Socio-genetic structure and mating system of a wild boar population

Reproductive performance and sex ratio adjustment of the wild boar (Sus scrofa) in South Korea

The wild boar (Sus scrofa), a polygynous species, rapidly expanded its geographical range and increased its population size in South Korea following the extinction of large carnivores and changes to rural environments. Understanding wild boar reproductive traits and strategies is essential for their effective management; however, studies in this area are lacking. Using samples collected from hunting bags, the relationships between 1) litter size and female weight and 2) fetal sex ratio and female body condition were examined to understand wild boar life-history strategies. Wild boars showed a seasonal breeding pattern that maximized reproduction. Litter size (mean = 5.7 ± 1.7) was correlated with female weight, whereas fetal sex ratio was not explained by female body condition. However, the heaviest ranked fetuses within the litters were male-biased. Wild boars aged three years or less accounted for 90% of the total population, and sexual dimorphism developed from two years of age. Considering that their reproductive strategy is more effective (i.e., early gestation and large litter size) than that of other polygynous species, the Trivers-Willard model was not supported for the wild boars in this study. Instead, females adjusted the sex of the heaviest fetus in the litter to maximize lifetime reproductive success.

Pseudorabies Virus Associations in Wild Animals: Review of Potential Reservoirs for Cross-Host Transmission

Pseudorabies virus (PRV) has received widespread attention for its potential health effects on humans, wildlife, domestic animals, and livestock. In this review, we focus on PRV dynamics in wildlife, given the importance of wild-origin PRV transmission to domestic and farm animals. Wild boars, pigs, and raccoons can serve as reservoirs of PRV, with viral transmission to domestic livestock occurring via several routes, such as wild herd exposure, contaminated meat consumption, and insect vector transmission. Many endangered feline and canine species can be infected with PRV, with acute disease and death within 48 h. The first confirmed human case of PRV infection in mainland China was reported in 2017. Thus, PRV exhibits potentially dangerous cross-host transmission, which is likely associated with inappropriate vaccination, poor awareness, and insufficient biosecurity. Currently, no vaccine provides full protection against PRV in all animals. Here, we summarize the epidemiology and pathogenesis of PRV infection in wild, domestic, and farmed animals, which may facilitate the design of novel therapeutics and strategies for controlling PRV infection and improving wildlife protection in China.

Multiple aspects of the maternal reproductive investment in a polytocous species: what do mothers really control?

One of the factors facilitating the expansion and proliferation of wild boar Sus scrofa is the plasticity of its reproductive biology. Nevertheless, the real influence of maternal and environmental factors on number and sex of the offspring is still controversial. While the litter size was shown to be related with the maternal condition, the strength of this relation remains to be understood, together with the possible role played by environmental conditions. Analogously, it is unclear whether wild boar females can adjust their offspring sex. We investigated multiple aspects of wild boar maternal investment by means of a 10 years-dataset of female reproductive traits and a set of biologically meaningful environmental variables. The maternal condition slightly affected the litter size but not the offspring sex, and environment did not affect the litter size or the offspring sex. Moreover, mothers did not cope with the higher costs entailed by producing sons by placing them in the most advantageous intrauterine position, nor by allocating less resources on daughters. Our set of results showed that the female reproductive investment is quite rigid in comparison with other aspects of wild boar reproductive biology. Wild boar females seem to adopt a typical r-strategy, producing constantly large litters and allocating resources on both sexes regardless of internal and external conditions. Such strategy may be adaptive to cope with environmental unpredictability and an intense human harvest, contributing to explain the extreme success of wild boar within human-dominated landscapes.

How do genetic relatedness and spatial proximity shape African swine fever infections in wild boar?

