To test the extension process, Dufour set up aquarium tanks with sediment to investigate how clams that require chemicals differ from those that do not. Clams that live in a symbiotic relationship with marine bacteria act as hosts that retrieve chemicals, typically sulfide or methane. The Nature paper explains that the symbiotic clams in the Thyasiridae family elongate their feet to burrow extensive mines in an effort to reach the sulfide. X-rays taken through Dufour's plexiglass tanks over several weeks revealed long, branch-like mines extending through the sediment, especially in cases tested under low sulfide conditions, which forced clams to stretch their feet farther.
While they had expected some extension, Dufour says the results were "amazing." She found clams with shells measuring 4.5 millimeters that had elongated their feet some 13 centimeters from the shell. "What I find the most interesting about this work is that only the clams with symbionts make these very long burrows," said Dufour, a graduate student in the marine biology curricular program at Scripps. "The thyasirids in my study that didn't have symbionts did not make such burrows. To get the sulfide the bacteria need, these clams have evolved the ability to mine the sediment with their feet--it shows that very different species can find amazing ways of cooperating." The study was supported by Scripps Institution's graduate departmen
Contact: Mario Aguilera
University of California - San Diego