Genome-wide fluctuating selection under demographic cycling in Icelandic rock ptarmigan

Genome-wide allele frequency change in northeastern Icelandic rock ptarmigan (Lagopus muta) over 11 years shows strongly fluctuating loci, including CTNNA2, tracking demographic cycling.

• Why it matters: Multi-annual population cycles create shifting selection, but genomic signals are hard to separate from drift and directional selection without high-resolution time series data.
• What they did: Whole-genome sequences from 91 individuals were sampled across two peaks (2010, 2018) and two troughs (2007, 2013); SNP allele frequency changes were tested against a drift-and-sampling null model and clustered by correlated temporal trajectories.
• The result: Cluster trajectories fluctuated through time, with two clusters closely correlated with regional census (one significantly tracking the demographic cycle) and a smaller set changing monotonically; loci were spread across many chromosomes, implying rapid, widespread fluctuating selection.

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