VOLUME OF PARASITES AS INDICATOR OF COMPETITION: THE CASE OF ACANTHOCEPHALUS

C. RAUQUE; L. SEMENAS

JOURNAL OF PARASITOLOGY

AMER SOC PARASITOLOGISTS

Año: 2011 vol. 97 p. 999 - 1002

0022-3395

In Lake Mascardi (Patagonia), 2 acanthocephalan species, Acanthocephalus tumescens and Pseudocorynosoma sp. share the amphipod intermediate host but they differ in its definitive host. Because in infected amphipods simultaneously with both species, one of the parasites has no opportunities to complete its life cycle, negative interactions between them can be expected. The purpose of the present work was to study competition in the intermediate host through the comparisons of A. tumescens and Pseudocorynosoma sp. cystacanth volume. Specimens of the amphipod Hyalella patagonica were monthly collected during almost 2 years. Amphids were measured (total length) and necropsied looking for cystacanths. Larvae obtai were easured (lengt and width) and their volume was calculated. Size of both acanthocepalan species was positively associated with amphipods length. Interactions in 3 periods were evaluated: high level of Pseudocorynosoma sp. infections (HP), high level of A. tumescens infections (HA) and high level of mixed infections (HM). For Pseudocorynosoma sp. only was found intra-specific competition in HM period. In contrast, for A. tumescens, inter-specific competition in HP period, intra-specific competion in HA period, and intra and inter-specific competition in HM period were found. We suggest that Pseudocorynosoma sp., is a non-plastic species being mostly found in single infections, meanwhile A. tumescens is a more sensitive species being found more frequently in co-infections.