Form, function, foam: evolutionary ecology of anuran nests and nesting behaviour

Amphibians exhibit an incredible diversity of reproductive and life-history strategies, including various forms of nest construction and nesting behaviour. Although anuran amphibians (frogs and toads) are not known for their nests, nesting behaviour in this clade-broadly defined as a location chosen or constructed for eggs and young-is tightly linked to the amphibious lifestyle of this group. Transitions to increasingly terrestrial living have driven reproductive diversity in anurans, including the repeated, independent evolution of nests and nesting. Indeed, a core feature of many notable anuran adaptations-including nesting behaviour-is the maintenance of an aquatic environment for developing offspring. The tight link between increasingly terrestrial reproduction and morphological, physiological and behavioural diversity in anurans provides inroads for studying the evolutionary ecology of nests, their architects and their contents. This review provides an overview of nests and nesting behaviour in anurans, highlighting areas where additional work may be particularly fruitful. I take an intentionally broad view of what constitutes nesting to highlight what we can learn from thinking and researching comparatively across anurans and vertebrates more broadly. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

Safety Bubbles: A Review of the Proposed Functions of Froth Nesting among Anuran Amphibians

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.