Not all plecs that graze on wood are the same, according to research to be published in a forthcoming issue of the journal Functional Ecology.
Nathan Lujan, Donovan German and Kirk Winemiller came to this conclusion after examining seven species of plecs that live among and feed on coarse woody debris in their study.
Of the seven species of plecs found living together in the Marañon River of northern Peru that the authors studied, five (Hypostomus pyrineusi, Panaque albomaculatus, P. cf. bathyphilus, P. gnomus and P. nocturnus) gouge into and feed on wood, while the other two (Lamontichthys filamentosus and Spatuloricaria puganensis) forage along the surface of the wood.
The authors examined six jaw functional morphological characteristics of each loricariid species as well as carbon and nitrogen stable isotope ratios of blood plasma, red blood cells and fin tissue of three wood-eating species (P. cf. bathyphilus, P. nocturnus and H. pyrineusi) and muscle tissues of all seven species.
The authors found that the wood-eating species had robust jaws specialised for gouging wood, and isotopic signatures in the tissues that suggested that the fishes utilised carbon primarily from cellulose (but not lignin) in the wood. The signature of the nitrogen isotopes from the fish tissues suggest that the wood-eaters digest most of the microbes and microbial digestive by-products produced during wood decomposition, rather than the wood itself.
Within the two non wood-eating species, the authors found specialisations in the teeth and jaws that also suggested that they feed differently from each other.
Lamontichthys is believed to graze the surface of the wood, feeding on the biofilm growing on it (this is supported by the carbon isotope signature of its tissues), while Spatuloricaria is believed to feed by inserting its jaws and teeth deep into crevices to remove aquatic insects.
For more information, see the paper: Lujan, NK, DP German and KO Winemiller (2011) Do wood-grazing fishes partition their niche?: morphological and isotopic evidence for trophic segregation in Neotropical Loricariidae. Functional Ecology doi:10.1111/j.1365-2435.2011.01883.x
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