Dynamic modification of hoarding in response to hoard size manipulation.

Food hoarding is an evolutionary adaptation whereby animals store food for later consumption when food is limited or when predation risk while foraging is high. It also occurs as part of normal appetitive behavior by humans and non-human animals when they are hungry. Contrary to popular belief, humans do not overeat after food restriction/fasting, rather they increase food hoarding, as do hamster species, but not in laboratory rats or mice. Thus, this aspect of human appetitive behavior is better modeled by hamsters than laboratory rats and mice. Here we tested whether male Siberian hamsters (Phodopus sungorus) modify their daily food hoard size under ad libitum-feeding and after food deprivation when we artificially increased or removed their food hoard. When the food hoard was completely removed, hamsters hoarded more food the next day than did animals where the hoard was surreptitiously increased. Hamsters that had alternating daily hoard increases/decreases rapidly adjusted their food hoarding inversely proportional to food hoard size. Similarly, after 48h of food deprivation, a stimulus that initiates high levels of food hoarding upon refeeding in this species, hamsters with artificially increased food hoard size hoarded significantly less than did hamsters where we left the hoard unaltered additionally suggesting that food hoard size directly affects food hoarding. Collectively, as we previously found when the caloric value of the food offered was increased or decreased, food hoard size is in some sense 'regulated' and not simply a reflexive response triggered by inter-meal hunger or food deprivation.