In giving their eggs tender loving care by mouthbrooding them, male cardinalfish have also placed severe constraints on their ability to modify their oral morphologies.
In a study to be published in a forthcoming issue of the Proceedings of the Royal Society B: Biological Sciences, Andrew Hoey and co-authors compared the feeding apparatus between sexes of nine species of cardinalfish and compared brood characteristics among species from different trophic groups, respectively.
They found that cardinalfishes have sacrificed morphological plasticity in order to maintain the use of the mouth for both feeding and reproduction.
This means that even though cardinalfishes have an evolutionary history that mirrors that of the wrasses in terms of the age of origination and timing of diversification, they show virtually no changes in oral morphologies within the group compared to the wide range seen in wrasses.
Unfortunately, cardinalfishes expect to face a grim future. "Apart from being left behind in terms of evolution, mouthbrooding makes them more vulnerable to the effects of climate change. As ocean temperatures warm, these fish will need to breathe more — and the last thing they need is having a mouthful of offspring when they need oxygen," said coauthor David Bellwood.
For more information, see the paper: Hoey, AS, DR Bellwood and A Barnett (2012) To feed or to breed: morphological constraints of mouthbrooding in coral reef cardinalfishes. Proceedings of the Royal Society B: Biological Sciences doi:10.1098/rspb.2011.2679.
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