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We tested liver samples from 372 Norway rats (Rattus norvegicus) from southern Ontario, Canada, during 2018–2021 to investigate presence of hepatitis E virus infection. Overall, 21 (5.6%) rats tested positive for the virus. Sequence analysis demonstrated all infections to be rat hepatitis E virus (Rocahepevirus ratti genotype C1).

Direct reciprocity requires the ability to recognize and memorize social partners, and to remember their previous actions. 'Insufficient cognitive abilities' have been assumed to potentially impair the ability to cooperate by direct reciprocity. Here we compare the propensity of rats to use direct reciprocity with their ability to memorize and recognize sensory cues in a non-social task. Female rats enriched in one of three sensory modalities (visual, olfactory or auditory) performed better in a learning task when they were tested with the specific sensory modality in which they have been enriched. For the cooperation test, during three subsequent reciprocity experiments the rats could provide two partners differing in their previous helpfulness with food. Individuals performing better in the non-social learning task that involved olfactory cues applied direct reciprocity more successfully in one experiment. However, in the experiment preventing visual cues and physical contact, rats applied direct reciprocity rules irrespective of their performance in the learning task with olfactory cues. This indicates that an enhanced olfactory recognition ability, despite being beneficial, is not a prerequisite for the rats' ability to cooperate by direct reciprocity. This might suggest that when rats have all types of information about their social partner, individuals may apply other criteria than the reciprocity decision rule when determining how much help to provide, as for instance coercion. Interestingly, when all individuals are constrained to mostly rely on olfactory memory, individuals apply direct reciprocity independently of their ability to memorize olfactory cues in a non-social context. 'Insufficient cognitive abilities' may thus not be the true reason when direct reciprocity is not observed. [ABSTRACT FROM AUTHOR]

Field trials are reported in this paper on a new bait containing 1% norbormide. Two separate field trials were recently completed on commercial chicken farms in South Auckland, New Zealand. Norway rats were abundant both inside the farm sheds and around the surrounding farmland. Monitoring undertaken before toxic baiting recorded high levels of rat activity. Post-treatment monitoring found no rat paw prints in any of the tracking tunnels from Site 1, and in only one tunnel at Site 2. The decrease of 100% and 96%, respectively, represented a marked reduction in the Norway rat population at both sites.

ABSTRACT Millions of Norway rats (Rattus norvegicus) inhabit New York City (NYC), presenting the potential for transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from humans to rats. We evaluated SARS-CoV-2 exposure among 79 rats captured from NYC during the fall of 2021. Our results showed that 13 of the 79 rats (16.5%) tested IgG- or IgM-positive, and partial SARS-CoV-2 genomes were recovered from all 4 rats that were qRT-PCR (reverse transcription-quantitative PCR)-positive. Genomic analyses suggest these viruses were associated with genetic lineage B, which was predominant in NYC in the spring of 2020 during the early pandemic period. To further investigate rat susceptibility to SARS-CoV-2 variants, we conducted a virus challenge study and showed that Alpha, Delta, and Omicron variants can cause infections in wild-type Sprague Dawley (SD) rats, including high replication levels in the upper and lower respiratory tracts and induction of both innate and adaptive immune responses. Additionally, the Delta variant resulted in the highest infectivity. In summary, our results indicate that rats are susceptible to infection with Alpha, Delta, and Omicron variants, and wild Norway rats in the NYC municipal sewer systems have been exposed to SARS-CoV-2. Our findings highlight the need for further monitoring of SARS-CoV-2 in urban rat populations and for evaluating the potential risk of secondary zoonotic transmission from these rat populations back to humans. IMPORTANCE The host tropism expansion of SARS-CoV-2 raises concern for the potential risk of reverse-zoonotic transmission of emerging variants into rodent species, including wild rat species. In this study, we present both genetic and serological evidence for SARS-CoV-2 exposure to the New York City wild rat population, and these viruses may be linked to the viruses that were circulating during the early stages of the pandemic. We also demonstrated that rats are susceptible to additional variants (i.e., Alpha, Delta, and Omicron) that have been predominant in humans and that susceptibility to infection varies by variant. Our findings highlight the reverse zoonosis of SARS-CoV-2 to urban rats and the need for further monitoring of SARS-CoV-2 in rat populations for potential secondary zoonotic transmission to humans.

Effective management of rodent pests requires an ecological understanding of how they move through their environment, and how those movements influence the invasion, persistence, or reinvasion of problematic colonies. Traditional methodologies used to describe rodent movement patterns, such as mark-recapture, are hindered by their time-consuming nature and limited geographic scope. As such, our understanding of how rodents interact with urban environments remains limited. Population genetic principles and tools have the capacity to greatly increase our understanding of rodent population dynamics, ecological relationships, and movements across space but this field is often unapproachable to non-scientist pest management professionals. In this paper we aim to promote collaborative and integrative rodent pest management by introducing relevant population genetic principles, providing examples of their applications in studies of urban brown rats, and proposing future initiatives that link scientific, private, and government entities. Using a densely-sampled brown rat population in the city of Vancouver, BC we show how genetic relationships among individual brown rats can be leveraged to understand the geographic distribution of genetic clusters (i.e., colonies), natural barriers to migration, and the spatial scale of dispersal. We describe how these results can be exploited by PMPs to directly inform the creation of management units and decrease the likelihood of rapid post-treatment reinvasion. Further, we discuss the difficulties inherent in population genetic studies and the potential for high-quality model sites to develop generalizable strategies. Overall, we hope to expand the toolbox of pest management professionals, foster collaboration, and move towards more informed and sustainable management strategies.

