The Strategies Of Social Behaviors In Root Voles (Microtus Oeconomus) And Its Fitness

Social behaviors involving in animal mating systems, such as parental care and mating behaviors, is one of bases in Animal Behavioral Ecology and especially important for gaining an insight of its life history strategies and fitness of those, which is one of key and profound topics in Ecology. The microtine rodents represent a group of elegant experiments in natrual selection with closely related species developing contrasting patters of social organization. However, it was dichotomous methodology prevailing throughout the area in the past that has been led to make res earch on mating systems of voles uncomprehensive and out of balance. One could detemine how differences between monogamous and polygamous species or between monogamous and promiscuous species, but be aware of contrast with those vs polygynous ones which are the vast majority of all mammals Thus, it is necessitous and important to carrying out research on social behaviors of the polygynous voles, fothurmore, challenging for us.By being conducted novel and perspective design of a series of animal behavioral experiments, it was made comprehensive studies of biparental and alloparental care, pup development in different social enviroments, mating choice according to various kinds of criteria, physical, morphological and behavioral factors for mating systems of Microtus oeconomus, in which there were considered to be promiscuity or polygyny in terms of mating system derived from diffrent data of social organization in field The predict that mating system of root voles was of polygyny was successfully confirmed by our laboratory-based data, fitness of the strategy was analysed. It was suggested first by us that male social rank could be regared as such a good scale that mate choice of it in different species would show contrasting individual of vole attribute relative to monogamy and polygyny and promiscuity ones, respectively. As a new critertion of mate choice provided by us first, experience of alloparental care may be helpful to be examined behavioral differences among monogamy , polygyny and promiscuity species.The studies were made in Northwest Plateau Institute of Biology, Aca-demia Sinica, from May in 1995 to August in 1996. These details were as following:1. Biparental care and alloparental care(1) It was observed in a home cage with a pair of male and female voles that father showed patters of paternal behavior including huddling over , grooming, retrieving his pups following the parturition. In per 30min period, mean duration (sec. ) of maternal care was significantly more than that of paternal care in the nest. The sexuall contrast in reproductive effort shows that there is polygamous in root voles. Root voles paternal care in was more time than that of promiscuous vole M. pennsyIvanicus , indicating that paternity in the same litter was liked to be singular in root voles in field.(2) As helpers, juveniles were remained in the nest with the mother and the subsequent litters (F-J family), or with both parent, the subsequent litters(B-J family), and exhibited a form of alloparental care including huddling over, grooming and retrieving younger siblings similar to paternal care. Mean duration of alloparental care showed a gradual dcrease as a function of pup ages.(3) Difference of mean durations of maternal behavior in 4 fmailies was significant (F=3. 5, P<0. 05) , the least in B-J family and the most in F-J one, suggesting that presence of father and/or juveniles reduced time of maternal care. The chagne in the durations of maternal behavior across the days of pup development decreased(r= -0. 56> P=0. 000) .(4) That mean duration of alloparental care in F-J family did not differ significantly from that in B-J family, and near equal time spent in both paternal care in B family (biparen family) and alloparental care in F-J one suggested that alloparental care substituted paternal care in term of role to maternal care, then the father shared the nest with mother or the mother and the juveniles impossible.(5) Female juvenile spent remarkably more time in alloparental care than male one did in F-J family, but male juvenile mounting mother would be in disadvantage of increasing direct fitness. Time female juvenile spent in the nest with mother nearly negatively correlated with time mother spent in the nest(r=-0. 23, P = 0. 051) , demonstrating that she could reduce time litter left alone in nest, neither did relation between male juvenile and mother. Thus it is derived from these data that the family consisting ofa mother and female juveniles remaining in the natal nest beyond weaning may be a ideal unit of social organization of root voles in nature.Providing alloparental care to youger siblings in the family, female helpers may enhance their indirect fitness, by improving the survival of younger pups, and their direct fitness, by sharing limited resouces with mother and learning parenting experience. Forthermore female helpers can easily gain their own reproductive success by sharing a mate with mother , if it is true that root voles is polygynous in field.Results and analyses above are supported by most of observaions to social organization of root voles in field that showed matiline family consisting female philopatry offsprings and their mother with subsequent litter. Female-biased weanling sex ratio resulting from it is primary to a polygyny mating system in root voles. The prevailing mating systems of root voles may be of polygyny.2. Pup physical and behavioral developmentThere was no noticeable difference of mean age of eye opening, being out of nest and freely feeding of pups among 4 families including B, B-J F and F-J famliy. The mean litter size at 20 days weaning had remarkable variation among the 4 families, in which F-J family had the largest size of pups surviving to 20 days, it was 4. 9 ± 0.6 pups.In F family, distance pup attching to nipple of the mother led to moved showed a significant variation among ages of 2, 6, 10 days, which it was the longest at 6 days. In term of the index, that of root voles was larger than that of prairie voles, M. ochrogaster and less than that of meadow vole.These data complemented some evidences to previous part and supported the view that root voles was polygynous species.3. Mate choice(1) Five experiments with aspect of familiarity affecting male or female mate choice in root voles showed that the female prefered the former to the latter between the familiar male vs the strange male or the partnervs the strange male or the partner vs the familiar male;The male made no preference between the familiar female vs the strange female, nor the partner vs the strange female.(2) In puberty period, the female root vole of first oestrus spent more time visiting, social-investigating, and being amicable to the dominant male vole than the subordinant one in a T-shape maze. After the test, the three voles were housed in a cage together for 24 hours, the dominant exhibfted less latency of intromission than that of the subordinant, the dominant male copulation with the female was not disrupted by the sudor-dinant male.(3) In puberty, a female root vole did not show mate choice between the male with alloparental experience and the male without it, so do a male.(4). In puberty, a female root vole did not show mate choice between the male mated with a stimulus female just and the male unmated just, so do a male.Combination between female preference for the familiar male in experiment 1 and female preference for the dominant male in experiment 2 suggested that root vole is probably polygyny only. Moreover, it is made a hiphypothesis that order of interspecific variation in male dominant rank is consistent with contrasts of body mass dimorphism among monogamy , polygyny, and promiscuity species in microtine redonts, and therefore, the mate choice of male dominant rank based on male mass can be determined how polygamy vole species differ from monogamy and promicuity ones.4. Mating system and strategy of social behaviorsCompared root vole to two vole species kown from filed studies to be nomogamous tendencies(praire vole and M. pinetorum) and two known to be promiscuous under most condtions (meadow vole and M. montanus) , and one well known to be polygynous in field( M. xanthognathas), by summarizing Lab studies of the dimorphism based on male : female body mass ratio and testes : body mass ratio, mean litter size, age last nipple attachment, distance nipple clining, time social contacting, mean ejaculation frequ-ecy, intromission latency, intromission frequency in first ejacultion series, and maternal time in nest in small cage, it was shown that the species differences in individual behavior and other characteristicsamong these species is consistent with interspicific differences of mating system, root vole is generally similar to the polygynous taiga vole , and dissimilar to the nomogamous praire vole and pine vole and, the promiscuous meadow vole and montane vole with respect to the suit of behaviors studied. So, the view that root vole is polygynous is comprehen-sivly proved.