Abstract
Animal social behaviour can have important effects on the long-term dynamics of diseases. In particular, preferential spatial relationships between individuals can lead to differences in the rates of disease spread within a population. We examined the concurrent influence of genetic relatedness, sex, age, home range overlap, time of year, and prion disease status on proximal associations of adult Rocky Mountain mule deer (Odocoileus hemionus hemionus) in a chronic wasting disease endemic area. We also quantified the temporal stability of these associations across different sex, age, and disease status classes. We used three years of high frequency telemetry data from 74 individuals to record encounters within 25 m of each other, and to calculate seasonal home range overlap measured by volume of intersection (VI). The strength of pairwise spatial association between adult mule deer was independent of genetic relatedness, age and disease status. Seasonal variation in association strength was not consistent across years, perhaps due to annual changes in weather conditions. The influence of home range overlap on association strength varied seasonally, whereby associations were stronger in pre-rut and fawning than in the rest of the seasons. The sexes of individuals also interacted with both VI and season. At increasing levels of VI, associations were stronger between females than between males and between females and males. The strongest associations in pre-rut were between males, while the strongest in rut were between females and males. The temporal stability of associations was markedly dependant on the sex and the diagnosis of the associating pair. Our findings highlight the importance of considering concurrent effects of biological and environmental factors when seeking to understand the role of social preference in behavioural ecology and disease spread. Applying this knowledge in epidemiological modelling will shed light on the dynamics of disease transmission among mule deer.
Highlights
The likelihood and duration of associations between individuals are influenced by social structure, inter-group mixing and the size and composition of social groups [1, 2]
Social behaviours that influence contact rates and the sharing of space in animal species are potentially important factors in information and disease spread within populations [1, 67]
Data on association patterns have proven useful in understanding the ecology of diseases that can be transmitted through both direct and environmental contacts, such as tuberculosis in wild animals [3, 68, 69], and Chronic wasting disease (CWD) in female white-tailed deer [4]
Summary
The likelihood and duration of associations between individuals are influenced by social structure, inter-group mixing and the size and composition of social groups [1, 2]. Chronic wasting disease (CWD) affects farmed and free-ranging mule deer (Odocoileus hemionus) and other cervids in USA and Canada, and most recently free-ranging reindeer (Rangifer tarandus tarandus) and moose (Alces alces) in Norway It is a fatal, neurodegenerative, contagious prion disease that is expected to reduce mule deer population sizes [6, 7]. It is proving extremely difficult to eradicate once established within wild populations [8] The complexity of this disease is due to its transmission through both animal-to-animal contact and through the environment, its lengthy infectious period (>1.5 years), and the persistence of prions in the environment for at least 2.5 years [9, 10]. While there have been relevant studies done on association patterns among female white-tailed deer (Odocoileus virginianus) [4, 12] and their home range establishment [13], it is important to collect data specific to mule deer and to both sexes
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