Federico Banfi

Several snakes possess cephalic appendages over their eyes and snouts, but their exact function remains largely unknown. In one aquatic species, such structures have been associated with a mechanosensory role, and this suggests that other horned snakes may have evolved analogous appendages. To be considered sensory structures, cephalic appendages should be highly innervated by specific cranial nerves like the trigeminal, and perhaps carry specialised integumentary sense organs. The identification of trigeminal branches reaching the cephalic appendages would be consistent with sensory capability of the structures. Here we tested whether the rostral appendage of the nose‐horned viper ( Vipera ammodytes ) could serve such a sensory function. We conducted an integrative anatomical exploration of the species' head and appendage using a combination of diffusible iodine‐based contrast‐enhanced micro computed tomography, classical histology and scanning electron microscopy and found support for our initial hypothesis. The rostral appendage of V. ammodytes is highly innervated by the ophthalmic branch of the trigeminal nerve, and we also found dermal sensory organs over the snake' snout and appendage scales. These findings suggest that a sensory function for cephalic appendages could also be possible in non‐aquatic species, hinting that more analogous sensory structures may have evolved across horned snakes and other reptile groups.

Melanism, the process of heavier melanin deposition, can interact with climate variation at both micro and macro scales, ultimately influencing color evolution in organisms. While the ecological processes regulating melanin production in relation to climate have been extensively studied, intraspecific variations of melanism are seldom considered. Such scientific gap hampers our understanding of how species adapt to rapidly changing climates. For example, dark coloration may lead to higher heat absorption and be advantageous in cool climates, but also in hot environments as a UV or antimicrobial protection mechanism. To disentangle such opposing predictions, here we examined the effect of climate on shaping melanism variation in 150 barred grass snakes (Natrix helvetica) and 383 green whip snakes (Hierophis viridiflavus) across Italy. By utilizing melanistic morphs (charcoal and picturata in N. helvetica, charcoal and abundistic in H. viridiflavus) and compiling observations from 2002 to 2021, we predicted that charcoal morphs in H. viridiflavus would optimize heat absorption in cold environments, while offering protection from excessive UV radiation in N. helvetica within warm habitats; whereas picturata and abundistic morphs would thrive in humid environments, which naturally have a denser vegetation and wetter substrates producing darker ambient light, thus providing concealment advantages. While picturata and abundistic morphs did not align with our initial humidity expectations, the charcoal morph in N. helvetica is associated with UV environments, suggesting protection mechanisms against damaging solar radiation. H. viridiflavus is associated with high precipitations, which might offer antimicrobial protection. Overall, our results provide insights into the correlations between melanin‐based color morphs and climate variables in snake populations. While suggestive of potential adaptive responses, future research should delve deeper into the underlying mechanisms regulating this relationship.

A phylogenetically diverse minority of snake and lizard species exhibit rostral and ocular appendages that substantially modify the shape of their heads. These cephalic horns have evolved multiple times in diverse squamate lineages, enabling comparative tests of hypotheses on the benefits and costs of these distinctive traits. Here, we demonstrate correlated evolution between the occurrence of horns and foraging mode. We argue that although horns may be beneficial for various functions (e.g. camouflage, defence) in animals that move infrequently, they make active foragers more conspicuous to prey and predators, and hence are maladaptive. We therefore expected horns to be more common in species that ambush prey (entailing low movement rates) rather than in actively searching (frequently moving) species. Consistent with that hypothesis, our phylogenetic comparative analysis of published data on 1939 species reveals that cephalic horns occur almost exclusively in sit-and-wait predators. This finding underlines how foraging mode constrains the morphology of squamates and provides a compelling starting point for similar studies in other animal groups.

Multiple hypotheses have been proposed to explain the variation of dorsal patterns observed in snakes, but no studies yet have tested them over broad taxonomic and geographical scales. The Viperidae offer a powerful model group to test eco-evolutionary processes that lead to disruptive and cryptic ornaments. We developed a database reporting dorsal ornamentation, ecological habitus, habitat features and climatic parameters for 257 out of 341 recognized species. Three patterns of dorsal ornamentation were considered: “zig-zag”, “blotchy” and “uniform” patterns. Phylogenetic comparative analyses were based on 11 mitochondrial and nuclear genes. Forty-eight species presented a zig-zag pattern type, 224 a blotchy pattern type and 32 a uniform pattern type. All the patterns showed a strong phylogenetic signal. Character phylogenetic reconstruction analyses suggested an ancestral state for blotchy ornamentation, with multiple independent evolutions of the other patterns. The blotchy pattern was more frequent in terrestrial species living in warm climates and sandy habitats, supporting the hypothesis of a disruptive function. The zig-zag pattern evolved independently in several isolated taxa, particularly in species living in cold climates and in dense vegetation or water-related habitats, supporting the hypothesis of disruptive and aposematic functions. Uniform coloration was particularly frequent in arboreal species, supporting the hypothesis of a cryptic function.