MUPs bind volatiles and extend the duration of odour signals

Hurst, J.L., Robertson, D.H.L., Tolladay, U. & Beynon, R.J. (1998) Proteins in scent marks of male house mice extend the emission of olfactory signals. Anim. Behav. 55, 1285-1297 [PUBMED] [PDF]

The binding of volatile semiochemicals to lipocalin proteins in many mammalian scent marks may provide a gradual release of volatile ligands, extending the life of airborne odour signals. We tested this by using menadione to displace semiochemical ligands from major urinary proteins (MUPs) in urine streaks obtained from adult male house mice, Mus domesticus, and assessed the responses of other males to these and to intact urine marks as they aged. Dominant male mice scent-mark their territories extensively with urine streaks; MUPs in these marks bind at least two semiochemically active molecules, 2-sec-butyl-4,5-dihydrothiazole (thiazole) and 2,3-dehydro-exo-brevicomin (brevicomin), associated with the males' aggressive status. Wild-caught males (N=24), housed in individual enclosures, were presented with two glass slides, behind mesh to prevent contact, on which 10 µl of both unfamiliar urine and 0.5 mg/ml menadione in ethanol had been streaked. On one slide the urine and menadione solution were mixed to displace ligands; on the other they were separate (intact urine). We carried out tests 0, 0.5, 1 or 24 h after deposition, and matched them to changes in the concentration of thiazole and brevicomin within the intact and displaced marks. Males were hesitant to approach intact urine up to 1 h old but, when ligands were displaced, or were reduced to low levels by natural evaporation from intact urine streaks aged 24 h, their approach was similar to that to water and to menadione controls. Ligands did not appear to cause any longer term avoidance and, after the first approach, investigation increased with the freshness of urine regardless of when the ligands were displaced. This is the first direct demonstration that proteins evince a slow release of olfactory signals from mammalian scent marks. The nature of their response suggests that, from a distance, mice may be unable to tell whether airborne signals emanate from scent marks or from the donor himself and we suggest that this may provide territory owners with a major advantage in defending their territories.