Tough as old boots: amphibians from drier habitats are more resistant to desiccation, but less flexible at exploiting wet conditions
Geographic variation in adult and embryonic desiccation tolerance in a terrestrial-breeding frog
Species everywhere are facing rapid climatic change, and we are increasingly asking whether populations will adapt, shift, or perish . There is a growing realisation that, despite limited within-population genetic variation, many species exhibit substantial geographic variation in climate-relevant traits. This geographic variation might play an important role in facilitating adaptation to climate change [2,3].
Much of our understanding of geographic variation in climate-relevant traits comes from model organisms [e.g. 4]. But as our concern grows, we make larger efforts to understand geographic variation in non-model organisms also. If we understand what adaptive geographic variation exists within a species, we can make management decisions around targeted gene flow . And as empirical examples accumulate, we can look for generalities that can inform management of unstudied species [e.g. 6,7]. Rudin-Bitterli’s paper  is an excellent contribution in this direction.
Rudin-Bitterli and her co-authors  sampled six frog populations distributed across a strong rainfall gradient. They then assayed these frogs and their offspring for a battery of fitness-relevant traits. The results clearly show patterns consistent with local adaptation to water availability, but they also reveal trade-offs. In their study, frogs from the driest source populations were resilient to the hydric environment: it didn’t really affect them very much whether they were raised in wet or dry environments. By contrast, frogs from wet source areas did better in wet environments, and they tended to do better in these wet environments than did animals from the dry-adapted populations. Thus, it appears that the resilience of the dry-adapted populations comes at a cost: frogs from these populations cannot ramp up performance in response to ideal (wet) conditions.
These data have been carefully and painstakingly collected, and they are important. They reveal not only important geographic variation in response to hydric stress (in a vertebrate), but they also adumbrate a more general trade-off: that the jack of all trades might be master of none. Specialist-generalist trade-offs are often argued (and regularly observed) to exist [e.g. 9,10], and here we see them arise in climate-relevant traits also. Thus, Rudin-Bitterli’s paper is an important piece of the empirical puzzle, and one that points to generalities important for both theory and management.
 Hoffmann, A. A., and Sgrò, C. M. (2011). Climate change and evolutionary adaptation. Nature, 470(7335), 479–485. doi: 10.1038/nature09670
 Aitken, S. N., and Whitlock, M. C. (2013). Assisted Gene Flow to Facilitate Local Adaptation to Climate Change. Annual Review of Ecology, Evolution, and Systematics, 44(1), 367–388. doi: 10.1146/annurev-ecolsys-110512-135747
 Kelly, E., and Phillips, B. L. (2016). Targeted gene flow for conservation. Conservation Biology, 30(2), 259–267. doi: 10.1111/cobi.12623
 Sgrò, C. M., Overgaard, J., Kristensen, T. N., Mitchell, K. A., Cockerell, F. E., and Hoffmann, A. A. (2010). A comprehensive assessment of geographic variation in heat tolerance and hardening capacity in populations of Drosophila melanogaster from eastern Australia. Journal of Evolutionary Biology, 23(11), 2484–2493. doi: 10.1111/j.1420-9101.2010.02110.x
 Macdonald, S. L., Llewelyn, J., and Phillips, B. L. (2018). Using connectivity to identify climatic drivers of local adaptation. Ecology Letters, 21(2), 207–216. doi: 10.1111/ele.12883
 Hoffmann, A. A., Chown, S. L., and Clusella‐Trullas, S. (2012). Upper thermal limits in terrestrial ectotherms: how constrained are they? Functional Ecology, 27(4), 934–949. doi: 10.1111/j.1365-2435.2012.02036.x
 Araújo, M. B., Ferri‐Yáñez, F., Bozinovic, F., Marquet, P. A., Valladares, F., and Chown, S. L. (2013). Heat freezes niche evolution. Ecology Letters, 16(9), 1206–1219. doi: 10.1111/ele.12155
 Rudin-Bitterli, T. S., Evans, J. P., and Mitchell, N. J. (2019). Geographic variation in adult and embryonic desiccation tolerance in a terrestrial-breeding frog. BioRxiv, 314351, ver. 3 peer-reviewed and recommended by Peer Community in Evolutionary Biology. doi: 10.1101/314351
 Kassen, R. (2002). The experimental evolution of specialists, generalists, and the maintenance of diversity. Journal of Evolutionary Biology, 15(2), 173–190. doi: 10.1046/j.1420-9101.2002.00377.x
 Angilletta, M. J. J. (2009). Thermal Adaptation: A theoretical and empirical synthesis. Oxford University Press, Oxford.
Ben Phillips (2019) Tough as old boots: amphibians from drier habitats are more resistant to desiccation, but less flexible at exploiting wet conditions. Peer Community in Evolutionary Biology, 100079. 10.24072/pci.evolbiol.100079
Revision round #12018-06-05
Decision round #1
This is a solid piece of work on an important and fascinating topic. It is a large dataset, is well reported, and the methods and analysis are appropriate. All reviewers saw the value of the work and none found any serious flaws. Consequently, all reviewers comments are in the nature of suggestions for improvement. I would encourage the authors to consider the reviewer's comments and, where improvements can be made, revise or clarify.
In particular, I thought Lohr's suggestion for the discussion to focus less on mechanism and more on broader implications (targeted gene flow, local adaptation, conservation) was good advice. Some meditation is warranted on how the plasticity you uncovered is relevant to these broader themes.
Gaitan-Espitia's review was particularly thorough, and he raises some interesting thoughts. Being a little more precise with your use of "selection" and being clear that you have evidence for local adaptation, rather than having measured selection per se will address several of his concerns. It would also be useful to report the random effects and residual variance for the fitted models. Doing so gives us more information about the model fit, but also provides information pertaining to maternal/paternal effects, and provides hints about how heritable the traits are. I also wondered about a formal heritability analysis, but felt that the manuscript is already substantial, and there might not be sufficient family groups in many of the populations for robust estimation of heritability. Some information on timing of oviposition would be useful in the methods (how synchronised was their breeding?). Finally, it is worth discussing briefly the role of behaviour (and sexual dimorphism in behaviour and traits) and how these might affect your conclusions.