Gut length and mass in herbivorous and carnivorous prickleback fishes (Teleostei: Stichaeidae): ontogenetic, dietary, and phylogenetic effects |
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Authors: | Donovan P German Michael H Horn |
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Institution: | (1) Department of Biological Science, California State University, Fullerton, CA 92834-6850, USA;(2) Department of Zoology, University of Florida, Gainesville, FL 32611-8525, USA |
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Abstract: | Relative gut length, Zihler’s index, and relative gut mass were measured in four species of prickleback fishes and the effects
of ontogeny, diet, and phylogeny on these gut dimensions were determined. Of the four species, Cebidichthys violaceus and Xiphister mucosus shift to herbivory with growth (>45 mm SL), whereas X. atropurpureus and Anoplarchus purpurescens remain carnivores. A. purpurescens belongs to a carnivorous clade, and the three other species belong to an adjacent, herbivorous clade. Gut dimensions were
compared in three feeding categories of the four species: (1) small, wild-caught juveniles representing the carnivorous condition
before two species shift to herbivory; (2) larger, wild-caught juveniles representing the natural diet condition of the two
carnivores and the two species that have shifted to herbivory; and (3) larger, laboratory-raised juveniles produced by feeding
a high-protein artificial diet to small juveniles until they have reached the size of the larger, wild-caught juveniles. Comparisons
of gut dimensions in categories (1) versus (2) tested for an ontogenetic effect, in (2) versus (3) for a dietary effect, and
within each category for a phylogenetic effect. C. violaceus and X. mucosus increased gut dimensions with increase in body size and did not change ontogenetic trajectory in gut dimensions on the high-protein
artificial diet, suggesting that they are genetically programmed to develop relatively large guts associated with herbivory.
X. atropurpureus increased its gut dimensions with increase in size similar to its sister taxon, X. mucosus, suggesting a phylogenetic influence, but decreased gut dimensions on the high-protein artificial diet, suggesting phenotypic
plasticity. Nevertheless, X. atropurpureus displayed a larger gut than A. purpurescens, further evidence that it evolved in an herbivorous clade. A. purpurescens possessed a relatively small gut that was little affected by ontogeny or diet. Ontogeny and phylogeny more than diet appear
to influence gut dimensions in the four species, thus favoring genetic adaptation over phenotypic plasticity as the major
force acting on digestive system features in the two prickleback clades. |
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