Commensal rodents are those species that have adapted to feeding, breeding and travelling around the world with humans, as opposed to their relatives who remain fully wild. Three species of commensal rodents each invaded New Zealand many times before about 1830. All carry in their genomes evidence of their origins, which not only confirm known precolonial trade routes in the south-western Pacific during the late eighteenth and early nineteenth centuries, but also extend them into conclusions invisible to archival records. Pacific rats (Rattus exulans) arrived with Polynesian colonists from their home islands in eastern Polynesia in about 1280 CE. They have become a mine of genetic information for deducing the history of human colonisation of the Pacific islands. House mice (Mus musculus) and Norway rats (Rattus norvegicus) both originated in Asia, and spread from there along with people to western Europe by the mid-1700s. Both were carried by the early European and American ships among cargo, livestock and immigrants to Australia, and thence to New Zealand. They provide evidence of a hitherto unknown short but important clandestine connection with China over about 20 years after 1800. A fourth species of commensal rodent to reach New Zealand, the ship rat (Rattus rattus), arrived only in about 1830-50. [ABSTRACT FROM AUTHOR]

One way to cooperate with others and avoid exploitation is reciprocal cooperation. Reciprocity is the selective helping of those who were cooperative before, which is commonly based on outcomes. Yet, outcomes may not reflect intentions, that is if an individual is unable but willing to help. Humans, including children, show such intention‐based reciprocity. However, it is unclear whether other animals consider intentions in reciprocal settings. Here, I tested whether Norway rats (Rattus norvegicus) reciprocate help based on intentions by manipulating the outcome while keeping the partner's cooperative intentions the same. Subjects experienced a partner that was able to help by providing food via a movable platform. In another condition, the same partner was unable to help because the platform was blocked. When the roles were exchanged afterwards, subjects provided food more often to "able" than "unable" partners, even though the latter attempted to help. I compared these findings to data using "willing" and "unwilling" partners that were able to help. Again, rats based their cooperative behaviour on outcomes rather than the intention to help. This suggests that rats reciprocate primarily based on outcomes and seem to not consider cooperative intentions. Although subjects provided consistently less food to partners that did not help, they provided them with some help. Potentially, rats use a cognitively less demanding strategy by helping defectors a bit to maintain cooperation. Thereby, cooperation might be resistant to situations in which an apparent defector was actually unable to help, but had cooperative intentions and might be a good cooperation partner in the future. [ABSTRACT FROM AUTHOR]

Brown rats (Rattus norvegicus) and roof rats (Rattus rattus) are among the most common mammals worldwide. Little is known about the effects of season on rat population size, which is important for understanding rat ecology and/or performing effective rat control campaigns. Tsukiji Market was a metropolitan central wholesale market in Tokyo and was located within 1 km from one of the biggest downtown areas. To control rats in the market, a pest management professional exclusively conducted annual campaigns at two fixed time points for many years. In addition, the pest management professional successfully confined all rats to the market and exterminated them when the market was closed and demolished. We analyzed these records to assess whether this rat population in Tokyo showed seasonal fluctuation and to provide information regarding rat management in a facility located in a downtown area. Multiple regression analyses revealed that trap success was affected by human activities (total trading volume and number of foreign tourists in Japan), but not by the month the campaign was performed. These results suggest that the rat population in this market did not show seasonal fluctuation. The results also suggest the importance of the effect of human activities on the ecological dynamics of rats in urban cities. We also described details of the campaigns performed as the market prepared to close to provide information regarding how to control rats in facilities in a downtown area. [ABSTRACT FROM AUTHOR]

Paraffinized rodent baits developed initially for use in control of Norway rats in sewers by Lloyd Plesse of San Jose, California, an experienced bait formulator for Santa Clara County, significantly enhanced longevity and effectiveness of toxic rodent baits. Within a couple of years, this paraffin type molded bait’s moisture resistant qualities and proven efficacy, especially for sewer rat (Norway rat) control, was the subject of several published articles. Those first three articles, 1959-1961, were responsible for rapidly launching this new paraffinized bait formulation into national usage, at first, mostly by health departments. The structural pest control operators and agricultural interests were soon to follow, using them initially for out-of-doors control of rats and indoors where high humidity normally caused bait deterioration. Recognizing the potential of paraffinized rodent baits, along with the published how-to information, commercial bait manufacturers were quick to get into production and distributors eager to market. Paraffinized rodent baits soon came into common usage and literally revolutionized rodent baits by not only making them more moisture and weather resistant but more convenient to use and versatile in applications. This resulted in greatly expanding the conditions under which commensal rodents could be more effectively controlled. The chronology and evolution of paraffinized rodent baits and their practical uses are followed from their beginning throughout much of their early existence, as are the changes in their manufacturing processes. The factors contributing to development and rapid acceptance for rodent control are enumerated, as are their advantages and disadvantages. The greatest emphasis is placed on the first two decades (1960s and 70s) of the existence of paraffinized rodent baits.

Norway rats and their fleas are associated with transmitting diseases, such as murine typhus and plague, to humans. The use of rodenticide baits may increase human exposure to rodent fleas due to loss of their preferred host. Therefore, flea control is an important component of risk reduction. However, the use of insecticide powder or spray can be difficult in certain situations. In this field study we used a feed-through insecticide, imidacloprid, in a grain-based pellet formulation without a rodenticide to determine the effect on the flea index of a well defined, problematic Norway rat focus in a dense urban area of Los Angeles. The flea index was determined to be 12.9 (116 fleas/9 rats) 5 days prior to applying the product. Rats were allowed to feed on the pellets ad libitum for 48 hours, in the presence of previously existing competing food sources. Flea counts were then taken, and again 7 days later, resulting in flea indices of 2.3 (25/11) and 1.5 (23/15), respectively. Since this field trial was conducted in a very dynamic urban area, attempts to survey a concurrent control group were not successful. However, Norway rat surveys conducted in the previous 4 years from the same urban area for the same months, July and August, produced flea indices of 7.4 and 10.1, respectively. In this field trial, we found that a rodent bait formulation containing imidacloprid reduced the flea index of a Norway rat focus from 12.9 to 2.3 (82%) in 48 hours, and to 1.5 (88%) 7 days later.

