Frequency of chimeric TE insertions compared with similar non-chimeric counterparts in North American strains of D. melanogaster. A) Pool frequencies of chimeric TEs (blue dots) versus those of their counterparts with lower length and recombination (red circles). Chimeric TE 44 has a significantly greater pool frequency than its counterpart, and was previously found to be adaptive [17, 18]. B) Pool frequencies of chimeric TEs (blue dots) versus those of longer counterparts with higher recombination rates (green triangles). Only one chimeric TE (number 21) has a significantly lower frequency than its counterpart. In both panels, the "population frequency" scale on the right-hand side gives maximum-likelihood estimates of the TE frequencies in the population (see Table 3 and the Methods for details).