Developmental responses to predation risk in morphologically defended mayflies.

Area of Science:

• Ecology
• Evolutionary Biology
• Aquatic Entomology

Background:

• Predator densities and species composition can influence prey life history traits, including morphology, development, and emergence timing.
• The ephemerellid mayfly, Ephemerella invaria, is prey to various fish species in stream ecosystems.
• Differential predation pressure may lead to adaptive responses in prey populations.

Purpose of the Study:

• To investigate the effects of varying predator densities and species composition on the morphology and life history of Ephemerella invaria.
• To determine if observed differences in mayfly life history are attributable to fish chemical cues.
• To assess the role of developmental plasticity in prey adaptation to predation risk.

Main Methods:

• Field surveys comparing Ephemerella invaria populations in streams with high vs. low fish diversity and density.
• Laboratory experiments exposing Ephemerella larvae to fish chemical cues or control water.
• Analysis of mayfly emergence timing, size, defensive morphology, and growth rates.

Main Results:

• Ephemerella from high-predation streams emerged earlier and at smaller sizes than those from low-predation streams.
• Fish chemical cues accelerated larval development and reduced adult size in laboratory experiments for both populations.
• No significant differences in defensive morphology or growth rates were observed between populations or in response to fish cues.

Conclusions:

• Variation in predator communities can drive the evolution of developmental plasticity in prey.
• Faster larval development in high-risk environments may increase survival but incurs a fecundity cost due to smaller adult size.
• Ephemerella invaria exhibits plasticity in life history traits, specifically development timing and size, as an adaptation to predation pressure.