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

Abstract

The 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.

Visual pathways in the brain of the jumping spider Marpissa muscosa

“…Our results demonstrate that in M. muscosa , the AL2/PL2 represents two closely adjoining second‐order visual neuropils of the ALE and PLE, respectively. In M. muscosa , the AL2/PL2 was also found to react less plastically to different environmental conditions than the MBp (Steinhoff, Liedtke, Sombke, Schneider, & Uhl, ), which was interpreted as further evidence for their function as discrete visual neuropils. Within the AL2/PL2, each glomerulus seems to consist of numerous synaptic complexes and Duelli () estimated roughly 400 synapses per glomerulus in the jumping spider Evarcha arcuta .…”

Old Brains in Alcohol: The Usability of Legacy Collection Material to Study the Spider Neuroarchitecture

“…Internal anatomy is inherently difficult to study due to the necessity of performing invasive histological techniques and dissections in order to document it. Nevertheless, the last decade has seen a growing number of studies that rely on the utilization of X-ray micro-CT scanning for reconstructing and quantifying various internal organs and tissues in spiders [25][26][27][28][29][44][45][46]. Still, we consider that the conscientious use of legacy material can be an important route to fill the taxonomic sampling gaps and more easily and promptly understand the evolution of the spider central nervous system.…”

“…The food level has been shown to have a strong positive impact on the body size development on the cellar spider Pholcus phalangioides, with females investing primarily in weight and size gain when food was abundant [48]. Likewise, the brain volume has shown be very plastic and at least partially dependent on the food supply during development of the jumping spider Marpissa muscosa [28]. (3) Urban Evolution.…”

“…Remarkably, in spiders, its use has allowed the documentation of a variety of sexual, muscular, and nervous organs and systems. This has permitted a quick and reliable way to generate 3D reconstructions and volume measurements that have the potential to become a powerful tool in studies as diverse as systematics, sexual selection, character evolution, and development, among many others [25][26][27][28][29][30]. Most of these studies on spiders have relied on the use of freshly collected material following, in many cases, specific fixation protocols.…”

Need for speed: Short lifespan selects for increased learning ability

“…the brain is costly 26,27 and should only be made if needed. Some experimental studies were able to show a change in brain size or brain compartments with a change in environmental complexity 28–30 and other studies could show a rapid response of brain size to artificial selection regimes 31 . These findings suggest that in nature, too, brain size may readily evolve in such a way as to suit a species’ present ecological conditions.…”