The dynamics of predation risk assessment: responses of anuran larvae to chemical cues of predators

1.  While the antipredator behaviour of prey has been well studied, little is known about the rules governing the predation risk assessment of prey. In this study, I measured the activity levels of predator-naive green frog ( Rana clamitans ) tadpoles during and after exposures to the chemical cue of predatory larval dragonflies ( Anax spp.). I then used the lengths of the time lags from the end of the cue exposures until the tadpoles returned to a control level of activity as an index of the perceived risk of the tadpoles. 2.  While tadpoles always responded upon exposure to the Anax chemical cue by strongly reducing their activity level, their perceived risk increased asymptotically over time during the initial period of the cue exposure. Tadpoles of all size classes perceived increasing risk in proportion to chemical cue concentration, but the length of time that tadpoles responded during cue exposure and the length of their post-exposure time lags decreased with increasing body mass. 3.  The results suggest that the perceived risk of green frog tadpoles varies over time and does not correspond directly to their behavioural response (i.e. activity level). However, their perceived risk does appear to vary in accordance with the predation risk associated with the Anax chemical cue and the reliability of the information from the cue, and therefore may be predictable.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73939/1/j.1365-2656.2008.01386.x.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/73939/2/JANE_1386_sm_Figs1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/73939/3/JANE_1386_sm_Figs2.pd

The influence of visual and tactile stimulation on growth and metamorphosis in anuran larvae

1.   Sensory modalities that allow tadpoles to assess their environment, and subsequently mediate their development, are not well understood. 2.   By putting clay model tadpoles into the tanks with live tadpoles we have enhanced tactile and visual stimuli for tadpoles of three species ( Rana sylvatica , Bufo americanus and Xenopus laevis ) in a controlled fashion. The goal was to determine whether visual and tactile cues in the absence of chemical signals influenced tadpole growth and development. 3.   The response to enhanced visual and tactile stimuli was strong in Rana , intermediate in Xenopus , but absent in Bufo tadpoles. Rana tadpoles that experienced both stimuli enhanced developed the fastest and metamorphosed at the smallest body size. Development was slower in the treatments with only one stimulus enhanced, and slowest in the controls. 4.   Our results suggest that tadpoles use both vision and mechanoreception for environment assessment, and that they are able to modify their growth and developmental rates in response to sensory enrichment. 5.   Tadpoles exposed to the combination of visual and tactile stimulation showed the highest whole-body content of the stress hormone corticosterone, suggesting that the enhanced stimuli were experienced as stressful. Corticosterone is known to synergize with thyroid hormone to promote metamorphosis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74112/1/j.1365-2435.2005.01051.x.pd