Coevolution in host–parasite systems: Behavioral strategies of native and invasive hosts

Abstract

Parasites are subject to selection upon traits that facilitate transmission between hosts. One such example is Polymorphus minutus, an acanthocephalan parasite, which alters the behaviour of their intermediate hosts, gammarids, to facilitate the transmission to its definitive host, waterfowl. A fundamental question is whether this ability of P. minutus to alter its intermediate host’s behavior or to increase intermediate host’s survival has evolved specifically to target sympatric gammarids, or gammarids in general? The non-host predator avoidance of P. minutus, towards the three-spined sticklebacks, Gasterosteus aculeatus, and rheotaxis of intermediate hosts was assessed in three gammarid species; two native species, Gammarus pulex and Gammarus fossarum, and one invasive species, Echinogammarus berilloni. We assessed the salinity tolerance of native species to determine if P. minutus affected its intermediate host’s salinity tolerance. The parasite P. minutus studied here has co-evolved with sympatric native gammarids, and not with invasive gammarids, which has resulted to a system to promote avoidance behaviour in native gammarids towards non-host predators. Furthermore, we found that the effect of infection on rheotaxis in native and invasive species is not different and there was no difference in salinity tolerance between infected native gammarids. The lower susceptibility to non-final host predators and increased negative rheotaxis behaviour of invasive species could lead to occupation of the whole ecological niche by invasive parasite and intermediate host species due to competitive exclusion. The findings of this thesis are useful for waterfowl conservation strategies and also for fish and domestic waterfowl farms.