Cost of prolonged diapause and its relationship to body size in a seed predator

Abstract

Summary Although metabolic resource losses are maintained at low rates during diapause, the accumulation of losses over a long period negatively affects organisms with prolonged diapause usually extending beyond 1 year. The seed‐predatory weevil Exechesops leucopis (Jordan) (Coleoptera: Anthribidae) enters winter diapause at the final‐instar larval stage within seeds of Styrax japonica Sieb. et Zucc. (Styracaceae) at a density of one larva per seed. After diapause, larvae pupate within the seeds and then emerge as adults. The adult emergence pattern of a single cohort of E. leucopis was monitored for 5 years under seminatural conditions in the laboratory. The duration of diapause varied from 1 year (single winter) to 4 years (four winters). Adults that emerged after 1 year were smaller than those that emerged after 2 years or more. When temperature was not decreased experimentally in winter, no adults emerged in the following season. Metabolic resource losses during diapause were examined by comparing adult body sizes between controls and groups in which emergence was delayed by 1 year under manipulated winter temperature regimes. Adults that emerged after an additional year in the larval stage were smaller than those in the control group. Moreover, the rates of reduction in body size as a consequence of diapause being extended experimentally were greater in smaller individuals. Thus smaller individuals have disadvantages in longer diapause, suggesting that weevils may vary the duration of diapause depending on individual body size. Exechesops leucopis shows sexual dimorphism in the degree of eye protrusion. Eyestalk length affects male fitness through intrasexual selection. The duration of diapause affected the length of the eyestalks: when an additional year was spent in diapause, eyestalk length was nearly maintained in larger males but was greatly decreased in smaller males. In all females eyestalk length decreased according to the duration of diapause.