The importance of social and spatial structuring of wildlife populations for disease spread, though widely recognized, is still poorly understood in many host-pathogen systems. In particular, system specific kin relationships among hosts can create contact heterogeneities and differential disease transmission rates. Here, we investigate how distance-dependent infection risk is influenced by genetic relatedness in a novel host-pathogen system: wild boar (Sus scrofa) and African swine fever (ASF). We hypothesized that infection risk would correlate positively with proximity and relatedness to ASF-infected individuals but expected those relationships to weaken with distance between individuals due to decay in contact rates and genetic similarity. We genotyped 323 wild boar samples (243 ASF-negative and 80 ASF-positive) collected in north-eastern Poland in 2014-2016 and modeled the effects of geographic distance, genetic relatedness, and ASF virus transmission mode (direct or carcass-based) on the probability of ASF infection. Infection risk was positively associated with spatial proximity and genetic relatedness to infected individuals with generally stronger effect of distance. In the high-contact zone (0-2 km), infection risk was shaped by the presence of infected individuals rather than by relatedness to them. In the medium-contact zone (2-5 km), infection risk decreased but was still associated with relatedness and paired infections were more frequent among relatives. At farther distances, infection risk further declined with relatedness and proximity to positive individuals, and was 60% lower among unrelated individuals in the no-contact zone (33% in10-20 km) compared with among relatives in the high-contact zone (93% in 0-2 km). Transmission mode influenced the relationship between proximity or relatedness and infection risk. Our results indicate that the presence of nearby infected individuals is most important for shaping ASF infection rates through carcass-based transmission, while relatedness plays an important role in shaping transmission rates between live animals. This article is protected by copyright. All rights reserved.

Do boars compensate for hunting with higher reproductive hormones?

The predation-stress hypothesis has been proposed as a general mechanism to explain the negative effect of predation risk on reproduction, through a chronic activation of the stress response. However, in some cases, stress appears to augment the reproductive potential of mammals. Wild boar (Sus scrofa) populations are on a rise worldwide, despite the high hunting pressure that they are exposed to. This hunting pressure instigates, among other effects, earlier sexual maturity in juvenile females, leading to the shortening of wild boars' generation time. The mechanism that underlies this earlier sexual maturity under high hunting pressure has not been examined to date. To explore the physiological effects that hunting has on the reproductive system and whether the stress response is involved, we examined steroid hormone levels in the hair of female wild boars in northern Israel, comparing populations exposed to high and low hunting pressure. Furthermore, we compared steroid levels in the hair of female wild boars that were roaming alone or as a part of a group. We found no hormonal signs of stress in the hunted boars. Cortisol levels were low in both the high and low hunting-pressure groups. Yet, progesterone levels were higher in females that were exposed to high hunting pressure. Females roaming in a group also had higher progesterone levels compared to females that were alone, with no distinguishable differences in cortisol levels. These elevations in reproductive hormones that were associated with hunting may lead to a higher reproductive potential in female wild boars. They further show that high hunting pressure does not necessarily lead to chronic stress that impairs the reproductive potential of female wild boars. This data suggests that a reproductive hormonal response may be one of the factors leading to the rapid wild boars population growth worldwide, despite the high hunting pressure.

An approach to assess stress in response to drive hunts using cortisol levels of wild boar (Sus scrofa)

Hunting can easily be linked to stress in wildlife. Drive hunts performed two to three times in one area during the respective hunting period, are thought to decrease the pressure hunting places on wildlife. Nevertheless, the expression of cortisol—one of the main mammalian stress hormones—is considered to have negative impacts on animals’ well-being if expressed excessively, which may occur during some (especially repeated) hunting events. We explored the effect of drive hunts on cortisol levels in wild boar in Lower Saxony, Germany, compared these cortisol levels to reference values given by a similar study, and investigated the effect of age, sex, and pregnancy. Blood collected from wild boar shot on drive hunts was analysed using a radioimmunoassay. As expected, we observed elevated cortisol levels in all samples, however, we still found significant differences between age groups and sexes, as well as an influence of pregnancy on cortisol levels. The effect of drive hunts on cortisol levels appears to be weaker than predicted, while the effects of other variables, such as sex, are distinct. Only half of the evaluated samples showed explicitly increased cortisol levels and no significant differences were found between sampling months and locations. Group living animals and pregnant females showed significantly higher cortisol levels. The impact of hunting is measurable but is masked by natural effects such as pregnancy. Thus, we need more information on stress levels in game species.

Observation of rescue behaviour in wild boar (Sus scrofa)

Here, we provide unique photo documentation and observational evidence of rescue behaviour described for the first time in wild boar. Rescue behaviour represents an extreme form of prosocial behaviour that has so far only been demonstrated in a few species. It refers to a situation when one individual acts to help another individual that finds itself in a dangerous or stressful situation and it is considered by some authors as a complex form of empathy. We documented a case in which an adult female wild boar manipulated wooden logs securing the door mechanism of a cage trap and released two entrapped young wild boars. The whole rescue was fast and particular behaviours were complex and precisely targeted, suggesting profound prosocial tendencies and exceptional problem-solving capacities in wild boar. The rescue behaviour might have been motivated by empathy because the rescuer female exhibited piloerection, a sign of distress, indicating an empathetic emotional state matching or understanding the victims. We discuss this rescue behaviour in the light of possible underlying motivators, including empathy, learning and social facilitation.

