The cestode parasite Schistocephalus pungitii: castrator or nutrient thief of ninespine stickleback fish?

Abstract

In this investigation, the host-parasite relationship of ninespine stickleback fish Pungitius pungitius and the cestode parasite Schistocephalus pungitii was studied using samples from Dog Bone Lake, Kenai Peninsula, Alaska, to test the hypothesis that S. pungitii is a castrator of ninespine stickleback. Infected, adult females of all sizes (ages) were capable of producing clutches of eggs. S. pungitii had a negative effect on the ability of host females to produce a clutch, which was related to increasing parasite:host mass ratio (parasite index, PI). Among infected females with egg clutches, both clutch size and egg size were reduced; and the reduction increased with greater PI. The results of this study are consistent with the hypothesis that S. pungitii causes host sterility as a result of simple nutrient theft and is not a true castrator as hypothesized in earlier reports. The degree of parasite-induced sterility appears to vary among populations of the ninespine stickleback, perhaps reflecting differences in resource availability. Populations of ninespine stickleback appear to show a greater reduction in host reproductive capacity with PI than populations of the threespine stickleback infected by Schistocephalus solidus, possibly owing, in part, to the length-adjusted somatic mass of the threespine stickleback being greater.

First Reports of Ligula intestinalis and a Schistocephalus sp. Infecting Small-Bodied Fish in New Brunswick, Canada

“…It remains to be determined whether these parasites are recent introductions or result from environmental change promoting their emergence. Despite outstanding species-level identification of the Schistocephalus sp., plerocercoids from species in both genera raise ecological concerns because they can induce sterility of host fishes ( Heins and Baker, 2010 ; Heins, 2017 ; Biswas and Ash, 2021 ). Their influence on local fish populations remains to be determined, but epizootics induced by plerocercoids of both parasites are reported ( Kennedy et al, 2001 ; Heins and Ecke, 2012 ).…”

“…Plerocercoids of Ligula and Schistocephalus can alter the behavior of their intermediate host fish to increase the odds of fish predation by their bird definitive host ( Loot et al, 2001 ; Barber et al, 2004 ), a phenomenon known as Parasite Increased Trophic Transmission (PITT; Lafferty, 1999 ). Plerocercoids of both species can also induce sterility of host fishes ( Heins and Baker, 2010 ; Heins, 2017 ; Biswas and Ash, 2021 ), and epizootics caused by both parasites are reported ( Kennedy et al, 2001 ; Heins and Ecke, 2012 ).…”