This study investigated how voles (Microtus pennsylvanicus) determine which scent is the top scen... more This study investigated how voles (Microtus pennsylvanicus) determine which scent is the top scent of an over-mark and how this information influences memory for the top scent. This series of experiments shows that a region of overlap is necessary for both a preference and a differential memory for 1 of the 2 scents, and a difference in the area covered by one of the two overlapping scents is not sufficient by itself to cause these effects. These results suggest that voles have specialized perceptual and evaluative mechanisms for the analysis of scent over-marks. Thus, voles may attach a greater importance to the odor of the top-scent donor than that of the bottom-scent donor of an over-mark. Animals often have to deal with a complex array of social signals to differentiate between conspecifics. For example, meadow voles, Microtus pennsylvanicus, and golden hamsters, Mesocricetus auratus, both have at least five different sources of individually or sexually distinctive odors (Ferkin
Self-grooming may provide a means for broadcasting scent to conspecifics. Four experiments invest... more Self-grooming may provide a means for broadcasting scent to conspecifics. Four experiments investigated this hypothesis in meadow voles. In the first experiment, male voles but not female voles groomed more in response to scent from an opposite-sex conspecific than a same-sex conspecific. In the second experiment, male voles groomed more in response to ovariectomized females receiving replacement oestradiol than to ovariectomized females receiving no oestradiol replacement. Selfgrooming by female voles did not vary with the reproductive state of male scent donors. In the third experiment, males showed no difference in grooming in response to odours of a short-photoperiod male versus a short-photoperiod female, again indicating that the grooming response of males depends on the reproductive state of scent donors. These three experiments all suggested a communicative function for scent-elicited grooming. In the final experiment, the responses of females to males that had engaged in self-grooming was examined. Females spent more time investigating scent collected from the anogenital area of a male that had recently self-groomed at a high rate than they did from a male that had groomed at a low rate. Thus self-grooming by males increases the attractiveness of at least one of their scents to females.
We examined the hypothesis that differences in androgen concentrations may cause differences in t... more We examined the hypothesis that differences in androgen concentrations may cause differences in the attractiveness of male odors to female meadow voles, Microtus pennsylvanicus. Males that were to be used as odor donors were castrated and implanted with Silastic capsules filled with no hormone or one of four different amounts of testosterone. Four different odors from males were assessed for each comparison; the odors were from the anogenital area, feces, urine, and posterolateral region. Treatment of scent donor males with the lowest dosage of testosterone was not sufficient to increase the attractiveness of their odors above that of males receiving no hormone. The three higher dosages increased attractiveness in a dose-dependent manner. The shape of the dose-response curve differed across scents: two scents reached maximum attractiveness in the middle of the dose range and remained there at higher doses, whereas the other two scents continued to increase in attractiveness as testosterone titers increased. The results suggest that scent glands produce graded signals that reflect circulating testosterone titers.
Scent over-marking is a common form of competitive advertisement among many species of mammals. R... more Scent over-marking is a common form of competitive advertisement among many species of mammals. Recent observations in golden hamsters, Mesocricetus auratus, have suggested that individuals have specialized mechanisms for interpretation of and response to such over-marks. In this study, we examined whether meadow voles, Microtus pennsylvanicus, have similar abilities. Female voles were first exposed to anogenital scent marks of two males and were then tested in a Y-maze for their preferences for whole-body odours of these two males. Experiments were run using a variety of configurations of scent marks during the exposure phase, but all experiments yielded consistent results. If the scent marks of the two males overlapped, females later preferred the whole-body odours of the male whose scent was on top; if the two scent marks did not overlap, females showed no preference. Females also preferred odours of familiar males over novel males, and preferred both top-scent and bottom-scent males over novel males. The results suggest that female voles can tell which individual's scent is on top in an over-mark and that they prefer this top-scent male, even though they know that both males' scents were present during the exposure phase. We suggest that these odour preferences reflect mate preferences and discuss possible reasons why females might prefer top-scent males.
The diet consumed by animals can influence their physical condition and potential for reproductiv... more The diet consumed by animals can influence their physical condition and potential for reproductive success. Do differences in diet quality affect the attractiveness of secondary sexual characteristics to the opposite sex? This study addressed this question by examining the attractiveness of odours produced by meadow voles, Microtus pennsylvanicus, that were fed diets that differed in protein content. Meadow voles that served as scent donors were maintained on one of three diets, consisting of 9, 15 or 25% protein, all of which are sufficient to maintain voles in reproductive condition. These diets influenced the attractiveness of all three odours tested (anogenital area, urine and faeces). Both male and female subjects preferred odours from donors on high-protein diets: subjects preferred odours of opposite-sex conspecifics fed a 15 or 25% protein diet over odours from donors fed a 9% protein diet. Females preferred two odours of males on a 25% protein diet over the same odours of males on a 15% protein diet. These results suggest a mechanism for mate choice via odour preferences based on the protein content of the food consumed by potential partners. Because animals compete for access to higher-quality diets in nature, the choice of a mate with a high-quality diet may also be a means of choosing a higher-'quality' individual.
