Abstract
To avoid predation, holothuroids produce feeding-deterrent molecules in their body wall and viscera, the so-called saponins. Five tropical sea cucumber species of the family Holothuriidae were investigated in order to study their saponin content in two different organs, the body wall and the Cuvierian tubules. Mass spectrometry techniques (MALDI- and ESI-MS) were used to detect and analyze saponins. The smallest number of saponins was observed in Holothuria atra, which contained a total of four congeners, followed by Holothuria leucospilota, Pearsonothuria graeffei and Actinopyga echinites with six, eight and ten congeners, respectively. Bohadschia subrubra revealed the highest saponin diversity (19 congeners). Saponin mixtures also varied between the two body compartments within a given animal. A semi-quantitative approach completed these results and showed that a high diversity of saponins is not particularly correlated to a high saponin concentration. Although the complexity of the saponin mixtures described makes the elucidation of their respective biological roles difficult, the comparisons between species and between body compartments give some clues about how these molecules may act as predator repellents.
Highlights
Holothuroids, known as sea cucumbers, are marine animals that are characterized by a slow motion and the absence of prominent structural defenses
They appear to be concentrated in the Cuvierian tubules, a specialized defense system developed by some sea cucumber species, all belonging to the family Holothuriidae [3,4,11]
A peculiar attention was paid to the differences that could occur between the body wall and the Cuvierian tubules in a given species
Summary
Holothuroids, known as sea cucumbers, are marine animals that are characterized by a slow motion and the absence of prominent structural defenses. They are abundant in the body wall which, in addition to its role as a physical barrier protecting the animal, is the largest organ [3,11,12] They appear to be concentrated in the Cuvierian tubules, a specialized defense system developed by some sea cucumber species, all belonging to the family Holothuriidae [3,4,11]. Chromatography-Mass Spectrometry) techniques, we were able to highlight remarkable differences between the saponin mixtures from the body wall and the Cuvierian tubules of Holothuria forskali [18] In this species, which was first studied by Rodrigez et al [19], only five saponins were described, with no indication on their organ of origin. A peculiar attention was paid to the differences that could occur between the body wall and the Cuvierian tubules in a given species
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