Pollen digestion by New World bats: Effects of processing time and feedinghabits

Although pollen is included in the diet of vertebrates and invertebrates, a nd extraction efficiency of its contents has been estimated for several flo wer visitors, the relationship between feeding habits and pollen digestion efficiency has not been carefully studied. We compared the efficiency with which four species of New World bats with different feeding habits extracte d the contents of different types of pollen, and we tested the hypothesis t hat flower-visiting bats have higher extraction efficiencies than fruit-eat ing bats. We gave doses of different types of pollen to two nectarivorous ( Anoura geaffroyi and Leptonycteris curasoae) and two frugivorous (Artibeus jamaicensis and Sturnira lilium) bats and collected their feces at regular intervals. We used pollen from three species of flowers that are associated with bat visitation: Pseudobombax ellipticum, Hylocereus undatus, and an u nidentified species of night-blooming, columnar cactus. In addition to esti mating the percentage of empty pollen grains in the feces, we determined di gesta time distributions in the gastrointestinal tract and interpreted them using chemical reactor theory. Extraction efficiency was higher in bats th at regularly include pollen in their diet. This pattern was not explained b y differences in the rare with which the bats processed pollen, or by the t ime that pollen was retained in the stomach, where little degradation of po llen grains occurs. Within species, however, the percentage of empty grains increased asymptotically with time in the gastrointestinal tract. In gener al, the digestive system of the bats seemed to process pollen grains as a c ontinuous stirred-tank reactor (CSTR) connected to a plug-how reactor (PFR) , with longitudinal mixing in the PFR: the food was retained for a relative ly short period in the stomach and then was moved through the intestine, wh ere it was mixed longitudinally. Artibeus jamaicensis was an exception to t his pattern in the way its digestive system processed H. undatus pollen; in this case, its gastrointestinal tract apparently functioned as a PFR with a considerable amount of longitudinal mixing. We hypothesize that differenc es among bats in extraction efficiency of pollen contents may be partly exp lained by differences in the intestinal activity of the enzymes responsible for pollen grain degradation.