Functional differences between the extraordinary eyes of deep-sea hyperiid amphipods

Area of Science:

• Marine Biology
• Sensory Ecology
• Evolutionary Biology

Background:

• The ocean's midwater presents a challenging visual environment characterized by low light levels.
• Organisms in this habitat require specialized adaptations for both vision and camouflage (crypsis).
• Hyperiid amphipods exhibit remarkable diversity in eye morphology, suggesting adaptation to this unique environment.

Purpose of the Study:

• To investigate the morphological and functional differences in the eyes of three hyperiid amphipod species: *Hyperia galba*, *Streetsia challengeri*, and *Phronima sedentaria*.
• To understand how these visual adaptations relate to survival strategies in the mesopelagic zone.

Main Methods:

• Utilized micro-computed tomography (micro-CT) data.
• Employed computational modeling to map visual field topography.
• Predicted visual detection distances for targets in various directions.

Main Results:

• *Hyperia galba* possesses eyes optimized for wide visual fields and short-distance spatial vision.
• *Phronima sedentaria* and *Streetsia challengeri* have eyes capable of enhanced sensitivity and longer detection distances through spatial summation.
• Reduced visual field size in *Phronima* and *Streetsia* is compensated by a second eye pair or behavioral strategies, respectively.

Conclusions:

• Eye size reduction, crucial for crypsis, is balanced with enhanced visual sensitivity in mesopelagic amphipods.
• The diversity of hyperiid eye structures is likely driven by the evolutionary pressure to balance predation risk and visual requirements.
• These findings offer insights into the adaptive strategies of elusive midwater organisms.