Feeding Ecology and Tetrodotoxin Resistance in Thamnophis sirtalis

Avila, Leleña A.

doi:10.18130/v3rv8s

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“…(2020) to calculate pairwise F ST differentiation at the DIV p‐loop in the program Arlequin (Excoffier and Lischer 2010) and used multiple regression of distance matrices (MRMs; see below) to test for a relationship between F ST differentiation in the DIV p‐loop and phenotypic differentiation in whole‐animal TTX resistance. Importantly, our analysis here of the DIV p‐loop does not account for other unknown factors that also contribute to variation in whole‐animal resistance (Avila 2015; Feldman et al. 2016).…”

Section: Methodsmentioning

confidence: 99%

The geographic mosaic of arms race coevolution is closely matched to prey population structure

et al. 2020

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Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co-occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of "trait remixing" in the geographic mosaic theory, the process by which nonadaptive forces dictate spatial variation in the interactions among species.

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