Abstract
Marine sediments can contain B vitamins, presumably incorporated from settled, decaying phytoplankton and microorganisms associated with decomposition. Because B vitamins may be advantageous for the energetically intensive processes of metamorphosis, post-metamorphic growth, and reproduction, we tested several B vitamins to determine if they would stimulate larvae of the deposit-feeding polychaete Capitella teleta to settle and metamorphose. Nicotinamide and riboflavin individually stimulated larvae of C. teleta to settle and metamorphose, generally within 1–2 hours at nicotinamide concentrations as low as 3 µM and riboflavin concentrations as low as 50 µM. More than 80% of the larvae metamorphosed within 30 minutes at a nicotinamide concentration of 7 µM. The pyridine channel agonist pyrazinecarboxamide also stimulated metamorphosis at very low concentrations. In contrast, neither lumichrome, thiamine HCl, pyridoxine HCl, nor vitamin B12 stimulated larvae of C. teleta to metamorphose at concentrations as high as 500 µM. Larvae also did not metamorphose in response to either nicotinamide or pyrazinecarboxamide in calcium-free seawater or with the addition of 4-acetylpyridine, a competitive inhibitor of the pyridine receptor. Together, these results suggest that larvae of C. teleta are responding to nicotinamide and riboflavin via a chemosensory pyridine receptor similar to that previously reported to be present on crayfish chela and involved with food recognition. Our data are the first to implicate B vitamins as possible natural chemical settlement cues for marine invertebrate larvae.
Highlights
The larvae of many benthic marine invertebrates are planktonic and are ‘forced to wander’ the sea until they become competent to metamorphose and locate a site suitable for settlement [1]
No control larvae exposed to 2 mM ketanserin alone settled or metamorphosed within 24 h; all of the larvae exposed to the positive controls of nicotinamide and pyrazinecarboxamide alone metamorphosed in less than an hour, indicating that most larvae were competent when tested. These data support our hypothesis that at least some B vitamins may act as chemical cues for habitat selection by the larvae of C. teleta and may stimulate the larvae of this species to metamorphose in the field
Nicotinamide (B3), nicotinic acid (B3), and riboflavin (B2) stimulated larvae of C. teleta to metamorphose, whereas thiamine HCl, pyridoxine HCl, biotin, vitamin B12, and the riboflavin breakdown product lumichrome did not. It may be advantageous for marine larvae to settle and metamorphose in response to environmental riboflavin and nicotinamide, as riboflavin is required for the synthesis of FAD, and nicotinamide serves as a building block for the synthesis of NAD; both products are important electron carriers for the electron transport chain, ATP production, and other aspects of cellular metabolism
Summary
The larvae of many benthic marine invertebrates are planktonic and are ‘forced to wander’ the sea until they become competent to metamorphose and locate a site suitable for settlement [1]. Particular chemical cues promote larval settlement and subsequent metamorphosis by competent larvae of many species [2,3,4]. These chemical cues may indicate the presence of appropriate food, conspecific adults to mate with, or other environmental factors that signal the suitability of a site to live in for juveniles and adults. For the vast majority of marine invertebrates, the specific chemical settlement cues remain undefined
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