Energetics of offspring production: a comparison of a marsupial (Monodelphis domestica) and a eutherian (Mesocricetus auratus)

This study compares the energetic cost of reproduction during gestation and lactation of a eutherian, the golden hamster (Mesocricetus auratus), and a similar-sized (60,120 g) marsupial, the gray short-tailed opossum (Monodelphis domestica). Food consumption was monitored in 20 reproductively active (RA) opossums and 16 RA hamsters from conception to weaning at equivalent intervals in 19 non-reproductive (NR) opossums and 21 NR hamsters, all maintained within their zone of thermoneutrality (30 degrees C). Total energy assimilated from conception to weaning [opossums: 1261.3 +/- 28.0 Kcal (1 Kcal = 4.1868 J) and hamsters: 1647.5 +/- 60.6 Kcal] was positively correlated with litter size and mass per young in both species. Maternal mass-specific assimilated energy was significantly greater in hamsters than in opossums during gestation (P < 0.001), but not during lactation or from conception to weaning (P > 0.05). Efficiency of offspring production (energy stored in young/incremental energy in RA females) was higher in hamsters than in opossums and, in both species, it was higher during lactation than in gestation. The energetic cost of reproduction (per young per day) was higher in hamsters than in opossums. The marsupial mode of reproduction, as seen in opossums, yields young at lower cost but requires a longer reproductive period than is the case for a similar-sized eutherian.