Previously, stress responses in gray Norway rats (Rattus norvegicus) selected for the absence or enhancement of aggressive and defensive behaviors toward humans (tame and aggressive behaviors, respectively) were studied mainly to nonsocial factors, whereas data on the consequences of social stress induced, specifically, by interactions with conspecifics are scarce. As has already been shown, the above selection of Norway rats causes attenuation or enhancement of intraspecific intermale aggression. To find out whether the differences in aggressiveness are accompanied by hormonal alterations, we addressed the dynamics of corticosterone and testosterone blood levels after intermale aggression testing in tame and aggressive rats, and unselected rats bred in a vivarium for 7–8 generations as a reference. The goal of this work was to investigate the effect of selection toward humans on agonistic interactions under conditions of an unfamiliar cage or neutral territory and on the subsequent dynamics of blood corticosterone and testosterone levels in tame, aggressive, and unselected rats. In our experiments, tame males, as compared to their aggressive or unselected conspecifics, demonstrated a longer attack latency, as well as a shorter duration and smaller number of patterns of aggressive behavior, approximating zero values. When tested on neutral territory, aggressive male rats were inferior to their unselected conspecifics in the total time of confrontations. More pronounced manifestations of aggression in unselected males compared to aggressive or tame animals arose against the background of elevated basal corticosterone levels and enhanced stress responsiveness to interacting with an unfamiliar male. At the same time, reduced aggressiveness of tame rats in the neutral territory test, as compared to unselected or aggressive animals, correlated with the lower testosterone level. [ABSTRACT FROM AUTHOR]

An alternative rodent control technology is presented. The patented discovery that specific plant-derived structural carbohydrate polymers are inhibitory to the water retentive mechanisms of rodents is discussed. Specifically, it has been discovered that when natural complex structural carbohydrates are formulated into a palatable pellet, target species of rodents (rats, mice, and ground squirrels), after ingesting the polymers, become less active and eventually die after 3 - 10 days. Captivity and in situ tests on the Norway rat have indicated the lethal dose for rats to be approximately 35 - 50 g consumed over a period of 72 - 96 hours, whereas for house mice it is 7 - 10 g over the same period. Captive trials on California ground squirrels have indicated a similar lethal dosage to that of rats, specifically 35 - 50 g consumed over 72 - 96 hours. The commercial product is exempt from registration in many countries including the U.S. This paper discusses laboratory and field test results on rodents to date and field use experiences.

Norway rats are an important commensal species of human settlements. They are abundant in urban areas and generate several problems to our societies. Integrated rat management programs, based on detailed knowledge of its biology, are needed to keep rat populations under control. One of the main habitats of rats in cities is the sewer system. Unfortunately, very few studies have been conducted on sewer rats due to the logistic challenges of such projects. Hence, information on the ecology of rats in a key habitat, crucial to management programs, is scarce. The aim of this study is to estimate the abundance of Norway rats in the sewers of the city of Barcelona and determine the main related ecological factors. We sampled 63 sewer sections 90 m long during the study. We obtained several rat activity estimates, we compared them, we calculated a minimum rat density, and with that, we estimated the minimum rat population size in the sewer system of Barcelona. Bait consumption and rat capture estimates showed low correlations. Sewer rats showed the highest activity in areas with high density of housing and in old sections. The presence of natural soil favoured the activity of rats only inside the areas with a high density of housing. The activity of rats showed a high variability among sewer sections. The citizen complaints for rats, which were positively related to the human density and negatively related to the mean disposable household income, were bad predictors of the activity of rats in the sewer system. [ABSTRACT FROM AUTHOR]

Rodents infest urban environments, causing damage and acting as vectors for disease transmission. Currently, anticoagulants are the most widely used chemical rodenticides, and their extensive and widespread use can contaminate the environment. To ensure effectiveness and avoid accumulation of rodent baits in the environment, it is important to evaluate how long rodent baits maintain their palatability and efficacy. In rodent control programs, rodent baits are placed in locations such as sewers, but after a few days, baits appear altered, causing doubts about the control efficacy. For this reason, baits are replaced periodically, which increases costs and generation of chemical waste. The objective of this study was to evaluate the palatability and efficacy of commercial paraffin-type rodent bait blocks placed in sewers in São Paulo City over a period of 90 days. Bait blocks were placed in sewers and collected after 30, 60, and 90 days. Additionally, in a laboratory two-choice test, wild-caught urban Norway rats were offered 40–60 g of bait and an equal volume of standard rat pellets. The amount of bait and rat pellet consumed was registered, the palatability was calculated, and the efficacy was measured as the percentage mortality over 14 days. The results showed that, even when they had an altered appearance, bait blocks remained palatable to the rats and were effective after at least 90 days. Leaving bait blocks for longer periods could be an effective strategy for reducing costs and could help to ensure the control of urban rodents in an environmentally sustainable way. [ABSTRACT FROM AUTHOR]

Urban Norway rat (Rattus norvegicus) populations can carry the bacteria methicillin‐resistant Staphylococcus aureus (MRSA). There are numerous knowledge gaps in the epidemiology of MRSA in these populations that limit understanding of its ecology in urban environments. For example, fecal shedding of MRSA, which may increase environmental contamination, has been reported in other species; however, it is unknown whether Norway rats carry the bacteria rectally. Furthermore, while intermittent MRSA shedding has been shown in other species and may dictate when the risk of transmission is highest, duration of carriage has not been examined for Norway rats. Previous work has shown that lethal animal‐control methods may increase the level of pathogens within reservoir populations, possibly by disrupting ecological patterns. However, the impact of rodent‐control on potentially environmentally acquired pathogens like MRSA has not been tested. Using capture‐mark‐recapture methods in an inner‐city neighborhood in Vancouver, Canada, we show that rats intermittently carry MRSA both in the rectum and oropharynx. By assessing the prevalence of MRSA before and after enacting a pest‐control intervention, we report that kill‐trapping had no impact on the prevalence of carriage of this environmentally‐acquired agent. [ABSTRACT FROM AUTHOR]

Feral cats (Felis catus) are predators that cause widespread loss of native wildlife in urban ecosystems. Despite these risks, cats are commonly released as control agents for city rats (Rattus spp.). Cats can influence their prey directly by killing or indirectly through changes to feeding or space-use. However, cats prefer defenseless prey, and there are no data suggesting that cats influence large (>300 g) urban rats. We used a pre-existing radiofrequency identification assay (microchipped rats and field cameras) and ethograms to assess the impact of cats, including temporal and space use patterns, on an active rat colony. From Dec 27, 2017 through May 28, 2018 we captured 306 videos of pre-identified cats and/or rats that shared the same space. There were three instances of predation and 20 stalking events. Logistic regression showed the likelihood of a rat being seen on a particular day is associated with the number of cats seen on the same day (OR = 0.1, p < 0.001) or previous day (OR = 0.15, p < 0.001). Space-use was also impacted. For every additional cat sighting, a rat is 1.19 times more likely to move in the direction of shelter. Our findings of low levels of predation support why ecologists believe the risks to native wildlife outweighs any benefits of releasing cats. Even though rats were less likely to be seen, they simply shifted their movements and remained present in the system. Our findings that cat presence led to fewer rat sightings may explain the common perception of their value as rat-predators despite the associated risks.

