Extraction of nutrients from Protea pollen by African rodents

Many of the species of Protea that are found in the south-western Cape of South Africa are pollinated by rodents. In Australia, where flowers of the same family are also mammal-pollinated, some of the mammal species that feed on Proteaceae flowers not only gain energy from nectar but also extract protein from pollen. This contrasts with the widely held belief that most mammals are unable to extract nutrients from pollen. To determine whether African rodents are also capable of using pollen as a source of protein, faecal samples were collected from mammals trapped at two sites in the Western Cape where Protea humiflora and P. subulifolia were common. The mammals included three rodent species, Rhabdomys pumilio, Aethomys namaquensis and Mus minutoides, and an elephant shrew, Elephantulus edwardsii. The mean percentage of empty or partially digested pollen grains was 50.3\% for E. edwardsii, 56.8\% for R. pumilio, 60.4\% for A. namaquensis and 83.0\% for M. minutoides. These four species are clearly capable of penetrating the pollen grains of Protea during digestion. Pollen is therefore a potential protein source for these species.