Navigation strategies in three nocturnal lemur species: diet predicts heuristic use and degree of exploratory behavior.

Humans generally solve multi-destination routes with simple rules-of-thumb. Animals may do the same, but strong evidence is limited to a few species. We examined whether strepsirrhines, who diverged from haplorhines more than 58 mya, would demonstrate the use of three heuristics used by humans and supported in vervets, the nearest neighbor rule, the convex hull, and a cluster strategy, when solving a multi-destination route. We hypothesized that the evolution of these strategies may depend on a species' dietary specialization. Three nocturnal lemur species were tested on an experimental array at the Duke Lemur Center. Frugivorous fat-tailed dwarf lemurs (Cheirogaleus medius) were expected to follow paths most consistent with distance-saving navigational heuristics because fruit trees are stationary targets. Gray mouse lemurs (Microcebus murinus) and aye-ayes (Daubentonia madagascariensis), which rely on more mobile and ephemeral foods, were expected to use fewer paths consistent with these heuristics and be more exploratory. Our data supported all of these hypotheses. Dwarf lemurs used paths consistent with all three heuristics, took the shortest paths, and were the least exploratory. Mouse lemurs were quite exploratory but sometimes used paths consistent with heuristics. Aye-ayes showed no evidence of heuristic use and were the most exploratory. Distinguishable patterns of inter- and intra-individual variation in ability to solve the route, speed, and behavior occurred in each species. This research suggests that these simple navigational heuristics are not part of a readily available set of cognitive tools inherited by all primates but instead evolve due to need in each lineage.