P3.9 Friday, Jan. 6 Comparison of visual orientation between two land crabs Sesarmops intermedium and Scandarma lintou in Kenting National Park, southern Taiwan HUANG, H.-D.*; LIU, H. C.; National Museum of Natural Science, Taiwan; Providence University, Taiwan email@example.com
This study aims to examine the visual orientation of two land crabs, Sesarmops intermedium and Scandarma lintou, in southern Taiwan, and to explore the ecological implication. Mid-sized S. intermedium are widely distributed among grasses, on river banks, and under maritime forests. Small-sized S. lintou are typical tree-living crabs, living on the vegetation close to running fresh water and seldom down to the ground except for larval release. On the contrary, S. intermedium mainly live on the ground, and occasionally get onto the plant preying other animals including S. lintou. Animal collection and experiments were conducted in Gangkou River estuary, Kenting National Park. Orientation of crabs was examined in circular arena with visual targets of various sizes. Both crabs perform significant orientation toward the targets larger than 45 degrees, and move directly to the center of 350-degree target, which represents the typical shelter-seeking behavior. However, tree-living S. lintou were significantly attracted by the shadow targets as small as 10 and 30 degrees, but ground-active S. intermedium showed random movements. This may reflect the characteristics of arboreal habitats where S. lintou lives and avoid predators.