Brushtail possum (Trichosurus vulpecula) social interactions and their implications for bovine tuberculosis epidemiology

in Behaviour
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The brushtail possum is the main reservoir of bovine tuberculosis in New Zealand. Disease prevalence is generally higher in males than in females. This has conventionally been assumed due to greater infection rates of males, but recent work has raised the hypothesis that it may instead be driven by survival differences. With bovine tuberculosis transmission among possums most likely occurring between individuals in close proximity, here we analyse social networks built on data from wild possums collared with contact loggers inhabiting a native New Zealand forest, to investigate whether there is mechanistic support for higher male infection rates. Our results revealed that adult female possums were generally just as connected with adult male possums as other adult males are, with male–female connection patterns not being significantly different. This result suggest that the new ‘survivorship’ hypothesis for the sex bias is more likely than the conventional ‘infection rate’ hypothesis.

Brushtail possum (Trichosurus vulpecula) social interactions and their implications for bovine tuberculosis epidemiology

in Behaviour



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    Definitions of the contact network parameters and the equation notations used in the population-level analysis (Lugton, 1997).

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    Distribution of the number of possums contacted by collared possums in the Orongorongo Valley during the entire study period (data combined across the four trapping grids).

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    Possum social network diagram for each trapping grid, generated by aIgraph in R software. Numbers located at the nodes denote individual possum IDs with males represented by light grey and females by dark grey nodes, respectively. Line thickness is proportional to edge strength. Note that individual placement in diagrams does not represent spatial location.

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    Mean (±SE) possum social network characteristics for each trapping grid. Relative values are adjusted for the number of radio-collared individuals in each grid.

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    Odds ratios for an edge occurring between two possums, given sex, grid assortativity, grid effect, home-range overlap, and the number of geometrically-weighted edge-shared partners (GWESP).

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    Scoring rule value for contact cut-offs from 1 to 20. The scoring rule is minimised for c=10.

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    Model diagnostic plots for degree and edge-shared partners for network with c=10.


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