Friend or foe? Disparate plant-animal interactions of two congeneric rodents

Food and water resources are limiting factors for animals in desert ecosystems. Fleshy fruits are a rare water source in deserts and when available they tend to attract a wide variety of organisms. Here we show that two congeneric rodent species, Acomys cahirinus and A. russatus, employ different fruit eating strategies that result in either dispersal or predation of the small seeds of the desert plant Ochradenus baccatus. The nocturnal A. cahirinus leaves intact seeds when consuming O. baccatus fruits and thus, acts mainly as a seed disperser; whereas the diurnal A. russatus consumes the whole fruit and digests the seeds and thus, acts mainly as a seed predator. Acomys russatus is subjected to the toxic products of the glucosinolates-myrosinase system found in O. baccatus fruits. Acomys cahirinus avoids the toxic compounds by consuming the pulp only, which contains glucosinolates but not the seeds that contain the enzyme that activates them. We suggest that the behavioral responses exhibited by A. russatus are the result of physiological adaptations to whole fruit consumption that are absent in A. cahirinus. Our results shed new light on the ecological divergence of the two congeneric species.