Seasonal Differences in Social Behavior among Adult and Juvenile Meadow Voles,Microtus pennsylvanicus

Seasonal differences in behavioral interactions between wild-caught adult and juvenile meadow voles, Microtus pennsylvanicus, were measured in paired encounters in a neutral arena. Seasonal differences existed in the adult-juvenile paired encounters. Early in the breeding season (May—Aug.) paired encounters between adult males and juvenile males were more agonistic than other adultjuvenile pairings. Late in the breeding season (Sep.—Dec.) adult female-juvenile male encounters were more agonistic than other adult-juvenile pairings. Odor preferences of juveniles were determined in a Y-maze olfactometer. Juveniles did not demonstrate seasonal differences in odor preference. Males preferred the odor of adult females to the odor of adult males or their own odor. Females preferred the scent of an adult male to the odor of an adult female, but did not show a preference between their own odor and the odor of an adult male or an adult female. The results are consistent with hypotheses that state in a promiscuous species, females should be philopatric, and males should disperse as a consequence of adult competition. The data suggest that agonistic behavior by adults may regulate juvenile dispersal and recruitment, and define the composition of overwintering groups.     

Dynamics of an enclosed population of pine mice,Microtus pinetorum

Enclosed populations of pine mice were studied over a 28-month period and compared with populations in surrounding natural areas. The enclosed populations reached densities far greater than any observed in surrounding natural areas. It is suggested that the restriction placed on dispersal by the enclosure walls and the addition of food in the form of trap bait could have allowed the enclosed populations to reach higher densities than normally observed at SRP.     

Female Meadow Voles, Microtus pennsylvanicus, Experience a Reduction in Copulatory Behavior During Postpartum Estrus

In many small mammalian species, females undergo postpartum estrus (PPE), mate, and become pregnant soon after delivering a litter. Mating during PPE implies a trade‐off between attending to the new litter and leaving that litter to mate. We tested the hypothesis that copulatory behavior is faster when a female mates during PPE than when it mates outside of PPE, during male‐induced estrus (MIE), a time when it is not lactating. We compared several variables of copulatory behavior in female meadow vole mating during both PPE and MIE. Females in PPE received significantly fewer intromissions, with shorter intervals between intromissions. Each ejaculatory series was also shorter for females in PPE. As a consequence, the total amount of time devoted to copulation was much shorter for females in PPE than for those in MIE. These data support the hypothesis that female meadow voles are able to reduce their copulatory behavior during PPE.     

棕色田鼠探究行为对同种个体气味源反应格局的分析

通过观察非动情期的棕色田鼠对麻醉的同种个体身体气味源的探究行为 ,包括雄鼠对麻醉雄鼠和雌鼠的嗅闻、雌鼠对麻醉雄鼠和雌鼠的嗅闻 ,分析了棕色田鼠在社会探究中对不同气味源的反应格局。结果表明 ,棕色田鼠对同种个体肛殖区和面部的嗅闻频次及嗅闻持续时间最多 (P <0 0 5 ) ;对背部、腹部、肋部嗅闻的频次和持续时间较少。在对同一部位的嗅闻中 ,在嗅闻频次上 ,雄鼠对雄鼠的嗅闻、雌鼠对雌鼠的嗅闻以及雌鼠对雄鼠的嗅闻都显著多于雄鼠对雌鼠的嗅闻 (P <0 0 5 ) ;在嗅闻时间上 ,性别组合对同一部位的探究行为没有显著影响 ,但气味源与性别组合有交互作用 (P <0 0 5 ) ,影响探究行为。这些结果说明棕色田鼠的肛殖区和面部是重要的气味源 ,而且在对同一气味源的探究中存在性别差异。但在非动情期 ,异性间的探究并不总是高于同性间的探究     

Food Deprivation and Restriction During late Gestation Affect the Sexual Behavior of Postpartum Female Meadow Voles,Microtus pennsylvanicus

