Population structure, phenology and ecology of a community of snakes (Reptilia Serpentes) in Migliarino San Rossore Massaciuccoli Regional Park

Gli studi sulle comunità naturali di serpenti sono in generale poco diffusi, sia per la naturale elusività dei serpenti sia per i lunghi tempi di ricerca necessari per raccogliere dati di base. Studi e ricerche di questo tipo in Europa e specialmente in Italia sono di fatto limitati a pochissimi casi. Sono inoltre poco note le strutture di popolazione, il rapporto sessi e la frequenza di incontro quando diverse specie di serpenti vivono in uno stesso sito e in uno stesso habitat. Si è pertanto voluto verificare la ricchezza specifica, la struttura di comunità e la fenologia di un popolamento naturale di serpenti in un'area costiera Mediterranea. La ricerca si è svolta sperimentalmente in un'area ecotonale della porzione costiera della provincia di Pisa, all'interno del Parco regionale Migliarino San Rossore Massaciuccoli, tra settembre 2016 e maggio 2017 (1000 m di lunghezza × 2 m di profondità, orientamento Nord-Sud; zona di Tombolo, a Sud del Podere Lamone). L'area è caratterizzata dal confine tra il margine arbustato di un bosco misto (leccio, pino) e una vasta area incolta con prevalenza di piante erbacee annuali. Il terreno è costituito da depositi alluvionali recenti. Sono state considerate tre specie di Colubridi (biacco maggiore, Hierophis viridiflavus; natrice dal collare, Natrix natrix; saettone comune, Zamenis longissimus) e una di Viperidi (vipera comune, Vipera aspis). Ho rilevato la lunghezza corporea (SVL = snout to vent length o capo-tronco) e la massa corporea di tutti gli individui catturati (mm e g). Degli individui catturati o osservati di ogni specie sono stati registrati posizione (mediante GPS), orario e data per associare i dati di presenza con le caratteristiche di habitat della zona. In totale ho catturato 11 biacchi (di cui 1 ricattura), 23 natrici (di cui 4 ricatture), 3 saettoni (nessuna ricattura), 45 vipere (17 ricatture), per un totale di 82 catture e 22 ricatture. Ho poi analizzato i dati di campo di precedenti ricerche nella stessa zona, svolte tra il 1992 e il 2010, per verificare eventuali variazioni dimensionali e ponderali delle specie in esame. In totale ho considerato 38 biacchi, 19 natrici, tre saettoni, 114 vipere, per un totale complessivo di 174 catture (tra neonati, giovani e adulti). Ho considerato per le analisi i soli adulti. La taglia di Hierophis viridiflavus varia da 1002 ± 104 mm nei maschi a 904 ± 29 mm nelle femmine; la massa corporea da 295 ± 76 g nei maschi a 176 ± 30 g nelle femmine (P < 0,005). La taglia di Natrix natrix varia da 685 ± 65 mm nei maschi a 902 ± 140 mm nelle femmine; la massa corporea da 125 ± 40 g nei maschi a 350 ± 155 g nelle femmine (P < 0,001). La taglia di Vipera aspis varia da 575 ± 61 mm nei maschi a 567 ± 63 mm nelle femmine; la massa corporea da 122 ± 39 g nei maschi a 143 ± 56 g nelle femmine (P > 0,05). I saettoni (solo maschi) misurano 1031 ± 172 mm e pesano 257 ± 102 g. In generale si osserva che le le vipere sono di dimensioni e massa corporea simili, mentre i maschi dei biacchi sono notevolmente maggiori (svl, massa) rispetto alle femmine e al contrario le natrici hanno le femmine molto più lunghe e pesanti dei maschi. Le catture/osservazioni sono state significativamente maggiori tra la fine dell'inverno e gli inizi della primavera (marzo-maggio) per tutte le specie, con maggiore frequenza nel biacco e nella vipera, che è quasi esclusivamente l'unica a essere attiva anche in estate-inizio autunno. La distribuzione delle catture/osservazioni lungo la fascia ecotonale è complessivamente omogenea per biacco, natrice e vipera. Non ho considerato i dati relativi al saettone in quanto troppo limitati. Complessivamente è emerso che le specie di serpenti più frequenti sono biacco e vipera (termofile e abbastanza euriecie), mentre la natrice e il saettone sono rispettivamente più collegate a zone umide e a boschi mesofili o termo-igrofili (meno rappresentati nell'area di studio). Va notato, come spesso ipotizzato o dimostrato in letteratura, che la comunità studiata è composta quasi esclusivamente da adulti di taglia medio grande, a conferma di una comunità di serpenti stabile. Ad esclusione della vipera comune, di cui sono stati ricatturati diversi individui, gli individui delle altre specie sono stati catturati in media una sola volta. Questo suggerisce che gli spazi vitali di biacco, natrice dal collare e saettone coprono un'area sicuramente più ampia di quella considerata, mentre è probabile che diversi individui di vipera comune abbiano nell'area di studio una parte rilevante del proprio territorio

