Egg-wrapping behaviour protects newt embryos from UV radiation

Abstract

Oviparous species that do not guard their eggs during development may suffer significant embryonic mortality. However, the way females lay eggs may help prevent this. For example, females of several newt species carefully wrap single eggs into leaves of aquatic vegetation in shallow water. Wrapping behaviour may protect eggs from predators and from mechanical damage. We hypothesized that egg-wrapping behaviour also protects newt embryos from the negative effects of ultraviolet (UV) radiation. In field experiments, we tested the effects of ambient levels of UV radiation on marbled newt, Triturus marmoratus, embryos exposed to sunlight. Of these embryos 95–100% died during the first 14 days of exposure. The eggs showed loss of their round shape, skin damage, oedemas and fungal infection. In contrast, during the same period, mortality of embryos protected by UV-blocking filters was only 20%. In laboratory experiments, we exposed marbled newt embryos to an artificially elevated intensity of UV-B radiation and tested the protective effect of leaves. The mortality of eggs wrapped in leaves and exposed to UV-B radiation was low and similar to that of unwrapped eggs that were shielded from UV-B radiation with a UV-blocking filter, whereas 119 of 120 unwrapped eggs exposed to UV radiation died within 5 days.