Shore crabs reveal novel evolutionary attributes of the mushroom body

Neural organization of mushroom bodies is largely consistent across insects, whereas the ancestral ground pattern diverges broadly across crustacean lineages resulting in successive loss of columns and the acquisition of domed centers retaining ancestral Hebbian-like networks and aminergic connections. We demonstrate here a major departure from this evolutionary trend in Brachyura, the most recent malacostracan lineage. In the shore crab Hemigrapsus nudus, instead of occupying the rostral surface of the lateral protocerebrum, mushroom body calyces are buried deep within it with their columns extending outwards to an expansive system of gyri on the brain's surface. The organization amongst mushroom body neurons reaches extreme elaboration throughout its constituent neuropils. The calyces, columns, and especially the gyri show DC0 immunoreactivity, an indicator of extensive circuits involved in learning and memory.

Automated summary

The neural organization of mushroom bodies is generally similar across insects, but varies greatly in crustaceans, with the structure in shore crabs showing a unique departure from the typical pattern. Specifically, the mushroom body calyces in Hemigrapsus nudus are buried deep within the brain, with columns extending outward to an expansive system of gyri on the brain's surface. The organization of mushroom body neurons in the shore crab reaches extreme elaboration, reflecting extensive circuits involved in learning and memory.