Allometric shape change of the lower pharyngeal jaw correlates with a dietary shift to piscivory in a cichlid fish |
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Authors: | Christoph J Hellig Michaela Kerschbaumer Kristina M Sefc Stephan Koblmüller |
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Institution: | 1. Department of Zoology, Karl-Franzens-University Graz, Universit?tsplatz 2, 8010, Graz, Austria
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Abstract: | The morphological versatility of the pharyngeal jaw of cichlid fishes is assumed to represent a key factor facilitating their
unparalleled trophic diversification and explosive radiation. It is generally believed that the functional design of an organism
relates to its ecology, and thus, specializations to different diets are typically associated with distinct morphological
designs, especially manifested in the cichlids’ pharyngeal jaw apparatus. Thereby, the lower pharyngeal jaw (LPJ) incorporates
some of the most predictive features for distinct diet-related morphotypes. Thus, considering that piscivorous cichlids experience
an ontogenetic dietary shift from typically various kinds of invertebrates to fish, concomitant morphological changes in the
LPJ are expected. Using Lepidiolamprologus elongatus, a top predator in the shallow rocky habitat of Lake Tanganyika, as model, and applying geometric and traditional morphometric
techniques, we demonstrate an allometric change in ontogenetic LPJ shape development coinciding with the completion of the
dietary shift toward piscivory. The piscivorous LPJ morphotype is initiated in juvenile fish by increasing elongation and
narrowing of the LPJ and—when the fish reach a size of 80–90 mm standard length—further refined by the elongation of the posterior
muscular processes, which serve as insertion for the fourth musculus levator externus. The enlarged muscular processes of
the fully mature piscivorous morphotype provide for the construction of a powerful lever system, which allows the large individuals
to process large prey fish and rely on exclusive piscivory. |
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