A.N.Severtsov Institute of Ecology and Evolution, Russian Academy of Science, Leninsky pr. 33, Moscow 117071, Russia

Abstract

Behavioural reactions of single tadpoles of 4 anuran species inhabiting Moscow region (Bufo bufo L., Rana arvalis Nilss., R.lessonae Cameron and R.temporaria L.) to 11 natural chemical stimuli were studied using the choice between test-stimulus and clean water (the control). These stimuli were excretions of potential predators (fish Rutilus rutilus, Perca fluviatilis, Gymnocephalus cernuus, Perccottus glenii, larvae of dragonfly Aeshna grandis) or crayfish Astacus astacus, on alarm signal (extract of crushed conspecific tadpole), excretions of nonpredatory mollusc Limnaea stagnalis and conspecific tadpoles, or, for comparison, potentially food stimuli (extract of the silt from native pool and extract of boiled nettle Urtica dioica). It was shown that tadpoles avoided most of stimuli, especially excretions produced by potentially predators (fish R.rutilus, P.fluviatilis and P.glenii, dragonfly larvae) as well as an alarm signal. Besides, turning reaction were registered after tadpole entered the stimuli cloud. For B.bufo tadpoles threshold concentration of Perccottus excretions causing significant avoidance was estimated less than 50 g.min/l and that for crushed conspecific was less than 0, 13 g/l (one tadpole per 1 litre of water). Excretions of crayfish and extract of boiled nettle caused moderate avoidance. Excretion of fish G.cernuus evoke different reactions of different tadpole species. The same was found in experiments with excretions of conspecific tadpoles. Excretions of mollusc was indifferent stimuli for all four species, and silt from native water pool was mainly attractive. Thus, tadpoles of all four anuran species percept different natural chemical stimuli and react to many stimuli by avoidance. Intensive avoidance of chemical stimuli from predators by tadpoles can be beneficial for decreasing predation risk in natural populations.