Triparental care in the collared flycatcher (Ficedula albicollis): Cooperation of two females with a cuckolded male in rearing a brood

Certain predominant forms of mating and parental care systems are assumed in several model species among birds, but the opportunistic and apparently infrequent variations of "family structures" may often remain hidden due to methodological limitations with regard to genetic or behavioral observations. One of the intensively studied model species, the collared flycatcher (Ficedula albicollis), is usually characterized by social monogamy with polyterritorial, facultative social polygyny, and frequent extrapair mating and extrapair paternity. During a brood-size manipulation experiment, we observed two females and a male delivering food at an enlarged brood. A combination of breeding phenology data (egg laying and hatching date), behavioral data (feeding rates) from video recordings at 10 days of nestling age, and microsatellite genotyping for maternity and paternity suggests a situation of an unrelated female helping a pair in chick rearing. Such observations highlight the relevance of using traditional techniques and genetic analyses together to assess the parental roles within a population, which becomes more important where individuals may dynamically switch from their main and presupposed roles according to the actual environmental conditions.

Social status and previous experience in the group as predictors of welfare of sows housed in large semi-static groups

Mixing gestating sows implies hierarchy formation and has detrimental consequences on welfare. The effects of social stress on the most vulnerable individuals may be underestimated and it is therefore important to evaluate welfare between individuals within groups. This study aimed at investigating the impact of social status and previous experience in the group on well-being of sows housed in large semi-static groups. We assessed aggression (d0 (mixing), d2, d27, d29), body lesions (d1, d26, d84) and feeding order on 20 groups of 46–91 animals. Social status was based on the proportion of fights won during a 6-hr observation period between d0 and d2. Dominants (29%) were those who won more fights than they lost, Subdominants (25%) won fewer fights than they lost, Losers (23%) never won any fight in which they were involved while Avoiders (23%) were never involved in fights. Resident sows (70%) were already present in the group in the previous gestation while New sows (30%) were newly introduced at mixing. Subdominants and Dominants were highly involved in fights around mixing but this was more detrimental for Subdominants than Dominants, Losers and Avoiders since they had the highest body lesion scores at mixing. Avoiders received less non-reciprocal agonistic acts than Losers on d2 (P = 0.0001) and had the lowest body lesion scores after mixing. However, Avoiders and Losers were more at risk in the long-term since they had the highest body lesions scores at d26 and d84. They were followed by Subdominants and then Dominants. New sows fought more (P<0.0001), tended to be involved in longer fights (P = 0.075) around mixing and had more body lesions throughout gestation than Resident sows. Feeding order from one-month post-mixing was influenced both by the previous experience in the group and social status (P<0.0001). New sows, especially with a low social status, are more vulnerable throughout gestation and could serve as indicators of non-optimal conditions.

Genital Brucella suis Biovar 2 Infection of Wild Boar (Sus scrofa) Hunted in Tuscany (Italy)

Brucellosis is a zoonosis caused by different Brucella species. Wild boar (Sus scrofa) could be infected by some species and represents an important reservoir, especially for B. suis biovar 2. This study aimed to investigate the prevalence of Brucella spp. by serological and molecular assays in wild boar hunted in Tuscany (Italy) during two hunting seasons. From 287 animals, sera, lymph nodes, livers, spleens, and reproductive system organs were collected. Within sera, 16 (5.74%) were positive to both rose bengal test (RBT) and complement fixation test (CFT), with titres ranging from 1:4 to 1:16 (corresponding to 20 and 80 ICFTU/mL, respectively). Brucella spp. DNA was detected in four lymph nodes (1.40%), five epididymides (1.74%), and one fetus pool (2.22%). All positive PCR samples belonged to Brucella suis biovar 2. The results of this investigation confirmed that wild boar represents a host for B.suis biovar. 2 and plays an important role in the epidemiology of brucellosis in central Italy. Additionally, epididymis localization confirms the possible venereal transmission.

