Food familiarity does not change nematode feeding behavior

Ability to identify familiar foods is a major driver of animal feeding behavior. Animals show preference for familiar foods over novel ones, presumably to avoid poisonous substances and better support their growth and reproduction. However, we do not know how their feeding behavior is affected when the familiar food is inferior to a novel food with regards to its palatability and nutritional properties. We tested the hypothesis that feeding preference is determined by specific food characteristics rather than food familiarity with fast-growing soil-dwelling nematodes. Two sequential experiments were designed to test the feeding behavior of soil bacterial-feeding nematodes (Mesorhabditis sp. and Acrobeloides sp.) resulting from familiar food recognition, including a 6-months training period to develop their food familiarity and a feeding experiment to test their food preference for five bacterial species. Nematodes showed clear preference for specific food sources, which were not necessarily the familiar food. Their feeding behavior was not affected by food familiarity, but correlated highly with bacterial traits such as cell size, growth rates, and water content. We conclude that nematode feeding behavior was controlled by food specificity rather than familiarity. We further suggest that physiological factors, possibly the physical size and presence of chemical receptors in the buccal cavity, allow nematodes to rapidly assess their food supply and switch from a familiar food to a preferred, novel food that is easier to ingest and better suited to support their growth and reproduction.