Experimental differences in mortality patterns between European minnows, Phoxinus phoxinus, infected with sympatric or allopatric trematodes, Diplostomum phoxini

Abstract

A factorial experiment was conducted to examine if the digenetic trematode parasite Diplostomum phoxini influences minnow growth and survival negatively and if different parasite populations differ in their effects on hosts. Juvenile full‐sibling minnows from a lake located at the northern edge of the Swiss Alps were infected experimentally with D. phoxini from either their own or another lake. When exposed to sympatric parasites, the minnows survived a low and a high infection dose more or less equally, but with allopatric parasites mortality increased with infection dose. Parasites did not reduce host growth and minnows exposed to a low infection dose grew quicker than either non‐infected ones or ones exposed to a high infection dose. Thus, the results show different patterns of pathogenicity between two parasite populations and suggest that (1) the observed differences are at least partially genetic and that (2) the co‐evolved, sympatric host‐parasite association has reached a degree of low pathogenicity. Differences between the findings presented here and those of a previously published study are discussed.