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Selective relationships are fundamental to humans and many other animals, but relationships between mates, family members, or peers may be mediated differently. We examined connections between social reward and social selectivity, aggression, and oxytocin receptor signaling pathways in rodents that naturally form enduring, selective relationships with mates and peers (monogamous prairie voles) or peers (group-living meadow voles). Female prairie and meadow voles worked harder to access familiar versus unfamiliar individuals, regardless of sex, and huddled extensively with familiar subjects. Male prairie voles displayed strongly selective huddling preferences for familiar animals, but only worked harder to repeatedly access females versus males, with no difference in effort by familiarity. This reveals a striking sex difference in pathways underlying social monogamy and demonstrates a fundamental disconnect between motivation and social selectivity in males—a distinction not detected by the partner preference test. Meadow voles exhibited social preferences but low social motivation, consistent with tolerance rather than reward supporting social groups in this species. Natural variation in oxytocin receptor binding predicted individual variation in prosocial and aggressive behaviors. These results provide a basis for understanding species, sex, and individual differences in the mechanisms underlying the role of social reward in social preference. What factors drive the formation of social relationships can vary greatly in animals. While some individuals may be motivated to find social partners, others may just tolerate being around others. A desire to avoid strangers may also lead an individual to seek out acquaintances or friends. Sometimes a mix of these factors shape social behavior. Studying motivation for social relationships in the laboratory is tricky. Traditional laboratory animals like mice and rats do not bond with specific peers or mates. But small burrowing rodents called voles are a more relationship-oriented alternative to mice and rats. Prairie voles form selective and enduring preferences for both their mates and familiar same-sex peers. Meadow voles on the other hand, live alone much of the year but move in with other animals over the winter. Beery et al. show that social motivation in voles varies by relationship type, species and sex. In the experiments, voles were first trained to press a lever to get a food reward. Then, the food reward was swapped with access to familiar or unfamiliar voles. Female prairie voles strived to be with animals they knew rather than to be with strangers, while male prairie voles tried hard to access any female. In contrast, meadow voles did not overly exert themselves to access other animals. Beery et al. then measured oxytocin receptor levels in the brains of prairie voles. Prairie voles that had more receptors for oxytocin in part of their brain known as the nucleus accumbens worked harder to access their familiar partner. But individuals with more oxytocin receptors in the bed nucleus of the stria terminalis were more likely to attack an unfamiliar animal. The meadow voles’ behavior suggests that they are more motivated by tolerance of familiar animals, while the female prairie voles may find it rewarding to be with animals they have bonded with. These differences may help explain why these two species of vole have evolved different social behaviors. The experiments also suggest that oxytocin – which is linked with maternal behavior – plays an important role in social motivation. Learning more about the biological mechanisms that underlie vole social behaviors may help scientists identify fundamental aspects of social behavior that may apply to other species including humans.

Candidatus Neoehrlichia mikurensis (CNM) and Hepatozoon spp. are important vector-borne parasites of humans and animals. CNM is a relatively recently discovered pathogen of humans. Hepatozoon are parasites of reptiles, amphibians and mammals, commonly found in rodents and carnivores worldwide. The present study aimed to determine the prevalence of CNM and Hepatozoon spp. in three species of Microtus and to assess the occurrence of vertical transmission in naturally-infected voles. Molecular techniques were used to detect pathogen DNA in blood and tissue samples of captured voles and their offspring. The prevalence of CNM in the vole community ranged 24–47% depending on Microtus species. The DNA of CNM was detected in 21% of pups from three litters of six infected Microtus dams (two Microtus arvalis and one M. oeconomus ) and in 3/45 embryos (6.6%) from two litters of eight CNM-infected pregnant females. We detected Hepatozoon infection in 14% of M. arvalis and 9% of M. oeconomus voles. Hepatozoon sp. DNA was detected in 48.7% of pups from seven litters (6  M.   arvalis and 1 M.   oeconomus ) and in two embryos (14.3%) obtained from one M. arvalis litter. The high prevalence of CNM infections in the Microtus spp. community may be a result of a relatively high rate of vertical transmission among naturally infected voles. Vertical transmission was also demonstrated for Hepatozoon sp. in M. arvalis and M. oeconomus . Our study underlines the significance of alternative routes of transmission of important vector-borne pathogens.

The humble prairie vole (Microtus ochrogaster) has long been revered for its unusual commitment to family. [...]a study published on 27 January in Neuron challenges decades of research that suggests the 'love hormone' oxytocin and the protein it binds to is responsible for the voles' domestic bliss. For decades, neuroscientists interested in understanding the biological underpinnings of human social behaviours have been fascinated by prairie voles.

