Zoological Studies

Vol. 38 No. 1, 1999

Population Dynamics and Mantle Autotomy of the Figsnail Ficus ficus (Gastropoda: Mesogastropoda: Ficidae)

Li-Lian Liu* and Sheau-Ping Wang

Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung, Taiwan 804

Li-Lian Liu and Sheau-Ping Wang (1999) Ficus ficus, a member of the Mesogastropoda, exhibits a special behavior of mantle autotomy as a defensive mechanism. This study was conducted to characterize the population dynamics of F. ficus and the occurrence of autotomic behavior in the field. Monthly collections of F. ficus were made between May 1992 and June 1993. A total of 2186 individuals were sampled with shell lengths ranging from 28 to 95 mm. Small individuals with shell lengths < 35 mm were found only between July and September 1992. Seasonal variation in the abundance of figsnails was observed: while few figsnails (less than 75 individuals) were collected from May to July, abundant snails were obtained from November to February. Sexual dimorphism in shell length (male < female) was also found. Sex ratios varied from 0.3 to 2.3 in favor of females between March and September. The male-biased sex ratios observed between October and February indicate that egg-laying migration might exist. The autotomic tissue weighed from 0.03 to 8.86 g and comprised 0% to 34% of the total body weight. A negative correlation between the percentage of autotomic tissue and shell length was observed (y = 30.88 - 0.27x; R2 = 0.35; p < 0.01). Figsnails with newly regenerated tissue (indication of recent occurrence of defensive autotomy) comprised < 1% of the total samples, with 0 to 3 individuals appearing in each monthly collection. The results indicate that autotomized figsnails might be more vulnerable to predation than are intact snails, or that the occurrence of defensive autotomy in natural environments might be low.

Key words: Ficus ficus, Figsnail, Population dynamics, Autotomy.

*Correspondence: Fax: 886-7-5255100. E-mail: lilian@mail.nsysu.edu.tw