Do benthic and planktonic diatoms produce equivalent effects in crustaceans?

Abstract

Hippolyte inermis Leach 1814 is a benthic shrimp characterized by a peculiar mechanism of sex reversal influenced by diatom foods. In fact, the appearance of primary females in spring is due to an apoptotic early disruption of the androgenic gland and of the male gonad, triggered by still unknown compounds present in diatoms of the genus Cocconeis. The influence of diatoms on the reproductive ecology and life cycle of planktonic crustaceans has been demonstrated previously: some planktonic diatoms produce aldehydes inducing apoptosis in the embryos and in the larvae of marine copepods, reducing their viability. Both benthic and planktonic diatoms therefore produce compounds having an apoptotic effect on some tissues of target crustaceans, although the ecological significance of the two processes is different: deleterious for copepod populations, regulative for shrimps associated with Posidonia oceanica. In the present article we experimentally administered specific planktonic diatoms, their fractions and compounds known to induce apoptosis in planktonic copepods, to H. inermis postlarvae, to check whether the apoptotic effect is due to an identical family of diatom compounds, and to establish whether the processes observed in the plankton and in the benthos, respectively, are analogous or homologous, from an ecological point of view. Our results indicated that diatom compounds acting in the two systems are different, since both planktonic diatoms and their aldehydes had negligible effects on the sex ratios of cultured shrimps.

Keywords:

• Hippolyte inermis
• shrimp
• sex reversal
• diatom
• apoptosis

Acknowledgments

This research was conducted within the research project ‘Pharmapox’, funded by the European Community (EU 4800) and aimed at investigating the chemistry, pharmacology, and bioactivity of the diatom factor acting as a sex regulator in decapod crustaceans. The research activities of Patrizia Messina and Michela Nappo were fully covered by the EU grant. English text was kindly revised by Mrs R. Messina. We are indebted to three anonymous referees for their accurate and wise revision of the manuscript.