THE INFLUENCE OF INTENSITY OF INFECTION BY A TREMATODE PARASITE ON THE REPRODUCTIVE-BIOLOGY OF GAMMARUS-INSENSIBILIS (AMPHIPODA)

Following the behavioural alterations induced by the trematode Microph allus papillorobustus Rankin 1940 (Trematoda, Microphallidae) on its s econd intermediate host, the amphipod Gammarus insensibilis, infected individuals are likely to mate among themselves. We investigated the i nfluence of parasite intensity on the reproductive biology of infected hosts. In the mating system of amphipods, males compete severely for access to females and large males have greater ability to obtain Large and more fecund females. We showed that the null hypothesis of random pair formation according to parasite intensity could not be rejected. In addition, infected males obtained females of the expected size acc ording to their own sizes, whatever their parasite intensities. Howeve r, in both males and females, the parasite intensity increased the int ermoult duration. Because size and reproductive success are strongly c orrelated in amphipods, we discuss the influence of this process on ho st fitness. Copyright (C) 1996 Australian Society for Parasitology. Pu blished by Elsevier Science Ltd.