INVESTIGADORES
SOMOZA Gustavo Manuel
congresos y reuniones científicas
Título:
Hormones and agonistic behaviour: What the South American cichlid fish, Cichlasoma dimerus, tell us about them.
Autor/es:
MARTÍN RAMALLO; AGUSTINA BIRBA; RENATO HONJI; LEONEL MORANDINI; RENATA GUIMARAES MOREIRA; GUSTAVO M. SOMOZA; MATÍAS PANDOLFI
Lugar:
Olhão
Reunión:
Congreso; 10th International Symposium on Reproductive Physiology of Fish; 2014
Resumen:
Introduction The so called ?chanchita?, Cichlasoma dimerus, is a South American cichlid fish with a hierarchical social system, established and sustained through agonistic interactions. Individuals in the top ranked positions aggressively guard a territory which grants them access to reproduction. It is a monogamous species with biparental care of the eggs and larvae. In this framework, the aim of the study was to characterize the agonistic behaviour of territorial (Tr) pairs and non-territorial (NTr) male fish, and its relationship with plasma androgens, estradiol and cortisol. Methods Experimental aquaria housed 6 size-matched fish (random sex ratio). Once the linear hierarchy was established, top and bottom ranked individuals were identified. When the Tr pair began with the reproductive displays, agonistic interactions were recorded with a camera and quantified for the Tr male and female, and the lowest ranked individual. Aggressive displays included chasings, bites and assaults, while submissive behaviour included escapes and passive coping. Blood samples were obtained and plasma levels of 11-ketotestosterone (11-KT), testosterone (T), estradiol (E2) and cortisol were measured by ELISA. Also, testes were weighed to calculate the gonadosomatic index (GSI). For every fish, 3 randomly chosen testes? slices were analyzed to assess its cellular composition (percentage of type A and B spermatogonia, spermatocytes, spermatids, spermatozoa and interstitial tissue). Results and Discussion Territorial males and females spent 50% of their time biting NTr individuals, while more than 80% of NTr males? displays were escapes. Even though Tr males and females did not differ in their overall frequency of aggressiveness, males performed almost twice more assaults and chases than females. The pair rarely attacked in synchrony, and the frequency of simultaneous attacks equalled the expected by chance. Tr males had 8 times more 11-KT than females and NTr males, and plasma levels positively correlated with male aggression. T was doubled in Tr males in contrast to NTr males, while females? levels did not differ from Tr or NTr males. Estradiol negatively correlated with male aggression, was highest in females, and twice in NTr males than in Tr males. The relation E2/T was 3 times lower in Tr males compared to NTr males, indicating a reduced conversion of T to E2. Cortisol levels didn?t vary between social range or sex. Tr males? IGS was 7% greater than NTr males?. Analyzes of the testes revealed that Tr males had 20% more spermatozoa than NTr males, while spermatids and spermatocytes were higher in NTr males. Conclusion In the highly social cichlid C. dimerus, social status is accompanied by changes in sex hormone profiles, behavioural repertoire and testicular physiology.