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Olfactory sensitivity to steroid glucuronates in Mozambique tilapia suggests two distinct and specific receptors for pheromone detection

Publication . Keller-Costa, Tina; Canario, Adelino V. M.; Hubbard, Peter

Cichlids offer an exciting opportunity to understand vertebrate speciation; chemical communication could be one of the drivers of African cichlid radiation. Chemical signals mediate key aspects in the lives of vertebrates and often are species specific. Dominant male Mozambique tilapia [Oreochromis mossambicus (Peters 1852)] release a sex pheromone, 5 beta-pregnan-3 alpha,17 alpha,20 beta-triol 3-glucuronate and its 20 alpha-epimer, via their urine. The objective of this study was to assess the sensitivity, specificity and versatility of the olfactory system of O. mossambicus to other steroids and their conjugates using the electro-olfactogram. Oreochromis mossambicus was sensitive to several 3-glucuronidated steroids, but did not respond to prostaglandins, unconjugated steroids or 17- or 20-conjugated steroids. Stimulation of the olfactory epithelium with increasing concentrations (1 pmol l(-1) to 10 mu mol l(-1)) of 5 beta-pregnan-3 alpha, 17 alpha,20 beta-triol 3-glucuronate, 5 beta-pregnan-3 alpha, 17 alpha,20 beta-triol 3-glucuronate, 3 alpha,17 alpha-dihydroxy-5 beta-pregnan-20-one 3-glucuronate, etiocholanolone 3 alpha-glucuronate and 17 beta-estradiol 3-glucuronate produced characteristic sigmoidal concentration-response curves. However, tilapia were most sensitive to 17 beta-estradiol-3-glucuronate, which also had the lowest apparent EC50 and maximal response amplitude. Cross-adaptation and binary mixture experiments suggested that 5 beta,3 alpha-reduced pregnan-and androstan-3-glucuronates share (a) common olfactory receptor(s), whereas 17 beta-estradiol 3-glucuronate is detected via (a) distinct olfactory receptor(s). In conclusion, the Mozambique tilapia has evolved high olfactory sensitivity and specificity to 3-glucuronidated steroids through two distinct olfactory receptor types; one detecting a male sex pheromone and a second detecting 17 beta-estradiol 3-glucuronate, a putative female-derived signal. However, O. mossambicus differs markedly in its olfactory perception from the more recently derived East African cichlid Astatotilapia burtoni, suggesting that chemical communication could, indeed, be involved in speciation.

2014-12Journal article

Open Access

Chemical diplomacy in male tilapia: urinary signal increases sex hormone and decreases aggression

Publication . Saraiva, João; Keller-Costa, Tina; Hubbard, Peter; Rato, Ana; Canario, Adelino

Androgens, namely 11-ketotestosterone (11KT), have a central role in male fish reproductive physiology and are thought to be involved in both aggression and social signalling. Aggressive encounters occur frequently in social species, and fights may cause energy depletion, injury and loss of social status. Signalling for social dominance and fighting ability in an agonistic context can minimize these costs. Here, we test the hypothesis of a 'chemical diplomacy' mechanism through urinary signals that avoids aggression and evokes an androgen response in receiver males of Mozambique tilapia (Oreochromis mossambicus). We show a decoupling between aggression and the androgen response; males fighting their mirror image experience an unresolved interaction and a severe drop in urinary 11KT. However, if concurrently exposed to dominant male urine, aggression drops but urinary 11KT levels remain high. Furthermore, 11KT increases in males exposed to dominant male urine in the absence of a visual stimulus. The use of a urinary signal to lower aggression may be an adaptive mechanism to resolve disputes and avoid the costs of fighting. As dominance is linked to nest building and mating with females, the 11KT response of subordinate males suggests chemical eavesdropping, possibly in preparation for parasitic fertilizations.

2017-08Journal article

Open Access