Meeting Abstract
Hyperiid amphipods are small crustaceans that live in the midwater (all the ocean water below the surface but above the sea floor) where light diminishes exponentially and there is nowhere to hide from predators. Hyperiids have developed a large variety of eyes, at least 11 distinct types, across the ~350 species. Many of these eyes are gigantic in size with various complexity. This study examined how hyperiid eye and brain size compared to other animals and how eye and brain size scale to body size within the group. Volumes of eyes, brains, and bodies of four hyperiid species were determined using 3D reconstructions from x-ray micro-computed tomography (µCT). The eyes and individual eye components, brains, and the whole body were manually reconstructed using Amira. Results show that larger hyperiid species don’t have equivalently larger brains as the rate at which brain size increases with body size in hyperiids is far smaller than those of other animals. Additionally, correlation between eye volume and brain volume against the body volume of four hyperiid species with large compound eyes shows that, on average, their eyes are 40 times larger than their brains. These results indicate a unique adaptation to living in the midwater. Possibly, hyperiids invest in large eyes for better low light vision, as larger eyes are more sensitive to light, but smaller brains for processing the relatively simple and homogenous visual field of the midwater. To understand the full range of hyperiid diversity and how they compare to other animals and to each other, reconstructing hyperiids with smaller eyes would be the next step.
