Frugivorous lemurs are thought to be important seed dispersers in Malagasy forests. To evaluate the seed dispersal service offered by dispersers, recent studies have frequently estimated dispersal kernels. To describe dispersal kernels for seeds consumed by lemurs, it is necessary to know the gut passage time (GPT) of seeds. Therefore, the GPT in the common brown lemur (Eulemur fulvus) and the mongoose lemur (Eulemur mongoz) was measured at Tsimbazaza Botanical and Zoological Park in Antananarivo. These species occur sympatrically in northwestern Madagascar. In addition, the size of seeds swallowed and spat out was measured to estimate the upper limit of the size that the lemurs can swallow. The average GPT of seeds in Eulemur fulvus was 229±23 min. The duration of excretion of experimental food was 217±49 min and defecation occurred 16±6 times during the period. Although the average GPT and duration of excretion in Eulemur mongoz were similar to those in E. fulvus, the frequency of defecation in E. mongoz was notably lower, 7±2 times. The GPT of small seeds and large seeds did not differ in the two lemur species. Among primates, these lemurs had a shorter GPT and more frequent defecation. This result reflects the frugivorous digestive strategy and will affect the shape of dispersal kernels. In the measurement of seed size, the width of spat out seeds was greater than the width of seeds swallowed in both species, although the seed length did not differ. Seed width probably decided the upper size limit of seeds that lemurs could swallow. Eulemur fulvus tended to spit out seeds greater than 16.0 mm in width and E. mongoz tended to spit out seeds larger than 7.8 mm in width. Considering the structure of frugivorous communities, this suggests that many large-seeded plants crucially depend on these frugivorous lemurs for seed dispersal in Malagasy forests.

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Cooperation plays an important role in daily social interactions in humans. Wild chimpanzees have been reported to act cooperatively during hunting, but whether or not they are really engaging in cooperation is under debate. Investigation of cooperation in captive chimpanzees dates back to Kohler&rsquos observation, but experimental examination of cooperative ability in chimpanzees has been limited. The present paper describes recent advances in the study of cooperation and other related behaviors in chimpanzees, focusing on two kinds of experiments. In one of the experiments, two individuals had to move a set of heavy stones in order to obtain food under them. Two chimpanzees never succeeded in the task, but a pair of a chimpanzee and a human succeeded, and the chimpanzee began to solicit the human partner when he was not responding. In the other experiment, two individuals had to pull both ends of a string simultaneously to obtain food. The two chimpanzees did not succeed initially, but they gradually began to adjust their behavior to succeed in the task, by watching the partner and waiting for her. These studies indicate that the chimpanzees are able to comprehend some aspect of cooperation, but they never showed ostensive communicative behavior to achieve cooperation with the partner. Taken together other related studies, competitive social skill hypothesis and emotional reactivity hypothesis may have a key in understanding evolution of cooperation. However, these hypotheses seem to be insufficient in explaining the whole picture, and future research in needed especially by focusing on the nature of mother-infant relationships.

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