The seasonal energetics of three species of Australian tropical frogs (Anura: Hylidae)

Abstract

Some aspects of eco-physiology were examined for one cocoon forming (Cyclorana australis) and two non-cocoon forming frogs (Litoria caerulea and Litoria dahlia) that inhabit the wet-dry tropics. Seasonal ecology was examined to measure species’ activity and field body temperatures. Precipitation was a good predictor of frog activity. Species were most active in the wet season and least active during seasonal dry conditions. Cyclorana australis were dormant for seven months, and their body temperature varied little among seasons. However, L. caerulea and L. dahlii were generally active year-round, and their body temperatures varied among seasons. The digestive function and gastrointestinal flexibility of frogs was measured as a consequence of seasonal activity. Cyclorana australis ingested three and four fold more energy in the wet season than L. caerulea and L. dahlii, respectively, but ingested none when dormant, whereas L. caerulea and L. dahlii generally ingested energy year-round. Respiratory physiology was measured to examine for any seasonal changes in energy metabolism. Wet and dry season daily energy flow models were constructed based on those respiratory measurements and on estimated energy ingested in the field. Cyclorana australis incurred an energy deficit when dormant. However, the large amount of energy ingested in the wet season compensated for the dry season deficit. Furthermore, C. australis reduced the deficit by depressing energy metabolism to 35% of normal resting levels. Some of this reduction may have resulted from the significant down-regulation of the gastrointestinal tract. Cellular changes in the villi, specifically enterocyte volume, contributed to significant differences between wet season and dormant frogs. Litoria caerulea and L. dahlii ingested less energy in the dry than in the wet season, but the lower energy intake was offset by reduced energy expenditure. For these two species, expenditure was reduced as a consequence of low dry season body temperatures on respiratory metabolism, rather than metabolic depression.

Date of Award	Mar 2007
Original language	English
Supervisor	Keith Christian (Supervisor)