DOI: 10.5061/dryad.7h44j1019
title: Assessing hybrid vigor using the thermal sensitivity of physiological trade-offs in tiger salamanders

description: Hybridization between species affects biodiversity and population
 sustainability in numerous ways, many of which depend on the fitness of
 the hybrid relative to the parental species. Hybrids can exhibit fitter
 phenotypes compared to the parental lineages, and this ‘hybrid vigor’ can
 then lead to the extinction of one or both parental lines. In this study,
 we analyzed the relationship between water loss and gas exchange to
 compare physiological performance among three tiger salamander genotypes –
 the native California tiger salamander (CTS), the invasive barred tiger
 salamanders (BTS), and CTS x BTS hybrids across multiple temperatures
 (13.5°C, 20.5°C, and 23.5°C). We developed a new index of performance, the
 water-gas exchange ratio (WGER), which we define as the ratio of gas
 exchange to evaporative water loss (µL VO2/µL H2O). The ratio describes
 the ability of an organism to support energetically costly activities with
 high levels of gas exchange while simultaneously limiting water loss to
 lower desiccation risk. We used flow-through respirometry to measure the
 thermal sensitivity of metabolic rate and resistance to water loss of each
 salamander genotype to compare indices of physiological performance. We
 found that temperature had a significant effect on metabolic rate and
 resistance to water loss, with both traits increasing as temperatures
 warmed. Across genotypes, we found that hybrids have a higher WGER than
 the native CTS, owing to a higher metabolic rate despite having a lower
 resistance to water loss. These results provide greater insight into the
 physiological mechanisms driving hybrid vigor and offer a potential
 explanation for the rapid spread of salamander hybrids. More broadly, our
 introduction of the WGER may allow for species- or lineage-wide
 comparisons of physiological performance across changing environmental
 conditions, highlighting the insight that can be gleaned from multi-trait
 analysis of organism performance.
description: # Assessing hybrid vigor using the thermal sensitivity of physiological
 trade-offs in tiger salamanders ## Description of the data and file
 structure **Tiger\_salamander\_phys\_data.csv** This data includes the
 metabolic rate [vo2 (uL\*h<sup>-1</sup>)], resistance to water
 loss [resistance (s\*cm<sup>-1</sup>)], and water-gas exchange
 ratio [wger (uL\*hr<sup>-1</sup> vco2 /
 uL\*hr<sup>-1</sup> evaporative water loss)] of all
 salamanders. Other data in this file include the salamander ID assigned to
 individuals (ID), the genotype of each individual [genotype - hybrid,
 barred tiger salamander (BTS), and California tiger salamander (CTS)], the
 temperature treatment at which that individual was measured [temperature
 (°C)], and the mass of the salamander prior to experiments [mass (g)].
 Methods for collecting the above data are described in the manuscript.
 **Tiger\_salamander\_phys\_analysis.R** This file includes the R script
 used to conduct all analyses and create all figures presented in this
 study using the above dataset.