Net costs of group living in a solitary forager, the Eurasian badger (Meles meles)

Group living is expected to evolve under two extreme conditions:when there are net benefits to the individual of living in agroup and when there are net costs to living in a group togetherwith strong ecological constraints on dispersal and independentbreeding. A third condition may facilitate group formation:when the territorial defense of resources that are dispersedwidely or renewed at high rates allows groups to form at nocost to group members. Eurasian badgers are solitary over alarge part of their geographic distribution and forage aloneeven where diey live in territorial groups. To determine whichof the three conditions best explains group living in badgers,we analyzed dispersal and breeding patterns. Using these datawe describe the mechanism of group formation and the net costsor benefits of group living in 16 badger groups in one population.Groups form primarily by the retention of young on their natalterritory. Typically, groups contain one or more sexually maturebut nonbreeding females in addition to one or more breedingfemales. Females do not benefit from group living as indicatedby the lack of relationships, or perhaps negative relationships,between the proportion of adult females that bred in a groupand mean reproductive success, on the one hand, and group sizeand components of group size, on the other. A high reproductivefailure rate among females in this and other populations ofsocial badgers, as compared with a population of solitary badgers,suggests that there is a cost of group living to females. Wepropose that if badgers defend resources whose spatial distributionor high renewal rates allow groups to form on a territory atlitde or no cost to group members, weak ecological constraintson dispersal and independent breeding are sufficient to explainthe formation of groups. Badgers appear to have not evolvedcooperative breeding in response to these ecological conditions,perhaps because badger groups represent an early stage in theevolution of carnivore sociality.     

The role of setts in badger (Meles meles) group size, breeding success and status of TB (Mycobacterium bovis)

This paper examines the relationship between the number of occupied setts in a badger social group territory and badger group size, breeding success, and status of infection with Mycobacterium bovis (TB). The data used were from a long-term epidemiological and ecological study of a high-density population of badgers Meles meles in south-west England. The number of occupied setts in a social group was significantly and positively related to the number of badgers caught in the social group, so that as a social group increases in size, badgers occupy more of the available setts. This relationship remained significant when numbers of adults, adult males and adult females were examined. The number of breeding females, number of cubs and sex ratio was not related to the number of occupied setts in a social group. It is possible that the advantages to breeding females of a larger number of setts available to breed in might be outweighed by the increased aggression found in larger groups. The TB score for prevalence and for incidence of social groups was significantly and positively related to the number of occupied setts in a social group, such that the more occupied setts there were in a territory, the higher the TB index of the group. Possibly the setts themselves contribute to the persistence of TB within social groups, or badgers infected with TB might show a difference in behaviour from uninfected badgers resulting in their increased use of outlying setts.     

Mating system of the Eurasian badger, Meles meles, in a high density population

Badgers are facultatively social, forming large groups at high density. Group-living appears to have high reproductive costs for females, and may lead to increased levels of inbreeding. The extent of female competition for reproduction has been estimated from field data, but knowledge of male reproductive success and the extent of extra-group paternity remains limited. Combining field data with genetic data (16 microsatellite loci), we studied the mating system of 10 badger social groups across 14 years in a high-density population. From 923 badgers, including 425 cubs, we were able to assign maternity to 307 cubs, with both parents assigned to 199 cubs (47%) with 80% confidence, and 14% with 95% confidence. Age had a significant effect on the probability of reproduction, seemingly as a result of a deficit of individuals aged two years and greater than eight years attaining parentage. We estimate that approximately 30% of the female population successfully reproduced in any given year, with a similar proportion of the male population gaining paternity across the same area. While it was known there was a cost to female reproduction in high density populations, it appears that males suffer similar, but not greater, costs. Roughly half of assigned paternity was attributed to extra-group males, the majority of which were from neighbouring social groups. Few successful matings occurred between individuals born in the same social group (22%). The high rate of extra-group mating, previously unquantified, may help reduce inbreeding, potentially making philopatry a less costly strategy.     

Male reproductive skew, paternal relatedness, and female social relationships

Female social relationships among primates are thought to be shaped by socio-ecological factors and phylogenetic constraints. We suggest that patterns of paternal relatedness among females influence measures of social tolerance that have been used to classify species into different social relationship categories. As kin support and kin preference have only been measured for matrilineal kin and related individuals exchange less aggression and have a higher conciliatory tendency, the observed low nepotism levels and high tolerance levels may be an artifact of hidden paternal relatedness among the nonkin category. Using comparative data on macaques, we investigate this hypothesis using male reproductive skew as a proxy for paternal relatedness. Within the limitations of the study we show that populations classified as being less nepotistic, and more tolerant exhibit higher levels of reproductive skew. This first result and the reasoning behind may motivate future students of social relationships to take paternal relatedness into consideration. Potential implications of this finding if repeated with larger samples include that variation in aspects of macaque social relationships may be explained without considering phylogeny or the strength of between-group contest competition for food.     

Polygynandry, extra-group paternity and multiple-paternity litters in European badger (Meles meles) social groups

The costs and benefits of natal philopatry are central to the formation and maintenance of social groups. Badger groups, thought to form passively according to the resource dispersion hypothesis (RDH), are maintained through natal philopatry and delayed dispersal; however, there is minimal evidence for the functional benefits of such grouping. We assigned parentage to 630 badger cubs from a high-density population in Wytham Woods, Oxford, born between 1988 and 2005. Our methodological approach was different to previous studies; we used 22 microsatellite loci to assign parent pairs, which in combination with sibship inference provided a high parentage assignment rate. We assigned both parents to 331 cubs at > or = 95% confidence, revealing a polygynandrous mating system with up to five mothers and five fathers within a social group. We estimated that only 27% of adult males and 31% of adult females bred each year, suggesting a cost to group living for both sexes. Any strong motivation or selection to disperse, however, may be reduced because just under half of the paternities were gained by extra-group males, mainly from neighbouring groups, with males displaying a mixture of paternity strategies. We provide the strongest evidence to date for multiple-paternity litters, and for the first time show that within-group and extra-group males can sire cubs in the same litter. We investigate the factors that may play a role in determining the degree of delayed dispersal and conclude that the ecological constraints hypothesis, benefits of philopatry hypothesis, and life history hypothesis may all play a part, as proposed by the broad constraints hypothesis.     

笼养狗獾东北亚种繁殖规律

2013年3~10月,使用红外监控设备对哈尔滨市松北区某狗獾养殖场的24只笼养东北亚种狗獾(Meles meles amurensis)的繁殖行为进行全天候观察记录。狗獾3月末至5月初交配,翌年3月末至4月初产仔,妊娠期长达11~12个月。以往国内文献报道狗獾交配时间主要分布于7~8月,这种交配时间的变化表明其延迟着床的时间可能也存在较大变化。对交配期内全天各时段交配频次的观察发现,交配可在全天任一时间段发生,昼、夜差异不大。交配时长10~110 min,多数交配的时长为60~80 min。观察还发现,狗獾交配期内交配频次和时长具有明显的周期性变化。