Large scale phenotypic characterisation of Hierophis viridiflavus (Squamata: Serpentes): climatic and environmental drivers suggest the role of evolutionary processes in a polymorphic species

Abstract

Colour variability is largely widespread in the animal world as it is tightly associated with fitness and survivorship. Therefore, the drivers and implications of such variability have been of great interest for zoologists in the past decades. Reptiles are excellent models to investigate colour variations and expression under different conditions. Here, we focused on melanism occurrence in the two main lineages of Hierophis viridiflavus at the scale of the species distribution, by extracting available data from iNaturalist, a citizen science network, with the aim of detecting any pure effect of climate or local habitat on colour expression. Our analyses highlighted that habitat does not explain differences in phenotypes, whereas marked effects of geographic and climatic variables were detected. However, the observed climatic effects could be a proxy of the geographical distribution of the two groups, and thus the high occurrence of bright colourations in western populations of the eastern lineage could be addressed to an ongoing event of asymmetric gene flow in contact zones. The current distribution of phenotypes could be the outcome of the evolutionary history of the species combined with the geological history of the Mediterranean region. This investigation, though, is only preliminary and molecular analyses on highly variable regions of the genome are mandatory to address this issue.

Hybrid zones of Natrix helvetica and N. natrix: Phenotype data from iNaturalist and genetics reveal concordant clines and the value of species-diagnostic morphological traits

“…The present study is another example indicating that georeferenced photos from iNaturalist and similar Citizen Science platforms can provide valuable morphological data for research and may also enhance our knowledge of the distribution of the depicted taxa or hybrid zones (e.g., Fritz and Ihlow 2022;Pizarro et al 2023;Storniolo et al 2023). In this vein, the iNaturalist records from northwestern Germany, where grass snakes are rare, may help to clarify their taxonomic identity.…”

The tale of the black viper: distribution and bioclimatic niche modelling of melanistic Vipera aspis in Italy

“…On the other hand, populations of V. a. hugyi from the rest of its geographic range were subject to more complex patterns of gene flow which involved introgression with V. a. francisciredi (Barbanera et al, 2009). The melanistic phenotype in the latter populations could have independently arisen via random mutation or, it may be the product of historic introgression with V. a. francisciredi as found in other species (McRobie et al, 2019;Storniolo et al, 2023).…”

“…Melanism is the condition whereby individuals are characterised by darker pigmentation either as intraspecific polymorphism or as consistent variation between closely related taxa (Majerus, 1988;True, 2003;Clusella-Trullas et al, 2007b;Pernetta and Reading, 2009). Melanism can occur not only as an anomalous condition but also as a common form in some taxa (e.g., in Hierophis viridiflavus carbonarius; see Storniolo et al, 2023).…”

The Endangered Sardinian Grass Snake: Distribution Update, Bioclimatic Niche Modelling, Dorsal Pattern Characterisation, and Literature Review

“…The Sardinian grass snake is characterised by a high level of colour polymorphism (e.g., [ 15 , 25 , 28 ]). In reptiles, this interspecific colour variation may be correlated with geographic, bioclimatic, and environmental factors (e.g., [ 42 , 43 , 44 ]). Therefore, we carried out a tentative characterisation of the dorsal patterns, based on both personally acquired and citizen science photographs (the unavailability of photos taken in a standardized way for all snakes, has not allowed the use of computer-based colour assessment methods).…”