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.

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.

Do olfactory behaviour and marking responses of Konik polski stallions to faeces from conspecifics of either sex differ?

The aim of the study was to assess whether adult stallions differentiate their olfactory and marking behaviour towards the excreta of their potential male rivals and mares. Four Konik polski stallions were individually exposed simultaneously to their own and each others' faeces as well as faeces of mares in oestrus vs. dioestrus. Five series of 30min observation sessions were conducted in a round pen each on two consecutive days from March to July, totaling in 5h observation per stallion. Stallions sniffed and displayed flehmen reaction towards mares' faeces significantly longer (P<0.01) than towards stallions' faeces. No significant differences were found in marking by defecations upon stallions' vs. mares' faeces. The stallions urinated exclusively on mares' faeces. Sniffing, flehmen, defecations and urinations performed towards faeces of mares in oestrus vs. dioestrus did not differ significantly. The results showed that stallions differentiate their olfactory behaviour towards excreta of conspecifics of different sex but perhaps not towards faeces of females in different reproductive status. This for the first time establishes that stallions exhibit different marking behaviour upon stallions' vs. mares' faeces. It is hypothesized that marking of other stallions' faeces by defecation may advertise presence of the stallion, whereas marking of mares' faeces by urination may serve to mask the presence of a mare to prevent potential rivals from locating the mare in an area where mares' faeces are found.

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.

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.