Effects of Variation in Natural Algal and Detrital Diets on Larval Anuran (Hyla regilla) Life-History Traits

The quality of algae as food for larval Pacific treefrogs, Hyla regilla, varies among algal taxa. Tadpole diets were manipulated in enclosures in the South Fork Eel River, northern California. Enclosed tadpoles were fed ad libitum one of the dominant filamentous green algae (Cladophora, Zygnema, Mougeotia, or Oedogonium), the dominant cyanobacterium in the habitat (Nostoc), flocculent detritus, or a commercial reptile/amphibian food. Tadpoles in a control treatment were not fed but had access to seston which deposited in all enclosures. Diet treatment significantly affected weekly growth rates, as well as time to and weight at metamorphosis. Tadpoles grew most rapidly on filamentous green algae with diatom epiphytes and on the commercial food. Tadpoles fed epiphytized Cladophora metamorphosed 27.1% (11.7 days) sooner and weighed 38.9% (70 mg) more than tadpoles fed Cladophora cleaned of diatoms. In comparison to tadpoles fed Mougeotia, which does not support epiphytes, tadpoles fed epiphytized Cladophora metamorphosed 37.4% (19.7 days) sooner and weighed 31.6% (50 g) more. Tadpoles with the lowest growth rates were those filtering deposited seston or flocculent detritus. Observed changes in life-history traits with diet are assessed in relation to models which predict the optimal timing of metamorphosis.