Intraspecific variation in diet within and between trophic morphs in larval tiger salamanders (Ambystoma tigrinum nebulosum)

Abstract

Larvae of Ambystoma tigrinum nebulosum are dimorphic. The "broad-headed" morph is cannibalistic and has a wider head and enlarged vomerine teeth compared with typical larvae. We collected larvae from tour habitats in Arizona, U.S.A., to quantify how diet varies within and betweeen morphs relative to habitat, and how diet varies relative to age in typical morphs from one habitat. Broad-headed or cannibalistic morphs occurred in both sexes and most of their diet [Formula: see text] was other salamanders. A variety of invertebrates comprised the remainder of their diet. Typical morphs ate primarily macroinvertebrates and plankton, and rarely (1 of 170 larvae analyzed) conspecifics. Young typical larvae consumed a narrow range of prey, mostly plankton, compared with older larvae, which consumed a diversity of macroinvertebrates in addition to plankton. Our results indicate that description of broad-headed larvae as cannibals is justified because most of their diet is other salamanders, while typical morphs rarely eat salamanders. Both morphs also eat invertebrates. With regard to diet in larval A. tigrinum, therefore, "cannibalistic" versus "typical" refers to a predilection and is not an absolute categorization.