Females in numerous taxa engage in mating with more than one male within a breeding season, usual... more Females in numerous taxa engage in mating with more than one male within a breeding season, usually to gain direct or indirect benefits from their male partners. Although effort has been directed towards the benefits females derive from multiple mating, we have less information as to decisions females make when choosing to mate with more than one male and if her decision is contingent upon previous mating experience with a male. In some instances, females must decide whether or not to mate with a previous mate or a novel male, the outcome of which would have ramifications on the acquisition of direct and indirect benefits. In this study, we tested whether female leopard geckos, Eublepharis macularius, would forgo mating with a previous male partner in favor of a novel male. We found no difference in a female's willingness to copulate with a previous mate versus a novel male. However, we found that smaller females initiated copulation termination with a previous mate whereas larger females allowed males to terminate copulations. This pattern was not exhibited when smaller females were paired with novel partners. Thus, smaller females appear to discriminate between previous mates and novel males, favoring novel males as mates.
The function of an odour may be reflected in its fade-out time in the environment. In this study,... more The function of an odour may be reflected in its fade-out time in the environment. In this study, we investigated fade-out times of two specific odours, the anogenital area scent and that of the posterolateral region. These two odours support opposite-sex preferences in male and female meadow voles, Microtuspennsylvanicus, but convey nonidentical information to conspecifics during the breeding season. The first experiment tested whether meadow voles respond preferentially to scents that were aged for 15 min (fresh) to 30 d. Males preferred female anogenital area scent to male anogenital area scent if both scents were s 10 d old. By comparison, females preferred male anogenital area scent to female anogenital area scent if the scents were s 2 5 d old. However, male and female voles preferred the posterolateral scent of males to that of females if the scents were 6 1 d old. Thus, fade-out times for these two scents differ for males and females, suggesting different functions. In the second experiment, male and female voles preferred fresh anogenital area scent and fresh posterolateral region scent compared with those same scents that were older. This result suggests that older scents may have lost information over time about the sex of the donor. Overall, data from both experiments indicate that voles may use specific scents for communication in different social contexts.
Much is known about the abilities of various taxa concerning discrimination of species, sex, fami... more Much is known about the abilities of various taxa concerning discrimination of species, sex, familiarity-based discrimination and individual discrimination. However, literature pertaining to the precision of discrimination within lizard taxa assumes that discrimination between familiar and unfamiliar individuals can be extrapolated to include individual discrimination between two familiar individuals. The present study had two aims. First, we determined that male leopard geckos (Eublepharis macularius) can concurrently become familiar with two different females and discriminate those females from a novel female. Second, we investigated the ability of male leopard geckos to distinguish between two familiar females using a habituation-dishabituation paradigm. Males habituated to the presence of the first female, exhibited by decreased typical courtship behaviours directed towards that female. Male courtship behaviours, however, were reinstated upon introduction of the second familiar female. These results indicate that males possess the ability to discriminate between two familiar females and adjust their courtship efforts appropriately.
Relatively little is known about the mechanisms of communication during the non-breeding season i... more Relatively little is known about the mechanisms of communication during the non-breeding season in species that are seasonal breeders. Previous work with meadow voles, Minotus pc,nnsyluanrcus, housed under long photoperiods, has shown that they prefer the odors of opposite-sex conspecifics. In this paper, we investigated the effects of short photoperiod on preferences for sex-specific odors and the production of such odors. Short-photoperiod females preferred anogenital and fecal scents of other short-photoperiod females over those of males, but did not show sexual preferences for three other scents. Shon-photoperiod males did not exhibit sexual preferences for any of the odors. Furthermore, scents from short-photoperiod voles did not elicit sex-specific preferences in longphotoperiod voles, and scents from long-photoperiod voles did not elicit preferences from shortphotoperiod voles. These and previous results indicate that both the odors and responses to odors change seasonally and that long-photoperiod voles respond selectively to scents from long-photoperiod voles and short-photoperiod voles respond selectively to scents from short-photoperiod voles. Taken together, these results suggest the co-evolution of seasonal changes in scents and in perceptual or other response mechanisms.
