Effect of suboptimal environment and host age on helminth community of black grouse (Tetrao tetrix)

Helminths have often been considered responsible in driving partially wildlife population density fluctuations, therefore more information have to be achieved when target hosts are endangered or threatened species, such as black grouse (Tetrao tetrix). During eight years (2003-2010), we collected and analyzed 431 intestinal contents of hunted black grouse from Central Alps (VB), recording age, body weights, biometric measures and the culling site to investigate (1) their helminth community structure, (2) how much infection varies in relation to age class and to prealpine and alpine origin area and (3) if parasites may act as population destabilizing factors. The helminth community is composed by two nematodes Ascaridia compar and Aonchotheca caudinflata: A. compar is the predominant species and a significant higher intensity of both helminths is recorded in juveniles. A. caudinflata has a negative effect on weights of all the population subjects (p<0.001), independently of age and origin area; prealpine population, characterized by significantly lower weights than those of the alpine ones (p<0.05), is found more infected by both helminths, with also a negative impact (p<0.001) of A. compar recorded on prealpine adults’ weights. The negative effect noticed for A. caudinflata emphasizes its pathogenicity and shows that this infection can be considered a further stressor for the studied population. Moreover A. compar affects essentially adults in prealpine area and this fact, together with the major infection of the entire prealpine population, supports the hypothesis that habitat characteristics play a role in the infectious process.