*Division of Biochemistry and Molecular Biology University of California, Berkeley, CA 94720, U.S.A.
Ecological and evolutionary consequences of the trophic polymorphism in Cichlasoma citrinellum (Pisces: Cichlidae)
Article first published online: 14 JAN 2008
Biological Journal of the Linnean Society
Volume 39, Issue 3, pages 279–299, March 1990
How to Cite
MEYER, A. (1990), Ecological and evolutionary consequences of the trophic polymorphism in Cichlasoma citrinellum (Pisces: Cichlidae). Biological Journal of the Linnean Society, 39: 279–299. doi: 10.1111/j.1095-8312.1990.tb00517.x
- Issue published online: 14 JAN 2008
- Article first published online: 14 JAN 2008
- Received 3 February 1989, accepted for publication 26 May 1989
- Trophic polymorphism;
- seasonal changes in morphology;
- pharyngeal jaws;
- intraspecific macroevolution;
- phenotypic plasticity;
- speciation through polymorphisms;
- cichlid fishes;
The neotropical cichlid fish Cichlasoma citrinellum is polymorphic in the structure of its pharyngeal jaw apparatus and external morphology. The pharyngeal jaws are either gracile and bear slender, pointed teeth (papilliform) or robust with strong, rounded teeth (molariform). Molariform morphs have a ‘benthic’, and papilliform morphs a ‘limnetic’ body form. Furthermore, this species is also polychromatic, with yellow and black morphs. The molariform morphology of the pharyngeal jaw apparatus adapts the fish for cracking and feeding on snails. Based on analysis of stomach contents, 94% of the molariform morph ate snails whereas only 19%, of the papilliform morph did so. This result suggests that the morphs occupy different ecological niches. The morphology of the pharyngeal jaw apparatus does not correlate significantly with sex, but it does with body colouration (P<0.005). Cichlasoma citrinellum mate assortatively with their own colour; therefore a mating preference for colour may lead to genetic isolation of trophic morphs.
The frequency of the molariform morph differs strikingly among populations of five Nicaraguan lakes and its abundance is correlated with the abundance of snails, the fishes' principal prey item. Among populations the frequency of molariform morphs decreases in the dry season. Morphology possibly changes reversibly within particular individuals between seasons. These results suggest that phenotypic plasticity and polymorphisms may be an adaptive characteristic of cichlid fishes. Patterns of intraspecific morphological variation match patterns of interspecific morphological diversification which suggests that universal developmental mechanisms canalize the possible expressions of morphology. The ability to respond morphologically to environmental shifts, in conjunction with genetically determined trophic polymorphisms and sexual selection via mate choice, could be the basis for speciation through intermediate stages of polymorphism of the impressive adaptive radiation of cichlid fishes.