Current Herpetology 1Q(2): 63-67, December 2001 

 © 2001 by The Herpetological Society of Japan 



2 5 FEB 2002 



Effects of Head Shape Variation on Diet Selection in Larvae 

 of the Salamander Hynobius retardatus 



YUKIHIRO KOHMATSU* 



Center for Ecological Research, Kyoto University, Kamitanakami, Hiranocho, Otsu, 



Shiga 520-2113, JAPAN 



Abstract: Using stomach content analysis, I assessed effects of liead mor- 

 phology of larval salamanders (Hynobius retardatus) on the selectivity of 

 diets in nature. Large-headed morphs of the larvae chiefly ate terrestrial 

 invertebrates, whereas the most abundant prey item of small-headed morphs 

 was Diptera larvae. This suggests that larvae of H. retardatus change their 

 prey in association with the head shape. I thus consider that the flexible 

 development of a larger head induced by larval density of this species would 

 change their diet selection. 



Key words: Diet selection; Head shape; Hynobius retardatus; Salamander; 

 Stomach contents 



Introduction 



Trophic polymorphism, in which different 

 morphs often exhibit different uses of food 

 resources even in sympatric conditions, has 

 been reported in many animals (Malm- 

 quist, 1992; Schluter, 1995; Skulasson and 

 Smith, 1995). Such feeding specialization 

 among morphs is thought to provide 

 organisms with potentials for intraspecific 

 niche divergence (Rosenzweig, 1978). 



Several salamanders have a dimorphic 

 life history, consisting of cannibalistic and 

 typical morphs in the larval period (see 

 review in Crump, 1992). Hynobius retar- 

 datus, a hynobiid salamander which breeds 

 in small, temporary ponds in northern 



* Corresponding author. Tel: +81-77-549- 

 8200; Fax: +81-77-549-8201. 



E-mail address: kohmatsu@ecoIogy.kyoto- 

 u. ac.jp (Y. Kohmatsu) 



Japan (Sato, 1993), is also reported to have 

 flexible development in larval head size 

 (Wakahara, 1995), with large-headed 

 morph larvae being characterized by a wide 

 head and mouth, and relatively round 

 snout (Fig. 1). Since prey items of larvae 

 of H. retardatus are limited by their gape 

 size (Ohdachi, 1994), the large-headed 

 morphs are expected to feed on larger prey 

 organisms than the small-headed morphs. 



In fact, the cannibalistic morph larvae of 

 the tiger salamander {Ambystoma tigri- 

 num), characterized by relatively broad 

 heads, are known to feed on animals 

 including conspecific larvae that are larger 

 than prey of the typical morph larvae of 

 this species (Collins and Holomuzki, 1984). 

 Moreover, a previous study on A. tigrinum 

 predicted that the shift of prey selectivity 

 of larvae involved in changes in head 

 morphology influences the dynamics of the 

 community of a pond where they occur 



i 



