Niche partitioning among three snail-eating snakes revealed by dentition asymmetry and prey specialisation

1. The level of dentition asymmetry in snail-eating snakes may reflect
their prey choice and feeding efficiency on asymmetric land snails. The
three species of Pareas snakes (Squamata: Pareidae) in Taiwan, which are
partially sympatric distribution on the island, provide a potential case
to test the hypothesis of niche partitioning and character displacement
with regard to dentition asymmetry and specialisation in feeding
behaviour. 2. In this study, behavioural experiments confirmed that P.
formosensis feeds exclusively on slugs, whereas P. atayal and P. komaii
consumed both. However, P. atayal more efficiently preys on land snails
than P. komaii, exhibiting a shorter handling time and fewer mandibular
retractions. 3. Micro-CT and ancestral character reconstruction
demonstrated the lowest asymmetry in P. formosensis (the slug specialist),
the highest dentition asymmetry in P. atayal (the land snail specialist),
and flexibility in P. komaii (the niche switcher): increased dentition
asymmetry when sympatrically distributed with the slug eater (character
displacement), and decreased asymmetry when living alone (ecological niche
release). 4. Ecological niche modelling showed that the distribution P.
formosensis is associated with the presence of slugs, while that of P.
atayal could be explained by the land snails. Combining the results from
morphology, phylogeny, behavioural experiments and ecological niche
modelling, we showed that competition in the sympatric region might have
facilitated character displacement among congeners, while absence of
competition in allopatric region has led to ecological niche release.