In many species of small mammals, including meadow voles, Microtus pennsylvanicus, females come into postpartum estrus (PPE) within 12–24 h of giving birth, allowing them to mate and become pregnant while raising the current litter. PPE females show increases in attractivity, proceptivity, and receptivity, the three components of sexual behavior, relative to females not in PPE. Several studies have shown that food deprivation and restriction reduce attractivity, proceptivity, and receptivity of females not in PPE. We tested the hypothesis that food deprivation and restriction during late gestation cause deficits and decrease the attractivity, proceptivity, and receptivity of females when they enter PPE. Our data support the hypothesis. On day 1 of lactation, females that were food deprived and food restricted produced scent marks that were significantly less attractive as those produced by control PPE females. Food deprivation but not food restriction caused females to no longer display significant preferences for the scent marks of males over those of females (proceptivity). Food deprivation and food restriction were sufficient to induce females to become significantly less sexually receptive than control females. Eleven of 12 control PPE females mated, 4 of 12 food‐restricted females mated, and 3 of 12 food‐deprived females mated. Dams facing food deprivation or restriction during late gestation may have to balance the benefits of mating during PPE with the increased costs associated with getting pregnant while they are lactating.     

Puberty in pine voles, Microtus pinetorum, and the influence of chemosignals on female reproduction

We investigated the reproductive biology of an induced ovulator, the pine vole (Microtus pinetorum). Male puberty, measured as age at first impregnation, was found to occur as early as 44 days of age. Female puberty measured as age at first conception, was found to occur as early as 32 days of age, considerably earlier than previously reported. Females paired with stud males exhibited a doubling of uterine weight within 12 h, and vaginal sperm were present after 48 h. This indicates that although behavioral responses to males--including mating--require prolonged contact, physiological responses to males occur rapidly. Chemosignals from males slightly increased uterine and ovarian weights of females, but chemosignals from other females did not. Young females paired with stud males for 48 h in the presence of soiled bedding from the female's family had significantly smaller increases in ovarian and uterine weights than similar females paired on clean bedding. Suppression of reproduction in female offspring while they remain with the extended family unit is discussed as a life-history tactic and as a possible mechanism for inbreeding avoidance.     

Clusters of Repetitive DNA Sequences in Chromosomes of Voles of the Subgenus Microtus (Microtus,Arvicolidae)

Russian Journal of Genetics - The study is focused on the analysis of the mechanisms underlying the formation and distribution of repeat clusters in mammalian chromosomes, as exemplified by a group...     

人工饲养条件下根田鼠肥满度的研究

实验室条件下,利用根田鼠1～70日龄体重和体长数据,计算其肥满度指数,目的在于分析其生长发育的基本规律。结果表明,根田鼠1～70日龄肥满度存在性别差异且随日龄增加而增大;雌雄个体的发育不同步;常见曲线回归模型对根田鼠1～70日龄的肥满度不能准确拟合,根据其生长发育状况,将其划分为3个阶段(其中幼体和成体阶段各含2个阶段)。     

Persistence of the Attractiveness of Two Sex-specific Scents in Meadow Voles,Microtus pennsylvanicus

The function of an odour may be reflected in its fade-out time in the environment. In this study, we investigated fade-out times of two specific odours, the anogenital area scent and that of the posterolateral region. These two odours support opposite-sex preferences in male and female meadow voles, Microtus pennsylvanicus, but convey nonidentical information to conspecifics during the breeding season. The first experiment tested whether meadow voles respond preferentially to scents that were aged for 15 min (fresh) to 30 d. Males preferred female anogenital area scent to male anogenital area scent if both scents were ≤ 10 d old. By comparison, females preferred male anogenital area scent to female anogenital area scent if the scents were ≤ 25 d old. However, male and female voles preferred the posterolateral scent of males to that of females if the scents were ≤ 1 d old. Thus, fade-out times for these two scents differ for males and females, suggesting different functions. In the second experiment, male and female voles preferred fresh anogenital area scent and fresh posterolateral region scent compared with those same scents that were older. This result suggests that older scents may have lost information over time about the sex of the donor. Overall, data from both experiments indicate that voles may use specific scents for communication in different social contexts.     

