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.     

Social environment regulates corticotropin releasing factor, corticosterone and vasopressin in juvenile prairie voles

Stressful social conditions, such as isolation, that occur during sensitive developmental periods may alter present and future social behavior. Changes in the neuroendocrine mechanisms closely associated with affiliative behaviors and stress reactivity are likely to underlie these changes in behavior. In the present study, we assessed the effects of post-weaning social housing conditions on the neuropeptides arginine vasopressin (AVP) and oxytocin (OT), and components of the hypothalamic-pituitary-adrenal axis (corticotropin releasing factor: [CRF], and corticosterone: [CORT]) in the prairie vole (Microtus ochrogaster), a socially monogamous bi-parental rodent. Following weaning at 21 days of age, prairie voles were maintained in one of three housing conditions: social isolation (isolate), paired with a same sex sibling (sibling) or paired with a stranger (stranger) of the same sex and age. Housing conditions were maintained for either 4 or 21 days. Central CRF, AVP and OT immunoreactivity (ir) were quantified and circulating plasma CORT, AVP and OT were assayed. Isolated voles had higher CRF-ir in the paraventricular nucleus of the hypothalamus (PVN) compared with sibling and stranger housed voles. Plasma CORT was significantly higher in isolates. AVP-ir was significantly lower in the PVN of isolate females compared to either sibling females or stranger females. However, AVP-ir was significantly higher in the supraoptic nucleus (SON) of isolates compared to siblings. There were no differences in central OT-ir or plasma OT. These results identify neuroendocrine mechanisms which respond to isolation and potentially modulate behavior.     

Age-related changes in plasma oestrogen concentration, behavioural responsiveness to oestrogen, and reproductive success in female gray-tailed voles, Microtus canicaudus

Age-related increases in the incidence of vaginal cornification were associated with increases in the reproductive success of female gray-tailed voles previously isolated from males. The pregnancy rate of females first paired with males at 30-50 days of age was significantly lower than that of females first paired at 90-120 or 150-200 days of age. The improvement was due to increases in propensities to display receptive behaviours and decreases in the incidence of sterile matings. Although plasma oestrogen concentrations increased with age and were higher in receptive than unreceptive females, plasma oestrogen values alone did not account completely for differences in receptive behaviours amongst females of different ages. Females ovariectomized at 30-50 days of age rarely displayed receptive behaviours when treated with large doses of oestradiol benzoate, whereas nearly all females similarly treated were receptive if ovariectomies were performed between 150 and 200 days of age. The receptivity rate of females ovariectomized between 90 and 150 days was intermediate between the rates of the other two groups.     

Growth and reproductive development of male Microtus montanus is affected by the prenatal photoperiod

Rates of growth and sexual maturation of microtine rodents vary in response to photoperiod. Previous work with Microtus montanus has shown that the photoperiod present prior to weaning influences how voles will respond to photoperiods seen following weaning. The data presented demonstrate that information about the photoperiod seen by the mother during pregnancy influences the postweaning development of male M. montanus. Adult M. montanus were paired in photoperiods consisting of 8, 14 or 16 h light/day. Their litters were conceived and born in these photoperiods. On the day of birth the litters were recorded and retained in the gestation photoperiod (Groups C8, C14 and C16) or transferred to the 14-h photoperiod (Groups E8 and E16). The growth of males was followed from weaning until 74 days of age, at which time the voles were sacrificed and their reproductive organs weighed. There were no differences in body weight or length between groups at 18 days of age. At 74 days of age the development of the voles could be ranked in the following sequence: C8 less than E16 less than C14 less than E8 less than C16.     

Effects of duration of daily illumination on reproductive organs and fertility of the meadow vole (Microtus pennsylvanicus).

The objective of this study was to determine the optimum simple, constant photoperiod for voles in a laboratory colony. Voles from an established colony maintained at 22 degrees C with a photoperiod of 14:10 hours of light:dark were transferred at 50 days of age to a photoperiod of 12:12, 14:10, 16:8 or 18:6 hours of light:dark. From Day 96 to Day 102, the 9--10 females per treatment group were paired with a male. Body and gonadal weights, spermatogenesis, ovarian activity and pregnancy were evaluated on Day 110. Reproductive function and body weight of both male and female voles maintained on a photoperiod of 16:8 exceeded (p less than 0.05) values for voles exposed to 12:12 hours of light:dark and tended to be more favorable than for voles in the 14:10 and 18:6 groups.     

