When to diapause or not to diapause? Winter predictability is not the answer
Diapause is not selected as a bet-hedging strategy in insects: a meta-analysis of reaction norm shapes
Winter is a harsh season for many organisms that have to cope with food shortage and potentially lethal temperatures. Many species have evolved avoidance strategies. Among them, diapause is a resistance stage many insects use to overwinter. For an insect, it is critical to avoid lethal winter temperatures and thus to initiate diapause before winter comes, while making the most of autumn suitable climatic conditions [1,2]. Several cues can be used to appreciate that winter is coming, including day length and temperature . But climate changes, temperatures rise and become more variable from year to year, which imposes strong pressure upon insect phenology . How can insects adapt to changes in the mean and variance of winter onset?
In this paper, Jens Joschinski and Dries Bonte  address this question by using a well conducted meta-analysis of 458 diapause reaction norms obtained from 60 primary studies. They first ask first if insect mean diapause timing is tuned to match winter onset. They further ask if insects adapt to climatic unpredictability through a bet-hedging strategy by playing it safe and avoid risk (conservative bet-hedging) or on the contrary by avoiding to put all their eggs in one basket and spread the risk among their offspring (diversified bet-hedging). From published papers, the authors extracted data on mean diapause timing and information on latitude from which they retrieved day length inducing diapause, the date of winter onset and the day length at winter onset.
They found a positive correlation between latitude and the day length inducing diapause. On the contrary they found positive but (very) weak correlation between the date of winter onset and the date of diapause, thus indicating that diapause timing is not as optimally adapted to local environments as expected, particularly at high latitudes. They only found weak correlations between climate unpredictability and variability in diapause timing, and no correlation between climate unpredictability and deviation from optimal diapause timing. Together, these findings go against the hypothesis that insects use diversified or conservative bet-hedging strategies to cope with uncertainty in climatic conditions.
This is what makes the study thought provoking: the results do not match the theory well. Not because of a lack of data or a narrow scope, but because diapause is a complex trait that is determined by a large array of physiological and ecological factors . Determining what are these factors is of particular interest in the face of the current climate change. This study shows what does not determine the timing of insect diapause. Researchers now know where to look at to improve our understanding of this key aspect of insect adaptation to climatic conditions.
 Dyck, H. V., Bonte, D., Puls, R., Gotthard, K., and Maes, D. (2015). The lost generation hypothesis: could climate change drive ectotherms into a developmental trap? Oikos, 124(1), 54–61. doi: 10.1111/oik.02066
 Gallinat, A. S., Primack, R. B., and Wagner, D. L. (2015). Autumn, the neglected season in climate change research. Trends in Ecology & Evolution, 30(3), 169–176. doi: 10.1016/j.tree.2015.01.004
 Tougeron, K. (2019). Diapause research in insects: historical review and recent work perspectives. Entomologia Experimentalis et Applicata, 167(1), 27–36. doi: 10.1111/eea.12753
 Bale, J. S., and Hayward, S. a. L. (2010). Insect overwintering in a changing climate. Journal of Experimental Biology, 213(6), 980–994. doi: 10.1242/jeb.037911
 Joschinski, J., and Bonte, D. (2020). Diapause is not selected as a bet-hedging strategy in insects: a meta-analysis of reaction norm shapes. BioRxiv, 752881, ver. 3 recommended and peer-reviewed by PCI Ecology. doi: 10.1101/752881
Bastien Castagneyrol (2020) When to diapause or not to diapause? Winter predictability is not the answer. Peer Community in Ecology, 100040. 10.24072/pci.ecology.100040
Evaluation round #2
DOI or URL of the preprint: 10.1101/752881
Version of the preprint: 2
Author's Reply, 21 Jan 2020
Decision by Bastien Castagneyrol, 16 Jan 2020
Dear Dr Joschinsky,
I re-read your paper entitled "Diapause is not selected as a bet-hedging strategy in insects: a meta-analysis of reaction norm shapes" as well a reviewers' comments and my own notes. I appreciated that you adapted the text and addressed most of previous comments. Because you did not provide a detailed reply to each comment (or maybe I did not find them), I assume that you disregarded some on purpose. Therefore, I am not sure that it is worth to bother the reviewers again and I will be pleased to recommend your paper for publication.
