Despite the importance of body growth in shaping life history tactics and population dynamics, exploring individual growth trajectories in the wild remains challenging. Here, we quantified wild boar growth trajectories at both the population and the individual levels using standard growth models (i.e. Gompertz, logistic, and monomolecular models) that encompass the expected range of growth shapes. According to current theories of life history evolution, we expect wild boar to display a sex-specific Gompertz type growth trajectory and lower size dimorphism in the poorer environment. While wild boar displayed the expected Gompertz type trajectory in the rich site at the population level, we found differences in growth shapes between the two populations and among individuals within each population. Asymptotic body mass, growth rate and timing of maximum growth rate differed as well, indicating a high flexibility of growth trajectories in wild boar. In addition, we found a cohort effect on asymptotic body mass suggesting that environmental conditions early in life shape body mass at adulthood. Our findings demonstrate that body growth trajectories in wild boar are context-, sex- and cohort-specific, differing between populations and among individuals within a population.

The study was conducted in two French wild boar populations subject to contrasting environments. The population in the 11,000 ha forest of Châteauvillain in north-eastern France (48.02°N, 4.56°E) is heavily harvested (on average 727.18 ± 282.07 individuals shot per year, see Veylit et al. 2020b), with hunting being oriented towards young individuals (juveniles, see Gamelon et al. 2011). The forest is characterised by a climate intermediate between continental and oceanic and dominated by beech (Fagus sylvatica) and oak (Quercus spp.), which produce preferred forage for wild boar (Gamelon et al. 2017; Servanty et al, 2011, Touzot et al. 2020). The second population is found in the 2,614 ha Réserve Biologique Intégrale at Chizé in south-western France (46.05°N, 0.25°W), characterized by mild winters and often warm, dry summers. As the soil in Chizé is of poor quality and the site is subject to frequent summer droughts, the forest productivity is low (Pettorelli et al. 2006). The site is therefore considered of poor quality (Douhard et al. 2013; Gaillard et al. 2003). The population in Chizé is subject to a light hunting pressure (on average 101.50 ± 80.94 individuals shot per year, see Veylit et al. 2020b).

In both sites, a capture-mark-recapture-recovery program allows for capturing, marking using traps, then releasing wild boars each year between March and September. Additionally, between October and February individuals are removed each year from both populations by either hunting or translocation. Sex, date, and body mass to the nearest 0.1 kg are recorded for each individual first caught below 20 kg (i.e. younger than 6 months of age) and later on, during subsequent captures (alive and dead when shot by hunters). Based on tooth eruption patterns, the youngest animals trapped were 3 months of age (Gamelon et al. 2011). Only measurements collected more than seven days apart were included in the analyses (see Veylit et al. 2020a).

For the large dataset, we only retained individuals with at least three body mass measurements, including two measurements taken in the first 6 months of age (i.e. below 20 kg) to assess the early-life growth rate during the stage when growth is linear (Gaillard et al. 1992, Veylit et al. 2020), and one measurement taken later in life (i.e. above 20 kg) to assess body growth later in life. In Châteauvillain and Chizé, there was an average of 411.46 (range 36-2722) and 608.70 (range 42-2052) days, respectively, between the first and the last captures.

For the small dataset, we then reduced the large dataset to only the individuals that were weighed the last time at least 2 years after the first measurement and had more than two mass measurements at or above 20 kg (i.e. older than 6 months).

Weight = live body mass in grams

years.from.capture = number of years elapsed between first and current mass measurement

Site = corresponds to the study area where an individual was captured

ID = unique identifiying number for each individual in each study area (i.e. unique to individuals within study areas)