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The ability to learn and to remember is essential for an animal’s survival. The mechanisms that lead to memory formation are highly conserved across species. Cyclic adenosine monophosphate (cAMP) is a second messenger that plays an important role in memory formation. Phosphodiesterases (PDEs) hydrolyse cAMP and cyclic guanosine monophosphate, reducing their levels. Dunce (Dnc) is a cAMP-specific PDE in Drosophila. dunce (dnc) is a complex gene that encodes several isoforms (Qiu et al., 1991). In general, Dnc is regarded as a PDE that reduces the overall cAMP concentration, leading to dnc mutants with short-term memory (STM) deficits (Aceves-Piña and Quinn, 1979; Davis and Kiger, 1981; Dudai et al., 1976). In this project we will investigate the role of different Dnc isoforms in learning and memory and their localisation at the cellular and subcellular level. We show in Drosophila larvae that DncPA and DncPB specific mutants display the opposite phenotype to classical dnc mutants, increased STM. This demonstrates that the Dnc memory phenotype is isoform-specific. The memory phenotype of a DncPA-specific mutant depends on PDE activity in neurons driven by the dncRA promoter. Of these, expression in a local interneuron projecting to the antennal lobe (AL) is most likely to affect memory formation. DncPB is localised in a group of neurons associated with gustatory signals (Melcher and Pankratz, 2005). As gustatory stimuli are used as reinforcers, they are likely to influence memory formation. We also localise other isoforms in the central nervous system. With large differences between the expression patterns of antibodies against the same isoforms, we show that Dnc is a highly interacting and highly modified protein. In mammals, the subcellular localisation of a PDE isoform has been shown to play an important role in memory formation (Martinez et al., 2023). We show that in Drosophila larvae, somatic PDE expression is essential for the memory phenotype in DncPA. The fly

Timing is essential for survival and reproduction of organisms across the tree of life. The core circadian clock gene Clk is involved in the regulation of annual timing events and shows highly conserved sequence homology across vertebrates except for one variable region of poly-glutamine repeats. Clk genotype varies in some species with latitude, seasonal timing and migration. However, findings are inconsistent, difficult to disentangle from environmental responses, and biased towards high latitudes. Here we combine field data with a common-garden experiment to study associations of Clk polymorphism with latitude, migration and annual-cycle timing within the stonechat species complex across its trans-equatorial distribution range. Our dataset includes 950 records from 717 individuals from nine populations with diverse migratory strategies. Gene diversity was lowest in resident African and Canary Island populations and increased with latitude, independently of migration distance. Repeat length and annual-cycle timing was linked in a population-specific way. Specifically, equatorial African stonechats showed delayed timing with longer repeat length for all annual-cycle stages. Our data suggest that at low latitudes with nearly constant photoperiod, Clk genotype might orchestrate a range of consistent, individual chronotypes. In contrast, the influence of Clk on annual-cycle timing at higher latitudes might be mediated by its interactions with genes involved in (circadian) photoperiodic pathways.