Somatolactin and background color adaptation in the cichlid fish (Cichlasoma dimerus)

En peces, el control de la coloración corporal está regulada por múltiples hormonas y por el sistema nervioso autónomo (SNA). En esta Tesis se propone también a Somatolactina (SL) como factor involucrado en este proceso. En primer lugar se clonó y secuenció a SL y su receptor putativo, el receptor de hormona de crecimiento tipo 1 (RGH1) en el pez cíclido, Cichlasoma dimerus. El análisis filogenético de ambos indica que se encuentran altamente conservados entre los peces del superorden Acanthopterygii tales como medaka, Oryzias latipes, y tilapia, Oreochromis mossambicus. Posteriormente, se evaluó la expresión de SL en hipófisis y el RGH1 en el tegumento mostrando que la expresión de ambos es mayor en animales mantenidos en un entorno negro. A continuación, se observó que las fibras inmunoreactivas (ir-) a MCH (hormona concentradora de melanina) y fibras ir-GnRH (hormona liberadora de gonadotrofinas) están relacionadas morfológicamente con las células de SL. Por último, estudios de liberación de SL a partir de hipófisis intactas en cultivo mostraron que tanto MCH como GnRH actúan como factores liberadores de SL. A partir de los resultados de esta Tesis se concluye que SL forma parte de un sistema multifactorial de regulación de la adaptación de la coloración del entorno actuando directamente sobre el tegumento.In fish, background color adaptation is regulated by multiple hormones and the autonomic nervous system. In this Thesis somatolactin is proposed as a factor involved in such process. Firstly, Cichlasoma dimerus SL and its putative receptor, growth hormone receptor type 1 (GHR1) were cloned and sequenced. The phylogenetic analysis showed that both proteins were highly conserved among species from the superorder Acanthopterygii such as the medaka, Oryzias latipes, and the Tilapia, Oreochromis mossambicus. Secondly, the expression of both was assessed under black and white background showing a higher expression in animals maintained in the black one. Then, a close association between immunoreactive (ir-) MCH (melanin concentrating hormone) or ir-GnRH (gonadotropin-releasing hormone) fibers and SL cells was found. Finally, MCH and GnRH increased somatolactin release in pituitary cultures. The results obtained in this Thesis suggest that SL takes part of a multifactorial regulation system of background color adaptation having probably a direct effect on the integument color.Fil:Cánepa, Maximiliano Martín. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina

Social and reproductive physiology and behavior of the Neotropical cichlid fish Cichlasoma dimerus under laboratory conditions

In this work we describe for the first time the social and reproductive behavior of the Neotropical fish Cichlasoma dimerus (Heckel, 1840) [Perciformes: Cichlidae], endemic to the Paraná River basin, using a comprehensive-integral approach, including morphological and physiological features. This substrate breeding fish has biparental care of the fry and presents a dominance hierarchy that determines access to breeding territories among males, and to males with territories among females. Gregarious behavior associated with a pale body color, was observed before reproductive behaviors started. Afterwards, a dominance hierarchy was established through aggressive interactions. Territorial individuals had bright body color patterns and non territorial an opaque grey one. Black ventral coloration was associated with reproductive individuals. Courtship displays, which were similar to threatening displays, had the common effect of increasing the visible area of the individual. The dominant male was always the largest one suggesting that size is probably a major factor determining the hierarchy establishment and that these intra-sexually selected traits may have been reinforced by inter-sexual selection. Reproductive males had higher pituitary levels of β-follicle stimulating hormone (β-FSH) and somatolactin (SL) than non reproductive ones, while no differences were found among females. No differences were found among male gonadosomatic indexes. Non reproductive individuals had higher plasma cortisol levels for both sexes. It is possible that dominant reproductive individuals may be inhibiting reproduction of subordinate fish through physical contact, increasing their cortisol levels and diminishing FSH and SL pituitary content. However, this was not reflected as an inhibition at the gonadal level in our experimental design

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