Although many sources of sexually specific chemical signals have been identified, few attempts ha... more Although many sources of sexually specific chemical signals have been identified, few attempts have been made to identify all the sources of sex-specific information in any species or to determine whether the various cues that provide this information have the same communicative functions. Sources of sex-specific odour information were identified using a preference task in meadow voles. An examination was made of the amount of time that long-photoperiod male and female voles investigated different scents from opposite-and same-sex conspecifics. The data indicate that there was a highly localized pattern of sexual information on the bodies of meadow voles. Three scents were preferentially investigated by opposite-sex subjects: both male and female voles investigated scents from urine, faeces and the anogenital area of the opposite sex more than those of the same sex. Two additional scents resulted in sexual preferences, but not in a symmetrical fashion. Males investigated scents from the mouth of females over the mouth scent of males, but females showed no preference. Both males and females investigated scent from the posterolateral region of males more than those of females. Mouth and posterolateral area may provide different information and/or have different functions compared to the sex-specific scents from urine, faeces and the anogenital area.
Scent marks are an important means of transmitting information between rodents, and they can be p... more 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.
Sexually reproducing organisms must process and respond to internal and external stimuli to succe... more Sexually reproducing organisms must process and respond to internal and external stimuli to successfully synchronize physiological and behavioural processes involved in reproduction. One such cue is an individual's social environment. Interactions with conspecifics affect a female's reproductive activity by inducing, suppressing, and/or accelerating reproductive processes. For example, many studies support the theory that the presence of a same-sex conspecific may suppress an animal's reproductive physiology, whereas an opposite-sex conspecific may stimulate an animal's reproductive physiology. The present study determined whether exposure to a conspecific male or female affects the onset of follicular development in sexually-experienced female leopard geckos (Eublepharis macularius). The data show that follicular growth was not affected by whether female geckos were housed next to a male conspecific, a female conspecific, or isolated from conspecifics. In addition, the number of days until the initiation of follicular development of female geckos was not affected by whether the females were housed in the presence of a conspecific or in isolation. The results are discussed within the theoretical framework of the effects of social cues on the reproductive physiology of females and the limited empirical data about such effects in squamate lizards.
Charnov and Finerty (1980) suggested that vole population density can be regulated by aggressive ... more Charnov and Finerty (1980) suggested that vole population density can be regulated by aggressive interactions that change with the relatedness of neighbors. As density increases, the relatedness of neighbors will decrease because of dispersal. Presumably, unrelated individuals will behave less amicably (more aggressively) toward one another. As density increases, dispersal will cause the relatedness of neighbors to decrease and therefore increase the levels of aggression in the population. Increased aggressive levels are postulated to cause the "crash" of numbers seen in vole population fluctuations. Inherent in this mechanism is the ability for voles to distinguish, and respond differentially between relatives and nonrelatives. As we will show, for this hypothesis to be correct, it must take into consideration cryptic relatedness, relatedness in which the members of the dyad cannot, in fact, determine that they are related. Familiarity, based on association prior to weaning, is the proximate cue that microtine rodents use to assess kinship (Blaustein et al. 1987a,b, Ferkin 1990). Familiar nestmates are recognized as close relatives, whereas unfamiliar nestmates are not identified as relatives (Schadler 1983, Gavish et al. 1984, Boyd and Blaustein 1985, Ferkin 1989, Ferkin and Rutka 1990). To date, there is no evidence to show that microtine rodents employ phenotype matching, recognition alleles, or the major histocompatibility complex to assess kinship (Yamazaki et al. 1980). Genetic relatedness, per se, plays no apparent role in kin recognition for microtine rodents (Bekoff 1981, Blaustein et al. 1987a,b, Ferkin 1990). Thus, the ability to assess genetic relatedness of unfamiliar relatives appears unlikely for microtine rodents. The persistence of kin recognition is dependent on repeated social contacts with close kin (Ferkin 1988, 1990). Although kin recognition and kin-directed behaviors, such as reduced agonism, sharing of nest sites, increased nepotism, and the avoidance of inbreeding, can operate without kin recognition if related individuals interact frequently (Hamilton 1964), repeated contacts with close relatives may not be a feature common to most microtine social organizations (Wolff 1985, Cockburn 1988). The opportunity to identify and be recognized as a close relative will be affected markedly by the type of mating system, population turnover rate, dispersal tendency, nesting patterns, and parental care displayed in a particular species. Therefore, the opportunity to identify and be recognized as a close relative will be affected markedly between microtine species. Microtine rodents that do not have protracted interactions with close relatives may not be able to recognize unfamiliar close relatives.
