. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. N. FIGURE 1. Orientation behavior of horseshoe crabs with normal vision on a sloped beach. Run A held 26 May, 1610-1850, bright sunlight, wind W less than 5 mph. Run B held 2 June, 1057-1323, cloudy with occasional drizzle, wind NNE 15 mph. Length and direction of mean vector r shown by solid arrow; Rayleigh's Test indicated significant mean population direction in both runs. Seaward direction indicated by open arrow. Typical "fish hook" path followed by a crab is shown in A. Orientation on sloped beach. All sighte
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. N. FIGURE 1. Orientation behavior of horseshoe crabs with normal vision on a sloped beach. Run A held 26 May, 1610-1850, bright sunlight, wind W less than 5 mph. Run B held 2 June, 1057-1323, cloudy with occasional drizzle, wind NNE 15 mph. Length and direction of mean vector r shown by solid arrow; Rayleigh's Test indicated significant mean population direction in both runs. Seaward direction indicated by open arrow. Typical "fish hook" path followed by a crab is shown in A. Orientation on sloped beach. All sighted crabs showed strong seaward orientation (Fig. 1). The path followed by nearly all crabs in these trials was the "fish hook" pattern illustrated in Figure la. Typically, a crab first walked in the direction it was placed (in this case, uphill) before turning to its left or right. More crabs turned left (n = 26) than right (n = 16) but the difference was non-significant (x2 - , .25 < P < .10). There was no significant difference in mean angle between a group of crabs run in late afternoon (n = 23) and a second group (n = 23) run in midday (Watson-Williams test, F = , ). In both trials, 22 animals (96%) completed the test and there was no significant difference in the time it took to complete the test (Mann-Whitney U-test, z = , ). The meandering score was significantly lower in the late day group (U = , P < .005). Pausing and circling behaviors were noted only five times each (Table II). Blinded crabs also showed strong seaward orientation on the sloped beach (Fig. 2). Mean angles of crabs tested in early morning and mid-afternoon were virtually identical. In both the morning and afternoon experiments, 20 animals (87%) com- pleted each trial. Animals in the morning trial took significantly longer (Mann-Whit- ney U-test, U = , P < .001) and had a higher meandering score (U = 316, P < .002) than the afternoon group. This di
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
