Meadow voles differentiate between scents of different sources

Scent marks are an important means of transmitting information between rodents, and they can be produced from several body sources. Previous studies have shown that scents from multiple sources can convey the same information; female meadow voles, for example, have three scent sources that communicate sex. However, possessing three separate sources that convey the same information is likely costly due to the metabolic energy required to produce these signals and the increased chance that eavesdropping individuals may intercept information present in these signals. In this study, we investigated if these scent sources could communicate other information, in addition to scent donor sex, by determining if male meadow voles could distinguish scent marks taken from different sources of a single female scent donor. This was accomplished with a habituation-test method, that allowed us to compare how male meadow voles differently investigate scent from a familiar and novel source of a female scent donor. Male meadow voles could distinguish between faeces and urine scent marks of a female, but could only distinguish mouth from urine and faeces scent marks when first familiarized with mouth scent marks. Our findings suggest that mouth, urine, and faeces scent marks of female meadow voles produce both redundant and distinct information. The overlap in information between scent marks produced from separate sources may be needed to provide social context, which allows receiving individuals to accurately weigh the tradeoffs associated with responding to an olfactory cue. While this overlap in information remains costly, this cost may be minimized by the different fade-out times of scent marks from distinct body sources, which may limit the amount of time information in a scent mark is available to a time period where this information is socially relevant.

Scent marks of rodents can provide information to conspecifics

For a scent mark to be informative it must provide a reliable, honest signal that allows individuals that detect it to predict fitness tradeoffs if they choose or not choose to respond to it. I argue that scent marks provide a great deal of information about the sender to receivers. The manner in which an animal uses this information to make decisions will depend on the context and manner in which it encounters these scent marks. Receivers can use the information found in the scent marks and odors to locate the donor, learn its identity, determine the donor's phenotype or genotype, and assess whether the scent marks were encountered earlier by conspecifics. For receivers to make potentially informed decisions, when they encounter the scent marks of conspecifics with whom they have had different experiences across a variety of contexts higher level cognitive processing involving procedural memory, episodic memory, autobiographical memory and making judgements of numerical discrimination would be required. Senders should have some insight into the receivers to increase the likelihood that the targets respond appropriately to the scent mark by reducing uncertainty. The sender's state or the current state of the environment and the context will affect when and where the scent marks were deposited. Decisions to deposit scent marks and respond to them must represent a tradeoff in the benefits and costs to the sender and receivers in terms of their fitness and survival. The actual tradeoff should be context dependent and reflect the experience, physiology, and life history constraints affecting the receiver. Calculating these tradeoffs likely involves some cognitive processing and requires some sort of information transfer between the sender and the receiver.

Odor Communication and Mate Choice in Rodents

This paper details how chemical communication is affected by ecological challenges such as finding mates. I list several conditions that affect the decision to attract mates, the decision to respond to the signals of potential mates and how the response depends on context. These mate-choice decisions and their outcomes will depend on the life history constraints placed on individuals such as their fecundity, sex, lifespan, opportunities to mate in the future and age at senescence. Consequently, the sender's decision to scent mark or self-groom as well as the receiver's choice of response represents a tradeoff between the current costs of the participant's own survival and future reproduction against that of reproducing now. The decision to scent nark and the response to the scent mark of opposite-sex conspecifics should maximize the fitness of the participants in that context.

Species differences in urine scent-marking and counter-marking in Peromyscus

Species comparisons indicate that scent-marking may differ as a function of mating system and co-housing with the opposite sex ("pairing"). We previously demonstrated that pairing may decrease male solicitation to unfamiliar females in the monogamous Peromyscus californicus but not in the non-monogamous P. leucopus. Whether urine scent-marking of females changes following pairing and whether scent-marking of paired males varies in response to scent-marks of their cagemate versus those of an unfamiliar female has not been examined. Therefore, we tested P. californicus and P. leucopus for within and between species differences in urine scent-marking of: 1) paired and non-paired females in an unscented arena, and 2) paired males in response to their female cagemate's or an unfamiliar female's scent-marks (counter-marking). Consistent with previous findings, P. californicus of both sexes deposited more urine scent-marks and covered greater surface area than P. leucopus. In both species, female scent-marking did not differ according to pairing status and male counter-marking did not differ in response to the scent-marks of their female cagemate versus an unfamiliar female. More females of both species and more P. leucopus, but not P. californicus, males scent-marked more around the perimeter than centrally. Potential explanations for these findings are discussed.

