LATITUDINAL VARIATION OF THE NUMBER OF MUSCLE FIBRES IN SALPA THOMPSONI (TUNICATA, THALIACEA) IN THE SOUTHERN OCEAN : IMPLICATIONS FOR THE VALIDITY OF THE SPECIES SALPA GERLACHEI (Ninth Symposium on Polar Biology)

• Main Authors: Beatriz Estela CASARETO, Takahisa NEMOTO
• Format: Report
• Language: English
• Published: Proceeding 1987
• Subjects: Pacific; Southern Ocean; Polar Biology; Proceedings of the NIPR Symposium on Polar Biology
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=5019; http://id.nii.ac.jp/1291/00005019/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=5019&item_no=1&attribute_id=18&file_no=1

The latitudinal variation is of common occurrence in epiplanktonic species with a wide north-south distribution. In Salpidae this phenomenon has been observed in the number of fibres of the body muscles, which is uniform in all tropical-temperate water species. Nevertheless, up to now it has not been observed in species restricted to the Southern Ocean. In this paper we discuss the existence of latitudinal variation in Salpa thompsoni, which is widely distributed and the most abundant salp species in the Southern Ocean. The number of muscle fibres of both aggregate and solitary forms of S. thompsoni showed a maximum at about 56°S and decreased gradually towards the higher latitudes. Body length varied latitudinally the same as the fibre numbers did. In the high latitudes of the Pacific Sector of the Southern Ocean, S. thompsoni is replaced by a sibling species, Salpa gerlachei. These two species differ only biometrically in fibre numbers per muscle band, being less in S. gerlachei. However, a broad overlap in the range of muscle fibre numbers was found between the two species. The present results suggest that these two species are synonymous and S. thompsoni is distributed with a clinal variation from the north to the south.