Capital-income breeding in wild boar: a comparison between two sexes

Organisms differ in the strategy adopted to fuel reproduction by using resources either previously acquired and stored in body reserves (capital breeding) or, conversely, acquired during their reproductive activity (income breeding). The choice of one or the other strategy is related to several internal and external factors which are counteractive in wild boar. Based on a large dataset of culled wild boar, we investigated individual body weight variability throughout the period of 1st September-31st January, which included the main part of the mating season, among different sex and age classes to determine their position along the capital-income breeding continuum. Though food resources were abundant during the rut, adult males lost body weight suggesting they adopted a predominantly capital breeding strategy, likely owing to the high intra-sexual competition entailed by the peculiar mating system of the species. On the contrary, subadult males seemed to behave as income breeders, likely enhancing the reproductive flexibility of wild boar populations. During the rut, females stored reserves, thus suggesting that they substantially relied on them to cover future reproductive costs.

Genetic relatedness in social groups of the emerald coral goby Paragobiodon xanthosoma creates potential for weak kin selection

Animals forming social groups that include breeders and nonbreeders present evolutionary paradoxes; why do breeders tolerate nonbreeders? And why do nonbreeders tolerate their situation? Both paradoxes are often explained with kin selection. Kin selection is, however, assumed to play little or no role in social group formation of marine organisms with dispersive larval phases. Yet, in some marine organisms, recent evidence suggests small-scale patterns of relatedness, meaning that this assumption must always be tested. Here, we investigated the genetic relatedness of social groups of the emerald coral goby, Paragobiodon xanthosoma. We genotyped 73 individuals from 16 groups in Kimbe Bay, Papua New Guinea, at 20 microsatellite loci and estimated pairwise relatedness among all individuals. We found that estimated pairwise relatedness among individuals within groups was significantly higher than the pairwise relatedness among individuals from the same reef, and pairwise relatedness among individuals from the same reef was significantly higher than the pairwise relatedness among individuals from different reefs. This spatial signature suggests that there may be very limited dispersal in this species. The slightly positive relatedness within groups creates the potential for weak kin selection, which may help to resolve the paradox of why breeders tolerate subordinates in P. xanthosoma. The other paradox, why nonbreeders tolerate their situation, is better explained by alternative hypotheses such as territory inheritance, and ecological and social constraints. We show that even in marine animals with dispersive larval phases, kin selection needs to be considered to explain the evolution of complex social groups.

Multiple paternity and the number of offspring: A model reveals two major groups of species

Parentage analyses via microsatellite markers have revealed multiple paternity within the broods of polytocous species of mammals, reptiles, amphibians, fishes and invertebrates. The widespread phenomenon of multiple paternity may have attending relationships with such evolutionary processes as sexual selection and kin selection. However, just how much multiple paternity should a species exhibit? We developed Bayesian null models of how multiple paternity relates to brood sizes. For each of 114 species with published data on brood sizes and numbers of sires, we compared our null model estimates to published frequencies of multiple paternity. The majority of species fell close to our null model, especially among fish and invertebrate species. Some species, however, had low probabilities of multiple paternity, far from the predictions of the null model, likely due to sexual selection and environmental constraints. We suggest a major division among species' mating systems between those with close to random mating and high levels of multiple paternity, and those with constraints that produce low levels of multiple paternity.

Community structure of domesticated pigs in livestock facilities

The social structure of animal groups is considered to have an impact on their health and welfare. This could also be true for animals under commercial conditions, but research in this area has been limited. Pigs for example are known to be very social animals, but information about their grouping behavior is mostly derived from wild boars and a limited number of studies in seminatural and commercial conditions. Specifically under commercial conditions it is still unclear to what extent pig herds organize themselves in subgroups and how such group patterns emerge. To answer these questions, we tracked the positions of about 200 sows inside a barn during ongoing production over a period of five weeks and used these data to construct and analyze the animal contact networks. Our analysis showed a very high contact density and only little variation in the number of other animals that a specific animal is in contact with. Nevertheless, in each week we consistently detected three subgroups inside the barn, which also showed a clear spatial separation. Our results show that even in the high density environment of a commercial pig farm, the behavior of pigs to form differentiated groups is consistent with their behavior under seminatural conditions. Furthermore, our findings also imply that the barn layout could play an important role in the formation of the grouping pattern. These insights could be used to monitor and understand the spread of infectious diseases inside the barn better. In addition, our insights could potentially be used to improve the welfare of pigs.

