Prior residency does not always pay off – co-infections inDaphnia

Abstract

SUMMARY: The epidemiological and ecological processes which govern the success of multiple-species co-infections are as yet unresolved. Here we investigated prior versus late residency within hosts, meaning which parasite contacts the host first, to determine if the outcomes of intra-host competition are altered. We infected a single genotype of the waterfleaDaphnia galeatawith both the intestinal protozoanCaullerya mesniliand the haemolymph fungusMetschnikowiasp. (single genotype of each parasite species), as single infections, simultaneous co-infections and as sequential co-infections, with each parasite given 4 days prior residency. Simultaneous co-infections were significantly more virulent than both single infections and sequential co-infections, as measured by a decreased host life span and fecundity. Further, in addition to theDaphniahost, the parasites also suffered fitness decreases in simultaneous co-infections, as measured by spore production. The sequential co-infections, however, had mixed effects:C. mesnilibenefited from prior residency, whereasMetschnikowiasp. experienced a decline in fitness. Our results show that multiple-species co-infections ofDaphniamay be more virulent than single infections, and that prior residency does not always provide a competitive advantage.