Habitat-based polymorphism is common in stream fishes.

Area of Science:

• Ecology
• Evolutionary Biology
• Ichthyology

Background:

• Morphological differences (size and shape) in fish are often linked to contrasting habitats like pelagic and littoral zones in lakes.
• Repeated occurrence of these morphs suggests adaptive habitat-based polymorphism, potentially driven by habitat stability.
• The potential for such polymorphism in temporally dynamic stream environments remains an open question.

Purpose of the Study:

• To investigate whether fish morphology consistently differs across stream habitats (riffle, run, pool).
• To assess if habitat-based morphological variation is a feature of stream fish, similar to lake systems.

Main Methods:

• Compared morphological variation (size and shape) in 10 fish species.
• Analyzed fish from riffle, run, and pool habitats across 36 streams in three watersheds.
• Controlled for body size when analyzing shape differences.

Main Results:

• For most species, body size and shape differed significantly across riffle, run, and pool habitats.
• The patterns of morphological differences were not consistent across all species, suggesting varied habitat use.
• Habitat-based polymorphism appears to be a significant feature in stream fishes.

Conclusions:

• Habitat-based polymorphism is likely an important characteristic of stream fish populations.
• Despite temporal variability in streams, contrasting morphologies can evolve or be induced.
• Further research is needed to determine the genetic basis versus phenotypic plasticity of these observed differences.