Many non-human animals are capable of discriminating a group or entity containing more objects fr... more Many non-human animals are capable of discriminating a group or entity containing more objects from one containing less of the same objects. The capacity for making judgments of numerousness may also allow individuals to discriminate between potential mates. Female meadow voles (Microtus pennsylvanicus) may use judgments of relative numerousness to distinguish between potential suitors by selecting males that signal their interest by depositing more scent marks relative to other males. We used a familiarization-discrimination paradigm in the absence of training to test the hypothesis that female voles will discriminate between the different numerosities of scent marks of two male conspecifics that are similar in features of their phenotype and quality. During the exposure phase, we presented female voles with different ratios of feces scent marks from two males. During the test phase, we presented females with a single, fresh fecal scent mark from each of the two male donors, whose marks they had previously encountered during the exposure phase. In both phases, females spent more time investigating the scent mark(s) of the male that deposited more scent marks than that of the male that deposited fewer scent marks provided the difference in the ratio of scent marks provided by the male donors in the exposure phase was greater than or equal to 2. Our results are consistent with studies on a variety of taxa suggesting that numerosity discriminations are evolutionarily ancient and spontaneously available to non-human animals and humans.
Little is known about the occurrence of individual variation in sexual behavior and how maternal ... more Little is known about the occurrence of individual variation in sexual behavior and how maternal nutrition can affect this variation. We tested the hypothesis that male offspring of female meadow voles, Microtus pennsylvanicus, that were 30% food restricted (FR) during days 1-7 of lactation (FR 1-7), days 8-14 of lactation (FR 8-14), or late days 15-21 of lactation (FR 15-21) lactation show persistent, negative effects on their sexual behavior as adults relative to male offspring of females that were not food restricted. We measured three components of sexual behavior, attractivity, proceptivity and receptivity, beginning when the males were 98 days of age. Food restriction during middle lactation (FR 8-14) but not during early (FR 1-7) and late lactation (FR 15-21) was sufficient to induce adult male voles to produce anogenital marks that were not as attractive as those produced by control males. Food restriction during lactation did not affect the proceptive behavior of male voles but did affect their receptivity. Only 4 of 12 FR 8-14 male voles mated compared to 9 of 12 FR 1-7 males, 8 of 12 FR 15-21 males, and 8 of 11 control males. However, no differences existed in their copulatory behavior among the males that did mate. The body weight of FR 1-7 and FR 8-14 males was lower than that of FR 15-21 and control males when they were between 22 days of age (weaning) and 48 days of age (puberty) but was similar when the males were 98 days of age. Food intake was similar for the FR and control males between day 22 and day 98. It remains unclear, however, if this type of maternal effect represents strategic programming of offspring behavior in response to the environment experienced by mothers or is a product of developmental processes of food restriction prior to weaning (Forstmeier et al. 2004).
Many terrestrial mammals scent mark in areas containing the scent marks of conspecifics, and thus... more Many terrestrial mammals scent mark in areas containing the scent marks of conspecifics, and thus, may deposit their own scent marks on top of those that were deposited previously by conspecifics. This phenomenon, known as over-marking appears to play a role in same-sex competition or mate attraction. The present study determines whether meadow and prairie voles avoid over-marking the scent
Social cues must be detectable by receivers or bystanders before they can respond to the informat... more Social cues must be detectable by receivers or bystanders before they can respond to the information contained in the cue. Information about conspecifics and heterospecifics can be extracted from social cues. At that point, the information in the cue becomes a fact and the cue becomes a signal. Chemical signals, such as scent marks, provide accurate information that can be used by conspecifics in sexual and social contexts. Scent marks of many conspecifics distributed in an area may be akin to a chemical bulletin board that provides information about the identity of senders and how recently they were in that area. These scent marks deposited by senders can provide both private and public information to receivers. The manner in which receivers use this information to make decisions will depend on the context and manner in which it encounters these scent marks. Thus, a learned rule of thumb that will allow the animal to respond in a predictable way to a scent mark and when to scent mark would not suffice. The sender and the receiver must identify the phenotype and genotype of their counterparts, recollect interactions with them, be aware of their own condition and the context of the communication. Higher level cognitive processing would likely be required for receivers and senders to make potentially informed decisions that reflect tradeoffs in their survival and fitness.
Models of age-related effects on behavior predict that among short-lived species younger adults a... more 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.
For a scent mark to be informative it must provide a reliable, honest signal that allows individu... more 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.