Presence of pathogenic Leptospira spp. in the reproductive system and fetuses of wild boars (Sus scrofa) in Italy

Leptospirosis is a re-emerging and globally spread zoonosis caused by pathogenic genomospecies of Leptospira. Wild boar (Sus scrofa) are an important Leptospira host and are increasing in population all over Europe. The aim of this investigation was to evaluate Leptospira spp. infection in the reproductive systems of wild boar hunted in two Italian regions: Tuscany and Sardinia. From 231 animals, reproductive system tissue samples (testicles, epididymides, uteri) as well as placentas and fetuses were collected. Bacteriological examination and Real-Time PCR were performed to detect pathogenic Leptospira (lipL32 gene). Leptospires were isolated from the testicles and epididymides of one adult and two subadult wild boar. Four isolates from the two subadult males were identified as Leptospira interrogans serogroup Australis by MLST, whereas Leptospira kirschneri serogroup Grippotyphosa was identified from the adult testicles and epididymis. Using Real-Time PCR, 70 samples were positive: 22 testicles (23.16%) and 22 epididymides (23.16%), 10 uteri (7.35%), 3 placentas (6.66%), and 13 fetuses (28.88%). Amplification of the rrs2 gene identified L. interrogans and L. kirschneri species. The results from this investigation confirmed that wild boar represent a potential source of pathogenic Leptospira spp. Isolation of Leptospira serogroups Australis and Grippotyphosa from the male reproductive system and the positive Real-Time PCR results from both male and female samples could suggest venereal transmission, as already demonstrated in pigs. Furthermore, placentas and fetuses were positive for the lipL32 target, and this finding may be related to a possible vertical transmission of pathogenic Leptospira.

Leptospirosis is an infectious zoonotic disease present worldwide and is caused by bacteria belonging to genus Leptospira. Several domestic and wild animals could serve as reservoir hosts of these bacteria and could transmit them to humans, directly or indirectly. Generally, in asymptomatic carriers the infection involves the urinary system, the kidneys in particular, and leptospires are eliminated via urine. In some animals, Leptospira could also colonize the reproductive system as consequence of a systemic infection or venereal transmission. In this work, the Authors describe, for the first time, the detection of Leptospira from male and female reproductive organs of hunted wild boar via culture-dependent and -independent methods. These findings could suggest a possible vertical transmission in wild boar, but also a possible venereal transmission cycle among wild swine, which could accidentally involve domestic pigs too. Manipulation of these organs by hunters during slaughtering could also expose them to Leptospira infection. Obtained data add information on Leptospira epidemiology and highlight the importance of wildlife monitoring programs.

Ecological drivers of African swine fever virus persistence in wild boar populations: Insight for control

Environmental sources of infection can play a primary role in shaping epidemiological dynamics; however, the relative impact of environmental transmission on host-pathogen systems is rarely estimated. We developed and fit a spatially explicit model of African swine fever virus (ASFV) in wild boar to estimate what proportion of carcass-based transmission is contributing to the low-level persistence of ASFV in Eastern European wild boar. Our model was developed based on ecological insight and data from field studies of ASFV and wild boar in Eastern Poland. We predicted that carcass-based transmission would play a substantial role in persistence, especially in low-density host populations where contact rates are low. By fitting the model to outbreak data using approximate Bayesian computation, we inferred that between 53% and 66% of transmission events were carcass-based that is, transmitted through contact of a live host with a contaminated carcass. Model fitting and sensitivity analyses showed that the frequency of carcass-based transmission increased with decreasing host density, suggesting that management policies should emphasize the removal of carcasses and consider how reductions in host densities may drive carcass-based transmission. Sensitivity analyses also demonstrated that carcass-based transmission is necessary for the autonomous persistence of ASFV under realistic parameters. Autonomous persistence through direct transmission alone required high host densities; otherwise re-introduction of virus periodically was required for persistence when direct transmission probabilities were moderately high. We quantify the relative role of different persistence mechanisms for a low-prevalence disease using readily collected ecological data and viral surveillance data. Understanding how the frequency of different transmission mechanisms vary across host densities can help identify optimal management strategies across changing ecological conditions.

Do wild boar movements drive the spread of African Swine Fever?