Under an Environmental Protection Agency Experimental Use Permit, a pelleted bait containing 0.0025% (25 ppm) of the new anticoagulant difethialone was tested to determine the effectiveness in controlling Norway rats (Rattus norvegicus) and house mice (Mus musculus). Sixteen (16) individual field studies were conducted in five (5) geographical locations of the United States. The results were conclusive in showing that difethialone bait formulated at 25 ppm was both palatable and efficacious in controlling both Norway rats and house mice under actual field conditions.

Highlights • R 0 for Leptospira infection in rodents is a non-linear function of multiple transmission routes. • Environmental transmission plays an important role in the maintenance of infection. • Infection in the host population can be reduced using rodent or environmental controls. Abstract Leptospirosis is a zoonosis that humans can contract via contact with animal reservoirs directly or with water contaminated with their urine. The primary reservoir of pathogenic leptospires within urban slum environments is the Norway rat (Rattus norvegicus). Motivated by the annual outbreaks of human leptospirosis in slum urban settings, the within population infection dynamics of the Norway rat were investigated in Pau da Lima, an community in Salvador, Brazil. A mechanistic model of the dynamics of leptospire infection was informed by extensive field and laboratory data was developed and explored analytically. To identify the intraspecific transmission route of most importance, a global sensitivity analysis of the basic reproduction number to its components was performed. In addition, different methods of rodent control were investigated by calculating target reproduction numbers. Our results suggest environmental transmission plays an important role in the maintenance of infection in the rodent population. To control numbers of wild Norway rats, combinations of controls are recommended but environmental control should also be investigated to reduce prevalence of infection in rats. [ABSTRACT FROM AUTHOR]

The three most invasive rat species, black or ship rat Rattus rattus, brown or Norway rats, R. norvegicus and Pacific rat, R. exulans have been incrementally introduced to islands as humans have explored the world’s oceans. They have caused serious deleterious effects through predation and competition, and extinction of many species on tropical islands, many of which are biodiversity hotspots. All three rat species are found in virtually all habitat types, including mangrove and arid shrub land. Black rats tend to dominate the literature but despite this the population biology of invasive rats, particularly Norway rats, is poorly researched on tropical islands. Pacific rats can often exceed population densities of well over 100 rats ha−1 and black rats can attain densities of 119 rats ha−1, which is much higher than recorded on most temperate islands. High densities are possibly due to high recruitment of young although the data to support this are limited. The generally aseasonally warm climate can lead to year-round breeding but can be restricted by either density-dependent effects interacting with resource constraints often due to aridity. Apparent adverse impacts on birds have been well recorded and almost all tropical seabirds and land birds can be affected by rats. On the Pacific islands, black rats have added to declines and extinctions of land birds caused initially by Pacific rats. Rats have likely caused unrecorded extinctions of native species on tropical islands. Further research required on invasive rats on tropical islands includes the drivers of population growth and carrying capacities that result in high densities and how these differ to temperate islands, habitat use of rats in tropical vegetation types and interactions with other tropical species, particularly the reptiles and invertebrates, including crustaceans.

Kin selection and reciprocity are two mechanisms underlying the evolution of cooperation, but the relative importance of kinship and reciprocity for decisions to cooperate are yet unclear for most cases of cooperation. Here, we experimentally tested the relative importance of relatedness and received cooperation for decisions to help a conspecific in wild-type Norway rats (Rattus norvegicus). Test rats provided more food to non-kin than to siblings, and they generally donated more food to previously helpful social partners than to those that had refused help. The rats thus applied reciprocal cooperation rules irrespective of relatedness, highlighting the importance of reciprocal help for cooperative interactions among both related and unrelated conspecifics. [ABSTRACT FROM AUTHOR]

Infectious diseases frequently have multiple potential routes of intraspecific transmission of pathogens within wildlife and other populations. For pathogens causing zoonotic diseases, knowing whether these transmission routes occur in the wild and their relative importance, is critical for understanding maintenance, improving control measures and ultimately preventing human disease. The Norway rat (Rattus norvegicus) is the primary reservoir of leptospirosis in the urban slums of Salvador, Brazil. There is biological evidence for potentially three different transmission routes of leptospire infection occurring in the rodent population. Using newly obtained prevalence data from rodents trapped at an urban slum field site, we present changes in cumulative risk of infection in relation to age-dependent transmission routes to infer which intra-specific transmission routes occur in the wild. We found that a significant proportion of animals leave the nest with infection and that the risk of infection increases throughout the lifetime of Norway rats. We did not observe a significant effect of sexual maturity on the risk of infection. In conclusion, our results suggest that vertical and environmental transmission of leptospirosis both occur in wild populations of Norway rats. [ABSTRACT FROM PUBLISHER]

