For amphibians that oviposit in temporary aquatic systems, there is a high risk of desiccation-induced offspring mortality when water evaporates prior to the completion of embryo or tadpole development. Such a strong selective pressure has led to the evolution of a variety of traits in reproducing females and their offspring to improve the odds of reproductive success when free-standing water is temporarily available. Herein, we describe an adaptive function of froth nesting in the Sandpaper Frog, Lechriodus fletcheri, as a possible maternal strategy for protecting embryos from the immediate risk of desiccating in highly ephemeral pools that frequently dry prior to hatching. Field observations revealed that embryos located near the core of nests remained alive and continued to develop for several days after becoming stranded out of water due to declining water levels, with embryo viability maintained long enough for additional rainfall to recharge pools and support hatching of tadpoles into water in some cases. In laboratory trials, the proportion of embryos surviving in nests exposed to desiccating conditions was positively correlated with nest volume, while the rate of water loss relative to nest mass declined, both of which are likely a function of reduced surface area relative to volume in larger nests. We suggest that the encapsulation of embryos within an aerated mucus shields them from desiccation by trapping moisture around their external surfaces. As embryos of L. fletcheri complete development rapidly, the ability for the froth nest to protect against desiccation for several days may allow embryogenesis to be completed largely out of water despite the larval phase not being terrestrial. These results suggest froth nesting has played an important role in facilitating this species' use of ephemeral habitats that most other amphibians with aquatic reproductive modes are incapable of exploiting.
Left High and Dry: Froth Nesting Allows Eggs of the Anuran Amphibian to Complete Embryogenesis in the Absence of Free-Standing Water
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John Gould, Jose Valdez, John Clulow, Simon Clulow; Left High and Dry: Froth Nesting Allows Eggs of the Anuran Amphibian to Complete Embryogenesis in the Absence of Free-Standing Water. Ichthyology & Herpetology 1 July 2021; 109 (2): 537–544. doi: https://doi.org/10.1643/h2020142
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