Cognitive morphs in Drosophila

Natural polymorphism affecting learning and memory in Drosophila:

Knowing which genes contribute to natural variationin learning and memory would help us understand how differencesin these cognitive traits evolve among populations and species.We show that a natural polymorphism at the foraging (for) locus,which encodes a cGMP-dependent protein kinase (PKG), affectsassociative olfactory learning in Drosophila melanogaster. Inan assay that tests the ability to associate an odor with mechanicalshock, flies homozygous for one natural allelic variant of thisgene (forR) showed better short-term but poorer long-term memorythan flies homozygous for another natural allele (fors). Thefors allele is characterized by reduced PKG activity. We showedthat forR-like levels of both short-term learning and long-termmemory can be induced in fors flies by selectively increasingthe level of PKG in the mushroom bodies, which are centers ofolfactory learning in the fly brain. Thus, the natural polymorphismat for may mediate an evolutionary tradeoff between short- andlong-term memory. The respective strengths of learning performanceof the two genotypes seem coadapted with their effects on foragingbehavior: forR flies move more between food patches and so couldparticularly benefit from fast learning, whereas fors fliesare more sedentary, which should favor good long-term memory.
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