This study investigated how voles (Microtus pennsylvanicus) determine which scent is the top scen... more This study investigated how voles (Microtus pennsylvanicus) determine which scent is the top scent of an over-mark and how this information influences memory for the top scent. This series of experiments shows that a region of overlap is necessary for both a preference and a differential memory for 1 of the 2 scents, and a difference in the area covered by one of the two overlapping scents is not sufficient by itself to cause these effects. These results suggest that voles have specialized perceptual and evaluative mechanisms for the analysis of scent over-marks. Thus, voles may attach a greater importance to the odor of the top-scent donor than that of the bottom-scent donor of an over-mark. Animals often have to deal with a complex array of social signals to differentiate between conspecifics. For example, meadow voles, Microtus pennsylvanicus, and golden hamsters, Mesocricetus auratus, both have at least five different sources of individually or sexually distinctive odors (Ferkin
Self-grooming may provide a means for broadcasting scent to conspecifics. Four experiments invest... more Self-grooming may provide a means for broadcasting scent to conspecifics. Four experiments investigated this hypothesis in meadow voles. In the first experiment, male voles but not female voles groomed more in response to scent from an opposite-sex conspecific than a same-sex conspecific. In the second experiment, male voles groomed more in response to ovariectomized females receiving replacement oestradiol than to ovariectomized females receiving no oestradiol replacement. Selfgrooming by female voles did not vary with the reproductive state of male scent donors. In the third experiment, males showed no difference in grooming in response to odours of a short-photoperiod male versus a short-photoperiod female, again indicating that the grooming response of males depends on the reproductive state of scent donors. These three experiments all suggested a communicative function for scent-elicited grooming. In the final experiment, the responses of females to males that had engaged in self-grooming was examined. Females spent more time investigating scent collected from the anogenital area of a male that had recently self-groomed at a high rate than they did from a male that had groomed at a low rate. Thus self-grooming by males increases the attractiveness of at least one of their scents to females.
We examined the hypothesis that differences in androgen concentrations may cause differences in t... more We examined the hypothesis that differences in androgen concentrations may cause differences in the attractiveness of male odors to female meadow voles, Microtus pennsylvanicus. Males that were to be used as odor donors were castrated and implanted with Silastic capsules filled with no hormone or one of four different amounts of testosterone. Four different odors from males were assessed for each comparison; the odors were from the anogenital area, feces, urine, and posterolateral region. Treatment of scent donor males with the lowest dosage of testosterone was not sufficient to increase the attractiveness of their odors above that of males receiving no hormone. The three higher dosages increased attractiveness in a dose-dependent manner. The shape of the dose-response curve differed across scents: two scents reached maximum attractiveness in the middle of the dose range and remained there at higher doses, whereas the other two scents continued to increase in attractiveness as testosterone titers increased. The results suggest that scent glands produce graded signals that reflect circulating testosterone titers.
Scent over-marking is a common form of competitive advertisement among many species of mammals. R... more Scent over-marking is a common form of competitive advertisement among many species of mammals. Recent observations in golden hamsters, Mesocricetus auratus, have suggested that individuals have specialized mechanisms for interpretation of and response to such over-marks. In this study, we examined whether meadow voles, Microtus pennsylvanicus, have similar abilities. Female voles were first exposed to anogenital scent marks of two males and were then tested in a Y-maze for their preferences for whole-body odours of these two males. Experiments were run using a variety of configurations of scent marks during the exposure phase, but all experiments yielded consistent results. If the scent marks of the two males overlapped, females later preferred the whole-body odours of the male whose scent was on top; if the two scent marks did not overlap, females showed no preference. Females also preferred odours of familiar males over novel males, and preferred both top-scent and bottom-scent males over novel males. The results suggest that female voles can tell which individual's scent is on top in an over-mark and that they prefer this top-scent male, even though they know that both males' scents were present during the exposure phase. We suggest that these odour preferences reflect mate preferences and discuss possible reasons why females might prefer top-scent males.
The diet consumed by animals can influence their physical condition and potential for reproductiv... more The diet consumed by animals can influence their physical condition and potential for reproductive success. Do differences in diet quality affect the attractiveness of secondary sexual characteristics to the opposite sex? This study addressed this question by examining the attractiveness of odours produced by meadow voles, Microtus pennsylvanicus, that were fed diets that differed in protein content. Meadow voles that served as scent donors were maintained on one of three diets, consisting of 9, 15 or 25% protein, all of which are sufficient to maintain voles in reproductive condition. These diets influenced the attractiveness of all three odours tested (anogenital area, urine and faeces). Both male and female subjects preferred odours from donors on high-protein diets: subjects preferred odours of opposite-sex conspecifics fed a 15 or 25% protein diet over odours from donors fed a 9% protein diet. Females preferred two odours of males on a 25% protein diet over the same odours of males on a 15% protein diet. These results suggest a mechanism for mate choice via odour preferences based on the protein content of the food consumed by potential partners. Because animals compete for access to higher-quality diets in nature, the choice of a mate with a high-quality diet may also be a means of choosing a higher-'quality' individual.
