Tadpoles rely on mechanosensory stimuli for communication when visual capabilities are poor

Abstract

The ways in which animals sense the world around them change throughout development. Young of many species have absent or limited visual capabilities, but still make complex decisions about individuals with whom they interact. Poison frog tadpoles display complex social behaviors that have been suggested to rely on vision despite a century of research indicating tadpoles have poorly-developed visual systems. Here, we examined visual system development in tadopoles of the Mimetic Poison Frog (Ranitomeya imitator) that use begging displays to stimulate egg feeding from their mothers. Neural activation in the retina increased in begging metamorphic tadpoles, but not in begging pre-metamorphic tadpoles. Molecular profiling of active eye neurons during begging identified numerous differentially expressed development-related transcripts, suggesting that developmental stage, not begging, was driving gene expression profiles. Using the neural tracer neurobiotin, we found that connections between the eye and brain proliferate during metamorphosis, with little retinotectal connections in recently-hatched tadpoles. To assess visual capabilities of tadpoles, we used a light/dark preference assay in early, middle, and late stages. All tadpoles showed a preference for the dark side, but the strength of preference increased with developmental stage and eyes were not required for this behavior. Taken together, these data indicate visual ontology of poison frog tadpoles is similar to that of other frogs, with poor visual capabilities at hatching and immense morphological and physiological changes occurring during metamorphosis. More broadly, this highlights the importance of multimodal cues, including photodetection via the pineal structure, in tadpole social interactions.

Dopamine neurons govern olfactory-gated infant begging behavior

“…We initially hypothesized that recognition of a potential caregiver would rely on vision rather than olfaction based on previous studies in the Strawberry poison frog ( Oophaga pumilio ) showing visual cues are necessary for tadpole begging [23] and influence mate choice later in life [24]. However, newborns and young of many species have limited or absent visual capabilities at birth/hatching [25], including tadpoles [26]. We found tadpoles would beg to a control object if paired with female conspecific odors and blind tadpoles still display begging behavior.…”

“…At the conclusion of the trial, the female was quickly removed from the arena, the light turned off, and the tadpole incubated in the arena for 30 min. We collected and processed brains as previously described for immunohistochemistry and phosphoTRAP [26].…”

“…To examine begging behaviors, we exposed naive tadpoles to reproductive females as described previously [26]. After an acclimation period, tadpoles were exposed to a reproductive R. imitator female and allowed them to interact for 20 minutes.…”

Proopiomelanocortin (POMC) is a negative regulator of tadpole aggression through opioid receptor signaling

“…Slides were blocked with a blocking solution (1X PBS, 0.2% BSA, 0.2% Triton-X, 5% NGS) at room temperature for 1 hour. Slides were then incubated in a mix of antibodies to detect pS6 (rabbit anti-pS6 (Invitrogen, cat #44-923G) at 1:500, validated in poison frogs previously [50]), and either vasopressin (pre-incubated with mesotocin, (mouse PS45, a gift from Hal Grainger)), or oxytocin (1:5000, MAB5296; Millipore Sigma, Burlington, MA, USA; validated in poison frogs previously [18]). After several washes in 1X PBS, slides were incubated in a mix of fluorescent secondary antibodies (1:200 AlexaFluor 488 anti-rabbit and AlexaFluor 594 anti-mouse in blocking solution) for two hours.…”

“…PhosphoTRAP data was first processed by aligning trimmed reads to an R.imitator transcriptome and a count table was generated as previously described [50]. In order to determine differentially expressed genes from the phosphoTRAP analysis, a paired t-test was run comparing count values of each transcript between the INPUT and immunoprecipitated (IP) samples.…”