The Pigmentation of Cavernicolous Animals

THE present paper records the results of some analyses of carotenoid material in cave detritus, carried out as part of a research on the causes of pigment lack in the cave fauna. There is reason to suppose that the ancestral pigment of the numerous unpigmented cavernicolous Crustacea was the carotenoid pigment astacin, since closely related above-ground species frequently contain this pigment. Thus the amphipods Orchestia gammarellus and Gammarus marinus have a wholly carotenoid pigmentation of astacin type, while Gammarus pulex is believed to contain astacin (Sorensen, 1936). It is a well-known fact that the pigment of many Amphipoda is soluble in the alcohol in which the animals are preserved, and we are justified in concluding that astacin-like pigments are typical of the group. It is unlikely that Crustacea can synthesize carotenoid pigment from non-carotenoid food (vide the discussion in Verne, 1926), and the present work forms a preliminary survey of the extent to which carotenoid-containing food is available to the cave fauna. Several modes of entry of food into caves have been noted. The excreta of bats, on which colonies of coprophagous beetles live, is of minor importance. Accidental entry of leaves, twigs, etc., at the mouth of the cave, does not contribute to the food of animals in the main region of the cave. Detritus carried in by underground rivers is the chief source of food for cave animals, and as shown here, carotenoid material is found in it in some quantity. Proteus, which is associated with subterranean rivers, was found to contain some carotenoid material. In the upper regions of caves drip pools are found, fed only by water percolating through the limestone. Detritus from such pools was found to be devoid of carotenoid material, and specimens of the cavernicolous amphipod Niphargus from such a pool were found to contain no carotenoid pigment.