Molecular Mechanisms that Regulate Scopolamine Effects on Inducible Fish Antipredation Responses in Daphnia Magna

Abstract

The central nervous system regulates many aspects of antipredator Daphnia responses, therefore antipredation responses can be especially sensitive to compounds that affect neurodevelopmental or neuro-functional functions. The aim of this study was to identify the molecular pathways that modulate scopolamine effects in inducible antipredation responses to fish kairomones. We used two clones showing two contrasting responses. The positive phototactic clone 85 responds strongly to fish kairomones showing a marked negative phototactism and higher developmental rates. Consistently, the negative phototactic clone F shows the opposite behaviour to the same stimuli. Adults of both clones were exposed to fish kairomones, scopolamine alone and a mixture of both. Scopolamine is a muscarine antagonist able to mimic fish kairomones inducible behavioural responses in both clones, while affecting differently morphological and life-history traits. Whole transcriptomic Illumina analyses indicated a greater number of de-regulated genes of the fish kairomone sensitive clone 85 (1650) compared to the F one (1138), which were grouped in four clusters (two per clone). The mixture of scopolamine and fish kairomone treatments on gene transcription was additive in both clones, indicating similar modes of action. Most enriched metabolic routes were related with neurological pathways and regulation of cell proliferation/differentiation. Our results indicate that fish kairomones and scopolamine deregulate not only neurological signalling pathways but also cell differentiation and proliferation pathways, which are linked to the observed behavioural responses as well as the developmental, morphological, and reproductive effects.

Keywords: predation, pollutants, life-history, Transcriptomics, Modes of action