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

Risk of inbreeding: problem of mate choice and fitness effects?

Mating with close kin may cause inbreeding depression with negative consequences to offspring and local populations. There exist mechanisms like kin-recognition or sex-specific dispersal to avoid mating with kin. In fluctuating population densities, like in many small mammals, both very low and very high densities provide conditions for inbreeding, if kin males are prone to stay in their natal area. Females are choosy and male dominance is thought to be the key feature when selecting mating partners. The aim of this study was to test the possible discrepancy in mate choice and negative fitness effects of inbreeding in two experiments, one in the laboratory and one in field enclosures. We asked (1) how the quality of the potential mating partners affects female choice regardless of relatedness and (2) how inbreeding affects the field populations created either from inbred or outbred individuals. Our results show that primiparous females in post-partum oestrus mated preferably with a dominant male, measured with their urine-marking behaviour, regardless if the selected male was brother or not. Only if the two males offered were of same dominance rank, the female mated with the non-kin male. However, the field experiment verified a negative effect of inbreeding in the bank vole. Thus, there seems to be a mismatch between female mate choice when selecting for dominance among resident males and population viability through long-term inbreeding depression. The study suggests the high importance of sex-biased dispersal as a mechanism to avoid kin individuals to meet in mate choice situations.

The time interval between sequential mating affects the response of male meadow voles to previous mates

Male meadow voles differed in their copulatory behaviour, mating and reproductive success, and odour preferences for successively encountered mates, when the interval between pairing with two females was 1 h, 1 day, 4 days, 7 days or 10 days. Male voles had shorter latencies to first ejaculation with female 2 than with female 1 when the interval was 1 h, which may be attributed to heightened sexual arousal in males for female 2. Males also had shorter copulatory bouts with female 2 than with female 1 when the intervals between pairings were 1 h and 1 day. Shorter copulation bouts may allow more mating opportunities for both sexes and encourage multiple mating. Male voles also preferred the scent marks of female 2 to those of female 1 when the interval between pairing was 7 or 10 days, suggesting that these females were treated as distinct entities.

Re-feeding food-deprived male meadow voles affects the sperm allocation of their rival males

An individual's nutritional status affects the manner in which same- and opposite-sex conspecifics respond to that individual, which may affect their fitness. Male meadow voles, Microtus pennsylvanicus, increase their sperm allocation if they encounter the scent mark of an unfamiliar male that is not nutritionally challenged. If, however, the scent mark comes from a male that has been food deprived for 24 hours, stud male voles do not increase their sperm allocation. Food deprived males may be viewed as being lower quality and a reduced risk of sperm competition by rival males. We hypothesized that stud males in promiscuous mating systems tailor their sperm allocations depending on whether rival males have been food deprived and then re-fed. We predicted that newly re-fed males will be considered a strong risk of sperm competition because of the potentially high fitness and survival costs associated with food deprivation in males, and that they will cause stud males to increase their sperm allocation. Our results, however, showed that the recovery period from 24 hours of food deprivation was a relatively slow process. It took between 96 hours and 336 hours of re-feeding male scent donors that were food deprived for 24 hours to induce stud males to increase their sperm allocation to levels comparable to when scent donors were not food deprived. Stud male voles may be conserving the amount of sperm allocated until the male scent donors have recovered from food deprivation and subsequent re-feeding.

Food deprivation and restriction during late gestation affects 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 causes deficits and decreases 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.

Meadow voles, Microtus pennsylvanicus, have the capacity to recall the "what", "where", and "when" of a single past event

Some non-human animals may possess the ability to recall the "what", "where", and "when" of a single past event. We tested the hypothesis that male meadow voles possess the capacity to recall the "what", "where", and "when" of a single past event associated with mate selection in two experiments. Briefly, male voles were allowed to explore an apparatus that contained two chambers. One chamber contained a day-20 pregnant female (24 h prepartum). The other chamber contained a sexually mature female that was neither pregnant nor lactating (REF female). Twenty-four hour after the exposure, the males were placed in the same apparatus, which was empty and clean. At this time, the pregnant female would have entered postpartum estrus (PPE), a period of heightened sexual receptivity. Males initially chose and spent significantly more time investigating the chamber that originally housed the pregnant female (now a PPE female) than the chamber that originally housed the REF female. Male voles also explored an apparatus containing a chamber with a PPE female and one chamber containing a REF female. Twenty-four hour later, males were placed into an empty and clean apparatus. The males did not display an initial choice and they spent similar amounts of time investigating the chamber that originally housed the PPE female (now a lactating female) and the chamber that originally housed the REF female. The results of these and additional experiments suggest that male voles may have the capacity to recall the "what", "where", and "when" of a single past event, which may allow males to remember the location of females who would currently be in heightened states of sexual receptivity.