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Tilapia male urinary pheromone stimulates female reproductive axis

Publication . Huertas, Mar; Almeida, O. G.; Canario, Adelino V. M.; Hubbard, Peter

Mozambique tilapia males congregate in leks where they establish dominance hierarchies and attract females to spawn in sandy pits. Dominant males store more urine than subordinates and the pattern of urination and the high sensitivity of females to male urine suggest chemical signalling via the urine. Here we show that pre-ovulated and post-spawn females when exposed to dominant male urine increased significantly, in less than 1 h, the release rate of the maturation-inducing steroid 17,20bdihydroxypregn- 4-en-3-one which is maintained elevated for at least 6 h. This indicates a pheromonal role for male urine in the synchronisation of spawning. Furthermore, we show that the lack of affinity of 17,20bP to sex steroid binding globulin explains, at least partly, its rapid release and lack of detection in the blood. Thus tilapia urine involvement in several communication processes confirms that cichlids have evolved a sophisticated chemical signalling system together with their complex visual, acoustic and behavioural displays.

2013-12-07Journal article

Open Access

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

Male urine signals social rank in the Mozambique tilapia (Oreochromis mossambicus)

Publication . Barata, E. N.; Hubbard, Peter; Almeida, O. G.; Miranda, A.; Canario, Adelino V. M.

The urine of freshwater fish species investigated so far acts as a vehicle for reproductive pheromones affecting the behaviour and physiology of the opposite sex. However, the role of urinary pheromones in intra-sexual competition has received less attention. This is particularly relevant in lek-breeding species, such as the Mozambique tilapia (Oreochromis mossambicus), where males establish dominance hierarchies and there is the possibility for chemical communication in the modulation of aggression among males. To investigate whether males use urine during aggressive interactions, we measured urination frequency of dye-injected males during paired interactions between size-matched males. Furthermore, we assessed urinary volume stored in the bladder of males in a stable social hierarchy and the olfactory potency of their urine by recording of the electro-olfactogram. Males released urine in pulses of short duration (about one second) and markedly increased urination frequency during aggressive behaviour, but did not release urine whilst submissive. In the stable hierarchy, subordinate males stored less urine than males of higher social rank; the olfactory potency of the urine was positively correlated with the rank of the male donor. Dominant males store urine and use it as a vehicle for odorants actively released during aggressive disputes. The olfactory potency of the urine is positively correlated with the social status of the male. We suggest that males actively advertise their dominant status through urinary odorants which may act as a 'dominance' pheromone to modulate aggression in rivals, thereby contributing to social stability within the lek.

2007-12-12Journal article

Open Access