Â鶹ÒùÔº

The Japanese mud shrimp, Upogebia major, constructs burrows that can reach two meters deep into the sandy shores of East Asia and Eastern Russia. The size and Y-shape of these double-entrance burrows make them appealing to other small dwelling species, resulting in a symbiotic relationship that effectively makes them roommates.

Recently, a collaborative team of researchers from Kyoto University and Kochi University confirmed that the Japanese mud shrimp has a new roommate: Betaeus levifrons, a rare species of alpheid shrimp that until now has only been found in the Russian Far East. The research is in the Journal of the Marine Biological Association of the United Kingdom.

When surveying burrows of the Japanese mud shrimp along the Pacific coast of Hokkaido, Japan's northernmost main island, the researchers collected five specimens of B. levifrons, all of which were found in U. major burrows. This suggests that B. levifrons is an obligate symbiont of U. major, meaning it depends on U. major for shelter.

In total, the research team surveyed 90 burrows at Akkeshi Bay and 50 at Usu Bay. At the latter location, the team also surveyed 35 burrows of the shrimp Alpheus brevicristatus to differentiate it from its alpheid relative.

This study also marks the first recorded sighting of ovigerous—or egg-bearing—females of B levifrons, providing additional data on this species, including its distribution, color variation, and genetic makeup.

"Species of the genus Betaeus have the unusual trait of possessing claws that are reversed in the orientation of fingers compared to those of many other snapping shrimp, which I find intriguing," says first author Yumi Henmi. "This research showed me there are still many interesting discoveries to be made within the alpheidae family."

Along with some free-living species, the genus Betaeus includes species that live in symbiosis with a variety of invertebrates, such as sea urchins, abalones, other decapods, and spoon worms. The diversification and evolutionary processes underlying these symbiotic relationships indicates important future research, with broader implications for the evolution of symbiosis in marine ecosystems.

B levifrons is not the Japanese mud shrimp's only roommate, however. The snapping shrimp, Stenalpheops anacanthus, another obligate symbiont of U. major, lives in the mud shrimp's burrows on the other three main islands of Japan but has not been found in Hokkaido.

"This likely reflects the ecological and evolutionary processes unique to each environment," says Henmi.

The regional variation in symbiotic associations likely influences interactions between hosts and symbionts, as well as interactions among different symbionts themselves. Understanding these patterns will provide important insights for future research on evolution and ecology.