Larval Settlement and Metamorphosis of Sabellariid Polychaetes, with Special Reference to Phragmatopoma Lapidosa, a Reef-Building Species, and Sabellaria Floridensis, a Non-Gregarious Species
Abstract:The naturally-occurring inducers of larval settlement and metamorphosis have recently been isolated and identified for the northeast Pacific reef-building sabellariid polychaete, Phragmatopoma californica, and the larval responses of this species compared, in reciprocal laboratory settlement assays, to those of its European counterpart, Sabellaria alveolata. The present study includes the larval behavior of two additional sabellariids from the western Atlantic, P. lapidasa, a reef-building species, and S. flaridensis, a non-gregarious species.
Larval responses of P. lapidosa were very similar to those of P. californica. In reciprocal laboratory assays of both species, greater metamorphosis occurred on conspecific than on heterospecific tube sand, but both metamorphosed more frequently on heterospecific tube sand than on control sand. Organic solvent extraction of the sand/cement matrix of tubes of P. lapidosa removed its capacity to induce conspecific metamorphosis. The capacity was retained in the lipid-soluble extract and was recovered as a single fraction by high-performance liquid chromatography. The inducers were identified by gas chromatography as a mixture of free fatty acids (FFAs) ranging from 14 to 22 carbons in length. The mixture contained the same component FFAs as the inductive fraction from the natural tube sand of P. californica, but the relative proportions were different. Of the FFAs found in the naturally-occurring mixture, larval metamorphosis was greatest in response to 16:1, 18:2, 20:4 and 20:5, with a significant response to 16:1 at as low as 1 μg/g sand (surface area ≅36 cm2). Metamorphosis-inductive FFAs were isolated from natural tube sand of P. lapidosa at approximately 4–5 μg/g sand, although extraction was believed to be incomplete. In assays of 37 FFA standards and 9 FFA derivatives, metamorphosis of P. lapidosa was dependent on the length and conformation of the acyl chain length and on the presence of a carboxylic acid functional group, as had previously been demonstrated for P. californica. Reciprocal cross-fertilization of gametes of P. lapidosa and P. californica resulted in larvae that developed and metamorphosed normally. Results of this and previous investigations suggest that P. lapidasa and P. califarnica are geographic races of the same species, and the trinomials Phragmatapoma lapidosa lapidosa and P. I. californica are proposed for each subspecies.
Larval responses of Sabellaria/floridensis resembled those of S. alveolata in three respects: (1) upon reaching maturity, a large percentage of the larvae metamorphosed spontaneously in culture vessels, (2) in laboratory settlement assays, a large proportion of the larvae metamorphosed on control sand, and (3) metamorphosis was not enhanced upon exposure to the FFAs that induce metamorphosis of Phragmatopoma larvae. Unlike the larvae of S. alveolata, which settle gregariously, larvae of the non-gregarious S. floridensis did not metamorphose to any greater extent on con specific tube sand than on control sand. Among sabellariid polychactes, enhanced settlement on conspecific tube sand may be the only requirement for reef formation.
Document Type: Research Article
Publication date: July 1, 1988
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