Citizen Science, taxonomy and grass snakes: iNaturalist helps to clarify variation of coloration and pattern in Natrix natrix subspecies

Abstract

We used a dataset of georeferenced photos of 5,751 grass snakes from iNaturalist to evaluate subspecific variation of Natrix natrix in coloration and pattern. Our results provide evidence that all four genetically delineated subspecies differ morphologically, although unstriped individuals of N. n. vulgaris are difficult to tell apart from the nominotypical subspecies. The iNaturalist dataset shows that the frequency of dark body coloration increases from south to north and from west to east. This trend is both concordant with taxonomic variation (the easternmost subspecies, N. n. scutata, being the darkest taxon) and variation within the same subspecies (in N. n. natrix and N. n. scutata more northern populations harbor more dark or melanistic individuals than more southern populations). Although available characters were limited to coloration and pattern traits, our study suggests that photo material from iNaturalist and similar platforms can be a valuable data source for studies on morphological variation. However, investigations using such databases can only supplement, but not replace, studies using museum material because only then measureable, meristic and genetic characters will be accessible.

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.…”

“…In this region, a southern subspecies of the common grass snake (N. n. vulgaris; see Asztalos et al 2021b) meets a southern subspecies of the barred grass snake (N. h. sicula). Some, but not all, populations of N. n. vulgaris comprise individuals with two dorsal stripes (Fritz and Ihlow 2022), and we identified many putative hybrids in this region due to the presence of back stripes combined with traits otherwise characteristic for N. helvetica (side bars, lacking dark anterior occipital spot, size of dark posterior occipital spot, etc.). However, the high percentage of putative hybrids with back stripes exceeds by far that of N. n. vulgaris with back stripes from Austria and Italy.…”

Temporal stability of the hybrid zone between Calocitta magpie‐jays revealed through comparison of museum specimens and iNaturalist photos

“…Still, the increasing geographic coverage of photographic databases offers a trove of information on geographic variation for the study of hybrid zones, speciation, and systematics (Leighton et al, 2016). iNaturalist has generally been used more for outreach and education (Aristeidou et al, 2021) and investigations of regional species diversity and species geographic ranges (Rosa et al, 2022) than for ecological and evolutionary studies, but this is now changing (Aguillon & Shultz, 2022; Bolt et al, 2022; Fritz & Ihlow, 2022; Putman et al, 2021). Analytical methods for tapping the full potential of citizen science photos (Hantak, Guralnick, Zare, et al, 2022; Leighton et al, 2016; Schiller et al, 2021), and better methods for imaging wildlife and specimens, including camera traps (Steenweg et al, 2017) and 3D models (Medina et al, 2020), will facilitate future studies bringing together photos and specimens in biodiversity science.…”

“…Continuing advances in data aggregation offer an opportunity to expand temporal comparisons of hybrid zones from opportunistic studies of historically well‐sampled clines to broader efforts. Specifically, the growth of online aggregates of photos (e.g., Google Images; Leighton et al, 2016) and citizen science platforms like iNaturalist offer crowd‐sourced, georeferenced voucher photos, which contain records of modern hybrid individuals (Minor et al, 2022) and potentially scorable hybrid traits (Fritz & Ihlow, 2022). Additionally, the continued aggregation of natural history collection databases (Hedrick et al, 2020; Peterson & Gordillo‐Martínez, 2002) means researchers can assemble densely sampled transects by combining specimens from multiple museums, often without the need to visit them thanks to continuing efforts toward photo‐digitization (Blagoderov et al, 2012; Medina et al, 2020).…”

Erythrism in the Eastern Grass Snake, Natrix natrix (Linnaeus, 1758)

“…Moreover, after many hundreds of personally observed individuals of N. natrix in the field, these three individuals were the only ones detected by us. Also, according to personal communication with Uwe Fritz (December 2021), he himself has never recorded a similar phenotype in the field or while investigating colour variability of more than 5,700 Grass Snakes based on citizen science data (Fritz and Ihlow 2022). However, an online search revealed one additional erythristic individual, a N. natrix from Ireo, Samos Island, Greece (37.677°N, 26.873°E, 28 August 2019) posted by Ivo Peranić who subsequently provided detailed information to us (Fig.…”