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Many parasites affect the development and survival of offspring. Because passerines exhibit determinate growth, parasites may have lasting effects on phenotypes. The life-history consequences of parasite-induced developmental modifications have rarely been analyzed, and require long-term experimental studies. Here we present the results of a four-year experimental study on the effects of a hematophagous ectoparasite, the hen flea (Ceratophyllus gallinae), on growth, survival, and lifetime reproductive success of nestlings of the Great Tit (Parus major). In a design A, half of the nests were heat-treated several times per year to kill parasites, while in the other half, fleas were allowed to immigrate naturally over several years. To allow for the estimation and statistical control of effects due to potentially nonrandom phenotype distribution within this design, a second design, design B, was applied. In design B, all nests were heat treated to kill parasites after nest box occupation, and the subsequent infestation of half of the nests was then randomized in space and time. In both designs, the fleas significantly reduced nestling body size but did not significantly affect the probability of nestling recruitment as local breeders. Parasitism reduced the clutch size of the nestlings' first recorded clutch, and of the subsequent clutches, and reduced the total number of recruits produced per nestling over the entire study period. Because body size of the recruited nestlings, both at the end of growth and as recruits, was not significantly different between treatments, the reduced fitness was not an indirect consequence of parasite-modified body size. This study provides experimental evidence for parasite-induced effects during growth on survival and development of offspring and shows the consequences of this phenotypic modification on lifetime reproductive success. It shows that parasite-induced effects during growth are important for understanding optimal resource allocation and life-history evolution under parasitism.

Host nests are the key habitat for ectoparasite species that live and reproduce within the nest material. Nest properties can influence host and parasite reproductive success, and therefore the outcome of host–parasite interactions, as well as the composition of parasite communities. Previous correlational results suggested that nest humidity may increase the negative effect of fleas on Great Tit (Parus major) reproductive success. Since the causality of the relationship was unknown, we simultaneously manipulated both hen flea (Ceratophyllus gallinae) infestation and nest humidity in order to investigate: (1) the effect of flea infestation on nest humidity, (2) the effect of nest humidity on the prevalence of flea infestations, (3) the effect of nest humidity on adult flea survival and reproduction, (4) the interaction between flea infestations and nest humidity on Great Tit reproductive performance, and (5) the effect of both factors on secondary infestations by ectoparasitic Protocalliphora flies. The p...

The hen flea Ceratophyllus gallinae (Siphonaptera: Ceratophyllidae) is a common ectoparasite in Blue Tit Parus caeruleus nests, whereby adult fleas draw blood from the incubating female host and from the nestlings. Host-parasite interactions are influenced by density-dependent growth of the parasite population, which may result from competitive exploitation or interference between parasite individuals, or from density- dependent host defenses. Understanding density dependence in host-parasite interactions is important for understanding the evolution of parasite virulence and of host defense. Here we investigate density-dependent processes in the dynamics of flea subpopulations. In a first experiment, intended to establish the importance of density dependence in this host- parasite system, the founder density of parasites was manipulated, and reproductive rates of parasites measured. A second experiment was designed to identify the demographic levels at which density dependence arises in the growth of the hen flea population. The experiments show that parasite reproductive rates significantly decrease with increasing founder density. The patterns of egg production, larval production, and adult flea survival suggest that competition between larvae is the main process behind the density-dependent pattern of subpopulation growth. Host mortality, body condition, and blood hematocrit level of the female host and the nestlings were not significantly affected by parasite load, sug- gesting that adult fleas are not food limited at high densities.

Experimental studies provide evidence that, in spatially and temporally heterogeneous environments, individuals track variation in breeding habitat quality to adjust breeding decisions to local conditions. However, most experiments consider environmental variation at one spatial scale only, while the ability to detect the influence of a factor depends on the scale of analysis. We show that different breeding decisions by adults are based on information about habitat quality at different spatial scales. We manipulated (increased or decreased) local breeding habitat quality through food availability and parasite prevalence at a small (territory) and a large (patch) scale simultaneously in a wild population of Great Tits (Parus major). Females laid earlier in high-quality large-scale patches, but laying date did not depend on small-scale territory quality. Conversely, offspring sex ratio was higher (i.e., biased toward males) in high-quality, small-scale territories but did not depend on large-scale patch quality. Clutch size and territory occupancy probability did not depend on our experimental manipulation of habitat quality, but territories located at the edge of patches were more likely to be occupied than central territories. These results suggest that integrating different decisions taken by breeders according to environmental variation at different spatial scales is required to understand patterns of breeding strategy adjustment.