Novel nematode in the grass snake (Natrix natrix)
Lizards and snakes often carry nematodes. Nematodes are commonly known as roundworms and are a speciose group with both free-living and parasitic species. Parasitic nematodes can have complex live cycles with a number of different host species, and reptiles typically become infected through their diet. Most parasitic nematodes of snakes and lizards primarily colonize the gastrointestinal tracts of their hosts. However, a recently discovered nematode appears to have evolved a novel life-style. In a common wall lizard (P. muralis) population in the French Pyrenees, we identified an undescribed nematode species that occurs in the reproductive tract of females and embryonic brain tissue. This localization of nematodes and the high genetic differentiation between lineages in different host animals suggests a vertical transmission from females to their offspring (Feiner et al. 2020. Am Nat). This was the first report of a transmission of a macro-parasite through the amniote egg. Here we report that a nematode closely related to the nematode found in the common wall lizard occurs in grass snake embryos. Embryonic tissue of ten individuals was subjected to a PCR screen for nematode 18S rDNA as described in Feiner et al. 2020. Am Nat. Four of these embryos (40 %) were tested positive and the detected 18S rDNA was Sanger-sequenced. Phylogenetic analyses suggest that the nematode 18S rDNA sequences from the grass snake and from the common wall lizard form a sister group and are more closely related to each other than to any other nematode with available genetic data.Further studies on this newly identified group of nematodes are expected to shed light on their evolutionary origin as well as on the distribution.