Genomic signatures of positive selection and relaxed selective constraints associated with convergent dietary specialisation
Year: 2026
Type: preprint
Abstract: Island radiations provide ideal frameworks for studying the molecular basis of convergent evolution. The rapid diversification of Dysdera spiders in Canary Islands provides a striking example, with repeated dietary shifts towards specialisation on woodlice, accompanied by morphological, metabolic, and behavioural modifications that facilitate the exploitation of this heavy-metal-rich prey. Here, we investigate two independent events of dietary specialisation on different islands. By analysing six high-quality genome-assemblies, including three newly generated in this study, we investigate the genomic signals of positive selection and relaxed selection in protein-coding genes, upstream regulatory regions, and gene family turnover rates. We detected signatures of positive selection associated with the two specialists, accompanied by a twofold increase in gene loss rates relative to generalist ancestors. Notably, positive selection targeted a smaller, functionally coherent set of genes, potentially involved in detoxification likely through heavy metal excretion. In contrast, relaxation of selection affected a broader set of genes associated with functions that may have become dispensable under the new dietary regime. Furthermore, we found contractions in gene families associated with vesicular transport, potentially reflecting a reduced reliance on vesicle-mediated metal accumulation. Overall, our findings suggest that similar ecological pressures can drive parallel, yet non-identical, adaptive and non-adaptive responses, pointing to partially predictable evolutionary trajectories in an island radiation.
Institutions: Universitat de Barcelona, Universidad de La Laguna
Language: English
Subfield: Genetics
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7225414816