Odour compounds of the diatom Cocconeis scutellum: effects on benthic herbivores living on Posidonia oceanica

Abstract

Polyunsaturated aldehydes released by marine planktonic diatoms upon wounding have been extensively studied since the discovery that they reduce the hatching success of copepods. Diatoms are also abundant in benthic marine ecosystems. For this reason we investigated the presence and the possible ecological roles of Cocconeis scutellum parva, a diatom found tightly attached to the leaves of Posidonia oceanica. This diatom was previously demonstrated to play an important trophic role for the shrimp Hippolyte inermis, by influencing its sex reversal. In the present study, C. scutellum parva was isolated and cultivated and the volatile compounds released upon cell disintegration were identified by mass-spectrometric methods. We demonstrated the presence of unsaturated aldehydes with chain lengths from C 5 to C 10 . Unexpectedly, we found C 6 compounds represented by 3(Z)-hexenal, 2(E)-hexenal, hexanal and hexanol-1 that resemble the typical bouquet observed in higher plants. Compounds not described before for diatoms were, among others, pentane-2, 3-dione and octane-2, 3-dione. Food choice experiments performed on 17 animal species associated with P. oceanica meadows indicated that these grazers recognise the presence of the odour compounds, exhibiting complex patterns of reactions according to their life strategies. The mosaic of results obtained at various concentrations, in different species, indicated that wound-activated infochemicals generate a web of communication among diatoms and benthic invertebrates.KEY WORDS: Infochemical · Odour · Seagrass · Behaviour · Feeding · Wounding · Diatom Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 400: [63][64][65][66][67][68][69][70][71][72][73] 2010 compound (whose structure has not yet been identified; Nappo et al. 2009) present in these diatoms acts as a spring signal for the production of young females, probably due to a long co-evolutionary process .In other cases, secondary metabolites produce deleterious effects on consumers. Compounds responsible for the biological effects have been demonstrated to be volatile organic compounds (VOC) not present in intact cells but released by a lipoxygenase cascade upon cell wounding (Pohnert 2000, Jüttner 2005. Unsaturated aldehydes of the lipoxygenase cascade in planktonic diatoms exhibit teratogenic effects on copepod larvae and reduce the viability of their eggs (Miralto et al. 1999). Wound-activated diatom cells also release unsaturated aldehydes (Pohnert 2002) that are inhibitors of mitotic proliferation in sea urchin embryos (Miralto et al. 1999). Similar relationships, although less striking, were demonstrated between the crustacean Daphnia pulicaria and some freshwater diatoms (Carotenuto et al. 2005).Secondary metabolites produced by the lipoxygenase pathway may also act as repellents against grazers ( Fink et al. 2006). The lipoxygenase product 2(E), 4(E),7(Z)-decatrienal has been shown to act as a repellent for freshwater crustacean grazers (Jüttner 2005). T...

Non-volatile oxylipins can render some diatom blooms more toxic for copepod reproduction

“…Interestingly, many diatom species seem to produce only these NVOs and not PUAs (Barreiro et al, 2011;Cutignano and Lamari, 2011;d'Ippolito et al, 2009;Fontana et al, 2007;Nanjappa et al, 2014). Similar compounds are also produced by benthic diatoms, where these compounds have been suggested to play a role as foraging kairomones, indicating the presence of abundant food (Jü ttner et al, 2010). NVOs were first reported at sea during a late-spring bloom of the non-PUAproducing diatom Cerataulina pelagica, the likely cause for reduced copepod egg production and hatching success at the time (Ianora et al, 2008).…”

“…The discovery of an enzyme cascade leading to the production of volatile and non-volatile biologically active oxylipins in marine phytoplankton is rather new (Miralto et al, 1999) even though the oxidative cleavage of fatty acids to form similar defensive compounds is well known in higher terrestrial plants (Farré -Armengola et al, 2013) and freshwater microalgae (Farré -Armengola et al, 2013;Fink, 2007;Ianora et al, 2008;Jü ttner et al, 2010). Oxylipins are believed to play a pivotal role in plant survival because they act as chemical attractors (e.g.…”

Centropages typicus(Crustacea, Copepoda) reacts to volatile compounds produced by planktonic algae

“…To test the effect of plant bouquets of odours on Centropages typicus , we conducted odour choice tests using a technique similar to the one proposed by Jüttner et al . (). Choice tests were conducted in order to distinguish positive and negative chemotaxis, mediated through the VOCs of each algal species (Wiesemeier et al .…”

“…) and the marine benthos (Jüttner et al . ). However, little is known about infochemicals involved in the interaction between copepods and their plant prey (Van Donk et al .…”

CULTURE CONDITIONS INFLUENCE THE GROWTH DYNAMICS AND THE PRODUCTION OF COCCONEIS SCUTELLUM (BACILLARIOPHYTA)1

“…These diatoms are routinely cultured at the Benthic Ecology Laboratory of the Stazione Zoologica Anton Dohrn, in Ischia. The strains were collected in the Bay of Naples, Italy (40.44.7 N, 13.56.4 E) in April 2001, isolated by a Leica micromanipulator, cleaned of bacteria and other diatoms through several passages in sterilized seawater, then identified under the SEM microscope (Jüttner et al. 2010).…”