Shy is sometimes better: personality and juvenile body mass affect adult reproductive success in wild boars, Sus scrofa

Abstract

There is increasing evidence that animal personalities are linked to different life history strategies. However, studies examining whether these effects differ under varying environmental conditions are rare. Here, we investigated how animal personality affects reproductive success in a pulsed resource consumer, the wild boar. We determined the exploratory behaviour of 57 female wild boars in nine novel object tests and additionally assessed their aggressiveness. Exploration behaviour (i.e. approach latency and investigation duration) and aggressiveness were repeatable within individuals and both mapped on a single principal component yielding an individual personality score. Afterwards the females were kept together with 28 males under seminatural conditions in two large breeding enclosures from 2011 to 2014. Over winter 2013/2014 we applied high versus medium feeding regimes to the two enclosures. Our results show that adult body mass and reproductive success were affected by juvenile body mass and thus already determined early in life, which may point to a silver spoon effect in the wild boar. Whether a female reproduced or not, as well as the litter size shortly after birth, was only affected by female body mass. The postweaning litter size (i.e. at the time of independence at the age of about 6 months), however, was additionally affected by the personality score in interaction with food availability. Under high food availability less aggressive and explorative individuals raised more juveniles to independence. We conclude that lower aggressiveness and reduced exploratory tendency of the mother lead to lower juvenile mortality and hence have a positive impact on postweaning litter size. Under slightly decreased food availability, however, this effect vanished. As the impact of personality on reproductive success differed between changing environmental conditions, our results support the hypothesis that different personality phenotypes are evolutionarily maintained by varying selection pressures in heterogeneous environments.