Acid sensing by the Drosophila olfactory system.

The odour of acids has a distinct quality that is perceived as sharp, pungent and often irritating. How acidity is sensed and translated into an appropriate behavioural response is poorly understood. Here we describe a functionally segregated population of olfactory sensory neurons in the fruitfly, Drosophila melanogaster, that are highly selective for acidity. These olfactory sensory neurons express IR64a, a member of the recently identified ionotropic receptor (IR) family of putative olfactory receptors. In vivo calcium imaging showed that IR64a+ neurons projecting to the DC4 glomerulus in the antennal lobe are specifically activated by acids. Flies in which the function of IR64a+ neurons or the IR64a gene is disrupted had defects in acid-evoked physiological and behavioural responses, but their responses to non-acidic odorants remained unaffected. Furthermore, artificial stimulation of IR64a+ neurons elicited avoidance responses. Taken together, these results identify cellular and molecular substrates for acid detection in the Drosophila olfactory system and support a labelled-line mode of acidity coding at the periphery

Phylogenetic studies in cyprinid species from central Europe by cytochrome b sequences of mitochondrial DNA.

Sequences of part of the cytochrome b genes from the cyprinides carp (Cyprinus carpio), bream (Abramis brama), bleak (Alburnus alburnus), chub (Leuciscus cephalus) and lake chub (Rutilus frisii meidingeri) were compared after polymerase chain reaction (PCR) amplification and direct sequence analysis. Together with the published sequences of carp (C. carpio), brown trout (Salmo trutta) and Atlantic salmon (S. salar), the new sequences were used to estimate genetic distances. The five species investigated displayed interspecific variation rather than intraspecific variation. Three of the various point mutations should result in an amino acid exchange in carp, bleak and bream