Behaviour 2019
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Complex behavioral plasticity is not lost in spiderlings with miniature brains
William Eberhard Eberhard1,2, Rosannette Quesada1, Gilbert Barrantes1. 1Universidad de Costa Rica, San Jose, SJ, Costa Rica; 2Smithsonian Tropical Research Institute, Panama City, Panama, Panama

The brains of smaller animals are smaller than those of their larger relatives, but it is not clear whether their adaptive behavioral flexibility is more limited. Previous tests found that aspects of orb web construction behavior of very small spiders (0.005 mg) were no less precise than those of much larger relatives (30 mg), but the behaviors tested were relatively simple. Here we perform a more sensitive test involving the multiple behavioral adjustments of orb web designs made by Leucauge argyra  to confinement in very small spaces. Spiderlings in constrained spaces made all of the complex adjustments made by adults in at least seven independent web design variables, and their adjustments were no less precise. Rough estimates based on previously published data on total brain volumes and the mean diameters of neuron cell bodies suggested that spiderlings and adult females of Leucauge may have similar numbers of neurons, due to spiderlings having smaller neurons and a greater percentage of body tissues dedicated to the brain. We speculate that this neural similarity may explain why L. argyra spiderlings showed no behavioral deficits compared with adults.