The deleterious pleiotropic effects of an adaptive mutation may be ameliorated by one of two modes of evolution: (1) by replacement, in which an adaptive mutation with harmful pleiotropic effects is replaced by one that confers an equal benefit but at less cost; or (2) by compensatory evolution, in which natural selection favors modifiers at other loci that compensate for the deleterious effects of the mutant allele. In this study, we have measured the potential of these two modes of evolution to ameliorate the deleterious pleiotropic effects of resistance to the antibiotic rifampicin in the soil bacterium Bacillus subtilis. One approach was to measure the fitness cost of a series of spontaneous rifampicin-resistance mutations from each of several strains. The potential for amelioration by the replacement mode was estimated by the variation in fitness cost among the mutants of a single strain. Another approach was to introduce a series of different rifampicin-resistance alleles into a diversity of strains, and to measure the fitness cost of rifampicin resistance for each allele-by-strain combination. The potential for amelioration by the replacement mode was estimated by the variation in fitness costs among rifampicin-resistance alleles; the potential for compensatory evolution was estimated by variation in the fitness cost of rifampicin resistance among strains. This study has shown that the cost of rifampicin resistance may be ameliorated by both the compensatory and replacement modes.

This study focuses on collaboration between student musicians in a wind quartet, saxophone quartet and string quartet. Devised as an explorative investigation using observation and interview methods, the roles of student musicians are defined within and across quartet rehearsals over a period of four weeks. The data indicate that there are common roles assumed by student musicians in a quartet: leader, deputy-leader, contributor, inquirer, fidget, joker, distractor and ‘quiet one’. The students represented one or more of these roles during a rehearsal and sometimes changed roles across rehearsals, normally through compensating for each other's mood changes. Quartets with a regular leader exhibited more stable team-role behaviour, a consistently focused group dynamic and better progress than those without one did, highlighting the impact of leadership on non-leadership roles and the success of a group.

We have investigated the potential for genetic exchange by transformation within a Mojave Desert population of Bacillus subtilis. Almost all strains surveyed were competent for transformation, and the strains varied over almost three orders of magnitude in their levels of competence. This high degree of variation suggests that natural selection toward an optimal level of competence is, at most, very weak in this population. Six of 24 competent strains showed sexual isolation from laboratory strain 168 (i.e., heterogamic transformation was reduced). Direct crosses between selected pairs of Mojave strains indicated sexual isolation within the Mojave population. Levels of sexual isolation observed within this population of B. subtilis were much less than those previously observed for transformation between named Bacillus species. Sexual isolation between 168 and Mojave strains, and among Mojave strains, was due to differences in restriction-modification systems and to DNA sequence divergence.

The cognitive and social processes underlying musical and social collaboration were explored in a smallscale study of two professional and two student singer-pianist duos. Each of the eight participants rehearsed one song with his or her regular partner and a second song with a new partner of the same level of expertise; four participants rehearsed a third song with a new partner of the other level of expertise. Their talk during rehearsal was analysed to determine a) numbers and initiators of verbal exchanges, b) interactional style, c) musical dimensions, and d) rehearsal strategies. The professional duos rehearsed more efficiently, in that they talked less and sang/played more. Interactional style was overwhelmingly positive. Students were more likely than professionals to show solidarity and ask for orientation, while professionals were more likely to give and ask for opinions. Basic, interpretive and expressive musical features were found to be as salient in these single rehearsals as evidenced in earlier research investigating protracted rehearsal periods; the present study also identified a range of rehearsal strategies, although the most common was working from the beginning to the end of the song. In conclusion we make some brief suggestions for performers.

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