Human selection and the relaxation of legume defences against ineffective rhizobia

Enforcement mechanisms are thought to be important in maintaining mutualistic cooperation between species. A clear example of an enforcement mechanism is how legumes impose sanctions on rhizobial symbionts that fail to provide sufficient fixed N2. However, with domestication and breeding in high-soil-N environments, humans may have altered these natural legume defences and reduced the agricultural benefits of the symbiosis. Using six genotypes of soya beans, representing 60 years of breeding, we show that, as a group, older cultivars were better able to maintain fitness than newer cultivars (seed production) when infected with a mixture of effective and ineffective rhizobial strains. Additionally, we found small differences among cultivars in the ratio of effective : ineffective rhizobia released from their nodules, an indicator of future rhizobial strain fitness. When infected by symbionts varying in quality, legume defences against poor-quality partners have apparently worsened under decades of artificial selection

Psychologic functioning of unspecified anonymous living kidney donors before and after donation

BACKGROUND: There has been discussion regarding the psychologic functioning of living donors who donate their kidney to an unrelated and unknown patient ("unspecified living donors"). This is the first prospective study to investigate group- and individual-level changes in psychologic functioning among a large group of unspecified donors. METHODS: Forty-nine medically and psychologically screened unspecified living kidney donors completed the Symptom Checklist before and after donation. RESULTS: Group-level analysis showed that overall psychologic symptoms increased after donation (P=0.007); the means remained within the average range of the normal population. Individual-level analysis showed that 33 donors showed no statistically significant change, 3 donors showed a statistically significant decrease, and 13 donors showed a statistically significant increase in psychologic symptoms. Two of the latter donors showed a clinically significant increase. CONCLUSIONS: We found more increases in psychologic symptoms than decreases, particularly if follow-up time was longer. However, for almost all donors, these increases were not clinically significant and the clinically significant changes found are comparable with natural fluctuations in psychologic symptoms in the general population. Possibly, the donors underreported their psychologic symptoms before donation to pass the screening. Due to the low level of predonation symptoms reported, regression to the mean could also explain the results. Although we found that changes were not associated with donation-related factors, it is possible that other donation-related factors or other life events not measured have an influence on psychologic functioning. Therefore, further research is needed to investigate whether the fluctuations are related to the donation process.Copyrigh