Diversification of growth strategies as antipredator adaptations among closely related land snails

Predators may cause diversification of life‐history traits between closely related prey species or between ecotypes within a species. Although divergence of life‐history traits might result in speciation, evidence on this idea – the predator‐driven speciation hypothesis – is insufficient both theoretically and experimentally. Recent research proposed that two land snails, Karaftohelix editha and K. gainesi , and their shared predators, malacophagous ground beetles, distributed in northern Japan, can be an excellent model to explore the prey divergence via antipredator adaptations. Although these two species were indistinguishable using several neutral DNA markers and shared their distribution area and habitats almost completely, there were vast interspecific differences in various phenotypic traits, and almost all of them appeared to function as antipredator strategies. In this study, the ontogenetic growth patterns of K. editha and K. gainesi and their closely related species K. blakeana were investigated, which revealed several interspecific differences in growth strategies. For instance, K. editha increased shell weight and thickness even during the early juvenile stage, whereas K. gainesi drastically increased the growth rate of shell thickness around the late juvenile to adult stage. Karaftohelix blakeana linearly increased its shell weight and thickness throughout all growing stages. All interspecific differences discovered in this study may function efficiently as species‐specific antipredator strategies for each species.