Diatom cultures exhibit differential effects on larval metamorphosis in the marine gastropod Ilyanassa obsoleta (Say)

Abstract

Abstract:Adult Ilyanassa obsoleta recruit from the plankton to surface sediments of intertidal mudflats along the U.S. East Coast as a result of metamorphic induction of planktonic larvae by environmental cues. A previous researcher discovered that seawater extracts of mud from juvenile habitats could induce metamorphosis and provided evidence that the inductive agent was of biological origin. Because juvenile I. obsoleta are herbivorous and grow when fed diets of benthic diatoms, we hypothesized that benthic diatoms or their associated microflora might be responsible for producing a metamorphic stimulus. We tested extracts of a culture of mixed diatoms and extracts of cultures of 6 diatom species isolated from mudflat sediments along the coast of North Carolina in which sexually mature and immature adult (juvenile) I. obsoleta commonly co-occur. We also tested extracts of one diatom culture isolated at the Friday Harbor Laboratories (Friday Harbor, WA). We found differential effects among the diatom species tested. One centric diatom, Coscino-discus sp., induced metamorphosis at levels close to those triggered by a known neuroactive compound, serotonin. Several species of benthic diatoms displayed neutral effects, showing little or no inductive capability. In one experiment, an unidentified pennate diatom species appeared to inhibit spontaneous metamorphosis that occurred in some competent larvae. We hypothesize that Coscinodiscus sp. or its associated microflora, is part of a suite of benthic species that is either indicative of a favorable juvenile environment or is itself part of the postmetamorphic diet. Our results also indicate that larval Ilyanassa demonstrated positive, neutral, and perhaps even negative responses to potential metamorphic cues.

GABA is an inhibitory neurotransmitter in the neural circuit regulating metamorphosis in a marine snail

“…Whereas earlier experiments have used multiple reagents in seawater to good effect (Baloun and Morse, ; Froggett and Leise, ), we chose to use separate applications of reagents to avoid any potentially confounding effects from direct interactions of reagents or their oxidative products that can occur in seawater (Pires and Hadfield, ). Lack of appropriate diatom cultures (Leise et al, ) precluded experiments investigating GABAergic effects on natural induction of metamorphosis in T. obsoleta .…”

“…Adult snails were maintained in four 75.7 L (20 gallon) breeding aquaria in a Figure 1 Diagram of the metamorphic pathway in T. obsoleta based on previous investigations. T. obsoleta metamorphoses in response to several species of diatoms that occur in intertidal mudflats (Leise et al, 2009;Leise and Cahoon, 2012). Odorants from these diatoms presumably activate epidermal sensory neurons that in turn excite serotonergic neurons in the AG.…”

“…In some cases, toxicity was only recognized as reduced growth or survival, sometimes days after reagent exposure (Bryan and Qian, 1998;Gapasin and Polohan, 2004;Li et al, 2006;Stewart et al, 2008;Yu et al, 2008;Roberts and Watts, 2010;Yu et al, 2010;Wassnig and Southgate, 2012;Mes ıas-Gansbiller et al, 2013;Yang et al, 2013;Galley et al, 2017). We typically end our experiments at 48 h because highly effective inducers will have triggered metamorphosis in 80%-100% of larval T. obsoleta by that time (Couper and Leise, 1996;Froggett and Leise, 1999;Leise et al, 2004Leise et al, , 2009). Researchers who conduct experiments for several additional days often include antibiotics in treatment solutions to reduce or eliminate bacterial overgrowth (Beiras and Widdows, 1995;Gapasin and Polohan, 2004;Roberts and Watts, 2010).…”

“…Larval metamorphosis in T. obsoleta can be initiated by the reception of various environmental cues, as happens in other marine molluscs. For example, several species of diatoms release water soluble compounds, or kairomones, that can induce metamorphosis in physiologically competent T. obsoleta (Leise et al, 2009;Leise and Cahoon, 2012). Two wellknown neurotransmitters are involved in the metamorphic pathway in this species and we have used these and related reagents routinely in our GABA induces metamorphosis in multiple species of invertebrate larvae (11), but some larvae respond to it only weakly (1/2, 15% metamorphosis or as judged by the authors), some with settlement (S), or not at all (o).…”

The influence of bacterial quorum-sensing inhibitors against the formation of the diatom-biofilm

“…During the formation of micro-fouling, diatoms, bacteria and their products such as extracellular polymeric substances (EPSs) constitute fouling biofilms, which have shown to affect the larval settlement of a wide range of fouling species including barnacles, bryozoans and polychaetes. [12,13] Some reports pointed out that most of the fouling animals preferred to attach on the place where diatoms gathered although bacterial biofilms also influenced the formation of subsequent macro-fouling communities. [14] And the growth and attachment of diatoms are closely related to bacteria.…”