Females in numerous taxa engage in mating with more than one male within a breeding season, usual... more Females in numerous taxa engage in mating with more than one male within a breeding season, usually to gain direct or indirect benefits from their male partners. Although effort has been directed towards the benefits females derive from multiple mating, we have less information as to decisions females make when choosing to mate with more than one male and if her decision is contingent upon previous mating experience with a male. In some instances, females must decide whether or not to mate with a previous mate or a novel male, the outcome of which would have ramifications on the acquisition of direct and indirect benefits. In this study, we tested whether female leopard geckos, Eublepharis macularius, would forgo mating with a previous male partner in favor of a novel male. We found no difference in a female's willingness to copulate with a previous mate versus a novel male. However, we found that smaller females initiated copulation termination with a previous mate whereas larger females allowed males to terminate copulations. This pattern was not exhibited when smaller females were paired with novel partners. Thus, smaller females appear to discriminate between previous mates and novel males, favoring novel males as mates.
The function of an odour may be reflected in its fade-out time in the environment. In this study,... more The function of an odour may be reflected in its fade-out time in the environment. In this study, we investigated fade-out times of two specific odours, the anogenital area scent and that of the posterolateral region. These two odours support opposite-sex preferences in male and female meadow voles, Microtuspennsylvanicus, but convey nonidentical information to conspecifics during the breeding season. The first experiment tested whether meadow voles respond preferentially to scents that were aged for 15 min (fresh) to 30 d. Males preferred female anogenital area scent to male anogenital area scent if both scents were s 10 d old. By comparison, females preferred male anogenital area scent to female anogenital area scent if the scents were s 2 5 d old. However, male and female voles preferred the posterolateral scent of males to that of females if the scents were 6 1 d old. Thus, fade-out times for these two scents differ for males and females, suggesting different functions. In the second experiment, male and female voles preferred fresh anogenital area scent and fresh posterolateral region scent compared with those same scents that were older. This result suggests that older scents may have lost information over time about the sex of the donor. Overall, data from both experiments indicate that voles may use specific scents for communication in different social contexts.
Much is known about the abilities of various taxa concerning discrimination of species, sex, fami... more Much is known about the abilities of various taxa concerning discrimination of species, sex, familiarity-based discrimination and individual discrimination. However, literature pertaining to the precision of discrimination within lizard taxa assumes that discrimination between familiar and unfamiliar individuals can be extrapolated to include individual discrimination between two familiar individuals. The present study had two aims. First, we determined that male leopard geckos (Eublepharis macularius) can concurrently become familiar with two different females and discriminate those females from a novel female. Second, we investigated the ability of male leopard geckos to distinguish between two familiar females using a habituation-dishabituation paradigm. Males habituated to the presence of the first female, exhibited by decreased typical courtship behaviours directed towards that female. Male courtship behaviours, however, were reinstated upon introduction of the second familiar female. These results indicate that males possess the ability to discriminate between two familiar females and adjust their courtship efforts appropriately.
Relatively little is known about the mechanisms of communication during the non-breeding season i... more Relatively little is known about the mechanisms of communication during the non-breeding season in species that are seasonal breeders. Previous work with meadow voles, Minotus pc,nnsyluanrcus, housed under long photoperiods, has shown that they prefer the odors of opposite-sex conspecifics. In this paper, we investigated the effects of short photoperiod on preferences for sex-specific odors and the production of such odors. Short-photoperiod females preferred anogenital and fecal scents of other short-photoperiod females over those of males, but did not show sexual preferences for three other scents. Shon-photoperiod males did not exhibit sexual preferences for any of the odors. Furthermore, scents from short-photoperiod voles did not elicit sex-specific preferences in longphotoperiod voles, and scents from long-photoperiod voles did not elicit preferences from shortphotoperiod voles. These and previous results indicate that both the odors and responses to odors change seasonally and that long-photoperiod voles respond selectively to scents from long-photoperiod voles and short-photoperiod voles respond selectively to scents from short-photoperiod voles. Taken together, these results suggest the co-evolution of seasonal changes in scents and in perceptual or other response mechanisms.
