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 (Monodel phis domestica). Food consumption was monitored in 20 reproductively active (RA) opossums and 16 RA hamsters from conception to weaning and at equival ent intervals in 19 non-reproductive (NR) opossums and 21 NR hamsters, all maintained within their zone of thermoneutrality (30 degrees C). Total ener gy 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 corre lated with litter size and mass per young in both species. Maternal mass-sp ecific assimilated energy was significantly greater in hamsters than in opo ssums during gestation (P < 0.001), but not during lactation or from concep tion to weaning (P > 0.05). Efficiency of offspring production (energy stor ed in young/incremental energy in RA females) was higher in hamsters than i n opossums and, in both species, it was higher during lactation than in ges tation. The energetic cost of reproduction (per young per day) was higher i n hamsters than in opossums. The marsupial mode of reproduction, as seen in opossums, yields young at lower cost but requires a longer reproductive pe riod than is the case for a similar-sized eutherian.