Abstract

This study examined host-parasite relations between cysticercoids of Microsomacanthus hopkinsi and the amphipod intermediate host Hyalella azteca throughout the latter's life history. There was a significant positive relationship in oncosphere consumption, parasite loads, and short-term survival in amphipods exposed during Instars 1, 2, 3, 4, 6, 8 and 9. Oncosphere consumption, short-term survival, and intensity of infection were generally similar among older amphipods. No correlation was found between oncosphere consumption and cysticercoid levels in any instar. Infected amphipods moulted less frequently than controls regardless of the instar at exposure. No differences were found in oncosphere consumption, short- or long-term survival, moult frequency, or intensity of infection among males and females. Infection during Instar 4 (i.e. prior to sexual development) had significant negative effects on reproduction. In pairing experiments, uninfected male H. azteca never paired with infected females. Infected male H. azteca paired with uninfected females, but less frequently than uninfected males. Overall, infections had a significant negative effect on short-term survival of young H. azteca, on the long-term survival of H. azteca infected during Instar 4, and on the number of moults over a 14 day period in H. azteca of all ages. Fecundity was markedly reduced in females infected before sexual maturity and uninfected males did not pair with infected females. The few infected males that paired suggests that they may be at a reproductive disadvantage relative to uninfected males. (Abstract shortened by UMI.)