Dietary protein content affects the response of meadow voles, Microtus pennsylvanicus, to over-marks

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.

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.

Female meadow voles, Microtus pennsylvanicus, do not alter their over-marking in response to female conspecifics that were food deprived

Many terrestrial mammals will deposit scent marks and over-marks, the latter being the overlapping scent marks of two conspecifics. Studies have shown that male rodents that are exposed to the overlapping scent marks of two female conspecifics later spend more time investigating the mark of the top-scent female than that of the bottom-scent female. This suggests over-marking is a form of competition and that the top-scent female is more likely than the bottom-scent female to be chosen as a potential mate. Thus, females should over-mark the scents of neighboring females at a rate that will maximize their chances of attracting males. However, meadow voles live in areas that may contain patchy food availability, and residents may differ in their nutritional status. Females in a better nutritional state may be more likely than those in poorer nutritional states to indicate their presence in an area, signal possession of a territory, and to attract mates. Thus, we tested the prediction that female meadow voles, Microtus pennsylvanicus, that were not food deprived would deposit more over-marks than female voles that were food deprived for six hours. Food-deprived female voles and female voles that had continuous access to food deposited a similar number of scent marks and used a similar proportion of those marks as over-marks when they encountered the scent marks of female conspecifics. These findings suggest that the nutritional status of female voles does not affect their ability to signal their presence in an area marked by a female conspecific.

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.