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Abstract The Geographic Mosaic Theory of Coevolution predicts that coevolutionary arms races will vary over time and space because of the diverse ecological settings and population histories of interacting species across the landscape. Thus, understanding coevolution may require investigating broad sets of populations sampled across the range of the interaction. In addition, comparing coevolutionary dynamics between similar systems may reveal the importance of specific factors that structure coevolution.Here, we examine geographic patterns of prey traits and predator traits in the relatively unstudied interaction between the Sierra garter snake (Thamnophis couchii) and sympatric prey, the rough‐skinned newt (Taricha granulosa), Sierra newt (Ta. sierrae) and California newt (Ta. torosa). This system parallels, in space and phenotypes, a classic example of coevolution between predatory common garter snakes (Th. sirtalis) and their toxic newt prey exhibiting hotspots of newt tetrodotoxin (TTX) levels and matching snake TTX resistance.We quantified prey and predator traits from hundreds of individuals across their distributions, and functional trait matching at sympatric sites.We show strong regional patterns of trait covariation across the shared ranges ofTh. couchiiand newt prey. Traits differ significantly among localities, with lower newt TTX levels and snake TTX resistance at the northern latitudes, and higher TTX levels and snake resistance at southern latitudes. Newts and snakes in northern populations show the highest degree of functional trait matching despite possessing the least extreme traits. Conversely, newts and snakes in southern populations show the greatest mismatch despite possessing exaggerated traits, with some snakes so resistant to TTX they would be unaffected by any sympatric newt. Nevertheless, individual variation was substantial, and appears to offer the opportunity for continued reciprocal selection in most populations.Overall, the three species of newts appear to be engaged in a TTX‐mediated arms race withTh. couchii. These patterns are congruent with those seen between newts andTh. sirtalis, including the same latitudinal gradient in trait covariation, and the potential ‘escape’ from the arms race by snake predators. Such concordance in broad scale patterns across two distinct systems suggests common phenomena might structure geographic mosaics in similar ways.
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This content will become publicly available on January 28, 2026
Tetrodotoxin, fungal pathogen infection, and bacterial microbiome associations are variable in the skin microecosystems of two Taricha newt species
A diverse metabolome exists on amphibian skin that mediates interactions between hosts and skin microbiomes. Tetrodotoxin is one such metabolite that occurs across a variety of taxa, and is particularly well studied in newts of the genusTarichathat are susceptible to infection with chytrid fungi. The interaction of tetrodotoxin with the skin microbiome, including pathogenic fungi, is not well understood, and here we describe these patterns across 12 populations ofTaricha granulosaandT. torosain Washington, Oregon, and California. We found no correlation of TTX andBatrachochytrium dendrobatidis(Bd) infection in eitherT. granulosaorT. torosa, a pattern inconsistent with a previous study. In addition, TTX, but not Bd, was significantly correlated with the skin microbiome composition inT. granulosa. InT. torosa, however, Bd, but not TTX, was correlated with the skin microbiome structure. The relationship between TTX and skin microbiome composition differed between species, with significant correlations observed only inT. granulosa, which exhibited higher TTX concentrations. We also detected significantly higher abundances of bacterial taxa (e.g., Pseudomonadaceae) associated with TTX production in newts with higher skin TTX. These taxa (ASVs matchingAeromonas, Pseudomonas, Shewanella, andSphingopyxis) were associated with all body sites of previously sampledT. granulosa, but not found in soil samples. Our results suggest that toxins can shape the newt skin microbiome and may influence pathogen infection through indirect mechanisms, as TTX showed no direct inhibition of Bd orB. salamandrivoransgrowth.
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- Award ID(s):
- 1845634
- PAR ID:
- 10656756
- Publisher / Repository:
- Frontiers
- Date Published:
- Journal Name:
- Frontiers in Amphibian and Reptile Science
- Volume:
- 2
- ISSN:
- 2813-6780
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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