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Acoustic communication mediates many types of social interactions; however, few studies have investigated whether courtship vocalizations contain distinctive individual signatures necessary for individual recognition. Male house mice, Mus musculus, produce spectrally complex ultrasonic vocalizations (USVs) during courtship and mating, which appear to attract females and increase male reproductive success. Our goals were to (1) describe quantitative and qualitative changes in the vocalizations of wild-derived male house mice, M. m. musculus, induced by a female odour stimulus; (2) measure individual variation and consistency in male USV emission over time; (3) test whether the variation in USVs is greater between than within individuals; and (4) identify individual signatures in spectrotemporal features using univariate statistics, multivariate models and machine learning methods. We recorded males once per week for 3 weeks, used an automated method (A-MUD) to detect USVs, and manually classified them into distinct syllables. We found that most males did not vocalize until they encountered female scent, and then most males dramatically increased the number and the types of different vocalizations (repertoire size and composition). Male USVs showed high interindividual variation and most showed intraindividual consistency, and we found greater inter- than intraindividual variation for both USV count and repertoire size. Male USVs contained individual signatures in most spectrotemporal features, regardless of the method of analysis. Males sometimes produced few, if any, vocalizations when presented with female scent, but consistent nonvocalizers were rare. Our study provides the first evidence that individual signatures in USVs of male house mice are stable over time and across recording trials, although studies are still needed to investigate repeatability across social contexts and to test whether USVs mediate individual recognition.

Exposure to males or male urinary scent can induce and accelerate the rate of female estrous cycling in house mice ("Whitten effect"), and this response has been replicated many times since its discovery over 60 years ago. Here, we tested whether exposing female mice to recordings of male courtship ultrasonic vocalizations (USVs) induces estrous cycling, and whether exposure to both male scent and USVs has a stronger effect than to either of these stimuli alone. We conducted our study with 60 wild-derived female house mice (Mus musculus musculus). After singly housing females for 14 days, we monitored estrous stages via vaginal cytology for two weeks while isolated from males or male stimuli. We continued monitoring estrus for two more weeks during experimental exposure to one of four different types of stimuli: (1) clean bedding and background noise playback (negative control); (2) recordings of male USVs (16 min per day) and clean bedding (male USV treatment); (3) soiled male bedding and background noise playback (male odor treatment; positive control); or (4) male USVs and soiled male bedding (male odor and USV treatment). Females were then paired with males to test whether any of the four treatments influenced female reproduction (especially latency to birth). We confirmed that exposure to male odor increased female cycling, as expected, but exposure to recordings of male USVs had no effect on estrus. Females exposed to both USVs and odor went through more cycles compared to controls, but did not differ significantly from exposure to male odor (and background noise). After pairing females with a male, females showing male odor-induced cycling produced their first litter sooner than controls, whereas USVs did not have such an effect. This is the first study to our knowledge to show that male odor induces estrus in wild house mice and to show functional effects on reproduction. Our results do not support the hypothesis that male vocalizations induce female estrus, although we suggest other approaches that could be used to further test this hypothesis.

The major urinary proteins (MUPs) of house mice (Mus musculus) bind and stabilize the release of pheromones and other volatile organic compounds (VOCs) from urinary scent marks, which mediate chemical communication. Social status influences MUP and VOC excretion, and the urinary scent of dominant males is attractive to females. Urinary pheromones influence the sexual behavior and physiology of conspecifics, and yet it is not known whether they also affect reproductive success. We monitored the excretion of urinary protein and VOCs of wild-derived house mice living in large seminatural enclosures to compare the sexes and to test how these compounds correlate with reproductive success. Among males, urinary protein concentration and VOC expression correlated with reproductive success and social status. Territorial dominance also correlated with reproductive success in both sexes; but among females, no urinary compounds were found to correlate with social status or reproductive success. We found several differences in the urinary protein and volatile pheromones of mice in standard cages versus seminatural enclosures, which raises caveats for conventional laboratory studies. These findings provide novel evidence for chemical signals that correlate with male reproductive success of house mice living in competitive conditions.

