Effects of high density on spacing behaviour and reproduction in Akodon azarae: A fencing experiment

Space Use and Social Mating System of the Hantavirus Host, Oligoryzomys longicaudatus

The long-tailed mouse, Oligoryzomys longicaudatus (Cricetidae: Sigmodontinae), is the major host of Andes hantavirus, the etiological agent of hantavirus pulmonary syndrome in the south of Argentina and Chile. Studying the ecology of this species is necessary to understand how Andes hantavirus is maintained in nature. In this study, we examine the home range size and intra- and intersexual overlap degree of male and female O. longicaudatus in order to elucidate the mating system of this species. To our knowledge, this research provides the first documentation, obtained from a specific design, of spacing and mating systems in this species in Argentina. The study was conducted seasonally from April (autumn) 2012 to October (spring) 2013 in a shrubland habitat of Cholila, Andean region, Argentina. We studied spacing patterns using 59 and 51 home ranges established by adult males and females, respectively, in two 3.24 ha capture-marked and recapture grids. Significant differences between sexes in home range size and overlap degree were found. Male home ranges were always larger than those of females. We observed exclusive space use both among males and females (13.15 ± 18.67, and 3.60 ± 3.43%, respectively). Considering only those males that get access to receptive females (40%), average intersexual overlap value was about 30.82 ± 19.73%. Sexual differences in home range sizes and the spatial avoidance between breeding males, that would reflect intrasexual competition for receptive females, allows us to propose a polygynous mating system for O. longicaudatus.

Is species richness driving intra- and interspecific interactions and temporal activity overlap of a hantavirus host? An experimental test

High species diversity of the potential animal host community for a zoonotic pathogen may reduce pathogen transmission among the most competent host, a phenomenon called the “dilution effect”, but the mechanisms driving this effect have been little studied. One proposed mechanism is “encounter reduction” where host species of low-competency decrease contact rates between infected and susceptible competent hosts, especially in directly transmitted diseases. We conducted an experiment in outdoor enclosures in northwestern Mexico where we manipulated rodent assemblages to assess the effect of species richness on the frequency of intra- and interspecific interactions and activity patterns of a hantavirus reservoir host (North American deermouse; Peromyscus maniculatus). Trials consisted of three treatments of rodent assemblages that differed in species richness, but had equal abundance of deermice; treatment 1 consisted of only deermice, treatment 2 included deermice and one non-competent host species, and treatment 3 included two non-competent host species in addition to deermice. To measure interactions and temporal activity, we strategically deployed foraging stations and infrared cameras. We did not find differences in the frequency of intraspecific interactions of deermice among treatments, but there were significantly more interspecific interactions between deermouse and non-competent hosts in treatment 2 than treatment 3, which is explained by the identity of the non-competent host species. In addition, there were differences in activity patterns between rodent species, and also between deermice from treatment 1 and treatment 2. These results indicate that at least at a small-scale analysis, the co-occurrence with other species in the study area does not influence the frequency of intraspecific interactions of deermice, and that deermice may be changing their activity patterns to avoid a particular non-competent host species (Dipodomys merriami). In conclusion, in this deermouse-hantavirus system a potential dilution effect would not be through intraspecific encounter reduction in the most competent hantavirus host. To identify variables of host assemblages that can influence pathogen transmission, we highlight the need to address the identity of species and the composition of assemblages, not only host species richness or diversity.