This study investigated the occurrence and ontogenetic changes of halogenated secondary metabolites in planktotrophic and
lecithotrophic larvae and adults 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 (alkyl 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 contain halogenated metabolites because they are not
protected by adult defenses, (2) quantitative and qualitative variation of planktotrophic larval halogenated metabolites parallels
that of adults, and (3) brooded lecithotrophic larvae initiate the production of halogenated metabolites only after metamorphosis.
To address these hypotheses, volatile halogenated compounds from polychaete extracts were separated using capillary gas chromatography
and identified and quantified using mass spectrometry with selected ion monitoring. All four life stages (pre- and post-release
larvae, new recruits, adults) of both
S. benedicti and
Capitella sp. I contained the halogenated metabolites previously identified from adults. This is the first report of halocompounds
identified and quantified in polychaete larvae. Allocation of potential defense compounds to offspring varied as a function
of species, feeding type and developmental stage. Pre-release larvae of
S. benedicti with planktotrophic development contained the lowest concentration of total halogenated metabolites (1.75 ± 0.65 ng mm
−3), post-release and new recruits contained intermediate concentrations (8.29 ± 1.72 and 4.73 ± 2.63 ng mm
−3, respectively), and planktotrophic adults contained significantly greater amounts (28.9 ± 9.7 ng mm
−3). This pattern of increasing concentrations with increasing stage of development suggests synthesis of metabolites during
development. Lecithotrophic
S. benedicti post-release larvae contained the greatest concentrations of halometabolites (71.1 ± 10.6 ng mm
−3) of all
S. benedicti life stages and developmental types examined, while the amount was significantly lower in new recruits (34.0 ± 15.4 ng mm
−3). This pattern is consistent with a previously proposed hypothesis suggesting a strategy of reducing potential autotoxicity
during developmental transitions. Pre-release lecithotrophic larvae of
Capitella sp. I contained 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
field trials. As a means of conferring higher larval survivorship, lecithotrophic females of both species examined may be
expending more energy on chemical defenses than their planktotrophic counterparts by supplying their lecithotrophic embryos
with more of these compounds, their precursors, or with energy for their synthesis. This strategy appears common among marine
lecithotrophic larval forms.
Received: 14 July 1999 / Accepted: 20 January 2000
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