LB 3-27 - Mycoplasma infection does not affect equalization of GUDs or micro-patch detection in Allenby’s gerbils (Gerbillus andersoni allenbyi)

Pathogens can impose substantial ecological costs on infected individuals including reduced cognition, foraging ability, and predator avoidance. In a prior experiment, gerbils infected with Mycoplasma haemomuris–like Bacteria had higher giving up densities, despite spending more time foraging, and were more likely to be killed by predators. One hypothesis to explain this is that infected gerbils suffer from cognitive impairment that reduces their ability to forage efficiently, causing them to spend more time foraging and placing themselves at higher risk of predation.We tested this hypothesis by comparing the performance of gerbils (Gerbillus andersoni allenbyi), uninfected, acutely infected, or chronically infected with Mycoplasma in two foraging experiments conducted in a semi-natural vivarium. First, we measured the ability of gerbils to equalize giving up densities (GUDs) between rich and poor patches. Theory predicts prescient animals will forage all patches to the same GUD regardless of how much food the patches start with. Animals using Bayesian sampling to estimate patch richness will oversample poor patches and undersample rich ones; while those unable to determine patch richness might use fixed time and take equal proportions from all patches. We predicted that uninfected gerbils would be more successful at equalizing GUDs between rich and poor patches, while infected gerbils would adopt a fixed time strategy. Contrary to this prediction, uninfected and infected gerbils equalized GUDs with similar success.Second, we measured the ability of the gerbils to detect micropatches of seeds within a patch. To do this, we set up three tray types, one with seed distributed evenly through the tray, one with seed mixed into one half of the sand at the edge of the tray, with a single vague boundary, and one with seed mixed into one half of the sand in the center of the tray with two vague boundaries. With perfect information about the location of the micropatch, the GUD in the boundary trays will equal ½ the GUD of full tray. With no information, the GUDs of the boundary trays are expected to equal the GUD of the full tray. We predicted that uninfected gerbils would be more successful at detecting micropatches than infected gerbils. Contrary to this prediction, infected gerbils performed equally well as uninfected gerbils at detecting micropatches. These experiments did not support the hypothesis that cognitive impairment explains past results regarding Mycoplasma and gerbil foraging.