Reproductive physiology and aggressive behaviour of females of the social cichlid fish Cichlasoma dimerus (Perciformes)

CECILIA TUBERT; FABIANA LO NOSTRO; MATIAS PANDOLFI

Cochin

Congreso; IX International Symposium on the Reproductive Physiology of Fish; 2011

Introduction: Teleost fish present a great variety of reproductive behaviours, including aggressive interactions hmong conspecifics and defense of a territory or progeny. The behaviour displayed during the reproductive season is critical for reproductive success. Among vertebrates, gonadotropin-releasing hormone (GnRH) plays a major role in the control of reproduction, regulating the hypothalamus-pituitary-gonad axis. GnRH type 3 (GnRH-3) neurons are located in the olfactory bulbs and project their axons toward the retina and pineal organ, which suggests a relationship with behavioural and physiological responses due to changes in light intensity and photoperiod [1, 2]. GnRH-3 has also been proponed as a potent neuromodulator of reproductive behaviour. Circulating androgens are potent mediators of male and female aggressive behaviour. In fact, several experiments have demonstrated that androgen depletion decreases aggression, whereas androgen supplementation recovers or increases aggression [3, 4, 5]. However, most of these studies were only performed in males. Cichlasoma dimerus is a South American freshwater cichlid species that presents social hierarchies, a highly organized breeding activity and biparental care. Territories are progressively established and defended by both male and female members of a pair. The dominant pair aggressively defends the spawning site and displays stereotypical prespawning behaviour. Spawning (egg clutch size of 1500) is followed by a period of parental care when the pair aggressively guards the eggs. Larvae hatch at day 3 post fertilization and remain adhere to the substrate through three pairs of adhesive glands located in the head. After 5 days, larvae swim freely. During this period, the reproductive pair also displays aggressive behaviour against subordinated individuals, protecting the offspring. Aggressive displays include biting, mouth holding, chasing, fin erection. Submissive displays of subordinate fish include escape reactions and fin retraction. Aggressive and submissive behaviour can be associated with differences in body color patterns [6, 7]. The present work characterizes the reproductive physiology and aggressive behaviour of females of the cichlid fish Cichlasoma dimerus at different phases during the reproductive stage. Methods: Fish were maintained in aquaria with constant temperature (26ºC) and a 14:10 h photoperiod. Aggressive behaviour of females throughout the different phases were identified and quantified. For this purpose, 12 females referred to as ?local females? were selected, 3 at each different previously established reproductive phase: (1) female with prespawning activity (FP), (2) female with eggs (FE), (3) female with hatched larvae (FHL) and (4) female with swimming larvae (FSL). Another 12 females were taken from established pairs at an early prespawning phase, and referred to as ?intruder female?. Males were removed from the ?local female? tank, and a random ?intruder female? was introduced. The number of aggressive interactions (biting and chasing) between ?local female? and ?intruder female? was recorded during 1 hour and quantified. Body color patterns and shape of dorsal fins were also examined. In another set of experiments, 16 females at the different established phases were weighed and measured, blood was extracted and circulating androgens (RIA), 17-beta estradiol and cortisol (ECLIA) were measured in plasma. Liver, spleen and gonadosomatic indexes were calculated. Brains were dissected, and GnRH-3 neural populations were studied by IHC and morphometrical analysis of immunoreactive cells (nuclear area, somatic area and optical density). Semiquantification of gonadotropins (beta-FSH and beta-LH) pituitary content was performed by Western blot. Ovaries were processed for histological analysis. Results: Females presented a great variation in the studied parameters between the different phases. FP displayed the most aggressive behaviour in terms of number of biting and chasing attacks. This is consistent with the maximum plasmatic androgen levels observed Turing this stage. FP also showed the highest nuclear and somatic area, and optical density of GnRH-3 neurons. Moreover, FP presented maximum levels of plasmatic 17-beta estradiol and GSIs. Cortisol reached its highest levels in FE. There were no detectable differences in beta-FSH and beta-LH pituitary content between the different phases. At the ovarian level, each phase was characterized by the preponderance of different structures (FP: mature oocytes, FE: post ovulatory follicles, FHL: atresic bodies, FSL: secondary growth oocytes). Conclusion: Taken together these results suggest that GnRH-3 and androgens regulate female reproductive physiology and aggressive behaviour in adult C. dimerus during the reproductive stage. References: [1]DUBOIS E.A., ZANDBERGEN M.A., PEUTE J.,GOOS H.J.T. (2002). Evolutionary development of three gonadotropin-releasing hormone (GnRH) systems in vertebrates. Brain Res. Bull., 57: 413-418. [2]PANDOLFI M., MUÑOZ CUETO J.A., LO NOSTRO F.L., DOWNS J.L. PAZ D.A., MAGGESE M.C., URBANSKI H.F. (2005). The GnRH Systems of Cichlasoma dimerus (Perciformes, Cichlidae) revisited: a localization and developmental study using antibodies and riboprobes to the GnRHassociated peptidel. Cell Tissue Res., 321: 219-232. [3]KINDLER P.M., BAHR J.M., PHILIPP D.P.(1991). The effects of exogenous 11-ketotestosterone, testosterone, and cyproterone acetate on prespawning and parental care behaviors of male bluegill. Horm. Behav., 25: 410-423. [4]FRANCIS R.C., JACOBSON B., WINGFIELD J.C., FERNALD R.D. (1992). Castration Powers aggression but not social dominance in male Haplochromis burtoni (Cichlidae). Ethology, 90: 255-347. [5]HUME J.M., WYNNE-EDWARDS K.E. (2005). Castration reduces male testosterone, estradiol, and territorial aggression, but no paternal behavior in biparental dwarf hamsters (Phadopus campbelli). Horm. Behav., 48: 303-310. [6]PANDOLFI M., CÁNEPA M.M., MEIJIDE F.J., ALONSO F., REY VAZQUEZ G., MAGGESE M.C., VISSIO P.G. (2009). Studies on the reproductive and developmental biology of Cichlasoma dimerus (Perciformes, Cichlidae). Biocell 33(1): 1-18. [7]ALONSO F., CÁNEPA M., MAGGESE M.C., PANDOLFI M. (2011). Reproductive physiology and behavior of the social cichlid fish Cichlasoma dimerus under laboratory conditions. Fish Physiol. 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