Allohormones in Lumbricus terrestris? Mass spectrometry of the setal gland product indicates possible role of ubiquitin

Summary

In organisms containing sperm storage organs, sperm competition constitutes an important sexual selection factor. Sexual conflicts and unilateral manipulation of the reproductive physiology of the mating partner are common in the copulation behaviour of such organisms. In hermaphrodites, such conflicts escalate even more because of the identical interests of all individuals and the unique possibility to manipulate the degree of “femaleness” of the partner. This often results in bizarre reproductive tactics and mating behaviours. The simultaneous hermaphrodite Lumbricus terrestris uses specialized setae to pierce the partner's skin and inject a gland product during copulation. This happens in addition to, and is spatially distinct from, reciprocal sperm transfer. For the identification of bioactive compounds in the transferred secretion, comparative proteomic studies were performed, applying mass spectrometry and two-dimensional gel electrophoresis. Although initially targeting a substance with so-called “allohormone” characteristics, ubiquitin, a highly conserved 76 amino acid protein, could be identified as one of the predominant compounds. This contributes to recent findings concerning general roles of ubiquitin in reproductive events. One possible mechanism proposed, namely, that of labelling sperm for phagocytotic removal, is discussed.

Key words:

• Mass spectrometry
• setal gland product
• Lumbricus terrestris
• allohormone
• ubiquitin