Evolution and patterns of reproduction in Philippine mammals

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In most groups of animals, there is a correlation between the rate of reproduction and body size: the larger the species, the smaller the number of babies per litter. Rodents of the family Muridae, commonly called “rats and mice”, are a classic example, with small species producing large litters many times each year, and larger species producing fewer young. However, preliminary data on native (non-pest) rodents in the Philippines indicate that many species, including species that weigh from a few ounces to 6 pounds, have litter sizes of only one or two young, probably once each year. It appears that this low rate of reproduction is limited to only two groups that have evolved within the Philippines; distantly related groups have the more typical, higher rates of reproduction.

Research methods and techniques:

REU participants will receive an introduction to rodent reproductive anatomy and methods of examining preserved museum specimens for reproductive data, will help to collect the data, and will learn to compile and analyze data for correlations with body size. They will be introduced to phylogenies and methods for examining the evolution of reproductive patterns within a phylogenetic context. The intended result is a publication that the participants will co-author.

Curator/Advisor: Dr. Lawrence R. Heaney, Zoology/Mammals


Evolutionary and Developmental Biology major

Northwestern University

Symposium Presentation Title: Evolution and Patterns of Reproduction in Philippine Mammals

Symposium Presentation Abstract: In most groups of animals, body size and litter size are allometrically related: the smaller the animal, the larger its litter size. This is typically true of mammals and of rodents specifically, which usually have large litters. However, anecdotal evidence obtained during field work in the Philippines has suggested that several speciose endemic clades of Philippine murid rodents (rats and mice) differ significantly from this pattern. A departure of this large set of species could have interesting implications for theories of life history and evolutionary aspects of island biogeography. Using field notes, published materials, and reproductive autopsies of about 600 specimens, we seek to document the reproductive characteristics of the Philippine murid fauna. This includes the two highly diverse “Old Endemic” clades (the cloud rats and the earthworm mice) which first arrived in the Philippines 12-20 million years ago, as well as several clades that arrived in the more recent geologic past, and some introduced by humans. Several species from Palawan, an area biogeographically distinct from the rest of the Philippines, were also included. Initial results suggest that the Old Endemics produce 1-2 offspring per litter, regardless of body size. This is much lower than “exotic pest” species of similar size, which are representative of continental species and have litters of 5-10 offspring. Some of the endemic clades which arrived in the Philippines more recently than the “Old Endemics” show intermediate litter sizes of 3-4 offspring. These data raise many currently unanswered questions about predation, longevity and reproductive strategies.