Reward Value Determines Memory Consolidation in Parasitic Wasps

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.

Flexible memory controls sperm competition responses in maleDrosophila melanogaster

“…After this initial investment, the maintenance time of this behaviour relies on exposure time [12]. This mirrors memory development in the wasp, in that long lasting behavioural change is only initiated if a threat [12] or reward [39] is substantial. In D. melanogaster, memory developed by the lobes is a more malleable form of memory than that which is developed in the / lobes after training [41], in that it controls both relatively short and long memory periods [34].…”

“…used to remember different species of host depending on the size of oviposition reward with which the host is associated [39]. As ARM is less costly than ASM [40] this means the wasp only invests in long term memory when the reward is large.…”

Breaking Haller's Rule: Brain-Body Size Isometry in a Minute Parasitic Wasp

“…The extremely small brains of this species, however, does not seem to affect their behavioural performance. Female Trichogramma wasps, even the small phenotypes, display a rich behavioural and cognitive repertoire similar to much larger insects, including flight, walking, courtship, deciding over the size and sex of their progeny, vision, olfaction, learning and long-and shortterm memory formation [Suzuki et al, 1984;Dutton and Bigler, 1995;Pompanon et al, 1997;Huigens et al, 2000Huigens et al, , 2004Huigens et al, , 2009Huigens et al, , 2010Huigens et al, , 2011Keasar et al, 2000;Fatouros et al, 2005Fatouros et al, , 2008Kruidhof et al, 2012]. For example, to find suitable host eggs in nature, even small female T. evanescens wasps that developed in small host eggs can learn to respond to pheromones emitted by mated (and thus egg-laying) female butterflies.…”

“…The wasps mount butterflies and when they hitch a single ride on a mated female butterfly that leads to an oviposition into freshly laid butterfly eggs , they learn to associate the butterfly's pheromones with the reward of fresh host eggs. After such a rewarding hitchhiking experience, the wasps form either shorter-or longerlasting memory depending on the reward value constituted by the butterfly eggs [Huigens et al, 2009[Huigens et al, , 2010Kruidhof et al, 2012]. These complex behavioural traits are essential to find and parasitize suitable host eggs in nature and might require a certain, minimal brain size.…”

Intraspecific variability in associative learning in the parasitic wasp Nasonia vitripennis

“…In parasitic wasps, closely related species may have rather different ecologies (Hoedjes et al 2011). Many species have been shown to be capable of associative learning of host-related chemical cues (Bleeker et al 2006;Hoedjes et al 2012;Kaiser et al 2003;Kruidhof et al 2012;Müller et al 2006;Schurmann et al 2009Schurmann et al , 2012Smid et al 2007;Takasu and Lewis 2003;Thiel et al 2013;van den Berg et al 2011). This behavior facilitates host finding and therefore increases a female's reproductive success (Papaj and Vet 1990).…”