Because many species of diprotodont marsupials (including all large ones) have litters of a single young, it seems to be assumed tacitly that there is little variation in litter size within and between species in this group. In contrast, polyprotodont marsupials have litters that are typically larger; variation in litter size between species is related to body size, diet, and ecology; and intraspecific variation in litter size also occurs. The largest litters in diprotodont marsupials are found in the small possums (eight species from the families Burramyidae, Acrobatidae, and Tarsipedidae), but there also is variation in litter size beyond that which can be explained by body size, reflecting a fast-slow continuum among small possums. There also are geographical differences in litter size within some species. Number of teats varies among species and also varies within three of the species. Production of supernumerary young occurs in some species such that number of teats effectively limits litter size. In other species, number of young at birth is smaller than number of teats, so litter size is limited by number of eggs shed at ovulation and embryos carried in utero. The largest mean litter sizes are found in species that produce supernumerary young, and these are the “fast” species among small possums.

Author notes

Associate Editor was Edward J. Heske.