Anti-fertility effect of levonorgestrel and quinestrol in Brandt’s voles(Lasiopodomys brandtii)

The combination of levonorgestrel and quinestrol(EP-1)has been shown to have anti-fertility effects on several wild rodents,but the mechanism underlying these effects is poorly understood.We investigated the effects of EP-1 and each of its components,levonorgestrel(P)and quinestrol(E),on the fertility of Brandt’s voles(Lasiopodomys brandtii)by using a gastric gavage method.The doses for EP-1,E and P were 1,0.34 and 0.66 mg/kg body weight,respectively.Male voles(n=98)were treated daily for 5 or 14 days,then the testes and epididymides were collected,weighed and examined histologically at 30(D30),60(D60)or 90(D90)days after the end of treatment.Four males were allowed to mate with normal females at D90.Female voles(n=75)were treated for 3 days and a further 3 days after a 7-day interval.The uteri and ovaries were weighed and examined histologically at 15(D15),30(D30)or 75(D75)days after the end of treatment.Each of three females were mated with fertile males at D30 and D75,respectively.Our results indicated that quinestrol(E)significantly decreased the sperm numbers in the testes as well as the weight of the testes and epididymides,with both of these tissues showing obvious structural abnormalities,and significantly reduced the litter size and the pup weight for females mated with males of the E treatment group.For female voles,treatment with E,P or EP-1 resulted in no marked influence on the fertility status.These data indicate that quinestrol(E)alone has a significant anti-fertility effect on male Brandt’s voles,but is ineffective in combination with levonorgestrel(P).

Kinship analysis reveals reproductive success skewed toward overwintered Brandt’s voles in semi-natural enclosures

Age structure and seasonality influence the population fluctuations of small rodents.Age determines body weight and social experience,while seasonality regulates the duration of the breeding season and onset of sex­ual maturity in newborn offspring.Therefore,reproductive success and skew usually occur in different age groups.Brandt’s vole(Lasiopodomys brandtii)is a social,short-lived and seasonal breeding small rodent with a dramatic seasonal population fluctuation,but reproductive skew is not fully understood in this species.In the present study,we determined kinship in semi-natural enclosure populations using microsatellite markers based on genotyping,analyzed the reproductive skew between sexes and between overwintered and newborn voles,and monitored variation in male reproductive activity by testing fecal testosterone levels throughout the year.Overwintered voles had the most reproductive success along with a striking increase in the population size in the enclosures,with all biological fathers and 77.8%of biological mothers,which had 100%and 87%of the to­tal offspring,respectively.Compared to overwintered voles,reproductive skews were significantly higher in po­tential overwintered and newborn parents,implying the possible reproductive suppression of newborn voles by dominant overwintered voles.Moreover,both heavier body weight and higher testosterone levels in overwin­tered males supported their potential social status in the population.Our study provided new evidence for repro­ductive skew and differentiation of postnatal gonadal development patterns of different age groups in Brandt’s vole.

Effects of maternal stress induced by predator odors during gestation on behavioral and physiological responses of offspring in Brandt’s vole(Lasiopodomys brandtii)

Maternal effects play a crucial role in regulating populations of small mammals and anti-predator behaviors of offspring.The present study investigated the effects of maternal stress induced by exposure to predator odors during gestation on the behavioral and physiological responses of offspring in Brandt’s vole(Lasiopodomys brandtii).Effects included changes in growth,behaviors,hormone levels in serum,and fosB/ΔfosB mRNA and FosB/ΔFosB protein expression in the hypothalamus.Our results showed that when pregnant voles were exposed to cat and rabbit urine odors for 18 days(1 h/day),the weight of the female offspring decreased;however,the thymus and ovary indices increased,compared with the control group.Male offspring of voles exposed to cat odor spent more time exploring and foraging,and showed a decrease in corticosterone(CORT)compared with voles in the control group.Both fosB/ΔfosB mRNA and FosB/ΔFosB protein expressions were downregulated in the hypothalamus of male offspring in the cat odor-exposed group compared to that in offspring in the control group.However,the mRNA levels of fosB/ΔfosB in the hypothalamus of female offspring did not decrease in response to cat urine odor.Our findings suggested that maternal stress induced by predator odors during gestation restrained the growth of female offspring and increased the duration of exploring and foraging behaviors of male offspring by regulating the HPA axis,which,in turn,reduced the sensitivity of offspring to unfamiliar environments and increased their probability of becoming prey.