The secret social lives of African crested rats, Lophiomys imhausi

Abstract

Abstract The crested rat, Lophiomys imhausi, is the only mammal known to sequester plant toxins. Found in eastern Africa, this large rodent is thought to defend against predation by coating specialized hairs along its sides with cardenolide toxins from the poison arrow tree, Acokanthera schimperi. To better understand the ecology of this unusual poisonous mammal, we used camera traps, livetrapping, and captive behavioral observations, to study L. imhausi in central Kenya. Although crested rats were rarely detected with camera traps, 25 individuals were caught in live traps, with estimated densities of up to 15 rats/km2 at one of nine trapping sites. Trapping records and behavioral observations suggest that L. imhausi live in male–female pairs, with juveniles that might exhibit delayed dispersal. We observed chewing of A. schimperi and/or anointing in 10 of 22 individuals, confirming the previous poison sequestration observation. We monitored crested rat activity using cameras and found that chewing on A. schimperi and cardenolide exposure had no effect on feeding, movement, or total activity. One crested rat also fed on milkweed (Gomphocarpus physocarpus; Gentaniales: Apocynaceae), but did not anoint with this cardenolide containing plant. This observation, combined with L. imhausi’s selective use of A. schimperi, suggests the potential for use of alternative poison sources. This research provides novel insight into the ecology of L. imhausi, while also suggesting that more field observations, feeding trials, and chemical analyses are needed to understand their behavior and physiology. Furthermore, their complex social interactions, slow life history, and fragmented populations suggest that L. imhausi could be at risk of decline.