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The electric field dependence of the mobilities of gas-phase protonated monomers [(MH+(H2O)n] and proton-bound dimers [M2H+(H2O)n] of organophosphorus compounds was determined at E/N values between 0 and 140 Td at ambient pressure in air with moisture between 0.1 and 15 000 ppm. Field dependence was described as alpha (E/N) and was obtained from the measurements of compensation voltage versus field amplitude in a planar high-field asymmetric waveform ion mobility spectrometer. The alpha function for protonated monomers to 140 Td was constant from 0.1 to 10 ppm moisture in air with onset of effect at approximately 50 ppm. The value of alpha increased 2-fold from 100 to 1000 ppm at all E/N values. At moisture values between 1000 and 10 000 ppm, a 2-fold or more increase in alpha (E/N) was observed. In a model proposed here, field dependence for mobility through changes in collision cross sections is governed by the degree of solvation of the protonated molecule by neutral molecules. The process of ion declustering at high E/N values was consistent with the kinetics of ion-neutral collisional periods, and the duty cycle of the waveform applied to the drift tube. Water was the principal neutral above 50 ppm moisture in air, and nitrogen was proposed as the principal neutral below 50 ppm.

Although the vast majority of higher animals are fixed for one chiral morph or another, the cause for this directionality is known in only a few cases. In snails, for example, rare individuals of the opposite coil are unable to mate with individuals of normal coil, so directionality is maintained by frequency-dependent selection. The snail subgenus Amphidromus presents an unexplained exception, because dextral (D) and sinistral (S) individuals occur sympatrically in roughly equal proportions (so-called ‘antisymmetry’) in most species. Here we show that in Amphidromus there is sexual selection for dimorphism, rather than selection for monomorphism. We found that matings between D and S individuals occur more frequently than expected by chance. Anatomical investigations showed that the chirality of the spermatophore and the female reproductive tract probably allow a greater fecundity in such inter-chiral matings. Computer simulation confirms that under these circumstances, sustained dimorphism is the expected outcome.

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