Early environmental conditions affect the volume of higher‐order brain centers in a jumping spider

Abstract

AbstractThe central nervous system is known to be plastic in volume and structure depending on the stimuli the organism is subjected to. We tested in the jumping spider Marpissa muscosa (Clerck, 1757), whether rearing environments affect the volume of two target higher‐order brain centers: the mushroom body (MB) and the arcuate body (AB). We reared female M. muscosa (N = 39) in three environments: solitarily (D: deprived), solitarily but in a physically enriched environment (P: physically enriched) and together with several siblings (G: group). We additionally investigated spiders caught from the field (W: wild). Volumes of MB and AB were compared using microCT analysis. We hypothesized that spiders reared in treatments P and G should have larger MB and AB than the spiders from treatment D, as the enriched environments are presumably cognitively more demanding than the deprived environment. Spiders from treatment P had significantly larger absolute brain volumes than spiders from treatment D, whereas brain volumes of treatment G lay in between. The relative volume of the MB was not significantly different between the treatments, whereas relative AB volumes were significantly larger in treatment P than in D, supporting the hypothesis that the AB is a center of locomotor control. W spiders had smaller absolute brain volumes and relatively smaller AB than spiders from laboratory treatments, which suggests developmental constraints under natural, possibly food‐limited conditions. Additionally, differences in the relative volume of MB substructures were found. Overall, our study demonstrates that brains of jumping spiders respond plastically to environmental conditions in that absolute brain volume, as well as the relative volume of higher‐order brain centers, is affected.