Reciprocity can generate stable levels of cooperation among unrelated social partners. If individuals interact repeatedly, costs of altruistic acts can be compensated through an exchange of donor and receiver roles. Frequent interactions are conducive to attaining evolutionarily stable reciprocal exchange. High interaction frequencies are typical for group members maintaining close relationships among one another, which may thereby facilitate reciprocity. Norway rats ( Rattus norvegicus) are highly social animals that were experimentally shown to reciprocally exchange food donations and allogrooming. Here, we tested experimentally the relationship between reciprocal cooperation and other social behaviours exchanged within dyads of wild-type Norway rats. In particular, we asked whether and how interactions differing in quality (characterised by affiliative and aggressive behaviours) influence reciprocal exchanges of different social services. Our experiment involved three steps: Focal individuals experienced social partners that were either providing them with food or not, via a learnt stick-pulling task. Thereafter, they could either interact physically with these partners, or not. Subsequently, we induced allogrooming among them by applying saltwater to an inaccessible part of the body, and tested for the reciprocation of allogrooming. When individuals were allowed to interact freely, previously cooperative food providers exhibited more aggression towards focal individuals than previously uncooperative partners, which might reflect an attempt to coercively demand a return of food provisioning from focal rats. Higher frequencies of affiliative behaviours and lower frequencies of aggressive behaviours experienced during the unrestricted interaction phase tended to increase the focal rats' propensity to engage in grooming the partner in the subsequent induced allogrooming phase. This suggests that affiliative and aggressive behaviours affect the allogrooming propensity of rats. In particular, higher frequencies of received aggression decreased the propensity to reciprocate previously received cooperation. We provide experimental evidence that rats are more likely to groom partners that pulled a stick to deliver food to them. Reciprocal exchange of allogrooming depends apparently on experienced cooperation, but also on the quality of the social relationship. Significance statement: Close social relationships among individuals may enhance reciprocal exchange of services and thereby ensure long-term cooperation. Thus, we tested whether in unrelated and previously unfamiliar Norway rats, the quality of social interactions, that is, the amount of exchanged affiliative and aggressive behaviours, affects reciprocal cooperation, and whether received cooperation in turn predicts subsequent social behaviour. Our results show that focal individuals are generally more helpful to previously helpful partners, but that the quality of social interactions may modify their decision to cooperate. Received aggressive and affiliative behaviours affected the subsequent reciprocal exchange of hygienic behaviour. Moreover, received food provisioning affected the exchange of cooperative, affiliative and aggressive behaviours also outside of a food-provisioning context. These data reveal a close relationship between the exchange of social behaviours between individuals and their propensity to cooperate with one another. [ABSTRACT FROM AUTHOR]

Direct reciprocity can establish stable cooperation. Nevertheless, the significance of this mechanism is yet unclear. A frequent assumption is that both commodity and context should be the same when help is exchanged between social partners. Yet, an exchange of different favours appears more likely in a natural setting. This is assumed to be cognitively demanding, however, because experienced help in one context needs to change the motivation to help by different means or in a different context. We tested whether Norway rats, Rattus norvegicus , transfer help from one cooperative task to another. Individuals could provide food to previously either cooperating or defecting partners by using a different mechanism to produce food for their partner than the partner had used to help them. Test subjects indeed helped previously cooperative partners more often than defecting ones by using a different provisioning mechanism. This implies that rats realize the cooperative propensity of social partners, which they consequently reward by help of a different kind; hence, they do not merely copy experienced helping behaviour. Our results suggest that animals other than primates are capable of transferring help between different contexts, which highlights new possibilities for the occurrence of reciprocal altruism involving different commodities and services in nature. [ABSTRACT FROM AUTHOR]

Prey species show specific adaptations that allow recognition, avoidance, and defense against predators. This study was undertaken to investigate the processing of a chronic, life-threatening stimulus to Norway rats ( Rattus norvegicus). One hundred forty-four Norway rats were tested by repeated presentation of cat urine for 1 h at different days in a defensive withdrawal apparatus. Rats exposed to urine for short periods showed significantly larger defensive behavioral and medial hypothalamic c-fos messenger RNA (mRNA) responses than other groups. These defensive responses habituated shortly after the presentation of cat urine. Serum levels of adrenocorticotropic hormone and corticosterone increased significantly when animals were repeatedly exposed to cat urine. However, the hormonal responses took longer to habituate than the behavioral and molecular responses did. We conclude that the behavioral and c-fos mRNA responses are 'primed' for habituation to repeated exposures to cat urine, while the hormonal responses show 'resistance.' The results support our hypothesis that the strongest anti-predator responses at three levels would occur during short-term exposure to cat urine and that these responses would subsequently disappear on prolonged exposure. This study assists understanding the way in which the different levels of defensive responses are integrated and react during chronic stress. [ABSTRACT FROM AUTHOR]

Social bonds reflect specific and enduring relationships among conspecifics. In some group-living animals, they have been found to generate immediate and long-term fitness benefits. It is currently unclear how important and how widespread social bonds are in animals other than primates. It has been hypothesized that social bonds may help in establishing stable levels of reciprocal cooperation. Norway rats ( Rattus norvegicus) reciprocate received help to an unrelated social partner. It is hitherto unknown, however, whether this cooperative behaviour is based on the establishment of social bonds among involved individuals. Norway rats live in social groups that can be very large; hence, without bonds, it may be difficult to keep track of other individuals and their previous behaviour, which is a precondition for generating evolutionarily stable levels of cooperation based on direct reciprocity. Here we tested whether wild-type female rats form bonds among each other, which are stable both over time and across different contexts. In addition, we scrutinized the potential influence of social rank on the establishment of bonds. Despite the fact that the hierarchy structure within groups remained stable over the study period, no stable social bonds were formed between group members. Apparently, social information from consecutive encounters with the same social partner is not accumulated. The lack of long-term social bonds might explain why rats base their decisions to cooperate primarily on the last encounter with a social partner, which may differ from other animals where cooperation is based on the existence of long-term social bonds. Significance statement: Social bonds have been hypothesized to favour reciprocal cooperation. Norway rats reciprocate help received from a social partner, but it is hitherto unclear whether they form social bonds that might further such cooperative behaviour. Here we tested whether female Norway rats engage in social relationships with a same-sex partner, which are stable over time and across contexts. In contrast to the hypothesized existence of bonds among long-term group members, our results provide no evidence that rats form specific social relationships. Rather than accumulating social information into social bonds, rats apparently base their decision to cooperate merely on the outcome of recent encounters. [ABSTRACT FROM AUTHOR]

In this study, the presence of toxigenic and pathogenic fungi was detected in individuals of natural populations of Norway rats from semiagricultural habitats. The presence of fungi was noted in 19 out of 30 (63%) individuals examined. Six fungal species were isolated and identified, of which majority belonged to Hyphomycetes (Deuteromycotina) and Mucor racemosus from Zygomycotina. All of detected species are of public health importance and some of them might influence animals health.