A long-term study of a snake community in north-western Tuscany (central Italy): population structure and density patterns

We analysed a snake species community of a Mediterranean 0.2 ha ecotonal area during a 21 year time span, monitoring two colubrid and one viperid snake species. We carried out analyses in seven years (1997, 1999, 2002, 2004–2005, 2016–2017) that had similar sampling efforts and, in the last two years of short-term monitoring, we applied a recently proposed monitoring protocol of the Italian Environment Ministry. In total, we captured 172 distinct individuals, 61 whip snakes (Hierophis viridiflavus), 26 barred grass snakes (Natrix helvetica) and 85 asp vipers (Vipera aspis). Regarding the long-term monitoring period, whip snakes were captured on average about nine times per year, grass snakes were captured four times per year and asp vipers were found 12 times per year. Captures decreased in whip snakes, while increased in grass snakes and remained constant in asp vipers. In 2016 and 2017, we captured 10 whip snakes, 19 grass snakes and 31 asp vipers. Density estimates of snake species (0.5 H. viridiflavus/ha, 0.3 N. helvetica/ha and 0.7 V. aspis/ha) differ, to a certain extent, from published results for some other areas of central, northern and western Europe, perhaps depending on the approach applied for habitat suitability estimation. The average body size between two years differed neither for whip snakes nor for grass snakes, but it decreased significantly in asp vipers

Species-Specific Spatial Patterns of Variation in Sexual Dimorphism by Two Lizards Settled in the Same Geographic Context

The evolution of sexual dimorphism (SD) results from intricate interactions between sexual and natural selections. Sexually selected traits are expected to depend on individual condition, while natural selected traits should not be. Islands offer an ideal context to test how these drivers interact with one another, as the size is a reliable proxy for resource availability. Here, we analysed SD in body size (snout-vent length) and head shape (assessed by geometric morphometric) in two species of lizards (Podarcis muralis and P. siculus) inhabiting the Tuscan archipelago (Central Italy). We found a strong SD variation among islands in both species. Furthermore, in P. muralis emerged some significant correlations between SD and island size, supporting the occurrence of possible effects of individual condition on SD. By contrast, SD in P. siculus followed opposite trajectories than in P. muralis, suggesting that in this species, natural selection could play a major role as a driver of SD. Our findings show that natural and sexual selection can interact in complex ways, and the responses are species-specific. Therefore, spatial patterns of variation in SD may strongly differ among species, even when they settle in the same geographic contest

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

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

Patterns of variations in dorsal colouration of the Italian wall lizard Podarcis siculus

Research on animal colouration has grown exponentially in the last decade thanks to multidisciplinary approaches. Most studies are focused on trade-offs between communication and mimicry, which represent the two main constraints and drivers of the evolution of body colourations. Reptiles are excellent model species for investigating this field of study and lizards in particular show great variability of body colourations and their functions. We studied the lizard Podarcis siculus, analysing the variations of dorsal colour of three populations and obtained clear patterns of seasonal and ontogenetical variation of dorsal colour. According to baseline colour, males were greener and brighter than females, although no difference in saturation was recorded. According to seasonal variations, analyses showed that both sexes significantly vary in colour over the year: males reached higher peaks of hue and saturation later than females during spring, while females showed higher peaks of brightness and reached earlier similarly to hue and saturation. Ontogenetic variations were recorded only in males, which become greener, less bright and saturated with growing size. Therefore, our results suggest the occurrence of two opposing strategies in colour expression between sexes: males' dorsal colouration plays a major role in communication, while females are more crypsis-oriented

Condition- and context-dependent variation of sexual dimorphism across lizard populations at different spatial scales

The evolution of sexual dimorphism (SD) is driven by intricate interplays between sexual and natural selection. When it comes to SD variation within populations, however, environmental factors play a major role. Sexually selected traits are expected to be strongly dependent on individual body condition, which is influenced by the local environment that individuals experience. As a consequence, the degree of SD may also depend on resource availability. Here, we investigated the potential drivers of SD expression at two sexually dimorphic morphometric traits, body size (snout vent length) and head shape (head geometric morphometrics), in the Italian wall lizard (Podarcis siculus). We assessed the existence of condition- and context-dependent SD across ten islands of the Aeolian archipelago (southern Italy), at within- and among-population scales. We observed strong geographical variation of SD among islands, and tested three potential SD predictors related to resource availability (individual body condition, ecosystem productivity, temperature). Body condition and ecosystem productivity were the main drivers of body size SD variation, and body condition was also the main driver for head shape SD. Our results highlight that the expression of SD in the Italian wall lizard is both condition- and context-dependent. These results are congruent at within- and among-populations scales highlighting that spatial multi-scale analysis represents a useful approach to understand patterns of SD expression