The Effect of Temperature on Drosophila Hybrid Fitness.

Mechanisms of reproductive isolation inhibit gene flow between species and can be broadly sorted into two categories: prezygotic and postzygotic. While comparative studies suggest that prezygotic barriers tend to evolve first, postzygotic barriers are crucial for maintaining species boundaries and impeding gene flow that might otherwise cause incipient species to merge. Most, but not all, postzygotic barriers result from genetic incompatibilities between two or more loci from different species, and occur due to divergent evolution in allopatry. Hybrid defects result from improper allelic interactions between these loci. While some postzygotic barriers are environmentally-independent, the magnitude of others has been shown to vary in penetrance depending on environmental factors. We crossed Drosophila melanogaster mutants to two other species, D. simulans and D. santomea, and collected fitness data of the hybrids at two different temperatures. Our goal was to examine the effect of temperature on recessive incompatibility alleles in their genomes. We found that temperature has a stronger effect on the penetrance of recessive incompatibility alleles in the D. simulans genome than on those in the D. santomea genome. These results suggest that the penetrance of hybrid incompatibilities can be strongly affected by environmental context, and that the magnitude of such gene-by-environment interactions can be contingent on the genotype of the hybrid.

Evolutionary Genetics: Reuse, Recycle, Converge.

Our understanding of how genetic changes underlie the evolution of traits is growing fast. Two new studies now show that changes in the same genetic loci can drive the evolution of the same trait in multiple Drosophila species.

Clinical and cosmetic outcomes in patients treated with high-dose-rate electronic brachytherapy for nonmelanoma skin cancer.

PURPOSE: To retrospectively analyze clinical and cosmetic outcomes in patients treated for nonmelanoma skin cancer (NMSC) with high-dose-rate (HDR) electronic brachytherapy (EBT) using surface applicators. METHODS AND MATERIALS: We identified 127 patients who had 154 NMSC lesions, 149 of which were basal cell carcinoma, treated with HDR EBT at our institution between July 2012 and March 2014. Lesions were treated to 40 Gy in 8 fractions. Local control, acute toxicity, late toxicity, and cosmetic outcomes were analyzed retrospectively. Acute and late toxicities were graded using the Common Terminology Criteria for Adverse Events, version 4.0. Cosmetic outcomes were graded using a standard scale based on the Radiation Therapy Oncology Group and European Organization for Research and Treatment of Cancer Late Radiation Morbidity Scoring Schema. RESULTS: Median (range) follow-up from completion of treatment was 16.1 (3.4-34.8 months). The overall crude recurrence rate was 1.3% (n = 2). Grade 0 to 1 acute radiation dermatitis was observed in 52.6% of treated lesions (n = 81), grade 2 in 34.4% (n = 53), and grade 3 in 13.0% (n = 20). No acute toxicity greater than grade 3 was observed and all acute toxic events resolved after treatment. Grade 0 to 1 late toxicity was observed in 94.2% of cases (n = 145), and grade 2 in 5.8% (n = 9). No late toxicity greater than grade 2 was observed. Across the 152 controlled lesions, cosmetic results were excellent in 94.2% of treated lesions (n = 145), good in 3.3% (n = 5), fair in 0.7% (n = 1), and poor in 0.7% (n = 1). CONCLUSIONS: HDR EBT confers promising local control, minimal toxicity, and excellent cosmesis in our institutional experience. It should be considered ideal for NMSC of the head and neck, particularly for basal cell carcinoma involving central facial locations where surgical cosmesis may be inferior.