Publication: Variation in the expression of migratory activity in blackcap (Sylvia atricapilla); effects of the origin, environmental conditions, dominance and personalities
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2016-07-04
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Universidad Complutense de Madrid
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Abstract
La migración es una respuesta a cambios estacionales del clima generando desplazamientos periódicos entre hábitats de cría y de invernada, permitiendo así el uso temporal de los recursos disponibles. La migración implica unos costes energéticos muy elevados, un aumento de la depredación potencial, variaciones ambientales y una disponibilidad de alimento impredecible a lo largo de la ruta migratoria; por lo que es una de las actividades más desafiantes de su ciclo vital. A pesar de ello, los beneficios de la migración compensan sus costes. La migración está programada genéticamente, siendo relativamente constante en su momento, distancia y dirección. Por otro lado, ambiente juega un papel predominante en algunas poblaciones, pudiendo modificar el comportamiento migratorio de una estrategia parcial o facultativa a un modo de vida sedentario. Con el fin de describir el origen y evolución del comportamiento migratorio en aves, se ha propuesto un “modelo de umbral” genético para determinar si un ave es migrante o sedentaria. Dentro de una variable continua (p.ej. la concentración de proteínas u hormonas), este modelo asume que existe una actividad migratoria subyacente implicada en su expresión génica. Este umbral divide cada variable en categorías dicotómicas que definen el fenotipo de un individuo. Los ejemplares sin actividad migratoria muestran valores por debajo de este umbral, siendo clasificados como sedentarios, mientras que los ejemplares migrantes muestran valores por encima del umbral definido. Los cambios de estrategia vital no dependen únicamente de la posición del umbral determinado genéticamente sino también de las variables ambientales, por lo que dichas variaciones deben ser añadidas al modelo. Este modelo de umbral ambiental predice que el carácter migratorio de los individuos situados en los extremos de distribución no se encuentra afectado por los factores ambientales, mientras que aquellos más próximos al umbral pueden más fácilmente cambiar su estrategia migratoria...
Migration is a response to predictable seasonal changes through adaptive movements between suitable breeding and wintering sites, allowing the use of their temporarily available resources. It implies substantial energy costs, predation risks and unpredictable weather conditions and food availability along the migratory route, making migration one of the most challenging activities migratory species have to perform. However, the benefits of migration, from seasonal exploitation of resources at both their breeding and wintering grounds, to the elimination of inter- and intraspecific competition in overpopulated habitats, do outweigh its costs. Migration is genetically programmed, being relatively constant in its timing, distance and direction, but in some populations the environment plays a more important role in its expression. In these populations, migratory behaviour is sufficiently plastic to follow variable environmental conditions and adapt by changing to partial or facultative migratory strategy, or even crossing to sedentary way of life, when environmental conditions are favourable. In order to clarify the mechanism which determines if a bird is migratory or resident, the “threshold model of migration” has been proposed describing inheritance and evolution of migratory behaviour. The model assumes that there is a continuous variable underlying migratory activity (e.g. amounts of proteins or hormones) involved in its expression. The threshold on that variable divides the continuous distribution into dichotomous categories defining the phenotype of the individual. Individuals with no migratory activity are classified as residents with their variable value below the threshold, and individuals with values above the threshold are classified as migrants. However, as changes in migratory activity not only depend on the genetically determined position of the threshold but also on environmental variables, the environmental factor was added to the model. This environmental threshold model predicts that individuals at the extremes of the distribution of the variable underlying migration are not affected by environmental factors, while those closer to the threshold can easily be tipped over to one side or the other...
Migration is a response to predictable seasonal changes through adaptive movements between suitable breeding and wintering sites, allowing the use of their temporarily available resources. It implies substantial energy costs, predation risks and unpredictable weather conditions and food availability along the migratory route, making migration one of the most challenging activities migratory species have to perform. However, the benefits of migration, from seasonal exploitation of resources at both their breeding and wintering grounds, to the elimination of inter- and intraspecific competition in overpopulated habitats, do outweigh its costs. Migration is genetically programmed, being relatively constant in its timing, distance and direction, but in some populations the environment plays a more important role in its expression. In these populations, migratory behaviour is sufficiently plastic to follow variable environmental conditions and adapt by changing to partial or facultative migratory strategy, or even crossing to sedentary way of life, when environmental conditions are favourable. In order to clarify the mechanism which determines if a bird is migratory or resident, the “threshold model of migration” has been proposed describing inheritance and evolution of migratory behaviour. The model assumes that there is a continuous variable underlying migratory activity (e.g. amounts of proteins or hormones) involved in its expression. The threshold on that variable divides the continuous distribution into dichotomous categories defining the phenotype of the individual. Individuals with no migratory activity are classified as residents with their variable value below the threshold, and individuals with values above the threshold are classified as migrants. However, as changes in migratory activity not only depend on the genetically determined position of the threshold but also on environmental variables, the environmental factor was added to the model. This environmental threshold model predicts that individuals at the extremes of the distribution of the variable underlying migration are not affected by environmental factors, while those closer to the threshold can easily be tipped over to one side or the other...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, Departamento de Zoología y Antropología Física, leída el 08/02/2016