Accounting for the abundance of genetic variation in the face of natural selection remains a central problem of evolutionary biology. Genetic polymorphisms are constantly arising through mutation, and although most are promptly eliminated, polymorphisms in functionally important traits are common. One mechanism that can maintain polymorphisms is negative frequency-dependent selection on alternative alleles, whereby the fitness of each decreases as its frequency increases. Examples of frequency-dependent selection are rare, especially when attempting to describe the genetic basis of the phenotype under selection. Here we show frequency-dependent selection in a well-known natural genetic polymorphism affecting fruitfly foraging behaviour. When raised in low nutrient conditions, both of the naturally occurring alleles of the foraging gene (for(s) and for(R)) have their highest fitness when rare-the hallmark of negative frequency-dependent selection. This effect disappears at higher resources levels, demonstrating the role of larval competition. We are able to confirm the involvement of the foraging gene by showing that a sitter-like mutant allele on a rover background has similar frequency-dependent fitness as the natural sitter allele. Our study represents a clear demonstration of frequency-dependent selection, and we are able to attribute this effect to a single, naturally polymorphic gene known to affect behaviour.

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Against the background of the increasing incidence of many immune mediated childhood conditions, this study aimed to identify recent time trends and ethnic patterns of childhood nephrotic syndrome. A population-based cohort of children (0-15 years) diagnosed according to strict criteria with nephrotic syndrome (NS) was ascertained within the northern UK region of Yorkshire between 1987 and 1998. South Asian ethnicity was assigned based on the child's full name using a dedicated computer algorithm and expert individual checks. NS was diagnosed in 194 children, 170 (88%) of whom were steroid sensitive. The incidence of steroid sensitive NS was 2.0/100,000 pyrs (95% CI 1.7-2.3), peaking in 1-4 year olds (4.1/100,000 pyrs). Over the 12-year study period incidence rates of steroid sensitive NS were fairly stable although south Asian children displayed significantly higher rates than non-south Asians (P<0.01). The size of our population-based series reflects the relative rarity of paediatric nephrotic syndrome but is nonetheless recent and includes larger numbers than previous reports. The absence of any increase in incidence over the last decade contrasts with other paediatric immune mediated conditions such as asthma and diabetes.

significantly aided growth at 6 months more so in prepubertal than pubertal children. This was accompanied by significantly better lipid and glucose metabolism profiles without increases in graft rejection or loss.

In a 6-month, multicenter, randomized, controlled, open-label, parallel-group trial, we investigated the efficacy and safety of adding basiliximab to a standard tacrolimus-based regimen in pediatric renal transplant recipients. Patients <18 years received tacrolimus/azathioprine/steroids (TAS, n = 93) or tacrolimus/azathioprine/steroids/basiliximab (TAS + B, n = 99). Target tacrolimus levels were 10-20 ng/mL between days 0-21 and 5-15 ng/mL thereafter. Steroid dosing was identical in both groups. Basiliximab was administered at 10 mg (patients <40 kg) or 20 mg (patients ≥40 kg) within 4 h of reperfusion; the same dose was repeated on day 4. Biopsy-proven acute rejection rates were 20.4% (TAS) and 19.2% (TAS + B); steroid-resistant acute rejection rates were 3.2% and 3.0%, respectively. Patient survival was 100%; graft survival rates were 95% in both arms. The nature and incidence of adverse events were similar in both arms except toxic nephropathy and abdominal pain, which were significantly higher in the TAS + B arm (14.1% vs. 4.3%; p = 0.03 and 11.1% vs. 2.2%; p = 0.02; respectively). Median serum creatinine concentrations at 6 months were 86 lmol/L in the TAS and 91 lmol/L in the TAS + B arm; glomerular filtration rate was 79.4 and 77.6 (mL/min/1.73 m 2 ), respectively. Adding basiliximab to a tacrolimus-based regimen is safe in pediatric patients, but does not improve clinical efficacy.

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The dispersal and migration of organisms have resulted in the colonisation of nearly every possible habitat and ultimately the extraordinary diversity of life. Animal dispersal tendencies are commonly heterogeneous (e.g. long vs. short) and non-random suggesting that phenotypic and genotypic variability between individuals can contribute to population-level heterogeneity in dispersal. Using laboratory and field experiments, we demonstrate that natural allelic variation in a gene underlying a foraging polymorphism in larval fruit flies (for), also influences their dispersal tendencies as adults. Rover flies (for(R) ; higher foraging activity) have consistently greater dispersal tendencies and are more likely to disperse longer distances than sitter flies (for(s) ; lower foraging activity). Increasing for expression in the brain and nervous system increases dispersal in sitter flies. Our study supports the notion that variation in dispersal can be driven by intrinsic variation in food-dependent search behaviours and confirms that single gene pleiotropic effects can contribute to population-level heterogeneity in dispersal.