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Genomic Data Revealed Distinct Continental and Baja California Cactus Wren Groups

Cactus wren standing in southeastern Arizona
Research · Genetics & genomics

A 2026 preprint found strong genomic differentiation between cactus wrens (Campylorhynchus brunneicapillus) from continental North America and birds from the Baja California Peninsula. The work was posted on bioRxiv on 26 March 2026 and has not yet been peer reviewed.

The researchers generated genomic data from cactus wrens sampled across Mexico and the southern United States and combined population-genetic analyses with ecological niche models. The genomic results separated a continental group from a peninsular group in Baja California. Individuals from Cataviña in central Baja California showed a small degree of assignment to the continental group, but the overall division between the two lineages was pronounced.

Both groups passed through strong historical bottlenecks

Reconstructions of demographic history indicated that both groups underwent severe reductions in effective population size around the Last Glacial Maximum. Effective population size is a genetic measure of how strongly drift acts in a population and is often smaller than the actual number of birds. Autosomal regions in both groups showed strong post-glacial recovery, but the Z chromosome in the Baja California group remained comparatively low through much of the Holocene. The authors suggest that sex-biased dispersal could have contributed to this difference, while noting substantial uncertainty among bootstrap replicates. Taken together with the strong genomic clustering, they argue that the peninsular taxon C. affinis should be treated as a species distinct from continental C. brunneicapillus.

Future climate projections differed between the groups

Ecological niche models also projected changes under future climate conditions for 2060–2080. Suitable areas along the Baja California coast declined in the projections, while suitable habitat for the continental group became more concentrated in the central part of its modelled range.

Sources and image credit

  1. Rodríguez-Rojas, P. C., Oceguera-Figueroa, A. F., Navarro-Sigüenza, A. G., & Vázquez-Miranda, H. (2026). Climate cycles drive demographic history and genomic divergence in cactus wrens (Campylorhynchus brunneicapillus) across North American warm deserts [Preprint]. bioRxiv. https://doi.org/10.64898/2026.03.24.714001Primary research preprint posted 26 March 2026; not peer reviewed. Genomic samples from Mexico and the southern United States revealed distinct continental and Baja California groups, reconstructed demographic bottlenecks and were combined with ecological niche models for past and future climates.

Image: Vickie J. Anderson / Wikimedia Commons — wild cactus wren in southeastern Arizona, USA, 8 November 2013; representative species image, not a sampled bird · CC BY-SA 4.0 · Source

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