Abstract
Animals can store learned information in their brains through a series of distinct memory forms. Short-lasting memory forms can be followed by longer-lasting, consolidated memory forms. However, the factors determining variation in memory consolidation encountered in nature have thus far not been fully elucidated. Here, we show that two parasitic wasp species belonging to different families, Cotesia glomerata (Hymenoptera: Braconidae) and Trichogramma evanescens (Hymenoptera; Trichogrammatidae), similarly adjust the memory form they consolidate to a fitness-determining reward: egg-laying into a host-insect that serves as food for their offspring. Protein synthesis-dependent long-term memory (LTM) was consolidated after single-trial conditioning with a high-value host. However, single-trial conditioning with a low-value host induced consolidation of a shorter-lasting memory form. For Cotesia glomerata, we subsequently identified this shorter-lasting memory form as anesthesia-resistant memory (ARM) because it was not sensitive to protein synthesis inhibitors or anesthesia. Associative conditioning using a single reward of different value thus induced a physiologically different mechanism of memory formation in this species. We conclude that the memory form that is consolidated does not only change in response to relatively large differences in conditioning, such as the number and type of conditioning trials, but is also sensitive to more subtle differences, such as reward value. Reward-dependent consolidation of exclusive ARM or LTM provides excellent opportunities for within-species comparison of mechanisms underlying memory consolidation.
Highlights
Rewards of different value offered during associative conditioning are known to induce changes in the conditioned response, such as floral odor preference in honey- and bumblebees [1,2], the duration of a feeding response to odors in parasitic wasps [3], win-shift tendency in birds [4], place preference in rats [5] and cache recovery preference in foodstoring birds [6], as well as changes in the duration of memory for, e.g., odors in fruit flies [7]
We investigated the effect of host-species on memory consolidation in two parasitic wasp species belonging to different families, Cotesia glomerata (Hymenoptera: Braconidae) and Trichogramma evanescens (Hymenoptera: Trichogrammatidae; Fig. 1, 2)
We tested whether the memory retention (MR) level changes with time after conditioning and whether this is dependent on the host-species used for conditioning
Summary
Rewards (e.g. food, hosts) of different value offered during associative conditioning are known to induce changes in the conditioned response, such as floral odor preference in honey- and bumblebees [1,2], the duration of a feeding response to odors in parasitic wasps [3], win-shift tendency in birds [4], place preference in rats [5] and cache recovery preference in foodstoring birds [6], as well as changes in the duration of memory for, e.g., odors in fruit flies [7]. We hypothesized that rewards of the same type but of different value may induce consolidation of a different memory form. In insects it has been shown that initial, labile anesthesiasensitive memory (ASM) can be consolidated into ARM and/or more stable, protein synthesis-dependent LTM [10,11,12,13,14]. In contrast to ASM, the formation of both ARM and LTM is insensitive to retrograde amnesia applied immediately after conditioning [15]. Both ARM and LTM are regarded as forms of ‘‘consolidated memory’’. Whether more subtle differences in the reinforcer can affect memory consolidation is currently still unknown
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