Esta Tesis ha sido desarrollada en la Estación Experimental de Zonas Áridas en Almería. Instituto perteneciente al Consejo Superior de Investigaciones Científicas (EEZA-CSIC). Memoria presentada por Jesús Veiga Neto para optar al título de Doctor por la Universidad de Granada.-- Esta tesis ha sido dirigida por el Dr. Francisco Valera Hernández, de la Estación Experimental de Zonas Áridas (CSIC) y el Dr. Gregorio Moreno Rueda, de la Universidad de Granada., Parasites are strongly influenced by numerous abiotic and biotic factors operating at different temporal and spatial scales. To understand parasites dynamics, host-parasite interactions and the underlying mechanisms of such interactions it is necessary to study how those factors influence parasites and their relationships with the hosts at the various scales.
Here we study the effect of off-host and host-related factors on the relationship between a cavity-nesting bird species, the European roller (Coracias garrulus) and its ectoparasites, mainly the haematophagous fly Carnus hemapterus. The main factors considered in this study involve habitat characteristics at the mesoscale (the host nest and the immediate surroundings) like nest-site type (a major source of habitat heterogeneity in our study area) as well as host and parasite density, breeding phenology of the host (i.e. seasonal effects) and host total brood mass (as a surrogate of cues for the parasites). We study the effect of these factors on the colonization success and distribution (prevalence and abundance) of the most common ectoparasite (Carnus hemapterus). However, since a given host species usually harbours several parasite species, the approach “one host-one parasite” overlooks the effect of the interactions among parasites that mainly occur at the infracommunity level. Therefore, we also explore the effect of the above-mentioned factors on the ectoparasite infracommunity of the European roller.
Our study is performed in a semi-arid environment, therefore contributing to our knowledge of host-parasite interactions in such habitats that are underrepresented in the scientific literature.
Both to fill the gaps on the basic biology of the study species and to build up our study on solid foundations, we also explore basic aspects of the natural history of Carnus hemapterus such as the characteristics of the pupal stage of the ectoparasite or its life span during the dispersal stage (closely related to colonization success).
We found that carnid flies have a very short life span during the dispersal stage (less than four days), in spite of which they are able to colonize ca. 100% of the host nests. Its longevity during this period increases with body size, environmental humidity and with access to food (flowers). Nest-site type influences colonization success of carnid flies, so that it is higher in nest boxes on sandstone cliffs-farmhouses than in nest boxes on trees. Colonization success also increased with host density and host brood mass but decreased as the season progressed. Interestingly, parasite density had no effect on host colonization success. Nest-site type also explained differences among nests in composition of the ectoparasite infracommunity and in abundance of various ectoparasite species. These variables were not affected by the spatial structure, nor by brood mass. However, host breeding phenology affects the ectoparasite infracommuity differences in abundance, acting mainly over Carnus hemapterus.
Our results also reveal that it is necessary to consider the non-infective stages of parasites when analysing host-parasite relationships since they are important for understanding habitat selection criteria, host-range and processes regulating coexistence with other species. In our study system, the observed patterns of prevalence and abundance of imagoes and pupae of three supposedly generalist ectoparasites (Carnus hemapterus and the louse flies Pseudolynchia canariensis and Ornithophila metallica) suggest that, for some parasite species, the requirements of non-infective stages may be more restrictive than the ones of the parasitic stages.
Since some of the ectoparasites here studied are vectors of haemoparasites and since the identification of associations host-vector-pathogens is critical for understanding the ecology of diseases, we studied the likely vectorial role of biting midges (Fam. Ceratopogonidae). We found that Culicoides paolae and C. circumscriptus were common visitors in nests of various species of troglodyte birds. These midges feed on various bird species and harbour four lineages of Haemoproteus. Thus, they can play an important role in the transmission of Haemoproteus in the study area.
Finally, this study reveals that the infracommunity of ectoparasites of a cavity-nesting bird species in a semi-arid environment is rich (made up of at least species of 8 different families, including a recently introduced species, C. paolae), with some species being particularly abundant.