Background Ixodid ticks are important vectors for zoonotic pathogens, with Ixodes ricinus being the most important in Europe. Rodents are hosts of immature life stages of I. ricinus ticks and are considered main reservoirs for tick-borne pathogens, e.g. Borrelia burgdorferi . The aim of this study was to analyse the prevalence as well as genospecies and sequence type (ST) diversity of Borrelia burgdorferi sensu lato in ticks and small mammals from central Germany and to elaborate on the influence of environmental and/or individual host and vector factors on Borrelia prevalence. Methods After species identification, 1167 small mammal skin samples and 1094 ticks from vegetation were screened by B. burgdorferi sensu lato real-time polymerase chain reaction, and positive samples were characterized by multilocus sequence typing. Generalized linear (mixed) models were used to estimate how seasonality, small mammal species/tick life stage and habitat affect individual infection status. Results In total, 10 small mammal species and three tick species, Ixodes ricinus , Ixodes inopinatus (both considered members of the I. ricinus complex) and Dermacentor reticulatus , were investigated. Borrelia DNA was detected in eight host species, i.e. the striped field mouse ( Apodemus agrarius ), the yellow-necked field mouse ( Apodemus flavicollis ), the wood mouse ( Apodemus sylvaticus ), the water vole ( Arvicola amphibius ), the bank vole ( Clethrionomys glareolus ), the field vole ( Microtus agrestis ), the common vole ( Microtus arvalis ), and the common shrew ( Sorex araneus ). Two species were Borrelia negative, the greater white-toothed shrew ( Crocidura russula ) and the pygmy shrew ( Sorex minutus ). The average prevalence was 6.2%, with two genospecies detected, Borrelia afzelii and Borrelia garinii , and at least three STs that had not been previously reported in small mammals. Borrelia prevalence in small mammals did not differ between seasons. Six genospecies of Borrelia —Borrelia afzelii , Borrelia valaisiana , Borrelia garinii , Borrelia lusitaniae , Borrelia spielmanii , and Borrelia burgdorferi sensu stricto—and 25 STs of Borrelia , of which 12 have not been previously described at all and five have not been previously reported in Germany, were detected in 13% of I. ricinus complex ticks. Prevalence was highest in adult females (25.3%) and lowest in nymphs (11.4%). Prevalence was significantly higher in ticks from grassland (16.8%) compared to forests (11.4%). Conclusions The high level of small mammal diversity in this region of Germany seems to be reflected in a wide variety of genospecies and STs of B. burgdorferi . Graphical abstract

Background Bartonella spp. cause persistent bacterial infections in mammals. Although these bacteria are transmitted by blood-feeding arthropods, there is also evidence for vertical transmission in their mammalian hosts. We aimed to determine: (i) the prevalence and diversity of Bartonella spp. in a Microtus spp. community; (ii) whether vertical transmission occurs from infected female voles to their offspring; (iii) the effect of concurrent Babesia microti infection on the success of vertical transmission of Bartonella ; and (iv) the impact of congenital infection on pup survival. Results We sampled 124 Microtus arvalis , 76 Microtus oeconomus and 17 Microtus agrestis . In total, 115 embryos were isolated from 21 pregnant females. In the following year 11 pregnant females were kept until they had given birth and weaned their pups ( n = 62). Blood smears and PCR targeting the Bartonella- specific rpoB gene fragment (333bp) were used for the detection of Bartonella . Bartonella DNA was detected in 66.8% (145/217) of the wild-caught voles. Bartonella infection was detected in 81.8% (36/44) of pregnant female voles. Bartonella -positive individuals were identified among the embryos (47.1%; 40/85) and in 54.8% (34/62) of pups. Congenitally acquired Bartonella infections and co-infection with B. microti had no impact on the survival of pups over a 3-week period post partum . Among 113 Bartonella sequences, four species were detected: Bartonella taylorii , Bartonella grahamii , Bartonella doshiae and a Bartonella rochalimae -like genotype. Bartonella taylorii clade B was the dominant species in wild-caught voles (49%), pregnant females (47%), their embryos (85%), dams (75%) and pups (95%). Conclusions High prevalence of Bartonella spp. infection maintained in Microtus spp. community is followed by a high rate of vertical transmission of several rodent species of Bartonella in three species of naturally infected voles, M. arvalis , M. oeconomus and M. agrestis . Congenitally acquired Bartonella infection does not affect the survival of pups. Co-infection with B. microti does not affect the effectiveness of the vertical transmission of Bartonella in voles. Bartonella taylorii clade B was found to be the dominant species in wild-caught voles, including pregnant females and dams, and in their offspring, and was also found to be the most successful in vertical transmission.

