IBBEA   24401
INSTITUTO DE BIODIVERSIDAD Y BIOLOGIA EXPERIMENTAL Y APLICADA
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Hormones and agonistic behaviour: what the southamerican cichlid fish, Cichlasoma dimerus, tell us about them.
Autor/es:
RAMALLO MARTÍN R.; BIRBA AGUSTINA; HONJI RENATO M.; MORANDINI LEONEL; MOREIRA RENATA G.; SOMOZA GUSTAVO; PANDOLFI MATÍAS
Lugar:
Olhão
Reunión:
Simposio; 10th International Symposium on Reproductive Physiology of fish; 2014
Institución organizadora:
ISRPF
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. E2
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 did not vary between social rank or
sex. Tr males? GSI 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.