The development of social behaviour between siblings and non-siblings of the voles Microtus ochrogaster and Microtus pennsylvanicus

It has been suggested that the strength and duration of sibling relations during the juvenile period may reflect the social structure of mammal species. Two Microtus species with contrasting social systems, M. ochrogaster and M. pennsylvanicus, were chosen for a comparative study of juvenile social behaviour. Young were observed in sibling and non-sibling dyadic encounters from the second until the seventh week of age. Social interactions consisted mainly of body nosing of the partner, and included behaviours interpreted as investigation, socialization and settling. Only minor sex differences in body nosing scores occurred, but some ontogenetic trends were noted. When the species were compared, M. ochrogaster received higher scores for body nosing and sitting in contact, and displayed more reciprocity in their nosing, than did M. pennsylvanicus, whether siblings or non-siblings were considered. When the sibling types were compared, non-sibling dyads received higher nosing scores than did siblings in both species, but the disparity was greater in M. ochrogaster than in M. pennsylvanicus. These results are interpreted with reference to known behavioural and developmental correlates of the extended family system in naturally occurring M. ochrogaster and the less communal social system in M. pennsylvanicus.     

A comparison of maternal behaviour in the meadow vole (Microtus pennsylvanicus), prairie vole (M. ochrogaster) and pine vole (M. pinetorum)

The maternal behaviour of three species of voles was compared using a semi-naturalistic laboratory system. Meadow vole females spent more time out of the nest, and exhibited less maternal behaviour in terms of nursing and brooding, and more non-social behaviour such as locomoting, eating, and drinking, than the females of the other two species. Across all species, maternal behaviour decreased from parturition onward, while non-social behaviour increased. Paternal care was well developed in the prairie vole and pine vole, but was never observed in the meadow vole. During the first postnatal week, male prairie voles showed a tendency to enter the nest when the female left the young unattended. This trend was not apparent in the male pine vole. The physical parameters of pup development, including eye opening and the development of fur, were similar in all three species. Behavioural development, however, was most rapid in the meadow vole, intermediate in the prairie vole, and slowest in the pine vole. These results are compared with those of previous field and laboratory studies, and are discussed with reference to the life-history strategy of each species.     

Self-grooming induced by sexual chemical signals in male root voles (Microtus oeconomus Pallas)

Sniffing is one-way animals collect chemical signals, and many males self-groom when they encounter the odor of opposite-sex conspecifics. We tested the hypothesis that sexual chemical signals from females can induce self-grooming behavior in male root voles (Microtus oeconomus Pallas). Specifically, we investigated the sniffing pattern of male root voles in response to odors from the head, trunk, and tail areas of lactating and non-lactating females. The self-grooming behavior of males in response to female individual odorant stimuli was documented, and the relationship between self-grooming and sniffing of odors from the head, trunk, and tails areas were analyzed. Sniffing pattern results showed that males are most interested in odors from the head area, and more interested in odors from the tail as compared to the trunk area. Males displayed different sniffing and self-grooming behaviors when they were exposed to odors from lactating females as compared to non-lactating females. Males also spent more time sniffing and engaged in more sniffing behaviors in response to odors from the lactating females’ tail area as compared to the same odors from non-lactating females. Similarly, males spent more time self-grooming and engaged in more self-grooming behaviors in the presence of individual odors from lactating females as compared to individual odors from non-lactating females. Partial correlation analyses revealed that the frequency of self-grooming was significantly correlated with the frequency of tail area sniffs. Results from this experiment suggest that sexual attractiveness of lactating females is stronger than that of non-lactating females. Furthermore, the partial correlation analysis demonstrated that self-grooming in males is induced by odors from the tail area of females. Collectively, these results support the hypothesis that sexual chemical signals from females can induce self-grooming behavior in male root voles. Self-grooming may also reflect the groomer's sexual motivation and facilitate sexual interactions.     

Fitness consequences of sociality in prairie voles, Microtus ochrogaster: influence of group size and composition

We used 7 years of live-trapping data from an Illinois population of prairie voles to examine how survival and reproductive success varied with size and composition of social groups. Specifically, we examined measures of fitness for residents of single female units, male-female pairs and communal groups. Reproductive success, measured as either the number of young that survived to 12 or 30 days of age per adult female in a group, was higher for groups of three adults than for smaller or larger groups. The ideal group composition with respect to reproductive success appeared to be one adult female and two adult males. Individuals born into groups with three adults survived longer than did those born into smaller or larger groups. There was no clear relationship, however, between group size and survival of adult members of groups. Sudden disappearance of a group, presumably to predation by weasels, was associated with relative group size such that the largest groups were more likely to disappear. Overall, our data indicate that prairie voles living in communal groups with three adult members have higher fitness than those living in smaller groups or in larger communal groups. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Aggressive behaviour of male Microtus breweri and its demographic implications

Patterns of laboratory-determined aggressive behaviour and exploratory activity were examined in wild-caught male beach voles (Microtus breweri), an island-endemic species. This species is ecologically interesting because it has been found not to exhibit the super-annual population cycles typical of other rodents in the subfamily Microtinae. We found that body weight and reproductive condition were good predictors of aggressive behaviour, with heavier and reproductively active voles showing higher incidences of several stereotyped aggressive acts. Aggression also increased as the percentage of males and females who were reproductively active in the control population increased. Aggression was negatively correlated with population density, and more or less independent of dispersal rate. Dispersers and residents exhibited similar aggressive behaviour patterns. These observations are consistent with models which have proposed that population cycles in other vole species are controlled through the social interactions of individuals.     