Age Affects Over-Marking of Opposite-Sex Scent Marks in Meadow Voles, Microtus pennsylvanicus

Models of age-related effects on behavior predict that among short-lived species younger adults are more attractive and attracted to opposite-sex conspecifics than are older adults, whereas the converse is predicted for long-lived species. Although most studies of age-related effects on behavior support these predictions, they are not supported by many studies of scent marking, a behavior used in mate attraction. Over-marking, a form of scent marking, is a tactic used by many terrestrial mammals to convey information about themselves to opposite-sex conspecifics. The present study tested the hypothesis that the age of meadow voles, Microtus pennsylvanicus ; a microtine rodent, affects their over- and scent-marking behaviors when they encounter the marks of opposite-sex conspecifics. Sex differences existed in the over-marking behavior of adult voles among the three different age groups that were tested. Male voles that were 5–7 and 10–12 mo olds over-marked a higher proportion of the marks of females than did 2–3 mo old male voles. Female voles that were 2–3, 5–7, and 10–12 mo old over-marked a similar number of marks deposited by male voles. Overall, the data were not consistent with models predicting the behavior of short-lived animals such as rodents when they encounter the opposite sex. The differences in over-marking displayed by older and younger adult male voles may be associated with life history tradeoffs, the likelihood that they will encounter sexually receptive females, and being selected as mates.     

Sexual dimorphism and gonadal control of ultrasonic vocalizations in adult pine voles, Microtus pinetorum

We investigated the vocalizations produced by adult pine voles during various social interactions by presenting an experimental animal with either an anesthetized or awake (unanesthetized) conspecific. Ultrasonic vocalizations (USVs) occurred frequently during tests in which an awake male was present, but were rarely detected in tests involving only awake females, or when a female was presented with an anesthetized conspecific. Higher rates of USVs were produced when males were tested with a familiar female than when tested with an unfamiliar male or female. Equivalent rates were produced when males were presented with either anesthetized or awake animals, but female-soiled bedding failed to elicit USVs from males. Sonic vocalizations (SVs) were produced by both sexes and were associated with aggressive behavior, but occurred only in tests between awake, unfamiliar animals. Castration greatly reduced and testosterone therapy restored USVs emitted by males in response to anesthetized conspecifics. Our results suggest that (i) USVs are emitted predominantly by males; (ii) familiarity enhances USV response; (iii) SVs are produced during aggressive interactions; and (iv) androgens regulate the production of USVs by males. Possible roles for pine vole vocalizations are discussed.     

The Outcome of a Previous Social Interaction with a Same‐sex Conspecific Affects the Behavior of Meadow Voles,Microtus pennsylvanicus

In species where conspecifics compete for resources such as territories, remembering where a neighbor was previously encountered and the outcome of that interaction may give individuals advantages over nearby conspecifics. We used a two‐phase experiment to test the hypothesis that female meadow voles, Microtus pennsylvanicus, who during the breeding season are territorial and agonistic toward one another, can use details of an encounter with another female in one location to later navigate nearby areas. During the encounter phase, pairs of females interacted for two minutes in one isolated section of a Y‐maze; control females were placed in alone. Females were scored as either winners or losers. Winners displayed twice as many agonistic acts against their opponent. The test phase took place after a retention interval of one hour, 1 d, or 1 wk. Single females were returned to a clean and empty Y‐maze and allowed to explore the entire apparatus for 15 min. We recorded the amount of time spent in each section of the maze. After retention intervals of one hour and 7 d winners, losers, and controls spent similar amounts of time in each section. However, after 24 h, winners spent more time in the encounter section; losers and control females spent similar amounts of time in each section. The results suggest that meadow voles' memory of the details of a single encounter is influenced by the emotional valence attached to that event. The duration of memory may be associated with the establishment of territories by female meadow voles.     

