An investigation of rodents' use of learned caloric information in diet selection and foraging
Creators: name: Arbour, Katherine Johanna
Publisher: name: University of British Columbia
Year: 2010

description: When given a choice between two foods of equal caloric value but different flavors, rats show a robust preference for that food whose flavor was previously associated with a higher calorie food. This finding suggests that rodents may identify food quality by sensory signals such as taste. The first portion of this thesis explores this flavor-calorie conditioning effect in other rodents, namely hamsters and gerbils. When hamsters were tested in the same paradigm as rats, the conditioning effect was not observed. This discrepancy may have resulted from the hamsters' ability to store food mash in their cheekpouches. Accordingly, hamsters were next presented with liquid diets which could not be cheekpouched. The conditioning effect was observed when different flavors were associated with different quality liquid diets. However, the effect was less robust than that discovered for rats. A second species, gerbils, did show robust conditioning effects. Thus, unlike rats and gerbils who show a robust flavor-calorie conditioning effect, hamsters are less likely to identify food quality by using taste cues. Once conditioned to detect caloric density by using flavor cues, hamsters and gerbils were placed on an 8-arm radial maze that consisted of four arms baited with high-calorie liquid and four arms baited with low-calorie liquid. The purpose of this second, part of the thesis research was to investigate the rodents' preference for food locations that contained food of varying qualities. Both species were expected to visit and drink first from the arm locations containing the higher calorie liquid. Although hamsters did not visit more high-calorie arm locations, they did drink from these arms more often. When visiting arm locations, hamsters appeared to use a circling strategy that began in the same arm each trial and consisted of visits to consecutive arms. Gerbils neither visited nor drank more often from the high-calorie arm locations. Gerbils also did not appear to use a circling strategy. Thus, when foraging on an 8-arm radial maze for food of varying quality, hamsters' use of a circling strategy prohibited them from first visiting high-calorie arms but not from preferentially drinking from these locations. Unlike hamsters, gerbils did not adopt a strategy to collect food rewards and were not selective about the food reward that was consumed. The foraging strategies of hamsters was further explored in the third part of the thesis. Hamsters were allowed to forage on an equally-baited 17-arm radial maze. Each arm location was baited with a sunflower seed. Once again, hamsters visited arm locations by using a circling strategy which consisted of visits to consecutive arms. However, on the larger maze hamsters did not begin each trial in the same arm location. In addition, hamsters that were placed on the same maze with 4 of the 17 baited arms blocked, given 13 arm location choices, removed from the maze while the blocks were also removed, and placed back on the maze to select 4 additional arm locations, did not preferentially select the previously blocked arms. Thus, hamsters whose response algorithm was disrupted did not show a memory-based strategy for collecting seeds from the maze. The major conclusions from this research are that 1.) Hamsters can learn to associate caloric density and flavor cues, but the learned effect is easily extinguished. 2.) This dietary information may be used when deciding what to eat but not where to forage. 3.) Hamsters appear to be harvesters who visit all foraging locations by adopting a response strategy. 4.) Gerbils can also learn to associate caloric density and flavor, and the learned effect is robust. 5.) Gerbils do not appear to use this information when deciding which foods to eat or where to forage. It will be interesting for future studies to see if rats use flavor-calorie information in foraging settings.