The number of male conspecifics affects the odour preferences and the copulatory behaviour of male meadow voles, Microtus pennsylvanicus

We hypothesized that male meadow voles adjust their odour preferences and sexual behaviours in response to the presence and number of male conspecifics they perceive to have visited a sexually receptive female conspecific. Male voles only preferred the odour of the female previously associated with 3 or 5 males to that of the unfamiliar female. Male voles also had a shorter latency to mate and a shorter mating duration when they were paired with the female that was previously associated with the bedding of 3 or 5 males compared to males paired with an unfamiliar female. Mating and reproductive success, however, were similar for males paired with either female. Thus, male voles use public information provided by scent marks of male conspecifics and adjust their responses in favour of a female that they perceive to been visited by several males, although she may represent a high risk of sperm competition.

A comparison of scent marking between a monogamous and promiscuous species of peromyscus: pair bonded males do not advertise to novel females

Scent marking can provide behavioral and physiological information including territory ownership and mate advertisement. It is unknown how mating status and pair cohabitation influence marking by males from different social systems. We compared the highly territorial and monogamous California mouse (Peromyscus californicus) to the less territorial and promiscuous white-footed mouse (P. leucopus). Single and mated males of both species were assigned to one of the following arenas lined with filter paper: control (unscented arena), male scented (previously scent-marked by a male conspecific), or females present (containing females in small cages). As expected, the territorial P. californicus scent marked and overmarked an unfamiliar male conspecific's scent marks more frequently than P. leucopus. Species differences in responses to novel females were also found based on mating status. The presence of unfamiliar females failed to induce changes in scent marking in pair bonded P. californicus even though virgin males increased marking behavior. Pair bonding appears to reduce male advertisement for novel females. This is in contrast to P. leucopus males that continue to advertise regardless of mating status. Our data suggest that communication through scent-marking can diverge significantly between species based on mating system and that there are physiological mechanisms that can inhibit responsiveness of males to female cues.

Urine marking in male common voles: does behavioural activity matter?

Rodent urine provides animals with a large amount of information, from the identity of the animal through its physical condition to social status. Many studies therefore focus on rodent urine-marking behaviour and use marking frequency as an indicator of social status or competitive ability. However, marking, like many other aspects of rodent behaviour, may be affected by individual behavioural activity, a factor that has not been examined so far. We therefore studied a relationship between male urine-marking in reaction to another male's marks (standard opponent) and individual personality profile, characterised by behavioural activity in an open field test (OFT). The marking appeared to be consistent and specific for particular individuals as there was a significant positive relationship between individual markings in two different phases of the experiment. The linkage between behavioural activity in the OFT and urine-marking frequency was non-linear (quadratic), which suggested that males with intermediate activity marked more intensively than males from the extremes of the behavioural spectra. The relationship between the opponent's and the tested males' markings was positive, however, we found no statistically significant evidence that the voles would attempt to overmark the opponent. Marking thus seems to have more of a self-advertising than a competitive function in the common vole. Further, as high marking activity is under strong intra- or intersexual selection, the result might suggest a stabilising selection of the personality trait described as behavioural activity in our study.

