Dwarf vipers on a small island: body size, diet and fecundity correlates

Abstract

Insular populations offer excellent opportunities to study the factors that influence phenotypes. We observed island dwarfism in a widespread snake, the nose-horned viper (Vipera ammodytes). Island vipers were ~20% smaller than mainland individuals. They also produced fewer and smaller offspring. In snakes, food availability has a positive influence on body size, fecundity and offspring size. Consequently, low energy intake is a plausible explanation for insular dwarfism. The diet of island vipers was principally represented by lizards and centipedes, whereas the most profitable prey items (e.g. rodents) were regularly found in the stomach of mainland vipers. Furthermore, the proportion of individuals captured with a full stomach and good body condition were lower on the island compared with the mainland. Thus, island vipers were likely to be experiencing permanent energy restriction, with cascading effects on adult body size and reproductive output. Large prey promotes high relative jaw length in snakes. Island vipers displayed smaller relative jaw length compared with mainland populations, suggesting that plasticity played a role in insular dwarfism. But the difference in relative tail length between island and mainland populations, a trait not subjected to food-induced plasticity, indicates local adaptation. Both plasticity and adaptation might influence the phenotype of island vipers.

Body size and body condition in the nose-horned viper (Vipera ammodytes): effects of sex and populations

“…Consequently, sexual size dimorphism (SSD) was detected only in SV vipers. This outcome mirrors the results from previous studies documenting a lack of, or a significant SSD with larger males in the nose horned viper depending upon study sites (Tomović et al 2002(Tomović et al , 2022Mebert et al 2017). Body condition results did not fully match those obtained with SVL.…”

“…The two other populations (Lazarev Canyon, Ibar River Gorge) are situated in markedly less disturbed rocky habitats where lizards are abundant. Smaller body size and lower mean body condition indicate that food availability and prey quality (lizards are less beneficial food items for vipers than micromammals; Zuffi et al 2010;Tomović et al 2022) might be lower compared to SV traditional agriculture landscape.…”

“…Preferred habitats of this species are xerothermic rocky places with shrubby vegetation cover, but nose-horned vipers can also be found in sparse forests and man-made stone walls (Agasyan et al 2009). Vipera ammodytes displays sexual dimorphism in tail length with males having longer tails, more subcaudal scales and larger body size, while females have wider ventral scales (Tomović et al 2002(Tomović et al , 2022.…”

“…Because environmental factors are likely to vary among sites (populations), differences in body size and body condition were expected. We also considered sex, because in this snake species, males tend to attain larger body size than females (Tomović et al 2022).…”

One Size Fits All—Venomics of the Iberian Adder (Vipera seoanei, Lataste 1878) Reveals Low Levels of Venom Variation across Its Distributional Range

“…Interestingly, significant correlations have been found between climatic and habitat conditions and differences in the frequency of consumption of the prey items V. seoanei mainly feeds on (i.e., amphibians, reptiles, and small mammals [ 50 ]). Such environment-related variation in diet composition, also observed in other Vipera species (e.g., Vipera ammodytes [ 54 ]; V. latastei [ 55 ]), suggests the presence of dietary differences across the species range.…”