Interspecific social interactions and behavioral responses of Apodemus agrarius and Apodemus flavicollis to conspecific and heterospecific odors

Surveillance Strategies of Rodents in Agroecosystems, Forestry and Urban Environments

Rodents belong to the group of occasionally economically significant to very significant pests. Some species, especially synanthropic species, cause material damage in various ways. Successful and sustainable management of rodent control strategies requires different procedures such as prevention and rodent control measures. The present study gives an overview of the most common rodent species and methods for estimating the rodent population to assess the risk of economic damage that may occur due to rodents feeding in field crops, gardens, orchards, and young forest plantations, as well as contamination of stored food. As a prerequisite for effective integrated control of mice and voles, it is necessary to implement an adequate long-term monitoring system of these species, as they are primary pests. The integrated approach improves the treatment efficacy and reduces the treatment costs but also is considered ecologically friendlier compared to conventional measures. An integrated approach should provide an effective strategy for rodent management and control in all types of rodent habitats, from agricultural and forestry production fields to residential and public areas. By combining different preventive measures, it is possible to prevent the presence of pests, which will therefore result in a reduction of pesticide use.

A newly discovered behavior ('tail-belting') among wild rodents in sub zero conditions

Rodents are among the most successful mammals because they have the ability to adapt to a broad range of environmental conditions. Here, we present the first record of a previously unknown thermal adaptation to cold stress that repeatedly occurred in two species of non-commensal rodents (Apodemus flavicollis and Apodemus agrarius). The classic rodent literature implies that rodents prevent heat loss via a broad range of behavioral adaptations including sheltering, sitting on their tails, curling into a ball, or huddling with conspecifics. Here, we have repeatedly observed an undescribed behavior which we refer to as “tail-belting”. This behavior was performed under cold stress, whereby animals lift and curl the tail medially, before resting it on the dorsal, medial rump while feeding or resting. We documented 115 instances of the tail-belting behavior; 38 in Apodemus agrarius, and 77 in Apodemus flavicollis. Thermal imaging data show the tails remained near ambient temperature even when temperatures were below 0 °C. Since the tail-belting occurred only when the temperature dropped below − 6.9 °C (for A. flavicollis) and − 9.5 °C (for A. agrarius), we surmise that frostbite prevention may be the primary reason for this adaptation. It is likely that tail-belting has not previously been documented because free-ranging mice are rarely-recorded in the wild under extreme cold conditions. Given that these animals are so closely-related to laboratory rodents, this knowledge could potentially be relevant to researchers in various disciplines. We conclude by setting several directions for future research in this area.

Living with relatives offsets the harm caused by pathogens in natural populations

Living with relatives can be highly beneficial, enhancing reproduction and survival. High relatedness can, however, increase susceptibility to pathogens. Here, we examine whether the benefits of living with relatives offset the harm caused by pathogens, and if this depends on whether species typically live with kin. Using comparative meta-analysis of plants, animals, and a bacterium (nspecies = 56), we show that high within-group relatedness increases mortality when pathogens are present. In contrast, mortality decreased with relatedness when pathogens were rare, particularly in species that live with kin. Furthermore, across groups variation in mortality was lower when relatedness was high, but abundances of pathogens were more variable. The effects of within-group relatedness were only evident when pathogens were experimentally manipulated, suggesting that the harm caused by pathogens is masked by the benefits of living with relatives in nature. These results highlight the importance of kin selection for understanding disease spread in natural populations.

Population increase and synurbization of the yellow-necked mouse Apodemus flavicollis in some wooded areas of Warsaw agglomeration, Poland, in the years 1983–2018

Studies on the contribution of the yellow-necked mouse Apodemus flavicollis and of other vertebrates to the diet of the tawny owl Strix aluco were carried out in Warsaw (central Poland) in the years 1983–2018. The frequency of the yellow-necked mouse in owl pellets increased at the break of the 20th and 21st centuries, particularly in some woodlands in the peri-urban area of the agglomeration. In the second half of the first decade of the twenty-first century, this mouse species colonised a park in the city centre. The yellow-necked mouse may become an important competitor for the synurbic population of the striped field mouse Apodemus agrarius.

Asian house rats may facilitate their invasive success through suppressing brown rats in chronic interaction

BACKGROUND

The Asian house rat (Rattus tanezumi) and the brown rat (Rattus norvegicus) are closely related species and are partially sympatric in southern China. Over the past 20 years, R. tanezumi has significantly expanded northward in China and partially replaced the native brown rat subspecies, R. n. humiliatus. Although invasive species are often more aggressive than native species, we did not observe interspecific physical aggression between R. tanezumi and R. n. humiliatus. Here, we focused on whether or not R. tanezumi was superior to R. n. humiliatus in terms of nonphysical competition, which is primarily mediated by chemical signals.

