Evolution and lineage dynamics of a transmissible cancer in Tasmanian devils.

Devil facial tumour 1 (DFT1) is a transmissible cancer clone endangering the Tasmanian devil. The expansion of DFT1 across Tasmania has been documented, but little is known of its evolutionary history. We analysed genomes of 648 DFT1 tumours collected throughout the disease range between 2003 and 2018. DFT1 diverged early into five clades, three spreading widely and two failing to persist. One clade has replaced others at several sites, and rates of DFT1 coinfection are high. DFT1 gradually accumulates copy number variants (CNVs), and its telomere lengths are short but constant. Recurrent CNVs reveal genes under positive selection, sites of genome instability, and repeated loss of a small derived chromosome. Cultured DFT1 cell lines have increased CNV frequency and undergo highly reproducible convergent evolution. Overall, DFT1 is a remarkably stable lineage whose genome illustrates how cancer cells adapt to diverse environments and persist in a parasitic niche.

Multiple Metabolic Innovations and Losses Are Associated with Major Transitions in Land Plant Evolution.

Investigating the evolution of plant biochemistry is challenging because few metabolites are preserved in fossils and because metabolic networks are difficult to experimentally characterize in diverse extant organisms. We report a comparative computational approach based on whole-genome metabolic pathway databases of eight species representative of major plant lineages, combined with homologous relationships among genes of 72 species from streptophyte algae to angiosperms. We use this genomic approach to identify metabolic gains and losses during land plant evolution. We extended our findings with additional analysis of 305 non-angiosperm plant transcriptomes. Our results revealed that genes encoding the complete biosynthetic pathway for brassinosteroid phytohormones and enzymes for brassinosteroid inactivation are present only in spermatophytes. Genes encoding only part of the biosynthesis pathway are present in ferns and lycophytes, indicating a stepwise evolutionary acquisition of this pathway. Nevertheless, brassinosteroids are ubiquitous in land plants, suggesting that brassinosteroid biosynthetic pathways differ between earlier- and later-diverging lineages. Conversely, genes for gibberellin biosynthesis and inactivation using methyltransferases are found in all land plant lineages. This suggests that bioactive gibberellins might be present in bryophytes, although they have yet to be detected experimentally. We also found that cytochrome P450 oxidases involved in cutin and suberin production are absent in genomes of non-angiosperm plants that nevertheless do contain these biopolymers. Overall, we identified significant differences in crucial metabolic processes between angiosperms and earlier-diverging land plants and resolve details of the evolutionary history of several phytohormone and structural polymer biosynthetic pathways in land plants.

Low Incubation Temperature Induces DNA Hypomethylation in Lizard Brains.

Developmental stress can have organizational effects on suites of physiological, morphological, and behavioral characteristics. In lizards, incubation temperature is perhaps the most significant environmental variable affecting embryonic development. Wall lizards (Podarcis muralis) recently introduced by humans from Italy to England experience stressfully cool incubation conditions, which we here show reduce growth and increase the incidence of scale malformations. Using a methylation-sensitive AFLP protocol optimized for vertebrates, we demonstrate that this low incubation temperature also causes hypomethylation of DNA in brain tissue. A consistent pattern across methylation-susceptible AFLP loci suggests that hypomethylation is a general response and not limited to certain CpG sites. The functional consequences of hypomethylation are unknown, but it could contribute to genome stability and regulation of gene expression. Further studies of the effects of incubation temperature on DNA methylation in ectotherm vertebrates may reveal mechanisms that explain why the embryonic thermal environment often has physiological and behavioral consequences for offspring.