LIFE HISTORY AND BEHAVIOR OF SLOW LORISES AND SLENDER LORISES: IMPLICATIONS FOR THE LORISINE-GALAGINE DIVERGENCE (NYCTICEBUS, LORIS, GALAGO)

It has been hypothesized that natural selection favors life histories characterized by slow development and long offspring dependence if such traits: (1) are advantageous in species with complex sociality by providing more time for socialization; (2) are favored by density dependent selection acting on species in stable environments; (3) are allometric consequences of large body or brain size; (4) occur in animals with low metabolic rates. To test predictions generated from these hypotheses data were collected on life history and behavior in captive slow lorises (Nycticebus coucang) and slender lorises (Loris tardigradus), and the results compared to published data on Galago crassicaudatus and Galago senegalensis.;Correlation and allometric analyses indicated that adult basal metabolic rate accounted for most of the variance in developmental parameters, while body and brain size did not. Qualitative analyses suggested that protracted development were not associated with species showing greater social complexity. Slowly developing species did exhibit increased parental care.;The low metabolic rates of lorises and their unique locomotor specializations may be consequences of adaptation to a diet of toxic insects, which would be advantageous in that the food supply is abundant, accessible, and stable. The reduction in developmental rates is associated with increased parental care of vulnerable offspring. These results suggest that the characteristic primate life-history pattern could have originated and evolved in response to dietary and other ecological specializations, rather than increasing body size or social complexity. Metabolic rate and diet are among the most important parameters to examine in studies of life-history evolution.;Nycticebus and Loris differed from galagos in having longer periods of gestation and lactation, smaller litter sizes, lower growth rates, longer durations of growth, lower diversity of social behaviors, lower scores on other sociality measures, greater female tolerance of adult males near offspring, greater maternal-offspring and paternal-offspring contact during development, and longer, more intensive periods of carrying and suckling of offspring. Loris differed from Nycticebus in being more altricial at birth, in being carried constantly for one month after birth, while infant Nycticebus were frequently parked, and in undergoing a relatively rapid period of behavioral development to attain independence earlier than Nycticebus.