Hard versus soft food: diet-induced phenotypic plasticity in head morphology in European elvers

• Main Authors: De Meyer, Jens, Christiaens, Joachim, Adriaens, Dominique
• Format: Conference Object
• Language: English
• Published: 2015
• Subjects: Biology and Life Sciences; elver eel stage; trophic plasticity; feeding; dimorphism; Anguilla anguilla
• Online Access: https://biblio.ugent.be/publication/7001489; http://hdl.handle.net/1854/LU-7001489

By bone remodeling and changing of muscle volume, fish can adapt to changes in mechanical loads they are confronted with, including dietary changes such as prey hardness. This capability of a genotype to develop different phenotypes in response to varying environment is known as phenotypic plasticity. It has been shown that differences in prey type being consumed, triggers such a phenotypic plasticity in fish. Also in the European eel (Anguilla anguilla), two morphotypes exist: broadheads and narrowheads. Studies based on gut content and stable isotope analysis have shown that broadheads consume larger and harder prey, such as fish and large crustaceans, whereas narrowheads feed on smaller prey, such as benthic invertebrates. These studies, however, are performed on yellow eels with a minimum length of 30 cm, and only provide indirect evidence that head shape is affected by differences in diet. Here, we performed a feeding experiment on glass eels that just swam up the European rivers to start feeding. These glass eels were captured and separated in three groups: one group was given hard feed requiring biting, the second group got soft feed that could be sucked in and the final group, which acted as a control group, was given a mixture of both. We found that hard feeders developed a broader general head width and a broader posterior eye region than soft feeders. This region is associated with the location of the jaw muscles, indicating that hard feeders develop larger muscles to cope with the harder prey. Hard feeders, however, also grew more slowly than soft feeders, suggesting that the net energy uptake of hard feeders was lower as prey handling required more energy and time. Specimens of the control group, finally, developed intermediate head widths, implying that they are not fully adapted to feed on either hard or soft prey. In conclusion, this study provides the first direct evidence that diet influences the head shape of European eel.