Remains of the North American water vole (Microtus richardsoni) have previously been recovered from late Pleistocene and Holocene deposits in southwestern Alberta, western Montana, and north-central Wyoming. All are within the historically documented modern range of the metapopulation occupying the Rocky Mountains; no ancient remains of this large microtine have previously been reported from the metapopulation occupying the Cascade Range. Four lower first molar specimens from the late Holocene Stemilt Creek Village archaeological site in central Washington here identified as water vole are from the eastern slope of the Cascade Range and are extralimital to the metapopulation found in those mountains. There is no taphonomic evidence indicating long-distance transport of the teeth, and modern trapping records suggest the local absence of water voles from the site area today is not a function of sampling error. The precise age of the Stemilt Creek Village water voles is obscure but climate change producing well-documented late Holocene advances of nearby alpine glaciers could have created habitat conditions conducive to the apparent modest shift in the range of the species represented by the remains.

There are no published studies on the diet of Mogollon voles (Microtus mogollonensis) although this species occurs throughout the Southwest in montane forestlands. Mogollon voles are believed to be herbivorous, selecting the vegetative portion of grass as their dominant food source. Herbivores frequently select more easily digested C sub(3) plants over C sub(4) plants; we thus expected Mogollon voles would feed primarily on C sub(3) plants. We collected hair samples from Mogollon voles captured in northern Arizona between 1967 and 2003 and plant samples from some capture sites. Then we compared stable carbon ( delta super(13)C) and nitrogen ( delta super(15)N) isotope ratios to investigate dietary preferences for C sub(3) or C sub(4) plants. Mean isotope ratios for C sub(3) plants we sampled were -26.84ppt (s = 0.17) for delta super(13)C and -0.02ppt (s = 0.32) for delta super(15)N. For C sub(4) plants, mean isotope ratios for delta super(13)C and delta super(15)N were -15.04 ppt (s = 0.38) and -0.74ppt (s = 0.55), respectively. Mogollon voles were largely herbivorous based on delta super(15)N (mean and standard error: 3.77 plus or minus 0.17ppt) and used C sub(3) plants more than C sub(4) based on delta super(13)C (-24.21 plus or minus 0.14ppt). Activities that lead to changes in plant species composition or reduction in C sub(3) plants in montane grasslands and forests (e.g., excessive ungulate grazing) may reduce habitat quality for Mogollon voles.

We analyzed the cranium dorsal projection and the mandible lateral projection in bone specimens from five Microtus guentheri and Microtus hartingi forms by geometric morphometrics (GM) methods (generalized Procrustes analysis, principal component analysis, canonical variance analysis, and discriminant function analysis). Analyses of the linear size and shapes of the cranium and lower jaw showed clear-cut differentiation among the forms into an eastern cluster and western cluster, matching M. guentheri and M. hartingi, respectively. Differences were revealed both between two subspecies of M. guentheri and between the subspecies M. h. strandzensis and Rhodopean M. hartingi, whose subspecies status has not yet been determined. M. h. ankaraensis bone specimens differ in many parameters of GM from the studied European specimens and to a lesser extent from M. g. guentheri and M. g. philistinus. Calculated morpho-ecological indices of the lower jaw revealed significant differences among all these forms, thereby possibly indicating adaptation of each to a specific habitat and dietary habits. Because of the emergence of impenetrable barriers for voles (the Anatolian Diagonal in the east and the Dardanelles and Bosporus in the west), the resultant vole groups have evolved independently.

Associations between species of Laelapidae (Mesostigmata: Dermanyssoidea) mites and small rodents have been studied insufficiently. The aim of this study was to investigate infestation patterns of small rodent species by laelapid mites at six locations in Lithuania. A total of 728 rodents were snap- and live-trapped in various locations during 2013–2016. Eight rodent species were identified, namely Apodemus flavicollis, Apodemus agrarius, Myodes glareolus, Micromys minutus, Mus musculus, Microtus oeconomus, Microtus arvalis and Microtus agrestis. A total of 343 (47.1%) rodents were found to be infested with up to eight species of parasitic mites from the Laelapidae family (n = 1363): Laelaps agilis, Laelaps hilaris, Hyperlaelaps microti, Haemogamasus nidi, Haemogamasus hirsutus, Eulaelaps stabularis, Hirstionyssus sunci and Myonyssus gigas. The dominant species of mite found on rodents was L. agilis (89.1%), found on 43.4% of all hosts. Abundance and mean intensity of infestation with mites varied among species of hosts and were highest for A. flavicollis. We document new geographical and host records for gamasid mites of eight rodent species in Lithuania.