THE LICHEN THELIDIUM-LITORALE ON SHELLS OF INTERTIDAL LIMPETS - A CASE OF LICHEN-MEDIATED CRYPTIC MIMICRY

On the intertidal rocky shores of central Chile, the lichen Thelidium litorale (Ascomycete: Verrucariacea) is commonly found encrusting shel ls of gastropods such as Scurria araucana, S. ceciliana and S. boehmit a, and plates of the intertidal barnacles Jehlius cirratus and Chthama lus scabrosus. This study focuses on the relationship between T. litor ale and shells of the limpet S. boehmita. In the field, this host show s the highest percentage of lichen prevalence among several intertidal species. Although T. litorale is able to penetrate the limpet shell l ayers lying above the myostracum (m), the observed penetration levels appear related to the width of the shell layers. Among the 3 species o f limpets, S. boehmita exhibits the thinnest m+2 layer and this could facilitate lichen penetration. As a result of the association, the lim pet develops an external shell pattern remarkably resembling the shape of the aperture of the intertidal barnacles J. cirratus and C. scabro sus. This lichen-mediated mimicry can be explained by lichen-induced e rosion, which leads to the disclosure of the internal and otherwise un exposed shell design of S. boehmita. The possible role of T. litorale as a biological modifier of external limpet shell pattern is discussed .