Feeding-deterrent properties of diterpenes of Dictyota mertensii (Phaeophyceae, Dictyotales)

Abstract

A B S T R A C TCrude extracts of the brown seaweed Dictyota mertensii (Martius) Kützing collected at two distant and different places on the Brazilian coast, Búzios (Rio de Janeiro) and Fernando de Noronha (PE), were evaluated for defensive chemistry against the crab Pachygrapsus transversus, and the sea urchin Lytechinus variegatus. The extract from Búzios specimens of D. mertensii significantly inhibited the consumption by both P. transversus and L. varigetaus. Fractionation of the extracts of specimens of D. mertensii from Búzios and F. de Noronha followed by complementary assays revealed one active fraction from each location, which contained distinct defensive secondary metabolites. In each active fractions prenylated guaiane diterpenes were the major compounds. Dictyol H and epoxypachydictyol A were the most abundant compounds in Búzios and F. de Noronha, respectively, followed by minor components. Our results show a differential production of secondary metabolites in the two distant and different populations of D. mertensii along the Brazilian coast. This suggests that defensive chemicals from this seaweed are not qualitatively absolute characteristics of the species, but may represent an ecological specialization to successfully prevent herbivory. R E S U M OOs espécimes da macroalga parda Dictyota mertensii coletados em dois diferentes locais no litoral brasileiro e distantes entre si, Búzios (Rio de Janeiro) e Fernando de Noronha (PE), foram avaliados quanto à atuação de seus extratos como defesa química contra o caranguejo Pachygrapsus transversus, e o ouriço do mar Lytechinus variegatus. O extrato dos espécimes de D. mertensii de Búzios inibiu o consumo por ambos P. transversus e L. variegatus. O fracionamento dos extratos dos espécimes de D. mertensii de Búzios e F. de Noronha avaliados em ensaios complementares revelaram uma fração ativa contendo distintos metabolitos secundários defensivos. Diterpenos do tipo guaiano prenilado foram as substâncias majoritárias em ambas as frações, mas dictyol H e epoxipachydictyol A foram os mais abundantes em Búzios e F. de Noronha, respectivamente, seguidos por componentes minoritários. Nossos resultados mostram uma produção diferencial de metabolitos secundários em duas populações distintas e distantes de D. mertensii no litoral brasileiro e sugerem que as defesas químicas desta macroalga marinha não são uma característica qualitativa absoluta desta espécie e pode representar uma especialização ecológica eficaz para prevenir a herbivoria.

Macrofauna associated with the brown algae Dictyota spp. (Phaeophyceae, Dictyotaceae) in the Sebastião Gomes Reef and Abrolhos Archipelago, Bahia, Brazil

“…Three alga species were identified, Dictyota ciliolata, D. mertensii and D. pinnatifida, all of which are morphologically similar and produce diverse metabolites that function as defense against feeding by many herbivores (Cronin and Hay, 1996b;Marques et al, 2006;Torrano-Silva and Oliveira, this issue; Vallim et al, 2007). A single frond was posteriorly identified as Dictyopteris plagiogramma; the data was reanalyzed without this sample and no differences were found in the results.…”

What Is the Relative Importance of Phytoplankton and Attached Macroalgae and Epiphytes to Food Webs on Offshore Oil Platforms?

“…Many reef crabs are considered algal grazers (e.g., Barry and Ehret 1993), although Kang et al (2008) reported that the decorator crab Hyastenus elongatius living in a macroalgal bed primarily consumed phytoplankton-based resources. Some algae may be unpalatable due to the production of secondary metabolites that deter grazers (Kain and Norton 1990;Vallim et al 2007). Furthermore, little is known about assimilation efficiencies of red algae, although some invertebrates are able to assimilate red algae with high efficiency (e.g., Cox and Murray 2006).…”

Marine chemical ecology

“…Dictyota mertensii was collected from two different locations in Brazil and found to vary in its diterpene composition. 33 The dichloromethane extracts from each collection and one chromatographic fraction from each extract deterred feeding by the crab Pachygrapsus transversus. The major components in the active fractions were dictyol H 9 from the southeast coast of Brazil and epoxypachydictyol A 10 from the northeast coast, 33 indicating that the chemical defenses of this seaweed are geographically variable.…”