Evidence for the effect of brief exposure to food, but not learning interference, on maze solving in desert ants

The combined role of visual and olfactory cues in foraging by Cataglyphis ants in laboratory mazes

Foragers use several senses to locate food, and many animals rely on vision and smell. It is beneficial not to rely on a single sense, which might fail under certain conditions. We examined the contribution of vision and smell to foraging and maze exploration under laboratory conditions using Cataglyphis desert ants as a model. Foraging intensity, measured as the number of workers entering the maze and arriving at the target as well as target arrival time, were greater when food, blue light, or both were offered or presented in contrast to a control. Workers trained to forage for a combined food and light cue elevated their foraging intensity with experience. However, foraging intensity was not higher when using both cues simultaneously than in either one of the two alone. Following training, we split between the two cues and moved either the food or the blue light to the opposite maze corner. This manipulation impaired foraging success by either leading to fewer workers arriving at the target cell (when the light stayed and the food was moved) or to more workers arriving at the opposite target cell, empty of food (when the food stayed and the light was moved). This result indicates that ant workers use both senses when foraging for food and readily associate light with food.

The value of spatial experience and group size for ant colonies in direct competition

Animals often search for food more efficiently with experience. However, the contribution of experience to foraging success under direct competition has rarely been examined. Here we used colonies of an individually foraging desert ant to investigate the value of spatial experience. First, we trained worker groups of equal numbers to solve either a complex or a simple maze. We then tested pairs of both groups against one another in reaching a food reward. This task required solving the same complex maze that one of the groups had been trained in, to determine which group would exploit better the food reward. The worker groups previously trained in the complex mazes reached the food reward faster and more of these workers fed on the food than those trained in simple mazes, but only in the intermediate size group. To determine the relative importance of group size versus spatial experience in exploiting food patches, we then tested smaller trained worker groups against larger untrained ones. The larger groups outcompeted the smaller ones, despite the latter's advantage of spatial experience. The contribution of spatial experience, as found here, appears to be small, and depends on group size: an advantage of a few workers of the untrained group over the trained group negates its benefits.

Can rats and ants exchange information between the horizontal and vertical domains?

Since traveling in nature involves encountering various vertical structures, integration of horizontal and vertical spatial information is required. One form of such integration is to use information acquired in one plane for spatial navigation in another plane. Here we tested whether rats and ants that learned a reward location in a horizontal maze could utilize this information when the maze was rotated to a vertical orientation and vice versa. Rats that were trained in a horizontal Y-maze required more time to reach the reward when the maze was vertically rotated, but they were more accurate in choosing the correct arm. In contrast, rats tested in a horizontal maze after being trained in a vertical maze were less accurate but reached the reward faster. Changes after maze rotation were moderate and non-significant in ants, perhaps since the number of ants arriving at the reward increased over trials, diminishing the effect of maze rotation in ants compared to rats. According to the notion that horizontal spatial information is encoded in more detail than vertical information, the slow performance of rats in the vertical domain could be due to a more physically demanding task whereas their accuracy was due to a preceding detailed horizontal encoding. In contrast, rats in the vertical maze could gather less detailed information and therefore were less accurate in subsequent horizontal trials, where the lower energy cost enabled them to swiftly correct wrong choices. Altogether, the present results provide an indication for transferring spatial information between horizontal and vertical dimensions.

Desert Ants Learn to Avoid Pitfall Traps While Foraging

Simple Summary

Animals living in nests leave their nests to search for food and often use constant routes. We tested how workers of ant colonies cope with pitfall traps placed on their way to food. Such pits can represent those dug by the ant-hunting pit-building antlions. The pitfall traps delayed the arrival at the food and increased the workers’ tracks, but the ants improved in searching after accumulating experience. Furthermore, workers learned to avoid falling into the pits with experience. Removing or adding pits led to a fast change in the worker behavior and they ignored the past conditions, except for tracks that were longer than expected, after pitfall traps were removed. The ants fell much more frequently into pits closer to the arena entry, suggesting that such positions are especially profitable for sit-and-wait predators, ambushing such ants.

Abstract

Central-place foragers, such as social insects or nesting birds, repeatedly use the same routes from and to their nests when foraging for food. Such species forage more efficiently after accumulating experience. We examined, here, a relatively neglected aspect of such an improvement with experience—the avoidance of pitfall traps. Similar pits are built by antlions, which co-occur with the ants, but they also resemble other natural obstacles. We used the desert ant Cataglyphis niger, common in sandy habitats, and allowed it to forage for three successive runs for a food reward. Ant workers discovered food more slowly and in smaller numbers when pits were in their path. Pit presence also led to longer tracks by ants and slower movement. However, with experience, the ants fell into such pits less often and reached the food more quickly. To understand how past conditions affect current behavior, we investigated whether removing or adding pits led to a different result to that with a constant number of pits. Workers adjusted their behavior immediately when conditions changed. The only carryover effect was the longer tracks crossed by workers after pit removal, possibly resulting from the mismatch between the past and current conditions. Finally, the workers were more likely to fall into pits that were closer to the nest than those that were further away. This is a good example of the advantage that ambush predators can derive from ambushing their prey in specific locations.