Melanism in polymorphic terrestrial snakes: A meta-analysis and systematic review

Background and aim
Color polymorphic populations constitute excellent model systems for testing ecological and evolutionary hypotheses, as alternate colorations are associated with differences in various biological, behavioral, and life-history traits. Melanism is the most common and most obvious form of polymorphism. In reptiles in general (and snakes in particular), thermal melanism has been a popular hypothesis used to explain the appearance of black individuals. It suggests that a trade-off exists between superior thermoregulation and reduced protection through the loss of crypsis. Surprisingly, despite the growing body of literature available, to date there are only two qualitative reviews on the evolutionary significance of melanism in reptiles and no quantitative synthesis. We conducted the first systematic review and meta-analysis summarizing the current knowledge on melanism in polymorphic terrestrial snakes and synthesized the evidence for an adaptive advantage of the melanis..., We conducted an extensive literature search up to 30th of June 2023 and records were screened using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines (Page et al., 2021). We used Google Scholar and Web of Science databases, with no limit on the year of the publication. In Google Scholar we used the general search terms “melanism snake”, “melanistic snake”, \"snake\" AND \"melanism\" OR \"melanistic\" OR \"melanic\" and \"snake\" AND \"melanism\" OR \"melanistic\" OR \"melanic\", which amounted to 16295 results (Figure 1). In Web of Science, we used the search terms “melanism snake” and “melanistic snake”, giving us a further 116 results. We removed 31 records as duplicates while the rest were screened directly in the search window, therefore saving only the relevant articles. In the end our database contained 150 papers, from which we further excluded 41 which did not contain usable data (i.e. data used for the analyses was not part of the study), 26 in which da..., , # Melanism in polymorphic terrestrial snakes: A meta-analysis and systematic review

[https://doi.org/10.5061/dryad.n5tb2rc55](https://doi.org/10.5061/dryad.n5tb2rc55)

## Description of the data and file structure

The zip archive contains the data and R script used for the meta-analyses and meta-regressions regarding polymorphic terrestrial snakes.

The Excel file contains three sheets, the first represing data for frequency of melanistics and non-melanistcs, the second sheet contains data on frequency of melanistic individuals for each sex, while the last sheet contains body size data for menalistics and standard-colored individuals.

The sheet used for the meta-analysis of mean body (lnRR_size) contains some NA cells for standard deviations. During the analysis these were replaced with standard deviatons generated using ImputeSD. For detailed explanations please read the article.

Measurement units for body sizes were not recorded during the data extraction phase.

The Word document...