helminth communities, our results suggest that parasite community structure in the red-legged partridge was primarily determined by the extrinsic influence of parasite habitat heterogeneity and its amplification of the differing probabilities of colonization of parasite species.

Descriptive study of an avian pox outbreak in wild red-legged partridges (Alectoris rufa) in Spain

This study describes the dynamics and epidemiology of an outbreak of avian pox in free-living, red-legged partridges (Alectoris rufa) in southern Spain. Between March 2000 and January 2001, 115 free-living, red-legged partridges (70 juveniles, 45 adults) were captured and radio-tagged. This, together with the necropsy of 44 carcasses (10 juveniles, 34 adults) found in the study area, and the inspection of 108 shot birds (74 juveniles, 34 adults) after a hunting drive in October, permitted a close monitoring of the course of the disease. Forty-one per cent of radio-tagged juveniles but none of 45 radio-tagged adults showed pox-like lesions at the time of capture, recapture, or necropsy. At least 40% of the juveniles that survived into the hunting season, but only 2.9% of the adults inspected at the same time, showed lesions suggestive of infection with avian poxvirus. The survival of juveniles during the peak of the outbreak was much lower than that of the adults, but we found no significant differences between the survival probabilities of juvenile partridges with and without pox-like lesions. Nevertheless, some birds may have developed lesions after their capture. The occurrence and course of the disease in a managed area with intense predator control underlines the need for studies on the combined influence of diseases and predators on population dynamics. Also the need for early detection of diseases for the management of game species is emphasized.

Pathology of avian pox in wild red-legged partridges (Alectoris rufa) in Spain

The diagnosis and pathology of an avian pox outbreak in free-living red-legged partridges in Cádiz, Southern Spain, is described. Diagnosis of the disease was based on histopathology, ultrastructural examination of, and virus isolation from lesions of necropsied animals. Lesions were present mainly in juvenile partridges (41%), and were observed primarily on the dorsal part of the digits or on the hock joint. The lesions ranged from small wartlike nodules to large tumor-like lesions. The presence of acute lesions of any grade as opposed to absence of lesions or healed lesions adversely affected body condition of the partridges (P <.01). Further investigations on the epidemiology of the disease and on the relation of the isolated strains to other avian poxviruses are under way.

Epidemiology of viral haemorrhagic disease and myxomatosis in a free-living population of wild rabbits

From January 1993 to June 1996, the epidemiology of myxomatosis and viral haemorrhagic disease (VHD) was studied in a free-living population of wild rabbits (Oryctolagus cuniculus) in Spain by means of serological surveys and radiotracking. Myxomatosis was endemic and associated with the breeding period. Its serological pattern was characterised by a 100 per cent prevalence of antibodies in adult rabbits and a rapid increase in antibodies in young rabbits in their first year. No mortality from myxomatosis was detected in adults, and mortality in young rabbits could not be estimated because of interference by predators and scavengers and the deaths of many radiotagged rabbits inside their burrows. VHD was also an endemic disease associated with the breeding period. Adults had a higher prevalence of antibodies against VHD than young rabbits, reaching values of 80 to 90 per cent. During the study, there was an increase in rabbit numbers as a result of a decrease in mortality from predation which was associated with an increase in mortality due to VHD and in the prevalence of antibodies to VHD. Mortality from VHD was lower in rabbits with VHD antibodies than in seronegative rabbits, but some mortality from the disease was also detected in seropositive rabbits. The annual mean mortality rate due to VHD in adult rabbits was estimated to be 21.8 per cent.

Marked differences in the splanchnometry of farm-bred and wild red-legged partridges (Alectoris rufa L.)

Relative weights of heart, spleen, pancreas, and liver and the relative lengths of the small intestine and the cecum were taken from 40 farm-bred and 43 wild juvenile red-legged partridges (Alectoris rufa Linnaeus) in central Spain. Expressed as a ratio to head and body length, farm-bred partridges had lighter hearts (17% lighter), spleens (78%), and livers (29%) and shorter small intestines (15%) and cecae (20%), than wild birds of the same age. When expressed as a ratio to body weight, farm-bred juvenile red-legged partridges had lighter hearts (12%) and livers (23%) and shorter small intestines (9%) and cecae (12%) than wild partridges. Those differences might have been produced by diet differences (such as fiber-poor, high-energy feeds used on farms) and may affect the survival of farm-bred partridges after release.

Habitat related differences in helminth parasites of red foxes in the Ebro valley

The prevalences of helminth parasites found on red foxes collected in two different habitats of the Ebro Valley, in north-eastern Spain were compared. Twenty helminth species, including one trematode, six cestodes, 12 nematodes and one acanthocephalan were found. Metorchis albidus, Uncinaria stenocephala and Dirofilaria immitis were more prevalent in the irrigated lands close to the main rivers of the study area, whereas Trichuris vulpis and Pterygodermatites affinis showed higher prevalences in the semiarid stepparian habitat. Habitat characteristics need to be considered when surveying helminths over large geographical areas. The study shows that in the Ebro Valley the fox constitutes a reservoir host for several helminth species that are parasites of the domestic dog or the wolf, or may have importance as zoonoses.

Physiological responses by lagomorphs to resource limitations imposed by habitat fragmentation: implications for condition-sensitive predation

Human land uses have resulted in landscape mosaics with habitat patches that vary in quality. Patch quality (including the abundance of food and the risk of predation) can affect the survival of animals that are sequestered in remnant patches of habitat. Recent investigations of the demography of New England cottontails (Sylvilagus transitionalis) have shown that cottontails on small (resource poor) patches were in poor physical condition (based on body mass) and often foraged at sites with limited cover. This resulted in a higher mortality rate than among rabbits occupying large (resource rich) patches. To gain additional insight into the consequences of habitat fragmentation, we tracked the physiological condition of rabbits occupying small and large patches during winter. The physiological condition of rabbits was determined using the urinary urea nitrogen:creatinine ratio, and the results were compared with similar indices obtained from captive rabbits. Consistent with our expectations, the nitrogen:creatinine ratios indicated that rabbits on small patches were nutrient limited for a longer period than rabbits on large patches. Transmitter-equipped rabbits on small patches had a lower survival rate and died earlier than rabbits on large patches. All mortalities were predator related. Using these data, we developed a simple model that supports the role of "condition-sensitive predation" as a major factor limiting populations of New England cottontails. Our results also demonstrate the utility of sampling physiological condition to provide an index of quality of lagomorph habitat in human-dominated landscapes.

First epizootic of rabbit hemorrhagic disease in free living populations of Oryctolagus cuniculus at Doñana National Park, Spain

The first known epizootic of rabbit hemorrhagic disease (RHD) occurred in two free-living wild rabbit (Oryctolagus cuniculus) populations at Doñana National Park, Spain. Rabbit population density was not correlated to RHD mortality. Only adult animals were affected; males and females had similar mortality rates.