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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 to 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.
Supplementary materials--including Movie S1, Intertemporal choice test Video recording of black lemur free-choice trials, and 2 data sheets plus R code for data analysis--are attached (below) as additional files.
Movie S1. Intertemporal choice test. Video recording of black lemur free-choice trials.
stevens.muehlhoff.2012.BP_data1.csv (311 kB)
Data sheet S1. Lemur intertemporal choice data.
stevens.muehlhoff.2012.BP_data2.csv (10 kB)
Data sheet S2. Comparative intertemporal choice data.
stevens.muehlhoff.2012.BP_rcode.R (18 kB)