The spatial behaviour of hosts can seriously affect the transmission of pathogens and spatial spread of diseases. Understanding the relationship between host movements and disease dynamics is of prime importance for optimizing disease control efforts. African swine fever (ASF), a devastating disease of wild and domestic suids, has been spreading continuously through eastern Europe since 2007. The wild boar (Sus scrofa) has been implicated in the epidemiology of this disease, but the role of wild boar movements in ASF dynamics and spread has not been studied and remains largely speculative. Here, we examined whether monthly parameters of wild boar movements (dispersal distance of yearlings, home range size of adult males and females) can explain variation in the spatio-temporal dynamics of the ASF outbreak in the wild boar population in north-eastern Poland, 2014-2015. We expected to observe a positive relationship between host mobility and disease spread. Contrary to our expectations, we found that movements of wild boar, despite their seasonal variation, were poor predictors of ASF dynamics in space and time. During the 2 years of the study, ASF spread gradually at a steady pace of 1.5 km/month without significant changes across seasons. None of the analysed movement parameters explained variation in the measures of ASF occurrence and spread (i.e., number of cases, prevalence, size and expansion rate of the outbreak area). We believe that the factor limiting the influence of host movements on ASF dynamics is the severity of the disease, which quickly hampers extensive movements and restricts disease transmission to only the most immediate individuals. Three natural factors constrain direct disease transmission: wild boar social structure, the short duration of low-level virus shedding and high virus-induced lethality, followed by indirect transmission through infected carcasses. These most likely shape the gradual spread of ASF in space and its persistence in already infected areas.

Introduction history overrides social factors in explaining genetic structure of females in Mediterranean mouflon

Fine‐scale spatial genetic structure of populations results from social and spatial behaviors of individuals such as sex‐biased dispersal and philopatry. However, the demographic history of a given population can override such socio‐spatial factors in shaping genetic variability when bottlenecks or founder events occurred in the population. Here, we investigated whether socio‐spatial organization determines the fine‐scale genetic structure for both sexes in a Mediterranean mouflon (Ovis gmelini musimon × Ovis sp.) population in southern France 60 years after its introduction. Based on multilocus genotypes at 16 loci of microsatellite DNA (n = 230 individuals), we identified three genetic groups for females and two for males, and concurrently defined the same number of socio‐spatial units using both GPS‐collared individuals (n = 121) and visual resightings of marked individuals (n = 378). The socio‐spatial and genetic structures did not match, indicating that the former was not the main driver of the latter for both sexes. Beyond this structural mismatch, we found significant, yet low, genetic differentiation among female socio‐spatial groups, and no genetic differentiation in males, with this suggesting female philopatry and male‐biased gene flow, respectively. Despite spatial disconnection, females from the north of the study area were genetically closer to females from the south, as indicated by the spatial analysis of the genetic variability, and this pattern was in accordance with the common genetic origin of their founders. To conclude, more than 14 generations later, genetic signatures of first introduction are not only still detectable among females, but they also represent the main factor shaping their present‐time genetic structure.

How much does it cost to look like a pig in a wild boar group?

Hybridization between domestic and wild species is known to widely occur and it is reported to be one of the major causes of the current biodiversity crisis. Despite this, poor attention has been deserved to the behavioural ecology of hybrids, in particular in relation to their social behaviour. We carried out a camera trap study to assess whether phenotypically anomalous colouration in wild boar, i.e. potentially introgressed with domestic pigs, affected the hierarchical structure of wild boar social groups. Chromatically anomalous wild boars (CAWs) were detected in 32 out of 531 wild boar videos. In most videos (75%) CAWs were the latest of the group, independently from their age class and group composition. Aggressions by their wild type fellows were recorded in 31.25% videos; by contrast, no aggression among wild type individuals was observed. The lack of camouflage may expose CAWs, and thus their group, to a higher predation risk, compared to wild type groups. This individual loss of local adaptation may increase predation risk by the wolf or detection by hunters, being maladaptive for the whole social group.

Cooperation improves the access of wild boars (Sus scrofa) to food sources

Wild boar is a highly polycotous ungulate species, characterized by a complex and dynamical social organization based on the maintenance of long-term bonds between mother and daughters. The roots of this social organization have to be researched at the individual level, considering adaptations that improve fitness in hostile environments. We used information collected by camera-traps at artificial feeding sites, in two contrasting environments in Bulgaria (mountain habitat) and Italy (sub-Mediterranean habitat). We recorded 417 and 885 distinct groups on 7 and 11 foraging sites in Bulgaria and Italy, respectively. We computed (controlling for time range, study area and supplementary feeding site) an index of effective foraging time of the different social groups. We observed a positive and significant effect of the number of conspecifics of the same social group on the effective foraging time. The impact of the other social classes on effective foraging time is also positive, and males, yearlings, and juveniles benefited more from the presence of other social classes, while females were less affected. The access of the different social groups to foraging sites is not random. Males and yearlings play producers (i.e., search for food) and are prone to attend foraging sites before adult females and subadults, so attaining a larger foraging efficiency with respect to a situation where other groups are already present on the feeding site. Wild boars exhibit a more complex social organisation than previously believed, where cooperation prevails largely on competition. A rough division of labour is also present: yearlings, males, and juveniles use to play producers and assume a significant amount of risk determined by the presence of predators or hunters.

