Complex behavioral plasticity is not reduced in spiderlings with miniature brains

Abstract

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 interspecific comparisons found that aspects of web construction behavior of very small orb weaving spiders (0.005 mg) were no less precise than those of much larger related orb weavers (30 mg), but the behaviors tested were relatively simple. Here we perform a more sensitive intraspecific test involving the multiple behavioral adjustments of orb web designs made by Leucauge argyra to confinement in very small spaces. Web adjustments of spiderlings as small as ~0.1 mg were compared to previously published observations of ~80 mg conspecific adults. 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.

White Paper: An Integrated Perspective on the Causes of Hypometric Metabolic Scaling in Animals

“…Furthermore, brain miniaturization is likely facilitated by adaptive changes in neuron function and structure and/or molecular mechanisms that maximize energy efficiency ( Niven and Laughlin 2008 ; Niven and Farris 2012 ; Kamhi et al 2016 ). Yet, in miniaturized invertebrates in which the brain may compose up to 15% of body size ( Seid et al 2011 ; Polilov and Makarova 2017 ) and brain size increase is accommodated by neuropil extension into the thorax or leg segments ( Quesada et al 2021 ), it seems likely that brains may contribute very significantly to whole-body metabolism. In general, we are lacking data on the metabolic scaling of brains to test this hypothesis in invertebrates.…”