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Meta-analysis on reptile developmental plasticity

It’s been many years in the making with Lisa Schwanz and Vaughn Stenhouse, but finally our utterly massive meta-analysis on the role of incubation temperatures on phenotypic variability and survival is finally out in Biological Reviews! We collated effect sizes from 92 different species across all major reptile orders taken from 175 different studies that manipulated incubation temperatures! Extracting all these data was no small task, but has lead to some important insights that have implications for our understanding of how climate change will affect reptiles and the role of early thermal environments more generally on developmental plasticity in reptiles.

There are lots of new stuff in the paper but a pretty graph (only one so as not to spoil anything) and the major conclusions are summarised below!

(1) The magnitude of the phenotypic effect of incubation temperature is moderate to large across orders, trait categories and ages. There is no evidence that this effect is substantially larger in any single order of reptiles, although data are sparse for Rhynchocephalia (a species-poor order) and Crocodilia.

(2) Effects of incubation temperature can persist for many months post-hatching. Sampling is poor for ages >1 year, thus more data would be useful in increasing our confidence in the persistence of effects.

(3) The effect of temperature on incubation duration is much stronger than on any other trait category. Survival also stands out with particularly strong effect sizes, while the relative strength of other trait categories varies in ways that compels more detailed comparison of reaction norms.

(4) Temperature fluctuations in the incubation environment potentially decrease the phenotypic effect of different mean temperatures, particularly when the temperature differences between treatments are large (although not significantly). More data are needed from fluctuating temperature regimes to assess more rigorously whether this tendency is real, and to quantify the impact of increasing fluctuation.

(5) On average, increased temperature changes lead to greater phenotypic effects. Despite expectations that the exact impact of warming incubation temperatures will depend on the trait studied and the shape of the reaction norm, we can say that, on average, nest temperatures that increase by 4°C would have a greater impact on nearly all phenotypes than would an increase of 2°C.

(6) The effect of increased incubation temperature depends on the temperatures experienced (mid-temperature), and this dependence varies according to trait type. Survival, morphology and performance were affected more strongly at extreme temperatures compared to intermediate temperatures indicating that increasingly warmer nest temperatures will accelerate change in these traits. Thus, collecting phenotypic data from extreme incubation temperatures is important.

Figure 1 – An example of how the average temperatures of pairwise treatments and their temperature difference impact the magnitude of effect for incubation duration.

(7) Substantial variation in the magnitude and direction of the phenotypic effects of incubation temperature remain unexplained. Future research should quantify the shape of the reaction norm to explore interspecific variation along with how parental and/or ecological effects might mediate responses.

If you want to find out more have a read of the paper!


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