Although many sources of sexually specific chemical signals have been identified, few attempts ha... more Although many sources of sexually specific chemical signals have been identified, few attempts have been made to identify all the sources of sex-specific information in any species or to determine whether the various cues that provide this information have the same communicative functions. Sources of sex-specific odour information were identified using a preference task in meadow voles. An examination was made of the amount of time that long-photoperiod male and female voles investigated different scents from opposite-and same-sex conspecifics. The data indicate that there was a highly localized pattern of sexual information on the bodies of meadow voles. Three scents were preferentially investigated by opposite-sex subjects: both male and female voles investigated scents from urine, faeces and the anogenital area of the opposite sex more than those of the same sex. Two additional scents resulted in sexual preferences, but not in a symmetrical fashion. Males investigated scents from the mouth of females over the mouth scent of males, but females showed no preference. Both males and females investigated scent from the posterolateral region of males more than those of females. Mouth and posterolateral area may provide different information and/or have different functions compared to the sex-specific scents from urine, faeces and the anogenital area.
Scent marks are an important means of transmitting information between rodents, and they can be p... more 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.
Sexually reproducing organisms must process and respond to internal and external stimuli to succe... more Sexually reproducing organisms must process and respond to internal and external stimuli to successfully synchronize physiological and behavioural processes involved in reproduction. One such cue is an individual's social environment. Interactions with conspecifics affect a female's reproductive activity by inducing, suppressing, and/or accelerating reproductive processes. For example, many studies support the theory that the presence of a same-sex conspecific may suppress an animal's reproductive physiology, whereas an opposite-sex conspecific may stimulate an animal's reproductive physiology. The present study determined whether exposure to a conspecific male or female affects the onset of follicular development in sexually-experienced female leopard geckos (Eublepharis macularius). The data show that follicular growth was not affected by whether female geckos were housed next to a male conspecific, a female conspecific, or isolated from conspecifics. In addition, the number of days until the initiation of follicular development of female geckos was not affected by whether the females were housed in the presence of a conspecific or in isolation. The results are discussed within the theoretical framework of the effects of social cues on the reproductive physiology of females and the limited empirical data about such effects in squamate lizards.
Charnov and Finerty (1980) suggested that vole population density can be regulated by aggressive ... more Charnov and Finerty (1980) suggested that vole population density can be regulated by aggressive interactions that change with the relatedness of neighbors. As density increases, the relatedness of neighbors will decrease because of dispersal. Presumably, unrelated individuals will behave less amicably (more aggressively) toward one another. As density increases, dispersal will cause the relatedness of neighbors to decrease and therefore increase the levels of aggression in the population. Increased aggressive levels are postulated to cause the "crash" of numbers seen in vole population fluctuations. Inherent in this mechanism is the ability for voles to distinguish, and respond differentially between relatives and nonrelatives. As we will show, for this hypothesis to be correct, it must take into consideration cryptic relatedness, relatedness in which the members of the dyad cannot, in fact, determine that they are related. Familiarity, based on association prior to weaning, is the proximate cue that microtine rodents use to assess kinship (Blaustein et al. 1987a,b, Ferkin 1990). Familiar nestmates are recognized as close relatives, whereas unfamiliar nestmates are not identified as relatives (Schadler 1983, Gavish et al. 1984, Boyd and Blaustein 1985, Ferkin 1989, Ferkin and Rutka 1990). To date, there is no evidence to show that microtine rodents employ phenotype matching, recognition alleles, or the major histocompatibility complex to assess kinship (Yamazaki et al. 1980). Genetic relatedness, per se, plays no apparent role in kin recognition for microtine rodents (Bekoff 1981, Blaustein et al. 1987a,b, Ferkin 1990). Thus, the ability to assess genetic relatedness of unfamiliar relatives appears unlikely for microtine rodents. The persistence of kin recognition is dependent on repeated social contacts with close kin (Ferkin 1988, 1990). Although kin recognition and kin-directed behaviors, such as reduced agonism, sharing of nest sites, increased nepotism, and the avoidance of inbreeding, can operate without kin recognition if related individuals interact frequently (Hamilton 1964), repeated contacts with close relatives may not be a feature common to most microtine social organizations (Wolff 1985, Cockburn 1988). The opportunity to identify and be recognized as a close relative will be affected markedly by the type of mating system, population turnover rate, dispersal tendency, nesting patterns, and parental care displayed in a particular species. Therefore, the opportunity to identify and be recognized as a close relative will be affected markedly between microtine species. Microtine rodents that do not have protracted interactions with close relatives may not be able to recognize unfamiliar close relatives.
