Picky eating by Chevron butterfly may be its downfall

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The picky diet of the Chevron butterflyfish may threaten the survival of this species, according to a study to be published in the journal Behavioral Ecology and Sociobiology.

The Chevron butterflyfish (Chaetodon trifascialis) is a widespread species found throughout the Indo-Pacific from the Red Sea and East Africa to the Hawaiian and Society islands.

The species, like many other butterflyfish, is an obligate feeder on hard corals; however, the Chevron butterflyfish is known to feed almost exclusively on a single species of hard coral, Acropora hyacinthus.

The study by Michael Berumen and Morgan Pratchett examined the dietary preference of the Chevron butterflyfish and a related species, the Bluespot butterflyfish (C. plebeius) by observing the feeding habits of fishes in the wild in Lizard Island on the northern Great Barrier Reef.

The authors also conducted controlled feeding experiments where juveniles of both species were fed exclusive diets of one of three coral species: Acropora hyacnthus, Pocillopora damicornis and Porites cylindrica.

Based on observations of the wild fish, the authors found the Chevron butterflyfish to be highly selective in diet, feeding on only 16 species of coral in the families Acoporidae and Pocilloporidae (by comparison, the bluespot butterflyfish consumed 38 species of corals from 7 families).

The results of the controlled feeding experiments were even more dramatic, with the Chevron butterflyfish that were fed Pocillopora and Porites corals losing weight over the study period (two of six fish that were fed Porites actually died during the experiment).

By contrast, the Bluespot butterflyfish fared just as well on exclusive diets of Acropora and Pocillopora corals, although, like the Chevron butterflyfish, individuals fed exclusively Porites lost weight.

The authors also found that contrary to expectations, the more specialized species (C. trifascialis) did not grow faster than the generalist species (C. plebeius) when both consumed their preferred prey.

They observe that ncreased dietary specialization appears to be a questionable evolutionary strategy for C. trifascialis because there is no apparent fitness benefit that outweighs the increased susceptibility to disturbance and resource depletion.

The increasing disturbances to coral reefs encountered in recent times may lead to the extinction of diet specialists such as the Chevron butterflyfish, since they are unable to withstand reductions in the availability of preferred prey resources by exploiting alternate prey resources.

For more information, see the paper: Berumen, ML and MS Pratchett (2008) Trade-offs associated with dietary specialization in corallivorous butterflyfishes (Chaetodontidae: Chaetodon). Behavioral Ecology and Sociobiology doi: 10.1007/s00265-007-0526-8