RESUMEN
In order to investigate the effects of nitrate and ammonium on the amphibians in a pasture zone of the Catalonian Pyrenees, larvae of Rana temporaria from several ponds were exposed to different concentrations of nitrate (0-500 mg/L) and ammonium (0-1.2 mg/L). High concentrations of nitrate in the water caused mortality and reduced larval size of R. temporaria, whereas no effects on larvae were observed in ammonium conditions. The results suggest that, if the levels of nitrate reach about 100 mg/L, the possibility of survival of R. temporaria larvae may be reduced.
Asunto(s)
Nitratos/toxicidad , Compuestos de Amonio Cuaternario/toxicidad , Rana temporaria/crecimiento & desarrollo , Contaminantes Químicos del Agua/toxicidad , Animales , Agua Dulce/química , Larva/efectos de los fármacos , Larva/crecimiento & desarrollo , Modelos Lineales , Nitratos/análisis , Compuestos de Amonio Cuaternario/análisis , Rana temporaria/anomalías , España , Contaminantes Químicos del Agua/análisisRESUMEN
The determination of the left-right body axis is unlike that of the two other axes because left-right positional information is not required to specify mirror-image structures on the two sides. When the left and right sides of the body are not mirror symmetrical such positional information is required, as is a mechanism for reading that information. There are several possible gradient schemes for left-right information, including symmetrical gradients from which the information is extracted by spatial differentiation. The genetic mechanisms for the control of handedness are not known. There is no evidence for 'left-handed' and 'right-handed' genes, only for mutations that can interfere with handedness in a non-specific manner. Such mutations never produce situs inversus with a frequency greater than 50%. The situs of individual organs shows a strong correlation, suggesting a global mechanism such as a gradient of left-right positional information. Many asymmetries in vertebrates follow a pattern in which growth on the left is favoured over growth on the right. This may be related to the 'dexiothetism' of chordate ancestors postulated by Jefferies.
Asunto(s)
Anuros/embriología , Peces/embriología , Lateralidad Funcional/genética , Desarrollo Humano , Ratas/embriología , Animales , Anuros/anomalías , Anuros/genética , Evolución Biológica , Polaridad Celular , Peces/anomalías , Peces/genética , Cardiopatías Congénitas , Humanos , Placenta/anomalías , Rana temporaria/anomalías , Rana temporaria/embriología , Rana temporaria/genética , Ratas/anomalías , Ratas/genética , Situs Inversus , Transcripción GenéticaRESUMEN
The fertilized eggs of the frog Rana temporaria immediately after fertilization were rotated on a clinostat in the vertical plane at the rate of 0.66 rotations per minute with a radius of 20 mm for 2.5 hours. A wide spectrum of developmental anomalies was found (33% in the experiment, 14% in the control) which, in the authors' opinion, result from abnormalities in the cortical reaction of symmetrization. These abnormalities manifest themselves in the irregular distribution of cortical pigment and in eccentric division lines.