Transposon Ecology and the Octopus Genome.

Recent discoveries of transposable element (TE) activity in the octopus genome suggest, to some, that these "jumping genes" facilitated the evolution of cephalopod brains and possibly contribute to cognitive flexibility in these animals. In contrast, TEs are often regarded as genomic parasites with net deleterious effects on host fitness. The octopus genome provides an opportunity to compare these proposals to a genome-ecological alternative. We review evidence of TE accumulation and somatic activity, showing compatibility with both organism-beneficial and selfish-DNA interpretations. To resolve this, we apply ecological thinking within the genome to generate novel predictions. If TEs are adapted to a "requirement niche" typically found in germline cells, then TE-population growth rates (replication rates) should be nonnegative under similar "environmental" conditions (e.g., similar gene expression patterns to testes). This invites a comparison of expression levels across tissues. It is reasonable to infer some organism-beneficial function only when TE expression levels deviate from those predicted by the degree of niche-overlap with germline cells.