One of these things is not like the other: mixed predator cues result in lopsided phenotypic responses in a Neotropical tadpole

Many organisms have evolved to produce different phenotypes in response to environmental variation. Dendropsophus ebraccatus tadpoles develop opposing shifts in morphology and coloration when they are exposed to invertebrate vs vertebrate predators. Each of these alternate phenotypes is adaptive, conferring a survival advantage against the predator with which tadpoles were reared but imposing a survival cost with the mismatched predator. Here, we measured the phenotypic response of tadpoles to graded cues and mixed cues of both fish and dragonfly nymphs. Prey species like D. ebraccatus commonly co-occur with both of these types of predators, amongst many others as well. In our first experiment, tadpoles increased investment in defensive phenotypes in response to increasing concentrations of predator cues. Whereas morphology only differed in the strongest cue predator, tail spot coloration differed even at the lowest cue concentration. In our second experiment, tadpoles reared with cues from both predators developed an intermediate yet skewed phenotype that was most similar to the fish-induced phenotype. Fish are more lethal than dragonfly larvae and thus tadpoles responded most strongly to the more dangerous predator, even though cues of each predator were evenly mixed. We demonstrate that not only do tadpoles assess predation risk via the concentration of predation cues in the water, but they also produce a stronger response to a more lethal predator even when the strength of cues is identical.

Methods
The data are collected from digital photographs taken of anesthetized animals. 14 landmarks are placed around the tadpole to quantify its shape using the StereoMorph package in R. Tail spot coloration is measured using ImageJ.