东方田鼠警觉对其功能反应的作用格局

植食性哺乳动物功能反应描述了摄入率与植物可利用性变量的动态关系。动物警觉因占用了处理食物时间即觅食中断时间而延迟与下一口食物相遇,引致摄入率降低,进而对功能反应构型产生影响。在新鲜白三叶叶片构成的各类食物密集斑块上,测定东方田鼠觅食行为,建立功能反应函数模型,检验觅食中断对功能反应的作用格局及机制。结果发现,除小叶片斑块觅食中断时间在觅食活动中所占的比例较低外,在大、中型叶片斑块的觅食中断时间比例均达到15.42%-26.82%;尽管,觅食中断使摄入率降低了33%,但东方田鼠功能反应仍为Ⅱ型功能反应。除东方田鼠采食时间及觅食回合时间随叶片重增大保持相对稳定外,处理时间及觅食中断时间均随叶片重增大呈线性递增趋势;采食时间、处理时间及觅食中断时间随口量的增大呈线性递增趋势;采食率随叶片重和口量增大呈指数递减趋势。研究结果揭示,东方田鼠因警觉引起的觅食中断事件是导致采食率及摄入率降低的主要因子。摄入率测定值与模型预测值的线性回归极显著(P < 0.01),表明,新建立的功能反应模型具有良好的可预测性。推测,东方田鼠因警觉引起采食率及摄入率减小的代价,是以延长觅食时间来补偿的。研究结果充分验证了,在可利用性植物密集斑块,由植物大小调控的动物口量决定其摄入率,且受采食和处理食物竞争及觅食中断的制约,其功能反应为Ⅱ型功能反应的假说。     

Agonistic behaviour in males of five species of voles Microtus

Agonistic behaviour of Microtus pennsylvanicus, M. montanus, M. californicus, M. longicaudus, and M. ochrogaster was observed in 160 staged encounters; a natural observation of sympatric species is included. No difference in the character and movements of agonistic behaviour was apparent when arena size was reduced; only a difference in the frequency of postures and movements was observed. In the smaller arena, M. montanus and M. ochrogaster exhibited a significant increase in frequency of agonistic components. The other three species did not show a significant increase. In interspecific pairings, M. montanus won over M. pennsylvanicus, M. californicus and M. longicaudus; M. ochrogaster won over M. montanus and M. pennsylvanicus. Three species used mutual avoidance in maintaining individual distance.     

Alloparenting experience affects future parental behavior and reproductive success in prairie voles (Microtus ochrogaster)

Various hypotheses have been proposed to explain the function of alloparental behavior in cooperatively breeding species. We examined whether alloparental experience as juveniles enhanced later parental care and reproductive success in the prairie vole (Microtus ochrogaster), a cooperatively breeding rodent. Juveniles cared for one litter of siblings (1EX), two litters of siblings (2EX) or no siblings (0EX). As adults, these individuals were mated to other 0EX, 1EX or 2EX voles, yielding seven different pair combinations, and we recorded measures of parental behaviors, reproductive success, and pup development. As juveniles, individuals caring for siblings for the first time were more alloparental; and as adults, 0EX females paired with 0EX males spent more time in the nest with their pups. Taken together, these results suggest that inexperienced animals spend more time in infant care. As parents, 1EX males spent more time licking their pups than 2EX and 0EX males. Pups with either a 1EX or 2EX parent gained weight faster than pups with 0EX parents during certain developmental periods. While inexperienced animals may spend more time in pup care, long-term benefits of alloparenting may become apparent in the display of certain, particularly important parental behaviors such as licking pups, and in faster weight gain of offspring.     

Sibling recognition in the prairie vole, Microtus ochrogaster

Since mating is seldom observed between sibling prairie voles, Microtus ochrogaster, this, behavioural discrimination was used to investigate sibling recognition in this species. Cross-fostering of 1–3-day-old pups demonstrated that unrelated pups reared together did not breed, whereas siblings reared apart bred readily when paired at weaning. When unrelated voles were paired at 14 days of age, prior to sexual maturity, significantly fewer pairs bred than when strangers were paired at 21 days of age. Separation of 21-day-old siblings for 8 days before pairing overcame incest avoidance; a 15-day separation was required for breeding by siblings that had remained together until they were 50 days old. These results indicate that sibling recognition and, consequently, incest avoidance depend on association prior to weaning.     

