Diet-induced phenotypic plasticity in European eel (Anguilla anguilla)

Abstract

Two phenotypes are present within the European eel population: broad-heads and narrow-heads. The expression of these phenotypes has been linked to several factors, such as diet and differential growth. The exact factors causing this dimorphism, however, are still unknown. In this study, we performed a feeding experiment on glass eels from the moment they start to feed. Eels were either fed a hard diet, which required biting and spinning behavior, or a soft diet, which required suction feeding. We found that the hard feeders develop a broader head and a larger adductor mandibulae region than eels that were fed a soft diet, implying that the hard feeders are capable of larger bite forces. Next to this, soft feeders develop a sharper and narrower head, which could reduce hydrodynamic drag, allowing more rapid strikes towards their prey. Both phenotypes were found in a control group, which were given a combination of both diets. These phenotypes were, however, not as extreme as the hard or the soft feeding group, indicating that some specimens are more likely to consume hard prey and others soft prey, but that they do not selectively eat one of both diets. In conclusion, we found that diet is a major factor influencing head shape in European eel and this ability to specialize in feeding on hard or soft prey could decrease intra-specific competition in European eel populations.

Extensive genetic differentiation between recently evolved sympatric Arctic charr morphs

“…Resource polymorphism can arise through developmental plasticity within a homogenic population, by natural selection on genetically encoded traits or a combination of these mechanisms. For instance, the broad and narrow‐headed morphs of the European eel ( Anguilla anguilla ) were found to be determined to a large extent by diet (De Meyer, Christiaens, & Adriaens, ) and ecomorphs of killer whales ( Orcinus orca ) were hypothesized to have originated through plastic responses of a small founder population (Foote et al, ). Examples of genetically determined resource polymorphism can be found in crater lake cichlid fishes, for example, were a single locus effects jaw and body shape (Fruciano et al, ).…”

Differential gene expression in narrow‐ and broad‐headed European glass eels (Anguilla anguilla) points to a transcriptomic link of head shape dimorphism with growth rate and chemotaxis

“…Instead, our results provide support for the third hypothesis that a combination of genetic differences and environment‐dependent developmental plasticity drives head shape dimorphism. On the one hand, there is definite support that differences in head shape are related to dietary differences in the elver and yellow eel stage (De Meyer et al., ). On the other hand, we found that the genes somatotropin‐1 (or GH1 ) and igf2 were significantly upregulated in narrow‐heads.…”

“…() showed that narrow‐headed yellow eels have a significantly lower trophic position than broad‐headed ones based on stable isotope analysis, independent of their body size. Finally, a study by De Meyer, Christiaens, and Adriaens () showed that elver eels developed a broad‐head when given hard food, whereas elvers fed soft food retained a narrow‐head, soon after pigmentation started. Consequently, head shape might be solely a plastic response to dietary differences.…”

Dimorphism throughout the European eel's life cycle: are ontogenetic changes in head shape related to dietary differences?

“…; De Meyer et al. ). Their diet mainly consists of harder prey items, such as large crustaceans and fish, whereas that of narrow‐headed phenotypes generally includes small invertebrates such as insect larvae.…”

“…In another study, De Meyer et al. () showed that dietary differences in the latter stage can stimulate the development of more extreme broad and narrow heads, with eels still being smaller than 15 cm.…”