However, before that, I shall suggest a few very minor changes anyway : add units on Fig. 3 and labels in subpanels embedded within Fig1B and 1C). In addition, I may have missed it, but I did not find the raw data used in the meta-analysis (only meta-data in Table S1), neither in the supplementary materials nor in an open archive. Likewise, although the analyses are well described, details of codes are not available to the readers. Both are required before the paper is eventually recommended (see below).
Finally, I may have missed it, but I did not find the raw data used in the meta-analysis, neither in the supplementary materials nor in an open archive. Likewise, although the analyses are well described, details of codes are not available to the readers. Both are required before the paper is eventually recommended. Indeed, from PCI website: https://ecology.peercommunityin.org/about/ethics ▶ "Authors, recommenders for PCI Ecology and reviewers must ensure that the data for recommended articles are available to readers, through deposition in an open data repository, such as Zenodo, Dryad or institutional repositories, for example. Deposited data must have a digital object identifier (DOI). Authors, recommenders and reviewers must also check that details of the quantitative analyses (e.g. data treatment and statistical scripts in R, bioinformatic pipelines scripts, etc.) in the recommended articles are available to the readers, as appendices or supplementary online materials (in this case, the supplementary material must have a digital object identifier (DOI)), for example."
Best regards, Bastien Castagneyrol
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Evaluation round #1
DOI or URL of the preprint: 10.1101/752881
Version of the preprint: 1
Author's Reply, 10 Jan 2020
Decision by Bastien Castagneyrol, 04 Nov 2019
Dear Dr Joschinski,
Thank you for your submission to Peer Community in Ecology. Your manuscript ‘Diapause is not selected as a bet-hedging strategy in insects: a meta-analysis of reaction norm shapes’ has now been assessed by three reviewers.
The three reviewers, and myself, agree that you collected an impressive dataset that is analysed in a smart way. However, they also had concerns on some conceptual and methodological aspects of the paper. I share most of their views. Although it will require substantial work to clarify some points in the introduction and discussion sections, I believe that the reviewers’ comments can easily be addressed and will help improve the readers’ understanding.
In particular, they suggested to expand the definition of the key concepts and to clarify the presentation of the relationship between the reaction norm properties and insect evolutionary strategies, for this is very central to the paper.
Should you address the reviewers’ concerns and propose a revised version of your paper, I will be please to recommend it and write the recommendation text at the next round.
Best regards, Bastien Castagneyrol
I don’t want to duplicate what the reviewers wrote. I only have a bunch of technical comments
I found that the structure of the paper was a bit hard to follow. Some information is missing in the main text, and it is sometimes hard to retrieve it directly in the supplementary material. For instance, I strongly suggest that you give more details on ‘Calculation of mean and variance comosition’ (SM5, L65) in the main text. Typically, formula given in the main text cannot be fully understood without a deep look at the supplementary material.
I would like to commend you for your accurate reporting on the different steps of the meta-analysis. I did appreciate very much the sensitivity analysis consisting in re-running the models with different thresholds for winter onset. However, a couple of additional tests/metrics could have been provided to evaluate the publication bias and level of consistencies among studies (see e.g. Q5, Q8 in Nakagawa et al. BMC Biology (2017) 15:18, DOI 10.1186/s12915-017-0357-7). But this is probably fine at present.
On climatic data (SM5, L153) – I am surprised that you could not use the mean temperature directly. The actual daily mean can differ from the difference between the min and max if the distribution is skewed.
I would not have disregarded study ID as a random factor, for it accounts for multiple datapoints stemming from the same original paper. Likewise, it can be a concern if multiple study cases from the same researcher·s are confounded with the ‘Species’ random factor. I would be curious to see whether the results would have been different, should you keep these random factors.
In the results section, it is not completely clear what is the effect size (slope?) and what is the criterion you used to tell that the observed effects are small vs. large.
Several information is missing in the figure or figure captions. In particular Fig. 1 (see reviewers’ comments), but also Fig. 2 (colour scale) and Fig. 3 (see reviewers’ comments)