Intertemporal choice in lemurs

Abstract

Different species vary in their ability to wait for delayed rewards in intertemporal choice tasks. Models of rate maximization account for part of this variation, but other factors such as social structure and feeding ecology seem to underly some species differences. Though studies have evaluated intertemporal choice in several primate species, including Old World monkeys, New World monkeys, and apes, prosimians have not been tested. This study investigated intertemporal choices in three species of lemur (black-and-white ruffed lemurs, Varecia variegata, red ruffed lemurs, Varecia rubra, and black lemurs, Eulemur macaco) to assess how they compare to other primate species and whether their choices are consistent with rate maximization. We offered lemurs a choice between two food items available immediately and six food items available after a delay. We found that by adjusting the delay to the larger reward, the lemurs were indifferent between the two options at a mean delay of 17 s, ranging from 9-25 s. These data are comparable to data collected from common marmosets (Callithrix jacchus). The lemur data were not consistent with models of rate maximization. The addition of lemurs to the list of species tested in these tasks will help uncover the role of life history and socio-ecological factors influencing intertemporal choices.

Evolutionary pressures on primate intertemporal choice

“…The strong relationship between waiting times and allometry matches a previous result demonstrating that waiting times correlated positively with body mass [3]. This result supports the adaptive nature of the allometric scaling hypothesis because waiting times scale with two factors rspb.royalsocietypublishing.org Proc.…”

“…Stevens & Mü hlhoff [3] showed that waiting times increased with mean species body mass. This could occur because metabolism allometrically scales with body size: species with lower body mass also tend to have faster metabolic rates [14 -16].…”

Time discounting and time preference in animals: A critical review

“…(B) In most implementations, a postreward buffer is added to make sure that the trial lengths for both options are equivalent; otherwise, the subject can advance to the next trial sooner. This postreward buffer is identified here as a potentially problematic element of the design of the task Rilling, 1965;Rachlin & Green, 1972;Rosati et al, 2007;Siegel & Rachlin, 1995;Snyderman, 1983;Stephens & Anderson, 2001;Stevens & Mühlhoff, 2012). Interestingly, these findings extend to normally patient humans in some contexts.…”

How comparative psychology can shed light on human evolution: Response to Beran et al.’s discussion of “Cognitive capacities for cooking in chimpanzees”

“…Moreover, other species do show preferences for the smaller, immediate reward in intertemporal choice tasks when the larger reward is delayed for even short periods, on the order of 10-20 s (Stevens & Stephens, 2008). This includes cotton-top tamarins (Saguinus oedipus), marmosets (Callithrix jacchus), and several lemur species tested in quite similar contexts with visible food rewards (Stevens, Hallinan, & Hauser, 2005;Stevens & Muhlhoff, 2012). Given that great apes show much more robust inhibitory control over prepotent reaching responses compared to other primates (see Maclean et al, 2014, for a large cross-species comparison), it is difficult to see how this pointing explanation could account for this complete set of results.…”