A helminth community in breeding Yellow-legged Gulls (Larus cachinnans): pattern of association and its effect on host fitness

Abstract

We studied the community of helminths parasitizing adult Yellow-legged Gulls (Larus cachinnans) sampled during three consecutive breeding seasons in a western Mediterranean colony. The helminth community was depauperate, probably because of the high trophic dependence of the gullery on waste food from refuse dumps. The prevalences of two helminth species varied both among years and between the sexes of gulls, while the intensity of parasitism did not vary significantly for any helminth species. No clear pattern of association between helminth species was detected, showing an unstructured helminth community in which the occurrence of any species was not restricted or favoured by the occurrence of any other species. The lack of associations might be influenced by the fact that only one core species occurred in the helminth community. Negative relationships were found between occurrence of certain helminths and body condition of hosts. Gulls infected by Tetrabothrius (Tetrabothrius) erostris were leaner than uninfected gulls; interestingly this negative relationship varied with the presence/absence of Cosmocephalus obvelatus. Moreover, body condition of gulls infected by C. obvelatus varied according to the year of sampling, while that of uninfected individuals showed no variability. High intensities of the parasites Eucoleus contortus and Brachylaima sp. were associated with poorer body condition of the host. In the case of E. contortus, this negative relationship with gulls' body condition was more pronounced in male than in female gulls. The results show that helminth pathogenicity can be affected by helminth community structure, environmental factors, and traits of the host.