Multiple paternity in domestic pigs under equally probable natural matings – a case study in the endangered Gochu Asturcelta pig breed

Abstract. Here we provide evidence of multiple paternities in naturally mated sows under conditions ensuring that (a) sows had the same probability of being mated by any of the available boars and (b) no differences in hybrid vigour existed. Total DNA was obtained from 19 Gochu Asturcelta piglets from three different sows, each with the same chance of natural mating with two different boars. A set of 20 microsatellites were typed on all the individuals. The program CERVUS was used to asses the informative ability of the microsatellite set and to perform paternity assignment. Allelic frequencies at population level were obtained using a total of 141 Gochu Asturcelta individuals. Offspring were always assigned to a candidate boar with high statistical confidence. All litters had different parents. Our results show that multiple paternities are possible in domestic pigs under natural mating. Furthermore, the current study can be useful to further understand the mating system of the wild boar.

Mother-offspring distances reflect sex differences in fine-scale genetic structure of eastern grey kangaroos

Natal dispersal affects life history and population biology and causes gene flow. In mammals, dispersal is usually male-biased so that females tend to be philopatric and surrounded by matrilineal kin, which may lead to preferential associations among female kin. Here we combine genetic analyses and behavioral observations to investigate spatial genetic structure and sex-biased dispersal patterns in a high-density population of mammals showing fission–fusion group dynamics. We studied eastern grey kangaroos (Macropus giganteus) over 2 years at Wilsons Promontory National Park, Australia, and found weak fine-scale genetic structure among adult females in both years but no structure among adult males. Immature male kangaroos moved away from their mothers at 18–25 months of age, while immature females remained near their mothers until older. A higher proportion of male (34%) than female (6%) subadults and young adults were observed to disperse, although median distances of detected dispersals were similar for both sexes. Adult females had overlapping ranges that were far wider than the maximum extent of spatial genetic structure found. Female kangaroos, although weakly philopatric, mostly encounter nonrelatives in fission–fusion groups at high density, and therefore kinship is unlikely to strongly affect sociality.

Males and females contribute unequally to offspring genetic diversity in the polygynandrous mating system of wild boar

The maintenance of genetic diversity across generations depends on both the number of reproducing males and females. Variance in reproductive success, multiple paternity and litter size can all affect the relative contributions of male and female parents to genetic variation of progeny. The mating system of the wild boar (Sus scrofa) has been described as polygynous, although evidence of multiple paternity in litters has been found. Using 14 microsatellite markers, we evaluated the contribution of males and females to genetic variation in the next generation in independent wild boar populations from the Iberian Peninsula and Hungary. Genetic contributions of males and females were obtained by distinguishing the paternal and maternal genetic component inherited by the progeny. We found that the paternally inherited genetic component of progeny was more diverse than the maternally inherited component. Simulations showed that this finding might be due to a sampling bias. However, after controlling for the bias by fitting both the genetic diversity in the adult population and the number of reproductive individuals in the models, paternally inherited genotypes remained more diverse than those inherited maternally. Our results suggest new insights into how promiscuous mating systems can help maintain genetic variation.

Long-lasting, kin-directed female interactions in a spatially structured wild boar social network

Individuals can increase inclusive fitness benefits through a complex network of social interactions directed towards kin. Preferential relationships with relatives lead to the emergence of kin structures in the social system. Cohesive social groups of related individuals and female philopatry of wild boar create conditions for cooperation through kin selection and make the species a good biological model for studying kin structures. Yet, the role of kinship in shaping the social structure of wild boar populations is still poorly understood. In the present study, we investigated spatio-temporal patterns of associations and the social network structure of the wild boar Sus scrofa population in Białowieża National Park, Poland, which offered a unique opportunity to understand wild boar social interactions away from anthropogenic factors. We used a combination of telemetry data and genetic information to examine the impact of kinship on network cohesion and the strength of social bonds. Relatedness and spatial proximity between individuals were positively related to the strength of social bond. Consequently, the social network was spatially and genetically structured with well-defined and cohesive social units. However, spatial proximity between individuals could not entirely explain the association patterns and network structure. Genuine, kin-targeted, and temporarily stable relationships of females extended beyond spatial proximity between individuals while males interactions were short-lived and not shaped by relatedness. The findings of this study confirm the matrilineal nature of wild boar social structure and show how social preferences of individuals translate into an emergent socio-genetic population structure.

