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- Chemical diplomacy in male tilapia: urinary signal increases sex hormone and decreases aggressionPublication . Saraiva, João; Keller-Costa, Tina; Hubbard, Peter; Rato, Ana; Canario, AdelinoAndrogens, 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.
- Endocrine responses of Tilapia (Oreochromis mossambicus) females to male pheromone(s)Publication . Rato, Ana; Canario, Adelino V. M.; Hubbard, PeterSeveral lines of evidence suggest that male Mozambique tilapia (Oreochromis mossambicus) release a reproductive pheromone via their urine. A recently identified steroid glucuronide, present in male urine, is probably one of the active components that increase levels of a steroid hormone responsible for oocyte maturation, 17,20β-P, in females. The aims of this study were to identify which fraction(s) of male urine is responsible for this increase and whether the steroid glucuronide is sufficient, on its own, to cause a similar increase in 17,20β-P metabolism. Pooled male urine was passed through C18 extraction cartridges, thus obtaining the filtrate (aqueous/polar) and eluate (hydrophobic/non-polar) fractions. Females were exposed to urine, its respective fractions, and the steroid glucuronide (and in combination with each-other). One hour after exposure, water samples were collected and steroids extracted. The same experiment was conducted in males, using a urine pool from dominant males. Steroid levels (17,20β-P, cortisol, 11-ketotestosterone, and testosterone) were measured by radioimmunoassay. Exposure to male urine, its eluate, and the steroid glucuronide (and combinations containing the eluate or steroid) evoked a dramatic increase in release rates of 17,20β-P by females. The filtrate alone had no such effect. In males, release rates of 11-ketotestosterone, but not testosterone, increased after exposure to male urine. These results suggest that the pheromonal activity of the urine is contained wholly in the C18 eluate. Furthermore, the steroid glucuronide (originally isolated from the urine eluate) is sufficient, on its own, to cause an increase in levels of 17,20β-P metabolism. Thus, the steroid glucuronide is responsible for the pheromonal activity of male urine, at least in this endocrine effect in females. The endocrine response of males to this urinary pheromone requires further investigation.
- The impact of climate Change on bivalve farming: combined effect of temperature and salinity on survival and feeding Behavior of clams Ruditapes decussatusPublication . Rato, Ana; Joaquim, Sandra; Matias, Ana Margarete; Roque, Cláudia; Marques, António; Matias, DomitíliaEuropean clam (Ruditapes decussatus) is one of the most relevant emergent bivalve species from the aquaculture sector in Europe with high economic value. Climate changes represent a potential limiting factor to this activity, directly interfering with the survival and behavior of bivalves. Severe fluctuations in temperature along with periods of heavy rainfall or periods of drought that significantly change the salinity can promote physiological stress in bivalves, resulting in changes in physiological and behavioral responses and, in extreme cases, leading to high mortalities. This study aimed to evaluate the combined effect of temperature and salinity on mortality and feeding behavior of R. decussatus. Juveniles and adults were exposed to combined ranges of temperature (5 degrees C-35 degrees C) and salinity (0-40). Mortality and feeding behavior were registered every 24 h of each 120-h trial. A control temperature range was set between 15 degrees C and 23 degrees C, where mortality and feeding behavior were considered as the normal scenario. Our data suggested salinity 15 as a "turning point," a point from which occurred distinct patterns in mortality and feeding behavior. The results evidently indicate that abrupt reductions in salinity and sharp increases in temperature will lead to high mortality of R. decussatus. Juveniles were revealed to be more sensitive to the increase of temperature in a less saline environment, to suffer greater and faster mortalities, and to be more resistant to extremely high temperatures under more saline conditions. The high temperatures and sporadic heavy rainfall that are predicted to occur in the south of Europe due to climate changes will contribute to compromise the recruitment of European clam, thus threatening the production of this species and consequently impacting the economic sector.
- What do oysters smell? Electrophysiological evidence that the bivalve osphradium is a chemosensory organ in the oyster, Magallana gigasPublication . Rato, Ana; Joaquim, Sandra; Matias, Domitília; Hubbard, PeterThe sensing of chemical cues is essential for several aspects of bivalve biology, such as the detection of food and pheromones. However, little is known about chemical communication systems in bivalves or the possible role of the osphradium as a chemosensory organ. To address this, we adapted an electrophysiological technique extensively used in vertebrates & mdash;the electro-olfactogram & mdash;to record from the osphradium in the Pacific oyster, Magallana gigas. This technique was validated using amino acids as stimulants. The osphradium proved to be sensitive to most proteinogenic l-amino acids tested, evoking tonic, negative, concentration-dependent 'electro-osphradiogram' (EOsG) voltage responses, with thresholds of detection in the range of 10(-)(6) to 10(-)( 5) M. Conversely, it was insensitive to l-arginine and l-glutamic acid. The current study supports the hypothesis that the osphradium is, indeed, a chemosensory organ. The 'electro-osphradiogram' may prove to be a powerful tool in the isolation and characterization of pheromones and other important chemical cues in bivalve biology.
- Identify of a tilapia pheromone released by dominant males that primes females for reproductionPublication . Keller-Costa, Tina; Hubbard, Peter; Paetz, Christian; Nakamura, Yoko; Silva, José P. da; Rato, Ana; Barata, E. N.; Schneider, Bernd; Canario, Adelino V. M.Knowledge of the chemical identity and role of urinary pheromones in fish is scarce, yet necessary to understand the integration of multiple senses in adaptive responses and the evolution of chemical communication. In nature, Mozambique tilapia (Oreochromis mossambicus) males form hierarchies and females mate preferentially with dominant territorial males which they visit in aggregations or leks.