Does the homing accuracy of intertidal chitons rely on active trail following? A simulation approach

The role of trailfollowing in the homing of three Acanthopleurachitons was investigated using a Monte Carlo simulation model. Four different sets of simulations were performed to assess: (1) the importance of an active mechanism of trailfollowing in producing trail overlap and allowing the animals to home; (2) its importance in the different segments of the excursions; (3) the range of probability values associated with trailfollowing behaviour, yielding ahoming performance not different from the empirical one; and finally, (4) if trailfollowing can be replaced, as ahoming mechanism, by a tactic behaviour. The comparison between simulated and empirical data shows that the degree of trail overlap and homing performance shown in the field by Acanthopleura gemmata and Acanthopleura brevispinosarely on an active mechanism of trailfollowing which begins to be important about midway in each foraging excursion, while the low trail overlap and homing performance of Acanthopleura granulata are due entirely to chance coincidence of different path segments. Specific simulations show that ahoming performance similar to that observed in the field can be obtained only within a narrow range of probability values of beginning and ending trailfollowing. Moreover the results of simulations also show that in A. gemmata and A. brevispinosaa strong homeward taxis during the return phase does not efficiently replace trailfollowing.