Keywords:acclimation;cold shock;development rate;egg hatching;heat shock;phenotypic plasticity;Orchesella cincta;oviposition temperature Summary 1. Temperature is considered one of the most important mediators of phenotypic plasticity in ectotherms, resulting in predictable changes in egg size. However, the fitness consequences of temperature-induced plasticity in egg size are not well understood and are often assessed at mild temperatures, whereas in the field, extreme temperatures will occur. 2. In this study we investigated egg size plasticity and fitness-linked traits of eggs in response to temperature in the springtail Orchesella cincta. Eggs were oviposited at two temperatures (16 and 20 °C), and transplanted to 10, 15 and 20 °C for rearing, or exposed to temperature shock (-6 and 38 °C) to measure survival, development rate and growth. 3. Eggs oviposited at 16 °C had a greater volume and dry weight than eggs oviposited at 20 °C but had similar lipid content. Eggs oviposited at 16 °C had high survival at all rearing temperatures, whereas survival of eggs oviposited at 20 °C declined at lower rearing temperatures and was significantly lower than survival of large eggs when reared at 10 and 15 °C. No difference in egg development rate was found between oviposition temperatures, although development rate increased with rearing temperature. Juveniles were 5–10% larger when hatching from eggs oviposited at 16 °C, independent of the temperature at which the eggs were reared. 4. Eggs oviposited at 16 °C were more resistant to thermal stress, as their survival after exposure to cold or heat shock was higher than survival of eggs oviposited at 20 °C. However, egg development rate of the eggs that survived temperature shock was not different from the control, independent of egg oviposition temperature. 5. Our results show that temperature-induced plasticity in O. cincta affects fitness-linked traits of offspring through increased hatchling size and increased thermal tolerance of eggs produced at lower temperatures. 6. The increased resistance to thermal stress of O. cincta eggs oviposited at lower temperatures may provide a protective strategy in uncertain thermal environments.
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