Plasma levels of gonadotropin and 17α,20β-dihydroxy-4-pregnen-3-one in relation to spawning behaviour of rainbow trout, Oncorhynchus mykiss(Walbaum)

Manipulation of the opportunity to spawn was used to investigate the relationship between endocrine events, egg viability and spawning behaviour in female rainbow trout. Females were prevented from spawning by isolating them from males and gravel for up to 21 days after ovula- tion. Blood samples were taken before pairing with a male, at the onset of nesting activity, and at the completion of spawning. Plasma hormone levels of gonadotropin (GtH) and 17α,20β-dihydroxy-4-pregnen-3-one (17,2OP) were measured by specific radioimmunoassays. There were no qualitative or quantitative differences in the spawning behaviour of females paired on the day of ovulation or 7. 14, or 21 days after ovulation. There was a general decrease in the viability of eggs with increasing retention times. In females paired on the day of ovulation, or after 7 or 14 days, GtH levels increased with the onset of nesting behaviour and declined as fish reached the post-spawning condition. By day 21, GtH levels before pairing were significantly higher than prepairing levels in the other three treatment groups, and did not increase at the onset of nesting, or decrease in post-spawning fish. Plasma 17,20P remained high in prepairing and nesting samples of all four groups and declined to low levels in fish in post-spawning condition. In females paired on the day of ovulation there was a significant increase in 17,20P from the prepairing to the nesting stage. These results suggest that 17,20P plays a key role in the synchronization of behavioural and maturational events at the time of spawning.     

光周期对布氏田鼠幼仔生长发育的影响

通过比较法对实验室内布氏田鼠 (Microtusbrandti)幼仔生长发育与光周期关系的研究表明 ,尽管出生和断乳时的窝仔数及断乳时窝仔存活率不受光周期的影响 (t test,P >0 0 5 ) ,每种光周期条件下出生和断乳时雌雄比例差异不显著 (Chi square检验 ,P >0 0 5 ) ,不同光周期间雄性比例无明显差异 (百分数的检验 ,P >0 0 5 ) ,但是 ,随着幼仔的生长 ,出生并饲养在长光照周期 (LD ,14L∶10D)下的个体体重、体长和肥满度显著大于短光照周期 (SD ,10L∶14D)下的幼体 ,尤在出生 9或 14天以后的各阶段 (t test,P <0 0 5 )。在 6 0日龄时 ,LD雄鼠的睾丸、附睾及储精囊成熟指数显著高于SD鼠 (t test,睾丸 ,t =3 30 9,df =14,P <0 0 1;附睾 ,t=3 6 2 2 ,df =14,P <0 0 1;储精囊 ,t=3 379,df =14,P <0 0 1)。但LD组的皮毛厚度和绒毛长度显著低于SD组 (t test,皮毛厚度t=- 5 185 ,df =14,P <0 0 1;绒毛长度t=- 2 415 ,df =14,P <0 0 5 )。作者认为体重、肥满度和性腺成熟指数 (GSI)高的LD鼠较SD鼠更适应于繁殖期的繁殖生存 ;而生长发育缓慢 ,皮毛厚度、绒毛长度高的SD鼠更能适应越冬生存。在自然环境中 ,光周期可能被布氏田鼠作为季节环境变化的信号 ,使其在形态和生殖方面提前作好准备 ,采取不同的策略以适     

Photoperiod influences reproduction in the prairie vole (Microtus ochrogaster)

Four experiments examined the role of photoperiod in the regulation of seasonal breeding in the prairie vole. Adult male voles maintained in short (8L:16D) as compared to long (16L:8D) photoperiods for 10 wk had reduced testicular and seminal vesicle weights, but fertility was not impaired. Male prairie voles reared from birth until 35 days of age in short as compared to long photoperiods also had reduced testicular and seminal vesicle weights, as well as diminished fertility. The incidence of pregnancy did not differ between long- and short-day female voles paired for 6 days with long- or short-day males (93%, 86%, 89%, and 88%, respectively). Photoperiod did not affect the incidence or the timing of postpartum pregnancies in long- or short-day females paired with long-day males through the birth of several litters. Adult male prairie voles retain only marginal sensitivity to short photoperiods, maturing males are highly responsive to short days, and adult females are insensitive to photoperiod. These data suggest that termination of the breeding season in the autumn may be due to the lack of fecund males in the population.     