Meadow Voles (Microtus pennsylvanicus, Arvicolidae) Over-mark and Adjacent-mark the Scent Marks of Same-sex Conspecifics

Scent over-marking occurs when an animal deposits its scent mark on top of the scent mark of a conspecific; adjacent-marking occurs when an animal deposits its scent mark next to the scent mark of a conspecific. Given that male rodents usually scent mark more than females and that animals spend more time investigating the odor of the top-scent donor of an over-mark, I tested the following three hypotheses. First, male meadow voles deposit more scent marks than female meadow voles. Second, male meadow voles will deposit more over-marks and adjacent-marks in response to the scent marks of a same-sex conspecific than females would. Third, meadow voles spend more time investigating the odor of the second vole placed in the arena than that of the first vole placed in the arena. To test these hypotheses, two age-matched, like-sex conspecifics (first vole and second vole) were placed successively into an arena in which they were allowed to freely explore and scent mark for 15 min. The first hypothesis was not supported. The first and second vole, independently of sex, deposited a similar number of scent marks. The second hypothesis was also not supported by the data: more conspecific scent marks were over-marked by the second female than by the second male. The third hypothesis was supported by the data. After investigating a scented arena, males and females spent more time investigating the odor of the second vole than that of the first vole. Sex differences in scent-marking behaviors of meadow voles are unlike those reported for other species of rodents.     

Maternal Food Restriction During Lactation Affects Body Weight and Sexual Behavior of Male Offspring in Meadow Voles (Microtus pennsylvanicus)

Little is known about the occurrence of individual variation in sexual behavior and how maternal nutrition can affect this variation. We tested the hypothesis that male offspring of female meadow voles, Microtus pennsylvanicus, that were 30% food restricted (FR) during days 1–7 of lactation (FR 1–7), days 8–14 of lactation (FR 8–14), or late days 15–21 of lactation (FR 15–21) lactation show persistent, negative effects on their sexual behavior as adults relative to male offspring of females that were not food restricted. We measured three components of sexual behavior, attractivity, proceptivity, and receptivity, beginning when the males were 98 d of age. Food restriction during middle lactation (FR 8–14) but not during early (FR 1–7) and late lactation (FR 15–21) was sufficient to induce adult male voles to produce anogenital marks that were not as attractive as those produced by control males. Food restriction during lactation did not affect the proceptive behavior of male voles but did affect their receptivity. Only four of 12 FR 8–14 male voles mated compared to nine of 12 FR 1–7 males, eight of 12 FR 15–21 males, and eight of 11 control males. However, no differences existed in their copulatory behavior among the males that did mate. The body weight of FR 1–7 and FR 8–14 males was lower than that of FR 15–21 and control males when they were between 22 d of age (weaning) and 48 d of age (puberty) but was similar when the males were 98 d of age. Food intake was similar for the FR and control males between day 22 and day 98. It remains unclear, however, whether this type of maternal effect represents strategic programing of offspring behavior in response to the environment experienced by mothers or is a product of developmental processes of food restriction prior to weaning (Evolution 58 , 2004, 2574).     

单宁酸对根田鼠断乳幼体生长和存活的影响

在食物中含10％和20％蛋白质条件下,测定了单宁酸对根田鼠幼体在断乳后20d内的生长和存活的影响。结果表明,食物中含蛋白质为10％的条件下,摄食含3％和6％单宁酸食物的试验个体生长速率分别为-0．135g/d和-0．25g/d,食物利用效率均显低于对照组,断乳后20d内平均存活天数较对照组分别下降26．23％和49．36％。在食物蛋白质为20％的条件下,摄食含3％和6％单宁酸食物的试验个体生长速率分别为0．134g/d和-0．116g／d,摄食6％单宁酸食物的试验个体食物利用效率显低于摄食3％单宁酸食物的试验个体和对照组个体,断乳后20d内的平均存活天数较对照组下降39．41％,摄食3％单宁酸食物的试验个体较对照组略有下降,但不显。上述结果验证了单宁酸能显影响植食性小哺乳动物生长和存活的假设。