Many non-human animals are capable of discriminating a group or entity containing more objects fr... more Many non-human animals are capable of discriminating a group or entity containing more objects from one containing less of the same objects. The capacity for making judgments of numerousness may also allow individuals to discriminate between potential mates. Female meadow voles (Microtus pennsylvanicus) may use judgments of relative numerousness to distinguish between potential suitors by selecting males that signal their interest by depositing more scent marks relative to other males. We used a familiarization-discrimination paradigm in the absence of training to test the hypothesis that female voles will discriminate between the different numerosities of scent marks of two male conspecifics that are similar in features of their phenotype and quality. During the exposure phase, we presented female voles with different ratios of feces scent marks from two males. During the test phase, we presented females with a single, fresh fecal scent mark from each of the two male donors, whose marks they had previously encountered during the exposure phase. In both phases, females spent more time investigating the scent mark(s) of the male that deposited more scent marks than that of the male that deposited fewer scent marks provided the difference in the ratio of scent marks provided by the male donors in the exposure phase was greater than or equal to 2. Our results are consistent with studies on a variety of taxa suggesting that numerosity discriminations are evolutionarily ancient and spontaneously available to non-human animals and humans.
Little is known about the occurrence of individual variation in sexual behavior and how maternal ... more Little is known about the occurrence of individual variation in sexual behavior and how maternal nutrition can affect this variation. We tested the hypothesis that male offspring of female meadow voles, Microtus pennsylvanicus, that were 30% food restricted (FR) during days 1-7 of lactation (FR 1-7), days 8-14 of lactation (FR 8-14), or late days 15-21 of lactation (FR 15-21) lactation show persistent, negative effects on their sexual behavior as adults relative to male offspring of females that were not food restricted. We measured three components of sexual behavior, attractivity, proceptivity and receptivity, beginning when the males were 98 days of age. Food restriction during middle lactation (FR 8-14) but not during early (FR 1-7) and late lactation (FR 15-21) was sufficient to induce adult male voles to produce anogenital marks that were not as attractive as those produced by control males. Food restriction during lactation did not affect the proceptive behavior of male voles but did affect their receptivity. Only 4 of 12 FR 8-14 male voles mated compared to 9 of 12 FR 1-7 males, 8 of 12 FR 15-21 males, and 8 of 11 control males. However, no differences existed in their copulatory behavior among the males that did mate. The body weight of FR 1-7 and FR 8-14 males was lower than that of FR 15-21 and control males when they were between 22 days of age (weaning) and 48 days of age (puberty) but was similar when the males were 98 days of age. Food intake was similar for the FR and control males between day 22 and day 98. It remains unclear, however, if this type of maternal effect represents strategic programming of offspring behavior in response to the environment experienced by mothers or is a product of developmental processes of food restriction prior to weaning (Forstmeier et al. 2004).
Many terrestrial mammals scent mark in areas containing the scent marks of conspecifics, and thus... more Many terrestrial mammals scent mark in areas containing the scent marks of conspecifics, and thus, may deposit their own scent marks on top of those that were deposited previously by conspecifics. This phenomenon, known as over-marking appears to play a role in same-sex competition or mate attraction. The present study determines whether meadow and prairie voles avoid over-marking the scent
Social cues must be detectable by receivers or bystanders before they can respond to the informat... more Social cues must be detectable by receivers or bystanders before they can respond to the information contained in the cue. Information about conspecifics and heterospecifics can be extracted from social cues. At that point, the information in the cue becomes a fact and the cue becomes a signal. Chemical signals, such as scent marks, provide accurate information that can be used by conspecifics in sexual and social contexts. Scent marks of many conspecifics distributed in an area may be akin to a chemical bulletin board that provides information about the identity of senders and how recently they were in that area. These scent marks deposited by senders can provide both private and public information to receivers. The manner in which receivers use this information to make decisions will depend on the context and manner in which it encounters these scent marks. Thus, a learned rule of thumb that will allow the animal to respond in a predictable way to a scent mark and when to scent mark would not suffice. The sender and the receiver must identify the phenotype and genotype of their counterparts, recollect interactions with them, be aware of their own condition and the context of the communication. Higher level cognitive processing would likely be required for receivers and senders to make potentially informed decisions that reflect tradeoffs in their survival and fitness.
Models of age-related effects on behavior predict that among short-lived species younger adults a... more 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.
For a scent mark to be informative it must provide a reliable, honest signal that allows individu... more 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.
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