How do face herbivory? A case of study in Cadiz bay

Isabel Casal*1, Fernando G. Brun1 and Eva Zub´ıa2

*Corresponding author: [email protected] 1Department of Biology (Ecology Area), University of C´adiz,Puerto Real (C´adiz)Spain 2Department of Organic Chemistry, University of C´adiz,Puerto Real (C´adiz),Spain

Keywords: Herbivory, Marine Angiosperms, Natural Products

Introduction

The marine angiosperms or seagrasses are vascular with leaves, rhizomes, roots, flowers and seeds that inhabit marine environment. Seagrasses are characterized by developing extensive crowded meadows in shallow coastal areas, forming one of the most important coastal habitats of the biosphere, bearing a great ecological value because of the services and functions they provide, both to humans and marine . Seagrasses are distributed along all the coasts of the world, except in Antarctica (Robertson and Mann, 1984) while only four species are found in the : noltei Hornemann (1832), Linnaeus (1753), Ascherson (1870) and Posidonia oceanica (Linnaeus) Delile (1813). With the exception of the P. oceanica, the other three species coexist in the Bay of Cadiz (Figure1, modified from Brun et al.(2015)).

Figure 1: (A) habitats in the Bay of Cadiz (B) Zostera noltei (C) Cymodocea nodosa (D) Zostera marina.

1 Marine angiosperms possess a secondary metabolism that synthetizes specific organic compounds known as natural products. These compounds play important roles in the survival of the plants, including their involvement in chemical defence mechanisms. One of the ecological functions played by these natural products could be their deterrent capacity against herbivores. The consumption preference of a herbivore over one species, is determined by the palatability of their tissues. Plants can modify this palatability through different strategies that are based on chemical, nutritionals, and mechanical adaptations (Fritz and Simms, 1992). Strategies based on chemical adaptations, that is, on the synthesis of natural products, have an important function in restricting the taste quality of marine plants, but also can make these tissues toxic for consumers (Braekman et al., 1998). In spite of that, little is known about the deterrent capacity of natural products in seagrasses and whether species-specific differences within the community may prone some species more vulnerable to herbivore attack. Therefore, the main objective of this work was to study the deterrent activity against herbivores of the extracts from Z. noltei and C. nodosa by developing a manipulative experiment using the sea urchin Paracentrotus lividus.

Material and Methods

Paracentrotus lividus was used (Figure2), since it is a generalist herbivore inhabiting the Bay of Cadiz and is known to feed in seagrass beds (Verg´eset al., 2011).

Figure 2: Paracentrotus lividus collected in La Caleta, Cadiz.

Sea urchins were collected by hand in a nearby rocky shore, La Caleta, in Cadiz (SW Spain, 36◦ 31’ 39” N, 6◦ 18’ 46” W). Once in the laboratory, sea urchins were distributed in 2 tanks (30 l; 36 ind./ tank) with aeration, and were fed with Ulva sp. for 5 days before starting the assays, to acclimate sea urchins to laboratory conditions. Were prepared butanolic extracts of C. nodosa and Z. noltei plants. In addition, a butanolic extract of Z. noltei was separated by using a sephadex column to obtain the phenolic natural products (rosmarinic acid and flavones). In order to demonstrate that temperate seagrasses (Zostera noltei and Cymodocea nodosa) contain natural products with deterrent capacity, we conducted a set of trials where various diets included in blocks of agar (Figure3), composed either of: 1) seagrass lyophilized tissues, 2) extracts of the plants or 3) phenolic natural products isolated from Z. noltei (rosmarinic acid and flavonoids) were used to feed P. lividus.

2 Figure 3: Agar blocks with pure product diets, Z. noltei and C. nodosa.

At the beginning of each test, each block of agar was weighed, placed for one hour in the aquarium and then removed. The surface was dried with paper and weighed again. The consumption rate was calculated by the difference between the final and initial fresh weight measured in the assay, divided by the time elapsed (1h).

Results and Discussion

The preliminary results showed that the diets formed by lyophilized leaves of C. nodosa and Z. noltei had higher consumption rates than diets composed by the extracts of these plants. The diets based on lyophilized leaves contained all the nutritional, structural, reserve, and chemical properties, while the diets formed by extracts only contained reserve and chemical properties. The diet formed by phenolic natural products showed the lowest consumption rate. This low consumption rate could indicate that the natural products have a deterrent activity against the consumption by P. lividus. Therefore, the diets containing few sugars and a high percentage of natural products showed low consumption rates which could indicate that both the presence of these natural products and the absence of sugars greatly influence the palatability of the tissues and the feeding behaviour of the herbivore.

Acknowledgments

Financial support from MINECO (Spain), research project CTM2017-85365-R, is acknowledged.

References

Braekman, J., Daloze, D., Pasteels, J., 1998. Alkaloids in animals. In Alkaloids: Biochemistry, Ecology and Medicinal Applications. 1 ed., Springer US, Plenum, New York. Brun, F., Vergara, J., P´erez-Llor´ens,J., Ram´ırez,C., Morris, E., Peralta, G., Hern´andez,I., 2015. Diversidad de angiospermas marinas en la bah´ıade C´adiz: redescubriendo a Zostera marina. Chronica naturae 5, 45–56. Fritz, R., Simms, E., 1992. Plant resistance to herbivores and pathogens: ecology, evolution and genetics. University of Chicago Press, Chicago. Robertson, J., Mann, K., 1984. Disturbance by ice and life-history adaptions of the seagrass Zostera marina. Marine Biology 80, 131–141.

Verg´es,A., Alcoverro, T., Romero, J., 2011. Plant defences and the role of epibiosis in mediating within-plant feeding choices of seagrass consumers. Oecologia 166, 381–390.

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