Cocoon Formation and Structure in the Estivating Australian Desert Frogs, Neobatrachus and Cyclorana

Abstract

Formation of a cocoon during aestivation is described for the Australian hylid frogs Cyclorana maini, C. novaehollandiae and C. platycephala, and the myobatrachid frogs Neobatrachus aquilonius, N. centralis, N. fulvus, N. kunapalari, N. pelobatoides, N. sudelli, N. sutor and N. wilsmorei. At the onset of aestivation, these frogs assume a 'water-conserving' posture and become inactive. A thin, transparent cocoon is observed to form within a week of onset of inactivity, and becomes progressively thicker and more opaque. The cocoon covers the entire body surface, including mouth, eyes and cloaca, except for the narial openings. The cocoon consists of an accumulation of multiple layers of single-cell-thick sheets of outer epidermal cells, formed at regular periods of about every two days (Cyclorana) to four days (Neobatrachus), that correspond to the normal shedding frequency. Each layer of the cocoon has a thickness of about 0.4 mu m (Cyclorana) to 0.6 mu m (Neobatrachus). The thickness of the cocoon and the number of layers increase progressively with duration of aestivation.