Halogenated metabolites in two marine polychaetes and their planktotrophicand lecithotrophic larvae

This study investigated the occurrence and ontogenetic changes of halogenat ed secondary metabolites in planktotrophic and lecithotrophic larvae and ad ults of two common, infaunal polychaetes, Streblospio benedicti (Spionidae) and Capitella sp. I (Capitellidae), with different life-history traits. S. benedicti contains at least 11 chlorinated and brominated hydrocarbons (al kyl halides) while Capitella sp. I contains 3 brominated aromatic compounds . These halogenated metabolites are potential defense compounds benefiting both larvae and adults. We hypothesized that: (1) planktotrophic larvae con tain halogenated metabolites because they are not protected by adult defens es, (2) quantitative and qualitative variation of planktotrophic larval hal ogenated metabolites parallels that of adults, and (3) brooded lecithotroph ic larvae initiate the production of halogenated metabolites only after met amorphosis. To address these hypotheses, volatile halogenated compounds fro m polychaete extracts were separated using capillary gas chromatography and identified and quantified using mass spectrometry with selected ion monito ring. All four life stages (pre- and post-release larvae, new recruits, adu lts) of both S. benedicti and Capitella sp, I contained the halogenated met abolites previously identified from adults. This is the first report of hal ocompounds identified and quantified in polychaete larvae. Allocation of po tential defense compounds to offspring varied as a function of species, fee ding type and developmental stage. Pre-release larvae of S. benedicti with planktotrophic development contained the lowest concentration of total halo genated metabolites (1.75 +/- 0.65 ng mm(-3)), post-release and new recruit s contained intermediate concentrations (8.29 +/- 1.72 and 4.73 +/- 2.63 ng mm(-3), respectively), and planktotrophic adults contained significantly g reater amounts (28.9 +/- 9.7 ng mm(-3)). This pattern of increasing concent rations with increasing stage of development suggests synthesis of metaboli tes during development. Lecithutrophic S. benedicti post-release larvae con tained the greatest concentrations of halometabolites (71.1 +/- 10.6 ng mm( -3)) Of all S. benedicti life stages and developmental mm types examined, w hile the amount was significantly lower in new recruits (34.0 +/- 15.4 ng m m(-3)). This pattern is consistent with a previously proposed hypothesis su ggesting a strategy of reducing potential autotoxicity during developmental transitions. Pre-release lecithotrophic larvae of Capitella sp. I containe d the highest concentration of total halogenated metabolites (1150 +/- 681 ng mm(-3)), whereas the adults contained significantly lower total amounts (126 +/- 68 ng mm(-3)). All concentrations of these haloaromatics are above those known to deter predation in previously conducted laboratory and fiel d trials. As a means of conferring higher larval survivorship, lecithotroph ic females of both species examined may be expending more energy on chemica l defenses than their planktotrophic counterparts by supplying their lecith otrophic embryos with more of these compounds, their precursors, or with en ergy for their synthesis. This strategy appears common among marine lecitho trophic larval forms.