Can. J. Zool. 87(11): 1087–1095 (2009)  |  doi:10.1139/Z09-102  |  Published by NRC Research Press / Publié par les Presses scientifiques du CNRC  

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

Allen W. Shostak

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.

Résumé : Les comparaisons inter- et intra-spécifiques révèlent fréquemment une relation inverse entre la fécondité et la taille des rejetons. Plusieurs animaux font aussi varier la taille de leurs œufs en réaction aux conditions du milieu. Une infection des vers de farine, les coléoptères Tribolium confusum Jaquelin Du Val, 1868, par le ver plat du rat Hymenolepis diminuta (Rudolphi, 1819) entraîne une importante réduction de la fécondité de l’hôte. Notre étude teste si la réduction de la fécondité est associée aux changements dans la taille des œufs de l’hôte. Des coléoptères de même âge ont été ou bien soumis au jeûne puis exposés aux parasites, ou alors soumis seulement au jeûne, ou enfin soumis à aucun de ces traitements; nous avons déterminé la production et la longueur des œufs pendant les 5 semaines après l’exposition. Les coléoptères témoins qui n’ont été soumis ni au jeûne, ni aux parasites ont une production soutenue d’œufs, mais ils produisent des œufs plus petits à mesure qu’ils vieillissent. Les coléoptères soumis seulement au jeûne produisent moins d’œufs, mais des œufs plus gros, pendant les 1–2 semaines qui suivent la fin du jeûne. Leur fécondité et la taille de leurs œufs reviennent ensuite aux valeurs des témoins. Les coléoptères infectés produisent aussi des œufs moins abondants mais plus gros pendant 1–2 semaines, mais à un rythme qui n’est pas distinct de celui des coléoptères soumis au seul jeûne. Après deux semaines, alors que la fécondité des coléoptères infectés reste basse, la taille de leurs œufs devient semblable à celle des œufs des hôtes sains. Les coléoptères semblent faire un compromis entre la fécondité et la taille des œufs en réaction à la réduction de l’alimentation, mais non au stress alimentaire présumé de l’infection parasitaire.

[Traduit par la Rédaction]

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