Seasonal differences in self-grooming in meadow voles, Microtus pennsylvanicus

We determined whether seasonal differences exist in the amount of time meadow voles, Microtus pennsylvanicus, self-groom when they encounter the scents of conspecifics. To do so, we used voles that were born and reared under long photoperiod (LP) and short photoperiod (SP). LP voles represent those found in free-living populations during the spring and summer breeding season, whereas SP voles characterize those found in free-living populations during the fall and winter nonbreeding season. Experiment 1 showed that LP male and female voles self-groomed more in response to odors of LP opposite-sex conspecifics as compared to those of other LP and SP conspecifics, suggesting that they may be self-grooming to signal sexual interest or excitement to potential mates. Experiment 2 demonstrated that SP males self-groomed more in response to scents of LP female voles and those of SP males as compared to scents of LP males and SP females, whereas SP females spent similar amounts of time self-grooming in response to scents of LP males, LP females, SP females, and SP males. These seasonal differences in self-grooming may reflect differences in the messages produced by groomers when they broadcast their odors as well as differences in the meaning of such odors to opposite-sex conspecifics. Alternatively, these data may be associated with seasonal differences in sexual motivation of the groomers when exposed to scents of particular conspecifics.     

Scent marking and mate choice in the prairie vole, Microtus ochrogaster

Scent marking is common among male and female rodents and might be used in male-male competition and as a mechanism for mate attraction. I tested the hypotheses that females would choose males based on their frequency and placement of scent marks, and that a female would advertise interest in a particular male by placing her scent marks on or near those of a preferred mating partner. In a series of experiments conducted with prairie voles, Microtus ochrogaster, females did not choose mates based on the frequency or placement of scent marks by males nor did they advertise their interest in a particular male through the frequency or placement of scent marks. The number of males chosen that scent-marked more than their opponents did not differ significantly between females exposed (11 of 15) and not exposed (10 of 15) to scents of males. Females exposed and not exposed to scents of males preferred seven of the same males that had scent-marked more than their opponents. When a third group of females was exposed to four times more scent of the less preferred than preferred males, they still chose the preferred males. Thus, the frequency and placement of scent marks by males were not used to assess males for mate choice nor did female prairie voles use scent to advertise their preference for a mating partner. In that scent marking is common in male and female mammals, scent quality might be more important than quantity in male-male competition and mate attraction.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

The behaviour of mature and immature male bank voles (Clethrionomys glareolus)

Neutral-arena encounters were staged between pairs of sexually mature male bank voles (Clethrionomys glareolus), between pairs of immature males, and between pairs consisting of one of each. Mature males exhibited more aggressive components of behaviour to each other than did immature males, but mature males did not attack immature males in ‘mixed’ encounters. The relevance of these results to the population ecology of voles is discussed.     

Precocial sexual behaviour in turkeys (Meleagris gallopavo L.)

Precocial struts were observed in 95 per cent of turkey poults of both sexes, wild and domesticated. In male turkey poults it occurred with about constant frequency up to day 100 (domesticated turkey: 0·6 struts per hr of observation time; wild turkeys: 0·1 struts per hr observation time) and dramatically increased in frequency after day 130, In female turkey poults, the incidence was much lower (about 0·01 struts per hr observation time) and did not shown any marked increase later on. Struts can be elicited by objects the poults are imprinted upon (mother hen, siblings, or human hand or foot in human imprinted poults). However, precocial struts can also occur spontaneously; i.e. in the absence of external stimulation by an imprinting object.     

The relationship between locomotor activity and sexual behaviour in ebony strains of Drosophila melanogaster

Male flies homozygous for the ebony¹¹ mutant allele suffer a severe visual impairment and consequently show poor mating success. However, ebony males show improved mating in darkness because they initiate courtship more quickly than in the light. They also exhibit a competitive superiority over wild-type males under darkened conditoons that correlates with the observed increase in the mutant's locomotor activity. Locomotor activity levels were subsequently shown to correlate with several indices of mating success under both dark and illuminated conditions. The evolutionary implications of this relationship between the two characters are discussed.     

Self-grooming and sibling recognition in meadow voles,Microtus pennsylvanicus,and prairie voles,M. ochrogaster

Self-grooming in response to the odours of an opposite-sex conspecific may reflect sexual motivation on the part of the actor. We tested the hypothesis that meadow voles, Microtus pennsylvanicus, and prairie voles,M. ochrogaster , both self-groom at different rates when exposed to the odours of their siblings as compared to those of nonsiblings. This prediction was studied under the context of social memory for siblings and the effects of isolation on memory for siblings. The hypothesis explains the self-grooming responses of meadow voles isolated from their siblings for 10 days and of prairie voles isolated from their siblings for 20 days. However, 20 days of isolation for male and female meadow voles, and 30 days of isolation for male prairie voles were sufficient to induce these animals to self-groom at a similar rate to both sibling and nonsibling odours, suggesting that after isolation these animals no longer recognized their opposite-sex siblings. Female prairie voles isolated for 30 days self-groomed more in response to the odours of male nonsiblings than to those of male siblings, suggesting that female prairie voles still recognize their male siblings after isolation. This study is the first to provide empirical evidence that, in the context of sibling recognition, self-grooming behaviour is directed at unfamiliar opposite-sex conspecifics, and that the communicative function of self-grooming (sexual motivation) is associated with social memory for siblings. Differences in the self-grooming behaviour of meadow voles and prairie voles may be associated with several aspects of their life history characteristics.