Transgenerational loss and recovery of early learning ability in foraging predatory mites.

The ability to learn is ubiquitous in animals but highly variable within and between species, populations and individuals. Diet-related circumstances, such as diet quantity and quality can influence both long-term constitutive (genetic; by selection) and short-term operational (non-genetic; by the immediate circumstances) learning performance. Here, we scrutinized the causes of loss of learning ability, following multi-generational feeding on pollen, in a line of the predatory mite Amblyseius swirskii, which was previously well able to learn prey during early life, enhancing foraging later in life. We investigated whether, and, if so, how quickly, a transgenerational diet switch to live prey restores the early learning ability of foraging predatory mites. The first experiment shows that the early learning ability was restored after switching the diet of the pollen-fed predator line to live spider mites for two generations before conducting the behavioral assay. The second experiment reveals that offspring regained their learning ability if the diet of their mothers was switched from pollen to spider mites for 3 or 10 days before offspring production. Both experiments in concert suggest transgenerational, pollen-induced operational loss of learning ability in the predatory mite A. swirskii. Maternally-transmitted nutrient deficiency and/or maternally-induced epigenetic changes are the most plausible explanations for the pollen diet-induced loss of learning ability. Our study represents a key example for maternal diet-induced variation in learning ability.