Evolutionary patterns and processes of migratory behaviour in Palearctic-Paleotropical birds = Patrones y procesos evolutivos del comportamiento migratorio en aves del Paleártico­-Paleotrópico

Abstract

[eng] One of the most fascinating aspects of birds is their capability of migrate from one area to another throughout the year. Unravelling the patterns and processes involved in the evolution of migration is paramount to understand the current biogeography, ecology and evolution of migratory birds. On this basis, the main aim of the present thesis was to extend the knowledge of the mechanisms involved in the evolution of bird migration. To achieve that two main sections are presented in this thesis. In the first one, the aims were to disentangle the patterns of evolution of migratory behaviour and the identifying the main factors that could play an important role in it, using Sylvia warblers as case of study. In the second section, we explored the climatic niche and the potential distribution of breeding and wintering ranges in the last glacial maximum (LGM) of trans-Saharan long migratory species, in order to unravel the changes in migratory behaviour. We explored the evolution of migration in Sylvia warblers as both a discrete and continuous character using ancestral state reconstruction methods. We recovered the basal node as migratory in most analyses, suggesting seven independent losses of migratory behaviour in Sylvia warblers. Both analyses performed with migration as discrete or continuous character recovered different probabilities of sedentariness or migratoriness in some conflicting nodes depending of the ASR elements used. This forced as to consider controversial hypotheses of evolution of migration in some clades that could evolved from migratory to sedentary in a very short period of time or going through a partial migratory status instead. We used phylogenetic comparative methods to assess whether the evolutionary patterns of migratory distances are correlated with several biometric, climatic and productivity variables in a phylogenetic context, using Sylvia warblers as a case study. Our results recover net primary productivity (NPP) in the breeding range and during the breeding season as the variable with stronger positive correlation with migratory distances. Several climatic variables show a correlation with the evolution of migration and among morphological variables, migratory lineages tend to have longer wings than sedentary ones. It is not possible to disentangle if NPP was a main driver in the evolution of bird migratory behaviour or a consequence of it, yet migration and NPP seem to be tightly related today and along their evolutionary history. Migratory birds occupy different geographic areas during breeding and wintering periods and are exposed to different factors. One of those factors is the climatic component of the niche. We tested if migratory birds display similar climatic conditions in both breeding and wintering areas, using 355 bird migratory species from Eurasian to Africa flyways. Our results show that there is not climatic niche overlap between both ranges. This suggests that the climatic niche of most Euro-African migratory species is larger than expected. Given these results, both breeding and wintering climatic data need to be considered when performing species distribution models, to incorporate the total width of the climatic niche.

During the Plio-Pleistocene, glacial cycles have shaped Northern Hemisphere birds' distributions that could result in changes in their migratory behaviour. In this context, it has been suggested that long-distance North American migratory species could have lost their migratory condition during cold periods regaining it later in warmer periods. We tested this hypothesis in Eurasian-African extant migratory bird species. We modelled present and LGM distribution of 80 trans-Saharan bird migratory species and we revised the available fossil record. Our results show a southwards reduction of the breeding distributions during the LGM compared to the present and similar wintering areas in the present and Pleistocene, with the Saharan belt gap always present through time. These results and the Pleistocene fossils from Africa not support the hypothesis of a loss of migratory condition in these species.

[spa] Uno de los aspectos más fascinantes dentro de la ornitología es el estudio de la migración. Saber cuáles son los patrones y procesos implicados en la evolución de la migración, permite descubrir tanto componentes ecológicos, biogeográficos como evolutivos dentro las aves. Por ello, en esta tesis se pretende aumentar el conocimiento acerca de los mecanismos implicados en la evolución de la migración en algunas aves. Por un lado, se investigó cómo evolucionó la migración y qué factores pueden actuar como motores de su evolución en un contexto filogenético usando el género Sylvia como caso de estudio. Encontramos que los procesos de cambio en el comportamiento migratorio ocurrían siempre de migratorio a sedentario, siendo el antecesor del género también migratorio. Esto supone que probablemente el coste de pasar de migratorio a sedentario es menor que al revés. Además, evaluando si factores como el clima, la morfología o la productividad eran importantes en la evolución de la migración en el género Sylvia, encontramos que la productividad juega un papel muy importante. Esto supone que probablemente las especies comenzaron a migrar aprovechando los picos de productividad que surgen en latitudes medias durante la época de cría. Por otro lado, se investigó la evolución de la migración en un contexto biogeográfico y macrecológico utilizando especies migratorias Euro-Africanas. Primero se evaluó si las especies migratorias están sometidas a las mismas condiciones climáticas tanto en las zonas de cría como en invernada. Si fuera así, las especies migratorias podrían moverse guiándose o en busca de condiciones similares a lo largo de todo el año. Sin embargo, encontramos que no es así y por lo tanto las especies migratorias presentan un nicho climático mayor de lo esperado que es necesario tener en cuenta a la hora de hacer modelos de distribución. Considerando esto, realizamos modelos de distribución de especies transaharianas tanto en el presente como durante el último glacial máximo. En este caso queríamos descubrir si las especies seguían migrando cuando parte del Paleártico estaba cubierto de nieve, o si se hicieron sedentarias como se ha sugerido para especies migratorias norteamericanas. Nuestros resultados, junto con el registro fósil consultado, no apoyan que las especies dejaran de migrar, sino que probablemente redujeran sus distancias migratorias.