Linkage disequilibrium network complexity reduction improves power to detect parallel evolution

Compelling evidence for natural selection comes from studying similar adaptations that have evolved in multiple independently colonized populations from shared ancestral variation (parallel evolution). However, finding genomic regions associated with fitness remains challenging due to inadequate control of false positive rates and overly conservative corrections for multiple testing. Using simulations parameterized on empirical data derived from the nine- and three-spined sticklebacks, four approaches to detect genomic regions associated with parallel evolution are compared in high-density genome-wide SNP data; linear mixed model (EMMAX), latent factor mixed model (LFMM), redundancy analysis (RDA) and BayPass. RDA and BayPass were the most conservative followed by EMMAX, and while LFMM was the most powerful, it was also the most prone to false positives, particularly at high levels of background genetic differentiation and low levels of parallelism. Because some methods were sensitive to similar biases, false positives were often shared between them. Using linkage disequilibrium (LD) network-based complexity reduction in combination with EMMAX, the cost of multiple corrections was greatly reduced increasing the power to detect signatures of natural selection relative to single locus- or window-based approaches, with well controlled false positive rates. This approach can further improve our ability to distinguish false positives caused by population demographic history (genome wide effects) from those affected by non-neutral evolutionary processes that affect LD-patterns locally. The outlined approach improves our ability to identify genomic targets of natural selection and pave the path towards better understanding adaptive evolution in the wild.