Background Rats ( Rattus norvegicus) are increasingly kept as pets, thus more and more requiring veterinary care. Important differences exist between pet and laboratory rats, but little information is available on pet rats. Diagnosis and treatment of pet rat diseases would benefit from RIs specific for this animal population. Objectives The aim was to establish RIs for biochemical blood variables, PCV, and body temperature in pet rats. Additionally, influences of sex and feed rationing method (ad libitum , restricted) on these variables were determined. Methods American Society for Veterinary Clinical Pathology ( ASVCP) recommendations were followed. Biochemical variables were measured using an automated chemistry analyzer, the VetScan VS2. Nonparametric statistical methods were used to determine RIs and effects of sex and feed rationing method. Results Reference intervals were established using values of 123 clinically healthy pet rats (except for globulins and albumin/globulin ratio, n = 120) and were: glucose 6.6-13.7 mmol/L, total proteins 66-88 g/L, albumin ≥ 38 g/L, globulins 12-35 g/L, albumin/globulin ratio 1.0-4.7, urea nitrogen 2.5-6.6 mmol/L, creatinine ≤ 53 μmol/L, total bilirubin 4-7 μmol/L, ALP 40-442 IU/L, ALT 22-137 IU/L, amylase 502-1113 IU/L, sodium 133-144 mmol/L, potassium 3.6-5.3 mmol/L, calcium 9.5-10.9 mg/dL, phosphorus 2.3-7.0 mg/dL, PCV 40-50%, and body temperature 35.8-39.3°C. Sex significantly affected 10 variables. No significant influence was found with feed limitation Conclusions Reference intervals reported in this study will be useful for interpretation of biochemistry analysis in pet rats and therefore improve pet rat medicine. [ABSTRACT FROM AUTHOR]

Leptospira interrogans, hantaviruses (particularly Seoul virus), hepatitis E virus (HEV), and Toxoplasma gondii are rat-associated zoonoses that are responsible for human morbidity and mortality worldwide. This study aimed to describe the infection patterns of these four pathogens in wild rats (Rattus norvegicus) across socioeconomic levels in neighbourhoods in Lyon, France. The infection or exposure status was determined using polymerase chain reaction or serology for 178 wild rats captured in 23 locations; additionally, confirmatory culture or mouse inoculation was performed. Multivariate logistic regression analyses were used to investigate whether morphological and socioeconomic data could predict the infection status of the rats. This study revealed that the rat colony's age structure may influence the prevalence of L. interrogans, hantavirus, and HEV. In addition, areas with high human population densities and low incomes may be associated with a greater number of infected rats and an increased risk of disease transmission. [ABSTRACT FROM AUTHOR]

The frequency of aa homozygous descendants was studied in crosses of Aa heterozygous Norway rat ( Rattus norvegicus (Berkenhout, 1769)) parents selected for tame and aggressive behavior. First, Aa heterozygotes were obtained in crosses between tame homozygotes for the wild-type allele ( AA) and aggressive homozygotes for the non- agouti allele ( aa). The most tame and the most aggressive descendants were selected from the progeny of the Aa genotype by using the glove test. Then Aa rats were crossed among tame and among aggressive descendants, and the AA and Aa genotypes of grey descendants were identified by polymerase chain reactions (PCR). The segregation of descendants into the AA, Aa, and aa genotypes was cumulatively analyzed in five generations of selection with regard to the phenotypic manifestation of tame and aggressive behavior in their parents. The frequency of aa descendants in the progeny of mothers with low aggressive behavior scores was less than expected and less than in the progeny of mothers with high aggressive behavior scores. [ABSTRACT FROM AUTHOR]

Abstract: Tame and aggressive rat lines were created during the long-term selection of Norway rats for elimination and enhancement of aggressiveness toward humans, respectively. Our previous experiments have demonstrated that selection for the elimination of defensive aggression toward humans is associated with attenuated intraspecific intermale aggression. However, the neuronal mechanisms underlying low and high intermale aggression in the tame and aggressive rats remain unclear. Here, we used c-Fos immunoreactivity to evaluate neuronal activation patterns in the main aggression-related areas in selected lines under basal conditions and after the resident–intruder (R–I) test. Although agonistic behavior of the tame and the aggressive rats differed significantly, social encounter caused similar brain activation patterns in both groups; we observed increased neuronal activation in the bed nucleus of stria terminalis, the hypothalamic attack area, and the medial amygdala 1h after the R–I test. However, neuronal activation in the hypothalamic attack area was significantly higher in the aggressive males compared to their tame counterparts. We propose that lower activation of the hypothalamic area is associated with the attenuation of intraspecific intermale aggression during selection for the elimination of aggressiveness toward humans. [Copyright &y& Elsevier]

Abstract: Although numerous studies have demonstrated strong differences in behavioral, hormonal and neurobiological characteristics between male rats selected for elimination (tame) and enhancement (aggressive) of aggressiveness towards humans, few studies have examined changes in female behavior under this selection. The objective of the current work was to evaluate the effects of bidirectional selection for aggressiveness towards humans on behavioral profiles of virgin and lactating rats compared with the behavior in tame, aggressive and unselected (wild-type) females. The behavior of virgin females was studied using the light–dark box, the startle response test and the modified glove test. Tame females were less anxious and more tolerant towards humans than unselected and aggressive rats. Principal component analysis of all behavioral parameters produced three independent factors, explaining 66.37% of the total variability. The measures of behavior towards humans and the measures of anxiety mainly loaded on PC1 (first principal component) which separated the tame females from the unselected and aggressive ones. These data suggest the genetic correlation between the selected behavior towards humans and anxiety-related behavior in virgin rats. No significant effect of line was found for PC2 scores, associated with risk assessment behavior. Measurements of freezing behavior mainly loaded on PC3, and this component separated rats of different genetic groups from each other. The behavior of lactating rats was studied in maternal defense and pup retrieval tests. Females of selected lines did not significantly differ in behavioral measurements of these tests and were characterized by higher maternal motivation than unselected rats. It is suggested that long-term breeding of tame and aggressive rats in captivity has reduced the threshold for maternal behavior. [Copyright &y& Elsevier]

