Abstract
The adults of several anuran amphibian species deposit their eggs externally in mucus secretions that are purposely aerated to produce a froth nest. This type of clutch structure has evolved independently several times in this group and has been proposed to serve a variety and often simultaneous adaptive functions associated with protecting offspring from sub-optimal conditions during embryogenesis and later stages after hatching has occurred. These functions range from buffering offspring from sub-optimal temperatures and desiccation, to defending against predation and improving oxygenation. This versatility has likely helped facilitate the reduced reliance of egg development on water and thus the penetration of anurans into environments where permanent aquatic systems are not always available. In this paper, I review the hypothesised functions of the anuran froth nest as a mucus-based solution to the environmental challenges offspring face during development, with consideration of the functions of froth nest breakdown and communal froth nesting, as well.
Highlights
An overwhelming majority of anuran amphibians are oviparous, laying their eggs externally and often providing little or no parental care thereafter [1]
It does not appear that females of any froth nesting species supply eggs with additional frothed mucus to compensate for nest breakdown, though C. xerampelina females are known to return to where they are more vulnerable to fluctuating conditions and predators [71,121]
It must be appreciated that such a comparison would not take into consideration the ability of un-frothed mucus to provide protection against exposure to sub-optimal conditions and, as such, would not indicate the true effect of mucus aeration. This may only be achieved in species that produce both frothed and un-frothed nests, such as L. tasmaniensis [40], as most froth nesting species aerate the mucus at the same time it is being excreted, which would make ascertaining un-frothed mucus relatively difficult
Summary
An overwhelming majority of anuran amphibians are oviparous, laying their eggs externally and often providing little or no parental care thereafter [1] Upon oviposition, these eggs are exposed to a variety of risk factors, the interaction of which has driven the evolution of a diversity of clutch structures to improve the odds of survival during embryogenesis [2]. These eggs are exposed to a variety of risk factors, the interaction of which has driven the evolution of a diversity of clutch structures to improve the odds of survival during embryogenesis [2] One of these includes the purposeful incorporation of air bubbles into mucus to produce a frothy spawn body into which the eggs are deposited and complete development. I present experimental protocols that should be followed in order to streamline future studies in this field
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