Reproductive phenology and conception synchrony in a natural wild boar population

Reproductive synchrony among gregarious mammals has a strong adaptive value and may lead to
cooperative behaviors aimed at maximizing offspring survival. Additionally, temporal clustering of
estrus has important implications on individual mating tactics and ultimately affects the degree of
polygamy in a population. Although several studies have examined the reproductive biology of wild
boar (Sus scrofa), much remains to be understood about the patterns of timing and synchrony of reproduction
in natural populations. We analyzed the spatiotemporal distribution of conception dates
in an Italian wild boar population taking into account the effects of environmental and individual
factors, in order to determine the main variables influencing the timing of reproduction and to detect
the signs of a socially-driven reproductive synchrony. Specifically, for each litter belonging to
354 pregnant sows culled between 2006 and 2013 in a mountain area of Tuscany, we determined
the conception date (CD) from an estimate of the mean fetal age and the culling date. We then investigated
which factors drove the variation in CD, by implementing linear mixed models, Mantel
tests and spatial autocorrelation analyses. The selected model showed significant effects of rainfall,
temperatures, and previous and current productivity on CD, as well as a strong correlation of CDs
among sows culled in close spatial and temporal proximity (i.e., in the same hunting ground and
hunting season). Likewise, autocorrelation analyses and Mantel tests consistently indicated that
closer sows had similar conception dates. Overall, our results confirm the effect of resource availability
and climate on wild boar reproductive phenology, and suggest socially-driven reproductive
patterns, in spite of a high turn-over in social groups due to hunting. Finally, possible advantages
and evolutionary implications of reproductive synchrony in wild boar are discussed.