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Species-specific patterns of the use of burrows of Upogebia Leach, 1814 (Decapoda: Gebiidea: Upogebiidae) by the symbiotic alpheid shrimps Stenalpheops anacanthus Miya, 1997 and Athanas japonicus Kubo, 1936 (Decapoda: Caridea: Alpheidae) as revealed by laboratory quantification


 Many alpheid shrimps live symbiotically on the body surface or inside the bodies of other invertebrates, while others use burrows made by other animals. The burrow symbiosis of alpheid shrimps is poorly studied in the context of ecology, probably because the cryptic infaunal nature of the relationship is hard to observe. The limited knowledge of the pattern of burrow use by alpheid shrimps leaves a gap in our understanding of their evolutionary history. We described and compared the behavior of Stenalpheops anacanthusMiya, 1997 and Athanas japonicusKubo, 1936, two alpheid species living symbiotically in the burrows of the same host, Upogebia yokoyaiMakarov, 1938. We found that both alpheid species used U. yokoyai burrows in aquaria, but their burrow use patterns were quite different. The average time taken for S. anacanthus to enter the burrow for the first time was much shorter (1 min) than that of A. japonicus (13 min). Subsequently, S. anacanthus made longer use of the burrow (80% of the observation period) than A. japonicus (49%). The tail-first exit frequency, which may indicate a sudden expulsion from the burrow by the host, was more frequent in A. japonicus (25%) than in S. anacanthus (7%). Such differences could be attributed to the nature of the symbiotic relationship, obligate in S. anacanthus but facultative in A. japonicus. Because of the diversity of symbiotic lifestyles, there is considerable potential to study the ecology and evolutionary biology of burrow-symbiotic alpheids further.