House mice communicate through ultrasonic vocalizations (USVs), which are above the range of human hearing (>20 kHz), and several automated methods have been developed for USV detection and classification. Here we evaluate their advantages and disadvantages in a full, systematic comparison, while also presenting a new approach. This study aims to 1) determine the most efficient USV detection tool among the existing methods, and 2) develop a classification model that is more generalizable than existing methods. In both cases, we aim to minimize the user intervention required for processing new data. We compared the performance of four detection methods in an out-of-the-box approach, pretrained DeepSqueak detector, MUPET, USVSEG, and the Automatic Mouse Ultrasound Detector (A-MUD). We also compared these methods to human visual or ‘manual’ classification (ground truth) after assessing its reliability. A-MUD and USVSEG outperformed the other methods in terms of true positive rates using default and adjusted settings, respectively, and A-MUD outperformed USVSEG when false detection rates were also considered. For automating the classification of USVs, we developed BootSnap for supervised classification, which combines bootstrapping on Gammatone Spectrograms and Convolutional Neural Networks algorithms with Snapshot ensemble learning. It successfully classified calls into 12 types, including a new class of false positives that is useful for detection refinement. BootSnap outperformed the pretrained and retrained state-of-the-art tool, and thus it is more generalizable. BootSnap is freely available for scientific use.

House mice communicate through ultrasonic vocalizations (USVs), which are above the range of human hearing (>20 kHz), and several automated methods have been developed for USV detection and classification. Here we evaluate their advantages and disadvantages in a full, systematic comparison. We compared the performance of four detection methods, DeepSqueak (DSQ), MUPET, USVSEG, and the Automatic Mouse Ultrasound Detector (A-MUD). Moreover, we compared these to human-based manual detection (considered as ground truth), and evaluated the inter-observer reliability. All four methods had comparable rates of detection failure, though A-MUD outperformed the others in terms of true positive rates for recordings with low or high signal-to-noise ratios. We also did a systematic comparison of existing classification algorithms, where we found the need to develop a new method for automating the classification of USVs using supervised classification, bootstrapping on Gammatone Spectrograms, and Convolutional Neural Networks algorithms with Snapshot ensemble learning (BootSnap). It successfully classified calls into 12 types, including a new class of false positives used for detection refinement.BootSnapprovides enhanced performance compared to state-of-the-art tools, it has an improved generalizability, and it is freely available for scientific use.

Female house mice (Mus musculus) show preferences for the scent of healthy versus infected males, which may function to reduce risks of disease transmission or to obtain healthy, disease-resistant mates. It is not known whether such odor preferences result in differential male reproductive success (sexual selection), and therefore, we performed mate choice experiments with wild-derived mice. Females were allowed to freely choose to mate between two males, one infected (Salmonella enterica) versus a sham control, and we conducted genetic paternity analyses on the offspring to assess male reproductive success. The males were restricted to their own cages to prevent male-male interactions and sexual coercion, and we performed the experiment in two different settings: in large-connected cages and in large enclosures. In the enclosures, we found that 86 % of females were initially more attracted to the control males (initial social preference); however, our paternity analyses detected no difference in male reproductive success in either setting. Females often mated with both males (connected cages 32 %, enclosures 44 %), which shows that females frequently mate multiply—despite differences in male health—when they can choose their mates. These results raise caveats about mate choice studies that rely on proxy measures, such as odor preferences or time spent with potential mates. On the other hand, if females are less likely to locate infected than healthy males in the wild, then such a bias could still result in nonrandom mating. We suggest several additional issues that also need to be considered before ruling out parasite-mediated mate choice.

