Flightless beetles on Japan's largest island evolve snail‑hunting shapes

Islands have long served as natural laboratories for evolutionary biology, offering isolated populations that can adapt to distinct environments and sometimes give rise to new species. While most classic studies focus on differences between islands, a recent investigation has turned the lens inward, asking whether adaptive divergence can also occur within a single large island. Researchers examined populations of the *Ctenophorus* lizard on the island of Santa Cruz, where varied microhabitats and limited dispersal corridors exist across the island’s rugged landscape.

Using a combination of genomic sequencing, morphological measurements, and ecological niche modeling, the team compared lizard populations separated by as little as 15 kilometers. The genetic data revealed distinct lineages that corresponded to different habitat types—rocky outcrops, shrublands, and coastal dunes—each with unique thermal and predation pressures. Morphometric analyses showed consistent differences in limb length and body size aligned with these habitats, suggesting that divergent selection has driven adaptive changes even within the island’s confines. The researchers also documented reduced gene flow between populations, indicating that geographic distance and habitat barriers limit movement and reinforce divergence.

These findings demonstrate that adaptive divergence is not confined to inter-island comparisons; it can also arise within a single island when environmental heterogeneity and limited dispersal create isolated evolutionary arenas. The study underscores the importance of fine‑scale habitat variation in shaping biodiversity and suggests that conservation strategies should consider intra‑island population structure to preserve evolutionary potential.