Abstract
Delayed or induced hatching in response to predation risk has been reported mainly in aquatic systems, where waterborne cues from predators and injured neighbouring eggs are available. Newly emerged larvae of the terrestrial predatory mite Neoseiulus womersleyi are vulnerable to predation by con- and heterospecific predatory mites, whereas their eggs are not. We examined whether N. womersleyi embryos delay hatching in response to artificial mechanical stimuli that simulates egg predation attempts. When embryos near the hatching stage were artificially stimulated every 5 min for 60 min, most stopped hatching for the duration of the 60-min period, whereas unstimulated embryos did not. Stimulated embryos resumed hatching when the treatment was stopped, and the proportion of hatched stimulated embryos caught up with that of unstimulated embryos within 120 min after stimuli stopped. Since hatching did not stop in response to changes in gravity direction, the effect of direct mechanical stimuli on the eggs was considered a proximate factor in delayed hatching. These results suggest that N. womersleyi embryos recognise immediate predation risk via mechanical stimuli, and delay hatching until the predation risk is reduced.
Highlights
Animals in quiescent stages cannot avoid immediate biotic risks by moving, they can avoid risks by regulating their advance toward the developmental stages
We demonstrate for the first time that arthropod embryos delay hatching in response to mechanical stimuli simulating predation attempts by egg predators, and discuss how predatory mite embryos cope with immediate predation risks
We demonstrated that nearly hatching embryos of predatory mites delayed hatching in response to periodic mechanical stimuli that simulated predation attempts by con- or heterospecific predatory mites
Summary
Animals in quiescent stages cannot avoid immediate biotic risks by moving, they can avoid risks by regulating their advance toward the developmental stages. Water-borne chemical cues emanating from predators and/or injured conspecific eggs in the same clutch are thought to be primal proximate factors affecting induced/delayed hatching[2,3,4,5] Such induced/delayed hatching in response to predator cues has yet been reported in arthropods including mites, some insect embryos synchronise hatching in response to vibrations produced by their mothers[6,7] or siblings[8], demonstrating the potential of arthropod embryos to detect and respond to mechanical stimuli. We demonstrate for the first time that arthropod embryos delay hatching in response to mechanical stimuli simulating predation attempts by egg predators, and discuss how predatory mite embryos cope with immediate predation risks
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