Pairing Patterns in Japanese Beetles (Popillia japonica Newman): Effects of Sex Ratio and Time of Day

Size-related patterns between unpaired and paired individuals and between males and females of a given pair give clues about both a species' sexual behavior and the environmental factors affecting its sexual behavior. We studied the mating patterns of Japanese beetles (Popillia japonica) in east–central Illinois. The frequency of male–female pairs varied significantly among days and within a day, with pairs being significantly more common in the morning and the evening. The sex ratio on the food plants was significantly male biased, but although the sex ratio fluctuated among days and among time periods, the variation in the frequency of mating pairs was not explained by variation in the sex ratio. We found no assortative pairing with respect to size, but sizes of paired and unpaired individuals did differ. Paired females were larger than unpaired females at all time periods. In contrast, paired males were larger at 0700 and smaller at 1000, and little difference existed at other times of the day. The size of males and females, sex ratio, and pairing frequency also differed among days. Much of this variation in size and pairing frequency was related to a seasonal effect: later in the summer, beetles of both sexes were smaller and pairs were less common. Interestingly, pairs were also less frequent on days with higher average temperatures. This between-day variation in pairing, in combination with the within-day pairing differences, suggests that the temperature may alter the cost, and hence likelihood, of pairing in this species.     

Prolonged mating in prairie voles (Microtus ochrogaster) increases likelihood of ovulation and embryo number

Prairie voles are induced ovulators that mate frequently in brief bouts over a period of approximately 24 h. We examined 1) impact of mating duration on ovulation and embryo number, 2) incidence of fertilization, 3) temporal pattern of embryo development, 4) embryo progression through the reproductive tract over time, and 5) embryo development in culture. Mating was videotaped to determine first copulation, and the ovaries were examined and the reproductive tracts flushed at 6, 8, 10, 12, 16, 20, and 24 h and 2, 3, and 4 days after first copulation. The number of mature follicles and fresh corpora lutea and the number and developmental stage of embryos were quantified. One, two-, and four-cell embryos were cultured in Whitten's medium. Mature follicles were present at the earliest time examined (6 h). Thirty-eight percent of females that had been paired for < 12 h after the first copulation ovulated, whereas all females paired >/= 12 h after the first copulation ovulated. Virtually all (> 99%) oocytes recovered from females paired for >/= 12 h after first copulation were fertilized. Pairing time after first copulation and mean copulation-bout duration were significant (p < 0.05) determinants of embryo number. Embryos entered the uterine horns and implanted on Days 3 and 4, respectively, after first copulation (Day 0). Embryos cultured in vitro underwent approximately one cell division per day, a rate similar to that in vivo. We conclude that prairie voles ovulate reliably after pairing for >/= 12 h, although some females showed exceptional sensitivity not predicted by the variables quantified. Prolonged mating for longer than 12 h increased the total embryos produced. This mechanism likely has adaptive significance for increasing offspring number.     

Development of stereotypies and polydipsia in wild caught bank voles (Clethrionomys glareolus) and their laboratory-bred offspring. Is polydipsia a symptom of diabetes mellitus?

The development of stereotypies and polydipsia was studied in wild caught bank voles (P: n=92) and their laboratory-bred offspring (F1: n=248). All animals were kept isolated in barren cages in the laboratory. In the P generation, no individuals developed stereotypies, but 22% developed polydipsia (>21 ml/day water intake against normally 10 ml/day). Polydipsia was more frequent among males (34%) than females (13%). In F1, 30% developed locomotor stereotypies alone, 21% showed polydipsia alone, and, additionally, 7% developed both stereotypies and polydipsia. Fewer males than females developed stereotypies (23% vs. 38%), whereas polydipsia was more frequent in males than in females (30% vs. 11%). The occurrence and distribution of polydipsia among sexes were the same in F1 and P. The distribution of different types of stereotypies in stereotyping voles were backward somersaulting (BS, 80%), high-speed jumping (JUMP, 29%), pacing following a fixed route (PF, 12%) and windscreen wiper movement (WIN, 5%). Some individuals (10%) showed two or more different types of stereotypies. The average age for developing stereotypies was 96 days while polydipsia was registered at the age of 63 days in both sexes. Voles showing both polydipsia and stereotypies developed polydipsia later (79 days) than polydipsic voles not showing stereotypies. This difference was especially pronounced in stereotyping females in which the occurrence of polydipsia was postponed to the age of 114 days. Polydipsic voles were tested positive for glucosuria indicating that polydipsia could be a symptom of diabetes mellitus. It is suggested that the development of stereotypies and polydipsia among bank voles in the laboratory are the results of frustration and prolonged stress. Stereotypies seem to depend on frustrative experiences early in life, while polydipsia may be related to diabetes mellitus caused by the experience of prolonged stress. Moreover, circumstances related to the development of stereotypies may be adaptive by reducing the risks of prolonged stress, including the development of fatal polydipsia.     