comparative analysis of intermale aggression in the resident-intruder test was conducted with gray rats from a wild unselected population bred at the laboratory for three generations and gray rats selected for elimination (tame) and enhancement (aggressive) of aggressiveness towards human for 71-72 generations. Males from the laboratory line Wistar were used as neutral opponents. Rats from the tame line were characterized by reduced aggression manifest as longer attack latency, decreased number of attacks, upright postures, chases, kicks, and shorter total time of aggressive behavior compared to unselected males. There was no significant difference in the attack latency and the total time of aggression between rats of the aggressive line and unselected rats. A trend to decrease in the number of attacks, chases and upright postures and to increase in contribution of lateral threat postures to the total time of aggression was observed for males of the aggressive line. Plasma corticosterone in unselected males not presented with intruders and after their presentation was higher than in males of both selected lines. Comparative behavioral analysis of agonistic behaviors in rats from the aggressive and tame lines to opponents of different lines (Wistar, tame, aggressive) showed that the presence of an intruder from the aggressive line can enhance aggressive responses in residents from the tame line. Thus, selection for domestication of gray rats caused a significant attenuation of aggressive behavior without affecting the basic agonistic repertoire. [ABSTRACT FROM AUTHOR]

Three species of rats ( Rattus exulans, R. rattus, R. norvegicus) are widely invasive, having established populations in terrestrial habitats worldwide. These species exploit a wide variety of foods and can devastate native flora and fauna. Rats can consume a variety of plant parts, but may have the most dramatic effects on plant populations through consumption and destruction of seeds. The vulnerability of vegetation to rat consumption is influenced by many factors including size of plant part, and mechanical and chemical defenses. We reviewed the literature to find out what plant species and plant parts invasive rats are consuming and what characteristics these sources share that may influence selection by rats. Many of the studies we found were preformed in New Zealand and our analyses are, therefore, focused on this location. We also performed feeding trials in the laboratory with R. norvegicus to determine if seed hardness and palatability would influence rat consumptive choices. We found more reports of rat consumption of fruits and seeds versus vegetative plant parts, and smaller fruits and seeds versus larger. R. norvegicus are reported to consume proportionally more vegetative plant parts than either R. exulans or R. rattus, possibly due to their more ground dwelling habits. Large size and hard seed coats may deter rat feeding, but unpalatable chemicals may be even more effective deterrents to rats. Scientists and managers can better manage vegetation in rat invaded areas by understanding the criteria rats use to select food. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that the early life experiences affect stress responses and other physiological and behavioral traits in adulthood. Both rat and human studies have shown that early postnatal effects are associated with methylation of the hippocampal glucocorticoid receptor gene exon 17 (rat) and 1-F (human) promoters. Methylation of these sites is also seen following methionine administration in adult rats. However, it remains unclear whether similar alterations in DNA methylation profiles can result from prenatal influences. To address this question, we fed pregnant rats a methyl-supplemented diet that resulted in alteration of the stress response. However, methylation analysis revealed no effect of methyl supplements on methylation patterns of the glucocorticoid receptor gene exon 17 promoter in offspring. These results suggest that the pre- and postnatal effects of methyl supplementation have different mechanisms. [Copyright &y& Elsevier]

Results of three previous experiments conducted in our laboratory (Galef & Whiskin 2006, Animal Behaviour, 72, 1169–1176) failed to provide support for the prediction from formal theory that increasing the potential cost of engaging in individual learning increases reliance on socially acquired information. However, weaknesses in the data of each of the three experiment reported in Galef & Whiskin (2006) complicated interpretation of results. Here, we repeated the three experiments using procedures that we modified to improve the quality of the data. Despite success in removing the problems with Galef & Whiskin''s (2006) methods, we again found no evidence that exposure to either direct or indirect cues of predation risk increased Norway rats'', Rattus norvegicus, reliance on socially acquired information. We discuss implications of our repeated failures to confirm a logically consistent prediction from formal theory. [Copyright &y& Elsevier]

Two rat lines, one tame, the other aggressive, differing by many behavioral features and stress reactivity were developed by long-term selection of wild gray rats for elimination and enhancement of aggressiveness towards humans. The aim of this work was to study the role of the maternal environment in the expression of these differences between the two rat lines using the cross-fostering paradigm. Fostering of tame rats of both sexes by aggressive mothers and aggressive females by tame mothers was without effect on behavior score towards humans, but the cross-fostered aggressive males had a small, yet significant, increase in aggressiveness score. Cross-fostering revealed that exploratory behavior in the hole-board test and the acoustic startle amplitude were weakly affected by maternal interactions, although there was an effect on body weight and on the stress corticosterone response. Body weight was decreased in tame males fostered by aggressive mothers only and it was increased in cross-fostered aggressive rats of both sexes. Fostering of tame males and females by an aggressive mother enhanced almost twofold the corticosterone response immediately after stress, while fostering of aggressive ratlings of both sexes by a tame mother was without effect. The current results demonstrated that the maternal postnatal environment had no substantial effect on the behavioral responses of both tame and aggressive rats, but it possibly contributed to the development of the corticosterone response to restraint stress in the tame, and not the aggressive rats, i.e. these effects of cross-fostering were dependent on ratling genotype. [ABSTRACT FROM AUTHOR]

