Historical genomes reveal scale-dependent predictability of climate adaptation

Predicting how species evolve over time is a major challenge in biology. Scientists often rely on current geographic patterns to estimate how organisms might adapt to changes in their environment. However, it is uncertain whether predictions are consistent across different biological scales. To investigate this, researchers examined historical and modern genetic data from the invasive plant Ambrosia artemisiifolia, which has spread to two continents over the past two centuries.

The study found that genomic predictions for flowering time remained stable within the plant's native range. However, when the invasive species established in new environments, it evolved new flowering time patterns. Researchers identified "haploblocks" - sections of the genome with similar genetic material - that remained stable over time in the native range. Two of these haploblocks exhibited a remarkable case of parallel evolution, evolving similarly across all three geographic ranges.

The strongest associations between climate and genetic variation occurred in contemporary populations. However, these associations showed the least parallelism among invasive populations, suggesting that adaptation trajectories can vary widely even when overall patterns are similar. In conclusion, the findings indicate that certain aspects of evolutionary adaptation, particularly at the genetic level, can be reasonably predicted.

Yet, individual genomic paths remain flexible and dependent on specific environmental contexts. Predictability appears to be most evident at the level of polygenic traits and large structural genetic variants.