雷公藤甲素对雄性布氏田鼠繁殖力的抑制效果

为评价植物源鼠类不育剂雷公藤甲素对雄性布氏田鼠的不育效果,本研究采用每千克体重0 mg、0.1 mg、0.2 mg,0.4 mg的雷公藤甲素溶液对雄鼠进行连续7 d灌胃处理,并在停药2周和4周后检测其体重、性腺重、精子密度及配对雌鼠怀孕率与胎仔数.结果表明,雷公藤甲素处理未显著降低雄性布氏田鼠的体重、性腺相对重量、附睾...     

Influence of sexual experience and social environment on fertility and incidence of mating in young female bank voles (Clethrionomys glareolus)

Between 30 and 40 days of age, female bank voles were kept singly, in female pairs, separated from an adult male by a wire mesh, or paired with a vasectomized male. At Day 40 they were paired with adult intact males. Fertility at the first mating was low (22-25%), but if the females had previously mated with the vasectomized male fertility of the subsequent mating with the intact male was significantly increased (63%). Sterile matings therefore had a priming effect on the females, and could be important for the development of puberty in wild females. Only 55-59% of the females without contact with males between Days 30 and 40 mated with the fertile male. Contact with a male through a wire mesh increased the proportion to 80% and co-habitation with a vasectomized male to 94%. In the last group, mating also occurred at a younger age.     

A natively paired antibody library yields drug leads with higher sensitivity and specificity than a randomly paired antibody library

Deep sequencing and single-chain variable fragment (scFv) yeast display methods are becoming more popular for discovery of therapeutic antibody candidates in mouse B cell repertoires. In this study, we compare a deep sequencing and scFv display method that retains native heavy and light chain pairing with a related method that randomly pairs heavy and light chain. We performed the studies in a humanized mouse, using interleukin 21 receptor (IL-21R) as a test immunogen. We identified 44 high-affinity binder scFv with the native pairing method and 100 high-affinity binder scFv with the random pairing method. 30% of the natively paired scFv binders were also discovered with the randomly paired method, and 13% of the randomly paired binders were also discovered with the natively paired method. Additionally, 33% of the scFv binders discovered only in the randomly paired library were initially present in the natively paired pre-sort library. Thus, a significant proportion of “randomly paired” scFv were actually natively paired. We synthesized and produced 46 of the candidates as full-length antibodies and subjected them to a panel of binding assays to characterize their therapeutic potential. 87% of the antibodies were verified as binding IL-21R by at least one assay. We found that antibodies with native light chains were more likely to bind IL-21R than antibodies with non-native light chains, suggesting a higher false positive rate for antibodies from the randomly paired library. Additionally, the randomly paired method failed to identify nearly half of the true natively paired binders, suggesting a higher false negative rate. We conclude that natively paired libraries have critical advantages in sensitivity and specificity for antibody discovery programs.     

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).     

布氏田鼠社会行为对光周期的适应格局

对实验室内不同光周期条件下的布氏田鼠陌生成体—亚成体间社会行为模式的初步研究显示:不同光周期下成体对亚成体（特别是对雄性亚成体）的行为反应具性二型特征,长光照周期下（light:dark,14L:10D)成体与亚成体同性组合间的争斗较异性组合间的明显,容忍性低,其中成体雄对亚成体雄尤甚。短光照周期下（light:dark,10L:14D）成体雄对亚成体雄、成体雌对亚成体雌及亚成体雄的相容性均较成体雄对亚成体雌的容忍性低,尤成体雌对亚成体雄的排斥表现更为突出,其容忍性也较长光照条件下对应组的低。结果表明,不同光周期条件下布氏田鼠成体与亚成体间的社会行为模式不同。在自然条件下,这些行为模式是其对环境季节变化的一种有效适应,它影响种群中未成年个体存活、补充、扩散重组以及社群结构、种群空间格局季节变化,对该鼠的生存和繁殖有利。     

The endocrinology of puberty and reproductive functioning in female cotton-top tamarins (Saguinus oedipus) under varying social conditions

