Abstract
Diatoms synthesise bioactive unsaturated short-chain aldehydes (SCAs) in response to wound-activation. The defensive SCAs are toxic to developmental stages of a range of invertebrate species including copepods, sea urchins, polychaetes and ascidians. Embryotoxicity is dose-depen- dent, with inhibition of cleavage, a reduction in hatching success, and teratogenic effects in neonates symptomatic. Bioactivity is directed at cellular and molecular targets. Diatom extracts and the SCA 2E,4E-decadienal (DD) affect microtubule and microfilament stability. Bioactivity is not restricted to embryogenesis, but has also been demonstrated to affect fertilization success in broadcast-spawning macroinvertebrates. This study has sought to further identify the responses of marine invertebrate gametes and the process of fertilization to DD exposure with particular reference to sperm motility. Incubation of gametes with the saturated aldehydes decanal and undecanal and the fatty acid 5, 8,11,14,17-eicosapentaenoic acid (EPA) did not affect fertilization success. Exposure of gametes to DD inhibits fertilization success in a dose-dependent manner. Fertilization rate declined to 50% of control values at concentrations of 1.55 µg ml -1 for Arenicola marina, 3.98 µg ml -1 for Nereis virens, 7.94 µg ml -1 for Psammechinus miliaris and 10 µg ml -1 for Asterias rubens. Pre-incubation of oocytes in DD affected fertilization success to a limited degree; however pre-incubation of sperm in DD caused a pronounced dose- and time-dependent decline. DD exposure inhibits sperm migration rates and flagellar beating at concentrations as low as 0.05 µg ml -1 . The sperm remained alive, as evi- denced by oscillation of the sperm head; however, flagellar beating was inhibited. The negative effect of DD exposure was further enhanced as sperm density was reduced. Analysis by general lin- ear model revealed a significant interaction between DD concentration, period of sperm exposure and fertilizing sperm density (F = 6.7, p = 0.01). We suggest that diatom-derived SCAs can signifi- cantly impact fertilization success in broadcast-spawning invertebrates. The identification of sperm motility inhibition as a symptom of DD exposure offers a potentially useful cellular model to further study the effects of novel diatom-derived bioactive molecules.
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