Monitoring wild pig populations: a review of methods

Wild pigs (Sus scrofa) are widespread across many landscapes throughout the world and are considered to be an invasive pest to agriculture and the environment, or conversely a native or desired game species and resource for hunting. Wild pig population monitoring is often required for a variety of management or research objectives, and many methods and analyses for monitoring abundance are available. Here, we describe monitoring methods that have proven or potential applications to wild pig management. We describe the advantages and disadvantages of methods so that potential users can efficiently consider and identify the option(s) best suited to their combination of objectives, circumstances, and resources. This paper offers guidance to wildlife managers, researchers, and stakeholders considering population monitoring of wild pigs and will help ensure that they can fulfill their monitoring objectives while optimizing their use of resources.

Microsatellite markers for identification and parentage analysis in the European wild boar (Sus scrofa)

BACKGROUND

The wild boar (Sus scrofa) is among the most widespread mammal species throughout the old world. Presently, studies concerning microsatellites in domestic pigs and wild boars have been carried out in order to investigate domestication, social behavior and general diversity patterns among either populations or breeds. The purpose of the current study is to develop a robust set of microsatellites markers for parentage analyses and individual identification.

FINDINGS

A set of 14 previously reported microsatellites markers have been optimized and tested in three populations from Hungary, Portugal and Spain, in a total of 167 samples. The results indicate high probabilities of exclusion (0.99999), low probability of identity (2.0E(-13) - 2.5E(-9)) and a parentage assignment of 100%.

CONCLUSIONS

Our results demonstrate that this set of markers is a useful and efficient tool for the individual identification and parentage assignment in wild boars.

Preferential sexual transmission of pseudorabies virus in feral swine populations may not account for observed seroprevalence in the USA

This paper compares the behavior of two competing models for the transmission of pseudorabies virus in feral swine in the USA. In first model, horizontal (non-sexual) density dependent transmission is the only transmission modality. In the second model, the only transmission modality is sexual transmission between mature males and females. The comparison of model behavior was carried out to test the hypothesis that preferential sexual transmission of PRV in feral swine can account for the seroprevalence observed in the field. The observed range of seroprevalence of PRV in mature feral swine in the USA is consistent with a preferential sexual transmission only if the feral swine mating system is a random mating system or a polygynous system in which there is a relatively large rate of acquisition of new mates. The observed range of seroprevalence of PRV in mature feral swine in the USA is not consistent with a preferential sexual transmission if there is mate guarding. This is important because the National Pseudorabies Surveillance Plan deems monitoring the risk of PRV introduction from feral swine to be a "minor objective" both in terms of the scope of the plan and with respect to the resources allocated. The rationale for this statement was derived from experimental studies, which suggested that the PRV indigenous to feral swine in the USA is preferentially sexually transmitted.

No difference between the sexes in fine-scale spatial genetic structure of roe deer

BACKGROUND

Data on spatial genetic patterns may provide information about the ecological and behavioural mechanisms underlying population structure. Indeed, social organization and dispersal patterns of species may be reflected by the pattern of genetic structure within a population.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated the fine-scale spatial genetic structure of a roe deer (Capreolus capreolus) population in Trois-Fontaines (France) using 12 microsatellite loci. The roe deer is weakly polygynous and highly sedentary, and can form matrilineal clans. We show that relatedness among individuals was negatively correlated with geographic distance, indicating that spatially proximate individuals are also genetically close. More unusually for a large mammalian herbivore, the link between relatedness and distance did not differ between the sexes, which is consistent with the lack of sex-biased dispersal and the weakly polygynous mating system of roe deer.

CONCLUSIONS/SIGNIFICANCE

Our results contrast with previous reports on highly polygynous species with male-biased dispersal, such as red deer, where local genetic structure was detected in females only. This divergence between species highlights the importance of socio-spatial organization in determining local genetic structure of vertebrate populations.