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Truncated Life History Underlies Rapid Local Adaptation in Island Rattlesnake Venom Expression.

Mark J Margres¹, Samuel R Hirst¹, Dylan G Gallinson¹

¹Department of Integrative Biology, University of South Florida, Tampa, FL 33620, USA.

Genome Biology and Evolution

|May 30, 2026

Summary

Rapid adaptation in island rattlesnakes primarily involved co-opting and truncating developmental changes in venom expression, rather than independent genetic shifts. This highlights how existing variation influences evolutionary trajectories.

Keywords:

Ontogeny chromatin accessibility gene expression structural variants transcription factor

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Area of Science:

Evolutionary Biology
Genomics
Herpetology

Background:

Snake venoms are complex mixtures of toxins that can shift during an individual's development (ontogeny).
These ontogenetic shifts in venom composition often correlate with dietary changes and are under strong selective pressure.
Understanding how populations adapt rapidly is key to evolutionary biology, with standing genetic variation and pre-existing developmental pathways being important factors.

Purpose of the Study:

To investigate the mechanisms driving rapid adaptive evolution in island versus mainland populations of eastern diamondback rattlesnakes (Crotalus adamanteus).
To determine if adaptation occurred via co-option of the developmental (ontogenetic) venom regulatory network, population-specific changes, or a combination.
To explore the role of standing genetic variation and pre-existing axes of variation in adaptation.

Main Methods:

Morphological measurements and comparative analysis of island and mainland rattlesnakes.
Venom proteomic analysis to assess toxin composition.
Transcriptomic (RNA-seq) and epigenomic (chromatin accessibility) analyses of venom glands.
Optical genome mapping for comprehensive genomic insights.

Main Results:

Island snakes were smaller than mainland counterparts, with a truncated ontogenetic venom expression shift.
Adult island snakes displayed juvenile-like expression patterns for key developmental regulators in venom glands.
Chromatin accessibility data predicted differential gene expression in venom loci that were co-opted during development.

Conclusions:

Rapid adaptation in island rattlesnakes predominantly resulted from the co-option and truncation of the existing ontogenetic venom shift.
Population-specific genetic changes played a secondary role in this adaptive divergence.
This suggests that rapid evolution may favor the repurposing of large, pre-existing developmental variation axes.