In the literature, nonindependent mate choice of females is frequently referred to as ‘mate choice copying’. The label seems particularly appropriate when the probability that a focal female will mate with a male increases after she has watched him engage in sexual behaviour with another female. However, the classic definition of mate choice copying requires only that a male''s attractiveness to a female change following his acceptance or rejection by another female regardless of whether such alteration in a female''s response results from seeing him mate or from some other process. Here, we provide evidence that female Norway rats prefer to affiliate with a male that has recently engaged in sexual activity, even when they did not observe the male''s previous mating. Furthermore, when we provided oestrous females with access to two males tethered some distance apart, the male that had recently copulated also mounted and achieved intromission and ejaculation sooner and more frequently than the male that had not recently copulated. We also provide evidence that increased attractiveness of male rats that had recently copulated was mediated by olfactory cues, and that female rats tended to affiliate with males that had engaged in sexual activity but not with males that had spent time with anoestrous females. [Copyright &y& Elsevier]

The presence of introduced Norway rats Rattus norvegicus has raised concerns for the fate of the large least auklet Aethia pusilla colony situated at Sirius Point, Kiska Island, Alaska. Previous studies have documented extreme interannual variation in least auklet reproductive success and potential drastic population declines, both of which have been attributed to the varying abundance of, and predation by, Norway rats. A diet study would resolve the uncertainty that remains about the role of rats in the auklet's reproductive failure and the colony's decline. Our main objectives here were to quantify the variation in diet of introduced Norway rats and assess predation on least auklets. Using stable isotope analysis we document wide variability in rat diet dependent on location and provide direct evidence that Norway rats are preferentially preying on least auklets at Sirius Point. In conclusion, we hypothesize that the observed wide variability in rat diet will contribute to the persistence of rats on Kiska long after auklets have been extirpated. The persistence of rats enabled by their foraging plasticity will increase their effects by creating ecological traps within which prospecting individuals will fall and be depredated. This has large conservation consequences as it suggests that when seabirds are extirpated recolonization by prospecting birds is virtually impossible and island ecosystems will continue to be negatively affected and altered as long as introduced predators, such as rats, remain within them. [ABSTRACT FROM AUTHOR]

The general hypothesis underlying this paper is that behavior in traditional paradigms of laboratory learning is based on niche-related mechanisms. The specific hypothesis is that the behavior of Norway rats in laboratory mazes is based on niche-related mechanisms related to trail following and navigating. I evaluate seven types of evidence for this hypothesis: (a) resemblance of maze behavior to behavior in unconstrained settings; (b) importance of experimenter tuning of apparatus and procedures; (c) overdetermination of laboratory behavior; (d) reverse-engineering of niche-related mechanisms from laboratory data; (e) prediction of laboratory results from ecological data; (f) contribution of specific relative to general mechanisms; and (g) phylogenetic conservation and ecologically-based convergence and divergence of maze mechanisms. I conclude there is strong evidence for the hypothesis that behavior of rats in laboratory mazes is based on niche-related mechanisms. I suggest that a niche-related approach to laboratory learning paradigms has conceptual generality and the potential to facilitate connections with the study of neurophysiology, genetics, and evolution. [Copyright &y& Elsevier]

In laboratory experiments, carbon disulfide (CS2) increases the attractiveness of feeding stations to rats and mice. Bait consumption is also increased, and the effects are more pronounced for females than for males. The present study was designed to assess whetherCS2 would enhance consumption of a standard bait formulation by wild Norway rats (Rattus norvegicus). The results showed that consumption was tripled when bait was paired with CS2. We speculate that CS2 could similarly enhance the effectiveness of rodenticide bait formulations to which it is applied. Extensive field tests of CS2 as a rodent attractant appear warranted.

Current rodent control practices for the Hawaiian sugar industry revolve around the use of single grain baits containing anticoagulants in bait stations and zinc phosphide for aerial applications. Neither type of control programs as they are now applied has been very effective against the Norway rat (Rattus norvegicus) which is becoming a major problem species for the industry. As a result, we have sought a more effective anticoagulant, to which the Norway rat is more susceptible, and an improved method of bait distribution. With a knowledge of the month-to-month variation in the field rodents' gestation rate, a new control program is being developed which involves the distribution of diphacinone oats in plastic bags to precede the major annual gestation peaks.

A detailed description of problems of Norway rat infestation of sanitary sewer systems is provided, as well as a review of control methods and materials. Design and maintenance of urban sewer systems can reduce rat problems, but ongoing effective rat control programs typically must include use of rodenticides. Commonly used active ingredients are discussed, as is the formulation and application of baits appropriate for use in sewer systems. The need for prebaiting when using acute toxicants is noted, as is the desirability of including mold inhibitors into bait formulations when using paraffin baits or anticoagulant baits, which require repeated feeding to be lethal. A method for locating rodents burrows that are connected to main sewer lines or laterals is described, using smoke bombs and portable blowers to force smoke through sewer systems and reveal locations where rats have points of access. Components of an effective strategy to control Norway rat infestations in sewers are discussed, and literature citations are provided.

While the problem of anticoagulant resistance in commensal rodents has been well-documented from certain areas of northern Europe in recent years, this paper describes its first known occurrence in North America in 1971. Over a rural area of about 5 square miles in Johnson County, North Carolina, it was noted that attempts to control Norway rats using typical warfarin rodenticide bait were increasingly ineffective. Diphacinone was alternated with warfarin with no success. On one farm, 200 lbs of bait had been used in bait boxes in a single month. Laboratory trials on rats captured at this location demonstrated resistance. It was concluded that at this location, intensive use of anticoagulants (mostly warfarin) over a decade, in the absence of adequate sanitation and building maintenance, provided the selective agent to develop resistant populations. This likely will be repeated elsewhere in the U.S.

Apart from using 0.005% concentration, the recommended field dose of 0.025% of the anticoagulant is used along with an alternate food for individual rats for a varying number of days. Those that had survived were taken as tolerant, provided they showed an mg/kg intake beyond the tolerance limit, survived a six days of feeding, exhibited bait-shyness, and did not exhibit hemorrhage after death. In determining the criteria for tolerance to an anticoagulant by a rat, one should take into account four composite factors. These are, six days of even 0.025% feeding, bait-shyness when alternate food is given, higher mg/kg intake than the tolerance level, and a loss of intensive hemorrhage after death.