Ceratotoxins are antibacterial 3-kDa molecular mass amphiphilic peptides isolated from the female reproductive accessory glands of the medfly Ceratitis capitata. They are physiologically related to bee melittin and show amino acid sequence homology with magainin peptides. In this paper, we report the complete sequence of cDNA coding for ceratotoxin A and the expression of the gene during the life cycle of the insect. Experimental data show that the ceratotoxin is a gene expressed exclusively in the imaginal stages and that it is female-specific, related to sexual maturity, and stimulated by mating. Differently from most antibacterial insect hemolymph peptides, it is not induced by microbial infection. Western blot analysis using an anti-ceratotoxin antibody indicates the female accessory glands as the only site where the production of the ceratotoxin peptide occurs.

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Extracellular Gram negative bacteria were found to be commonly associated to the oesophageal bulb of Ceratitis capitata with Klebsiella oxytoca and Enterobacter agglomerans as the most common species. All the isolates tested in vitro, except one, were sensitive to the antibacterial material present on the medfly laid egg surface.

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Predation and microbial infections are the major causes of natural mortality for early life stages of oviparous species. The parental traits reducing the effects of predation are rather well described, whereas antimicrobial mechanisms enhancing offspring survival are largely unexplored. In this paper, we report that a male sexually dimorphic trait, the anal glands, of the redlip blenny (Ophioblennius atlanticus atlanticus) and the peacock blenny (Salaria pavo), two fish species with paternal egg care, produce a mucus enriched with antimicrobial substances. Histological and histochemical analyses showed that the anal glands of these species are characterized by the massive presence of mucus-secreting cells. Anal gland extracts, from both the hydrophilic and the hydrophobic protein fraction, exhibited a lysozyme-like activity. Field observations demonstrated that redlip blenny males, while performing egg care, rub the anal region over the nest internal surface, probably facilitating the transfer of mucus to eggs. These results strongly indicate that this sexually dimorphic trait is involved in egg defence against microbial infections.

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