Sexual maturation and fertility were assessed in fourteen cotton-top tamarin (Saguinus oedipus) females under various social conditions. Six tamarin females (20-28 mo of age) showed a suppression of fertility while living with their families. Hormonal profiles demonstrated low, acyclic levels of urinary luteinizing hormone (LH) and estrone-conjugates (E1C). A rapid onset of ovarian and pituitary cyclicity occurred when four of the six females were removed from their families and paired with an unrelated male. In one female, an ovulatory LH peak occurred as early as eight days after pairing and resulted in conception and full-term pregnancy. Two of the six females were housed in total isolation for 30 days following their removal from the family and prior to pairing. Gradual increases in hormone concentrations occurred during isolation; however, there was no ovarian cyclicity until each female was paired with an unrelated male. In all six females, conception occurred before or as a result of the third ovulatory cycle. Partial isolation of a 36-mo-old female resulted in elevated LH and E1C levels, but cyclicity was not observed until the female was paired with an unrelated male. These findings indicate that removal of a female from the family alone does not initiate ovarian cycling. Sexual maturation, or puberty, occurs in female tamarins living with their families between 15 and 17 mo of age when mean LH and E1C levels began to increase. However, when a female is removed and paired at 9 mo of age with an unrelated male, elevated levels of LH and E1C may be seen by 10 and 11 mo of age. Our findings indicate that a suppression of fertility occurs in cotton-top tamarins living with their families, but that reproductive suppression does not affect the process of sexual maturation. Both removal from the family environment and stimulation by an unrelated male tamarin were necessary to induce normal reproductive activity. An acceleration of puberty occurred when a female tamarin was removed from her family early in development and paired with a male.     

Androgen Exposure and Reproductive Behavior of an Induced Ovulator, the Pine Vole (Microtus pinetorum)

The actions of steroid hormones on brain and behavior are classically divided into organizational effects that are permanent and occur early in development and activational effects that are temporary and occur throughout life. Here, we test the hypothesis that in an induced ovulator, testosterone defeminizes only those neural tissues that rely on synergistic interactions of estrogen and progesterone for normal function in adulthood. Female voles,Microtus pinetorum,injected with testosterone (T) or oil neonatally were paired with males for an 8-week period. During the pairing, androgenized and oil-treated females spent a similar amount of time investigating the caudal and rostral regions of the males. Males spent significantly less time investigating the caudal and rostral regions of androgenized females. Androgenized females mounted males, did not exhibit lordosis, and were less likely to be mounted by males. Moreover, none of the 10 androgenized females gave birth, whereas 8 of 9 control females gave birth. Androgenized females were also not capable of being stimulated into reproductive condition by males. Injection of 0.5 μg of estradiol benzoate for 4 consecutive days resulted in reduced uterine hypertrophy in androgenized females. These results support the original organizational–activational hypothesis by showing that neonatal androgenization defeminizes and masculinizes female pine voles.     

Meiotic configurations in female trisomy 21 foetuses

Summary Analysis of the meiotic configurations formed by the three No 21 chromosomes in oocytes from two trisomy 21 foetuses was undertaken using a spreading technique. Light microscope analysis of the first gave limited resolving power, such that over half the oocytes could not be classified as to presence or absence of trivalent or bivalent plusunivalent. In the second, investigated at the electron microscope level, all 65 cells analysed were informative and precise detail of meiotic pairing in trivalents could be obtained. Two principal forms of trivalent occurred, one in which pairing was initiated at opposite ends of the three No 21's, each initiation point involving only two of the three homologous lateral elements; the other in which pairing was initiated by all three elements at the same end, a triple synaptonemal complex being formed. Only in one oocyte out of the 65 analysed at EM level, however, did triple pairing occur along the entire length of the No 21 trivalent. All others showed splitting into bivalent and univalent at some point along the structure. Unpaired regions within trivalents and all univalents were consistently seen to be thickened and dark staining with silver over the whole period from pachytene to diplotene. This contrasted with the desynapsing lateral elements of previously paired synaptonemal complexes which appeared thin by comparison at diplotene. The significance of the thickening remains, as yet, obscure.     

Reproductive features of the Russian vole in laboratory breeding.

Reproductive features of newly bred Russian voles (Microtus rossiaemeridionalis) as a laboratory animal were studied. This species is a copulatory ovulator, and most couples copulated 6 to 16 h after pairing. The gestation period varied from 18 to 22 days (mean +/- SD: 20.6 +/- 0.9, n = 72), and the average litter size was 4.6 +/- 1.9 (n = 125). Compared with the litter size at the first parturition (3.6 +/- 1.6, n = 72), the litter size in the subsequent parturitions increased to 5.9 +/- 1.4 (n = 53). The animals exhibited postpartum estrus, and repeated pregnancy accompanied with suckling pups and parturition continuously in the laboratory condition unlike other vole species. In view of their complex stomach and good proliferation, the Russian voles were evaluated as a good laboratory animal, especially as a model animal for ruminant studies.