We conclude that socioenvironmental characteristics at small scale are major determinants of the spatial distribution of nest-based ectoparasites in an arid environment., Este trabajo ha sido posible gracias a la concesión de una beca predoctoral de formación de personal investigador (BES-2015-075951) del Ministerio de Economía, Industria y Competitividad asociada al proyecto CGL2014-55969-P, financiado con fondos FEDER y del Ministerio de Economía, Industria y Competitividad., Peer reviewed

Memoria presentada por Daniel Parejo Pulido para optar al grado de Doctor con mención internacional por la Universidad de Castilla – La Mancha., Instituto de Investigación en Recursos Cinegéticos (CSIC-UCLM-JCCM) Doctorado en Ciencias Agrarias y Ambientales: Departamento de Ciencia y Tecnología Agroforestal y Genética Universidad de Castilla – La Mancha., [EN] The current understanding of begging signals and parent-offspring conflict over parental investment is largely shaped by influential models of scramble competition and signalling of need in avian broods. Godfray’s model of differential benefits, in particular, has become the dominant paradigm, inspiring extensive theoretical and empirical research. This model posits that offspring signal their need honestly, with those in greater need signalling more intensely due to higher benefits from food, allowing parents to allocate resources efficiently through an active choice mechanism. The system stabilizes via a signalling cost, creating a highly informative separating equilibrium. However, this model has faced significant criticism regarding its applicability to natural systems. While much of this criticism is theoretical, few empirical studies rigorously test the model’s assumptions, with many This thesis aims to experimentally test several assumptions and predictions of Godfray’s model that have been subject to criticism.researchers instead assuming its validity without question., [ES] La comprensión actual de las señales de petición y el conflicto entre padres e hijos por la transferencia de recursos está en gran medida influenciada por los modelos de competencia igualitaria y de señalización de la necesidad en familias de aves altriciales. En particular, el modelo de Godfray de beneficios diferenciales se ha convertido en el paradigma dominante, inspirando una amplia investigación teórica y empírica. Este modelo propone que las crías indican de forma sincera su nivel de necesidad, siendo las más necesitadas las que solicitan con mayor intensidad debido a los mayores beneficios que reciben por el alimento, permitiendo que los padres asignen recursos de manera eficiente a través de un mecanismo de elección activa. El sistema se estabiliza mediante un coste de señalización, lo que conlleva a un equilibrio de separación de señales bien diferenciadas muy informativo. Sin embargo, este modelo se ha enfrentado a numerosas críticas relacionadas con su aplicabilidad en los sistemas naturales. Aunque gran parte de estas críticas son teóricas, pocos estudios empíricos han ensayado rigurosamente los supuestos del modelo, y muchos investigadores asumen su validez sin cuestionarla.
Esta tesis tiene como objetivo principal ensayar experimentalmente ciertos supuestos y predicciones controvertidas del modelo de Godfray que han sido objeto de críticas., Los objetivos de esta tesis se llevaron a cabo gracias a la financiación proveniente de los siguientes proyectos y ayudas: - Proyecto ref. CGL2014-55969-P del Ministerio de Economía y Competitividad. - Proyecto ref. CGL2017-83843-C2-1-P del Ministerio de Ciencia y Universidades. - Proyecto ref. PGC2018-099596-B-I00 cofinanciado por el Ministerio de Ciencia, Innovación y Universidades, la Agencia Española de Investigación (10.13039/501100011033) y por FEDER – Una manera de hacer Europa. - Proyecto ref. PID2021-126673NB-I00 del Ministerio de Ciencia e Innovación. - Microproyectos EBD, Programa Severo Ochoa para Centros de Excelencia; Ref. SEV-2012-0262. Daniel Parejo Pulido fue beneficiario durante la tesis de un contrato predoctoral del Plan Propio de la Universidad de Castilla – La Mancha (referencia: 2019-PREDUCLM-11785) cofinanciado por el “Fondo Social Europeo”, seguido de un contrato asociado al Programa INVESTIGO asociado al Plan de Recuperación, Transformación y Resiliencia del Ministerio de Trabajo y Economía Social, la Junta de Comunidades de Castilla – La Mancha y el Consejo Superior de Investigaciones Científicas (CSIC), cofinanciado por los fondos NextGenerationEU., Peer reviewed