Policing the legume-Rhizobium symbiosis: a critical test of partner choice

In legume-Rhizobium symbioses, specialised soil bacteria fix atmospheric nitrogen in return for carbon. However, ineffective strains can arise, making discrimination essential. Discrimination can occur via partner choice, where legumes prevent ineffective strains from entering, or via sanctioning, where plants provide fewer resources. Several studies have inferred that legumes exercise partner choice, but the rhizobia compared were not otherwise isogenic. To test when and how plants discriminate ineffective strains we developed sets of fixing and non-fixing strains that differed only in the expression of nifH - essential for nitrogen fixation - and could be visualised using marker genes. We show that the plant is unable to select against the non-fixing strain at the point of entry, but that non-fixing nodules are sanctioned. We also used the technique to characterise mixed nodules (containing both a fixing and a non-fixing strain), whose frequency could be predicted using a simple diffusion model. We discuss that sanctioning is likely to evolve in preference to partner choice in any symbiosis where partner quality cannot be adequately assessed until goods or services are actively exchanged

Union decline and renewal in Australia and Britain: Lessons from Closed Shops

Declining union density in Australia and Britain has focused attention on the need for union reorganization. This article examines how the development of closed shops in the two countries influenced member exit rates and the internal union relations now affecting union renewal. Findings show that legislative support for the Australian closed shop tended to foster more union dependency on state and employers, union bureaucratization, less active stewards and more dissatisfied members than in Britain. The subsequent outlawing of the Australian closed shop and increasing employer hostility resulted in higher levels of density decline than in Britain. While the greater resilience of British density supports the case for developing strong workplace unionism, the relative bureaucratization of Australian unions within an increasingly antagonistic context, against the British situation of relatively indifferent employers and steward independence, limits the transferability of strategies designed to achieve union renewal