Olfactory experience affects the response of meadow voles to the opposite-sex scent donor of mixed-sex over-marks

Scent marking and over-marking are important forms of communication between the sexes for many terrestrial mammals. Over the course of three experiments, we determined whether the amount of time individuals investigate the scent marks of opposite-sex conspecifics is affected by four days of olfactory experience with those conspecifics. In experiment 1, female meadow voles, Microtus pennsylvanicus, spent more time investigating the scent mark of the novel male conspecific than that of the familiar male donor, whereas male voles spent similar amounts of time investigating the scent mark of the familiar female and a novel female conspecific. In experiment 2, voles were exposed to a mixed-sex over-mark in which subjects did not have four days of olfactory experience with either the top-scent donor or the bottom-scent donor. During the test phase, male and female voles spent more time investigating the scent mark of the opposite-sex conspecific that provided the top-scent mark than that of a novel, opposite-sex conspecific. Male and female voles spent similar amounts of time investigating the scent mark of the bottom-scent donor and that of a novel opposite-sex conspecific. In experiment 3, voles were exposed to a mixed-sex over-mark that contained the scent mark of an opposite-sex conspecific with which they had four days of olfactory experience. During the test phase, male voles spent more time investigating the mark of the familiar, top-scent female than the scent mark of a novel female donor but spent similar amounts of time investigating the mark of the familiar, bottom-scent female and that of a novel female donor. In contrast, female voles spent more time investigating the mark of a novel male donor than that of either the familiar, top-scent male or that of the familiar, bottom-scent male. The sex differences in the responses of voles to scent marks and mixed-sex over-marks are discussed in relation to the natural history and non-monogamous mating system of meadow voles.

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 mo-old and 10-12 mo-old over-marked a higher proportion of the marks of females than did 2-3 mo-old male voles. Female voles that were 2-3 mo-old, 5-7 mo-old, 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.

Meadow voles, Microtus pennsylvanicus, can distinguish more over-marks from fewer over-marks

Is it possible that voles have a sense of number? To address this question, we determined whether voles discriminate between two different scent-marking individuals and identify the individual whose scent marks was on top more often than the other individual. We tested whether voles show a preference for the individual whose scent marks was on top most often. If so, the simplest explanation was that voles can make a relative size judgement-such as distinguishing an area containing more of one individual's over-marks as compared to less of another individual's over-marks. We found that voles respond preferentially to the donor that provided a greater number of over-marks as compared to the donor that provided a lesser number of over-marks. Thus, we concluded that voles might display the capacity for relative numerousness. Interestingly, female voles were better able than male voles to distinguish between small differences in the relative number of over-marks by the two scent donors.

Female prairie voles do not choose males based on their frequency of scent marking

We conducted an experiment to test three alternative hypotheses for the function of frequency of scent marking in male prairie voles, MICROTUS OCHROGASTER: (1) sexual attraction (to advertise male quality for mating); (2) reproductive competition; and (3) self-advertisement or individual identity. In laboratory experiments, males deposited scent on all areas of a bare substrate, and more in an area next to a stimulus animal than other areas, regardless of the stimulus animal's sex. Females did not choose mates based on their frequency of scent marking and scent marking did not antagonize or stimulate aggression between males. The frequency of scent marking by males supports the individual identity hypothesis, and is less consistent with the sexual attraction or reproductive competition hypotheses. Mate choice is likely based on a complex suite of characters, but at least in prairie voles, the frequency of scent marking by males does not appear to be one of them.

Scent-marking behaviour by male prairie voles, Microtus ochrogaster, in response to the scent of opposite- and same-sex conspecifics

We conducted an experiment using the prairie vole (Microtus ochrogaster) to test predictions associated with the proposed functions of scent marking as a sexual attractant, in reproductive competition, and as a self-advertisement. We allowed an oestrous female, an anoestrous female, and an adult male to scent mark three portions of a clean substrate and then exposed a second male to this substrate for secondary marking. We did not support a sexual attraction hypothesis in that males did not place more scent marks in response to oestrous than anoestrous females. Similarly, we did not support a reproductive competition hypothesis in that males did not place more scent marks in response to marks of males than to those of females or bare substrate. Males did not overmark the scent of males or females and thus we did not support a scent-masking or scent-blending hypothesis. In that males deposited scent similarly in response to males, females, and on bare substrate, our results suggest that the frequency and placement of scent marks by males function primarily to advertise individual identity in an area.