Sociospatial structure explains marked variation in brucellosis seroprevalence in an Alpine ibex population

In a context of (re)emerging infectious diseases with wildlife reservoirs, understanding how animal ecology shapes epidemiology is a key issue, particularly in wild ungulates that share pathogens with domestic herbivores and have similar food requirements. For the first time in Europe, brucellosis (Brucella melitensis), a virulent zoonosis, persisted in an Alpine ibex (Capra ibex) population and was transmitted to cattle and humans. To better understand disease dynamics, we investigated the relationships between the spatial ecology of ibex and the epidemiology of brucellosis. Combining home range overlap between 37 GPS-collared individuals and visual observations of 148 visually-marked individuals monitored during the 2013–2016 period, we showed that females were spatially segregated in at least 4 units all year round, whereas males were more prone to move between female units, in particular during the rutting period. In addition to ibex age, the spatial structure in females largely contributed to variation in seroprevalence in the whole population. These results suggest that non-sexual routes are the most likely pathways of intraspecific transmission, crucial information for management. Accounting for wildlife spatial ecology was hence decisive in improving our ability to better understand this health challenge involving a wildlife reservoir.

Seasonal variation in space use and spatial structure in 37 GPS-collared Alpine ibex (Capra ibex) from the Bargy massif based on overlap between seasonal home ranges as a measure of distance between individuals.
In order to evaluate the potential seasonal variation in the spatial structure we identified, we performed the same classification procedures as previously presented but using overlap between seasonal UD distinguishing spring (April-June), summer (July-August), autumn (September-09 November), the rutting period ("rut"; 10 November -14 January) and winter (15 January -March). Only individuals monitored during at least half of the focal season are included in analyses. The corresponding home ranges are represented on sex-specific maps. Colors correspond to the different units identified using overlap between annual home ranges as a measure of distance between individuals (see Figure 1). These maps were created using R version 3.4.1 80 : https://cran.r-project.org.
Do the locations of 148 visually-marked individuals confirm the spatial structure identified in the 37 GPS-508 collared individuals ? 509 To check whether the visual observations of the seronegative individuals marked with ear tags or collars allowing individual 510 identification confirmed the existence of the spatial structure identified in the 37 GPS-collared individuals (see Figures 1 and 2   511 for details), we assigned each visually-marked individual to the closest spatial unit based on its capture location (possible for 512 n=148 individuals; number of individuals per sex and spatial unit are given in the figure after "n=").

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Then, for each spatial unit, we calculated the proportion of locations of individual assigned to a given unit that actually fell 514 within the range used by GPS-collared females from the same unit (given in figure as "number of observations in the correct 515 spatial range" / "total number of observations from individuals assigned to the focal unit" and as percentages). 516 We collected these locations in 2012-2015, during the snow-free season (May-September) by recording the composition 517 (sex/age classes) of all the ibex groups observed, identity of marked individuals and by reporting group location on a 100×100m 518 grid. We recorded most of these observations during the censuses that we repeated once a month between May and August, 519 during which 1-2 observers travelled on 1 of the 9 tracks in the morning of a single day or 2 consecutive days.

(B) Males
Locations of observations from visually-marked Alpine ibex (A=71 females; B=77 males) and ranges used by the GPS-collared females (n=21) from the corresponding population unit in the Bargy massif (French Alps). These maps were created using R version 3.4.1 80 : https://cran.r-project.org.

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Model selection table investigating how several classifications of males affect the ordering of models investigating brucellosis seroprevalence in the Alpine ibex (Capra ibex) population from the Bargy massif (northern French Alps).
These models included either (i) the same sociospatial structure in both sexes ("unitsMFall", i.e. individuals divided in units #1 to #5, same approach as that presented in the manuscript), (ii) a sex-specific sociospatial structure ("unitsMF", i.e. females divided in units #1 to #5 and males divided in units #1, #2, #5 and #6 [unit #6 grouping males from units #3 and #4]), or (iii) a sociospatial structure only for females, males being considered a unique group not spatially structured ("unitsF"). In model acronyms, "+" corresponds to additive effects and "×" to the interaction between the 2 factors. k is the number of parameters, LL is the maximum log-likelihood, ∆AIC c is the difference in the Akaike information criterion between the model with the lowest AIC c and the other models, and AIC c weight is Akaike weight. "Age" and "sex" are ibex age (quadratic term) and sex, respectively. "Periods" opposed data collected before and after the slaughtering operations that occurred during autumn 2013 and early spring 2014.  Candidate models fitted to investigate variation in brucellosis seroprevalence in the Alpine ibex Capra ibex population from the Bargy massif (northern French Alps). In model acronyms, "+" corresponds to additive effects and "×" to the interaction between the 2 factors. k is the number of parameters, LL is the maximum log-likelihood, ∆AIC c is the difference in the Akaike information criterion between the model with the lowest AIC c and the other models, and AIC c weight is Akaike weight. "Age" and "sex" are ibex age (quadratic term) and sex, respectively. "UnitsMFall" are sociospatial population units (see Figure 1 and Supplementary information 1). "Periods" opposed data collected before and after the slaughtering operations that occurred during autumn 2013 and early spring 2014. General information on the Alpine ibex Capra ibex equipped with GPS collars in the Bargy massif (French Alps) between 2013 and 2016.
"Begin" and "End" are the dates the GPS monitoring began and ended, respectively. "Nb. relocations" is the total number of relocations recorded by GPS collars during the monitoring duration.