Meeting Abstract
Since the early 20th century, head shape dimorphism in European eel was documented, but it was only in the early 21st century that statistical support for the two morphotypes was provided. Most prominent at the yellow eel stage, broad-headed eels are known to feed more on harder and larger prey than their narrow-headed conspecifics, as well as they show different foraging behaviour. The onset of this dimorphism could be traced back to the earlier glass eel stage, where both phenotypic plasticity responses to different diets as well as genetic mechanisms seem to control for it. Although the underlying musculoskeletal differences in the feeding apparatus suggest that broad-heads show adaptive modifications to deal with larger and harder prey, the integration of multiple lines of evidence suggest the story is more complex, also including aspects of differential growth rates and habitat preference. Paradoxically, the adaptive benefit of broad-heads in a natural environment actually becomes maladaptive as this environment increasingly became polluted. Dimorphic bio-accumulation of especially highly lipophilic pollutants may even compromise the reproductive success of broadheads.