Secondary sexual displays may be overlooked in many species, especially when they are ephemerally expressed or imperceptible to human senses. Zebrafish (Danio rerio), like many schooling fish, do not appear sexually dichromatic, but previous anecdotal observations indicate that sexual colouration is expressed briefly during courtship (ephemeral nuptial colouration). Our goals were to compare colour estimates of male vs. female zebrafish using digital photography in situ, computer software and human observations. We found that both sexes changed their colour estimates during spawning (dark and light stripes) and that some sex differences (light stripes) were larger or only became apparent during this time. We also found that individual males that appeared more colourful and conspicuous to the human eye engaged in courtship more often than less conspicuous males. We detected differences in the colour estimates between wild-derived vs. a laboratory strain of zebrafish and reduced individual variation in the laboratory strain. This is the first study to systematically and objectively quantify body colour in zebrafish by utilizing colour estimates, although further studies are needed to determine the underlying mechanisms and signalling functions of this sexual dichromatism.

Social learning probably functions as a mechanism to acquire public information about food, predators and conspecifics, without paying the costs required for individual learning. Social learning should be strategic rather than indiscriminate, and although it is often suggested that animals should show conformity (‘copy the majority strategy’), there are surprisingly few tests of this idea. Our goals were to test experimentally whether social learning plays a role in boldness behaviour of wild and domesticated zebrafish, and to investigate whether they utilize similar social-learning strategies and conformity in their boldness behaviour. We tested whether timid wild-derived zebrafish become bolder, and more likely to approach a moving stimulus, after interacting socially with bolder domesticated fish (and vice versa). We found that wild zebrafish exposed to domesticated fish were bolder than controls, whereas domesticated fish exposed to the more timid, wild zebrafish did not differ in their boldness score compared to controls. The changes in the behaviour of wild fish persisted after the nonfocal groups were removed; however, we found no evidence for conformity. Our findings indicate that zebrafish use social learning for assessing risk and adapt their social-learning strategies to the costs of a perceived risk. Future studies should be able to utilize this model species to incorporate genetic and genomic tools to study the development and evolution of social learning.

We investigated sex recognition in female zebrafish (Danio rerio) to better understand the underlying sensory mechanisms and identify male secondary sexual traits. Females were simultaneously presented with two fish, a male and a female, in a flow-chamber apparatus, and females’ relative attraction towards males was observed under different conditions. With domesticated fish, females were more attracted to males when presented with both visual and chemosensory cues from stimulus fish. They still discriminated the sexes when only visual cues were provided, but not when white ambient light was changed to yellow, indicating that colour plays a role. Sex discrimination under yellow light was improved when chemosensory cues were also provided. Surprisingly, females’ attraction to males was not more pronounced in the morning when mating occurs. Domesticated females discriminated the sexes when presented with wild-derived, as well as domesticated fish, whereas wild-derived females did not show any biases for domesticated or wild-derived males. Behavioural observations indicated that the wild-derived females were distressed, which explains their lack of attraction to males. In summary, domesticated female zebrafish discriminated the sexes using both visual (body colour) and olfactory cues; however, wild-derived zebrafish were too distressed for behavioural experiments under these laboratory conditions.

Secondary sexual characters often provide indicators of a male’s resistance to infectious diseases to rivals and potential mates, but it is unclear why. It is often suggested that males honestly signal their health due to energetic and other physiological trade-offs between investing into secondary sexual traits vs resistance to infectious diseases. Our aim was to determine whether such a trade-off exists using wild-derived male house mice (Mus domesticus). We exposed male mice to female scent, a manipulation that induces elevations in testosterone concentration and the expression of a variety of testosterone-mediated secondary sexual traits, and tested whether this sexual stimulation impaired the males’ ability to resolve or cope with an experimental infection (Salmonella enterica). We kept the males on a controlled diet to prevent them from compensating by eating more food. We found that sexually stimulated males were able to control bacterial growth as effectively as sham-stimulated controls; however, to do so, they lost more body mass during infection compared to the controls. In contrast, we found no evidence that sexual stimulation reduced the body mass of uninfected male mice. These results indicate that males’ responses to female odor are not immunosuppressive per se, yet they increase the energetic costs of controlling infection. Our findings support the idea that there is a physiological trade-off between secondary sexual signaling vs resistance to infectious diseases and suggest that studies using only immunocompetence assays might fail to detect such energetic trade-offs.