RESULTS

We performed two laboratory experiments to test different paradigms in domesticated R. tanezumi and R. n. humiliatus. In Experiment 1, we caged adult male rats of each species for 2 months in heterospecific or conspecific pairs, partitioned by perforated galvanized iron sheets, allowing exchange of chemical stimuli and ultrasonic vocalization. The sexual attractiveness of male urine odor showed a tendency (marginal significance) to increase in R. tanezumi caged with R. n. humiliatus, compared with those in conspecific pairs. Hippocampal glucocorticoid receptor (GR) and brain-derived nutrition factor (BDNF) mRNA were upregulated in R. n. humiliatus and R. tanezumi, respectively, when the rats were caged in heterospecific pairs. In Experiment 2, we kept juvenile male rats in individual cages in rooms with either the same or the different species for 2 months, allowing chemical interaction. The sexual attractiveness of male urine was significantly enhanced in R. tanezumi, but reduced in R. n. humiliatus by heterospecific cues and mRNA expression of hippocampal GR and BDNF were upregulated by heterospecific cues in R. n. humiliatus and R. tanezumi, respectively. Although not identical, the results from Experiments 1 and 2 were generally consistent.

CONCLUSIONS

The results of both experiments indicate that nonphysical/chronic interspecific stimuli, particularly scent signals, between R. n. humiliatus and R. tanezumi may negatively affect R. n. humiliatus and positively affect R. tanezumi. We infer that chronic interspecific interactions may have contributed to the invasion of R. tanezumi into the range of R. n. humiliatus in natural habitats.

Analysis on Population Level Reveals Trappability of Wild Rodents Is Determined by Previous Trap Occupant

Live trapping is central to the study of small mammals. Thus, any bias needs to be understood and accounted for in subsequent analyses to ensure accurate population estimates. One rarely considered bias is the behavioural response of individuals to the trap, in particular the olfactory cues left behind by previous occupants (PO). We used a data set of 8,115 trap nights spanning 17 separate trapping sessions between August 2002 and November 2013 in Wytham Woods, Oxfordshire, UK to examine if the decision to enter a trap was affected by the PO, if this was detectable in traditional Capture-Mark-Recapture trapping data (i.e., individuals not uniquely marked), and if it was possible for this effect to bias the population estimates obtained. Data were collected on Apodemus sylvaticus, Myodes glareolus, and Microtus agrestis. Three Generalised Linear Models revealed a significant tendency for the three species to enter traps with same-species PO. With, for example, A. sylvaticus 9.1 times more likely to enter a same species PO trap compared to one that contained a M. agrestis in the grassland during the nocturnal period. Simulation highlighted that, when all other factors are equal, the species with the highest PO effect will have the highest capture rate and therefore return more accurate population estimates. Despite the large dataset, certain species-, sex-, and/ or age-combinations were under-represented, and thus no effects of any additional individual-specific characteristics could be evaluated. Uniquely marking individuals would allow for the PO effect to be disentangled from other biases such as trap-shyness and spatial heterogeneity, but may not be possible in all cases and will depend on the aims of the study and the resources available.

Social information and community dynamics: nontarget effects from simulating social cues for management

Artificially creating social stimuli may be an effective tool for facilitating settlement by rare and/or declining species into suitable habitat. However, the potential consequences for other community members have not been explored and should be considered when evaluating the overall utility of using such management strategies. I report on nontarget, community-wide effects that occurred when manipulating social cues of two competitors that are species of concern in the western United States, the dominant Least Flycatcher (Empidonax minimus) and the subordinate American Redstart (Setophaga ruticilla). The experiment consisted of surveying birds during a pretreatment year, which allows for the control of baseline communities, and a treatment year, in which treatments were applied just prior to settlement by migratory birds. Treatments included broadcasting songs of flycatchers and redstarts and were compared to controls. While the addition of redstart cues did not significantly influence community structure, the addition of flycatcher cues reduced species richness of migratory birds by approximately 30%. This pattern was driven by an absence of local colonizations of small-bodied migrants to sites with added flycatcher cues, rather than by local extinctions occurring from manipulations. The artificial flycatcher stimuli were more responsible for declines in species richness than were changes in actual flycatcher densities. I conclude by identifying some fundamental issues that managers and conservation practitioners should weigh when considering simulating social cues for species conservation prior to implementation.