![]() Because of the lack of recognition of prey handedness, this snake frequently fails in capturing the sinistral prey with its mouthparts, and thus this prey survives. Pareas iwasakii strikes at prey by tilting the head leftward only and attempts to capture by the same handling manner irrespective of the direction of snail coil (handedness) 5, which can either be clockwise (dextral) or counterclockwise (sinistral) ( Fig. Southeast Asian snakes of the genus Pareas typically specialize in the predation of snails by extracting the soft body from the shell 16, 17 and exhibit directional asymmetry in mandibular dentition 5. Directional asymmetry in the feeding apparatus of snail-eating specialists may represent a direct role of secondary asymmetry in predator-prey interactions which drive dynamics of ecology and evolution in living communities 5, 10, 11, 12, 13, 14, 15. This secondary asymmetry often plays crucial roles in interactions with the external environment, in contrast to internal asymmetry which results from primary asymmetry expressed in early development 8, 9. Left-right asymmetry has repeatedly evolved in the external morphology and behavior of many bilaterian animals which are symmetric in body plan 1, 2, 3, 4, 5, 6, 7. The novel warning, instead of sheltering, effect of sinistrality benefitting both predators and prey could further accelerate single-gene ecological speciation by left-right reversal. Under dextral-predation by Pareas snakes, adaptive fixation of a prey population for a reversal gene instantaneously generates a sinistral species because interchiral mating is rarely possible. Prey-handedness recognition should be advantageous for right-handed snail-eating snakes where frequently encountering sinistrals. iwasakii with little access to sinistrals on small peripheral islands attempts and frequently misses capturing a given sinistral. Whenever it strikes, however, the snake succeeds in predation by handling dextral and sinistral prey in reverse. We show that Pareas carinatus living with abundant sinistrals avoids approaching or striking at a sinistral that is more difficult and costly to handle than a dextral. However, whether the snake predator in turn evolves any response to prey reversal is unknown. Snails have countered the snakes’ dextral-predation by recurrent coil reversal, which generates diverse counterclockwise-coiled (sinistral) prey where Pareas snakes live. ![]() Southeast Asian snail-eating snakes ( Pareas) have more teeth on the right mandible and specialize in predation on the clockwise-coiled (dextral) majority in shelled snails by soft-body extraction. Specialized predator-prey interactions can be a driving force for their coevolution.
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