Tapeworm (Hymenolepis diminuta) infection in flour beetles (Tribolium confusum): does it cause a trade-off between host fecundity and egg size?

Abstract

Inter- and intra-specific comparisons commonly reveal an inverse relationship between fecundity and offspring size. Many animals also vary egg size in response to environmental conditions. Infection of flour beetles Tribolium confusum Jaquelin Du Val, 1868 with the rat tapeworm Hymenolepis diminuta (Rudolphi, 1819) causes a major reduction in host fecundity. This study tested if this fecundity reduction was associated with changes in host egg size. Age-matched beetles were either fasted and then exposed to parasites, fasted only, or neither, and egg production and egg length determined for 5 weeks postexposure. Control beetles that were neither fasted nor exposed to parasites had steady egg production, but produced smaller eggs as they aged. Beetles that were fasted only, produced fewer but larger eggs for 1–2 weeks after the fast ended. Then, fecundity and egg size returned to control levels. Infected beetles also produced fewer, larger eggs for 1–2 weeks, but at levels indistinguishable from beetles that had been fasted only. After 2 weeks, while fecundity of infected beetles remained low, egg size became similar to noninfected hosts. Beetles appeared to trade-off fecundity and egg size in response to reduced feeding, but not to the presumed nutritional stress of parasitic infection.