Resource instability undermines predictable plasticity-mediated morphological responses to diet in a postglacial fish

Area of Science:

• Ecology
• Evolutionary Biology
• Ichthyology

Background:

• Phenotypic plasticity is a key mechanism for organisms to cope with environmental instability.
• Freshwater fish in recently glaciated ecosystems face altered invertebrate prey communities.
• Understanding diet-resource plasticity is crucial for predicting fish adaptation.

Purpose of the Study:

• To investigate how the rate of diet change affects phenotypic development in juvenile brown trout.
• To determine if phenotypic plasticity can facilitate adaptation to fluctuating prey resources.

Main Methods:

• Juvenile brown trout were fed alternating pelagic and littoral diets at different frequencies (daily, sub-seasonal, constant).
• Stable isotope analysis (carbon and nitrogen) tracked proportional diet intake.
• Morphometric analysis of head and jaw shape assessed phenotypic responses.

Main Results:

• Trout on constant diets developed predictable morphologies linked to diet type.
• Trout on alternating diets exhibited unpredictable morphologies.
• Rapid diet fluctuations (daily or monthly) disrupted the diet-phenotype association.

Conclusions:

• Extreme resource instability can overwhelm phenotypic plasticity.
• The efficacy of plasticity for adaptation to rapidly fluctuating prey resources is questionable.
• This challenges the role of plasticity in rapid adaptation to dynamic environments.