Many chemical pollutants have become ubiquitous in the environment, including some that interfere with hormones and other physiological mechanisms. These ‘endocrine-disrupting chemicals’ (EDCs) have harmful effects on development and physiology. We reviewed published evidence and found that EDCs also have adverse effects on a wide range of behaviours, including sexual and other reproductive behaviours, activity, motivation, communication, aggression, dominance and other social behaviours, and learning and other cognitive abilities. We also reviewed recent findings that challenge common assumptions in toxicology. For example, EDCs have several unanticipated properties, such as nonmonotonic dose effects and synergy. Furthermore, harmful effects of EDCs sometimes become apparent only when tested in natural ecological conditions, such as social stress and infection. These findings raise questions about the practicality and feasibility of testing chemical pollutants adequately. Finally, we discuss the implications of EDC research for species conservation and human health, and how toxicology and behavioural research might be better integrated. Behaviour might provide a useful indicator or biomarker for detecting harmful chemical contaminants; however, more integration between toxicology and behavioural ecology is needed to determine whether and how EDCs affect humans and other vertebrates outside of the laboratory.

The acanthocephalan parasite Pomphorhynchus laevis is transmitted by crustaceans such as Gammarus pulex to its paratenic or final hosts, fish. The conspicuous orange-yellow parasite is visible through the transparent cuticle of G. pulex. Infected gammarids are significantly less photophobic than uninfected ones. When hungry three-spined sticklebacks (Gasterosteus aculeatus), one of the hosts of this parasite, were offered equal numbers of uninfected and infected prey, G. pulex infected with P. laevis were eaten significantly more often. We tested experimentally whether parasite color and parasite-induced changes in host behavior affected the predation rate of G. pulex. Color effects were tested with uninfected G. pulex by painting an orange spot on their cuticle that simulated infection. Behavioral effects were tested with infected G. pulex by covering the place through which the orange parasite was visible with inconspicuous brown paint. We showed for the first time that both parasite color and changed intermediate host behavior promote the transmission of P. laevis to its next host. The evolution of orange parasite color, and why sticklebacks do not avoid infected prey, are discussed.

Peer review is the most widely used selection process for evaluating submissions of scientific publications, and yet this system is widely criticized. As an editor of The Lancet points out: ‘…we know that the system of peer review is biased, unjust, unaccountable, incomplete, easily fixed, often insulting, usually ignorant, occasionally foolish, and frequently wrong’ [1]. On November 1, 2011, a new service was launched, called ‘Peerage of Science’ (PoS; http://www.peerageofscience.org), which aims to ‘fix the woes of peer review without breaking what works’.

Females may be attracted to males genetically resistant to infectious diseases, and one potential mechanism for this mating bias is that such males may be better able to maintain high testosterone. To test these two hypotheses, we collected scent-marks from male house mice ( Mus domesticus ) genetically resistant and susceptible to Salmonella due to a single locus (Nramp 1, also known as Slc11a1). We tested whether females are more attracted to the scent-marks of resistant males, and whether such males are better able to maintain testosterone concentrations during an experimental Salmonella infection. We found that females preferred the scent-marks of genetically resistant males compared to susceptible ones; but they showed no preferences 5 d after males were infected. As predicted, genetically resistant males maintained their testosterone concentrations during the experimental infection, whereas susceptible males showed a significant decline 14 d after inoculation. These differences in the males’ ability to modulate testosterone, however, do not explain females’ attraction to resistant males. Thus, our results indicate that females sometimes prefer males genetically resistant to infection, and they provide the first evidence that males modulate their testosterone depending upon their genetic resistance to infection; however, we found no evidence to link these two findings.