No abstract

Aquatic organisms must cope with both rising and rapidly changing temperatures. These environmental changes can affect numerous traits, from molecular to ecological scales. Biotic stressors can induce the release of chemical cues which trigger behavioural responses in other individuals. In this study, we infer whether abiotic stressors, such as fluctuating temperature, may similarly propagate stress responses between individuals in fish not directly exposed to the stressor. To test this hypothesis, zebrafish (Danio rerio) embryos were exposed for 24 hours to fluctuating thermal stress, to medium in which another embryo was thermally stressed before (“stress medium”), and to a combination of these. Growth, behaviour, and expression of a panel of genes were used to characterise the thermal stress response and its propagation between embryos. Both high temperatures and stress medium significantly accelerated development and altered embryonic behaviour. Thermal stress significantly decreased the expression of the antioxidant gene SOD1, eight hours after the end of exposure. Of note, we found that the expression of sulfide:quinone oxidoreductase (SQOR), likewise a part of the antioxidant metabolism relevant in vertebrate stress response, and of interleukin-1β (IL-1β), involved in the immune response, were significantly altered by stress medium. This study illustrates the existence of positive thermal stress feedback loops in zebrafish embryos that induce stress in conspecifics. This evidence that thermal stress due to fluctuating, high temperatures can be propagated may be relevant for species found in high densities, either in aquaculture or in the natural environment, in a context of global change.

<p>Plastic production has soared since the 1950s, with the last decade seeing an  increase of 43% from 250Mt (million tonnes) in 2009 to 368Mt in 2019. Plastics and their associated chemical congeners (variants of chemical structures) which enter the environment further exacerbate pollution within already contaminated ecosystems. In this study, we investigated the effect of plastic leachate on the common littoral marine hermit crab Pagurus bernhardus,  a species  at great risk from potential adverse effects of microplastics. The effects of  plastic additives released into the environment via microplastic leaching, and of contaminants adsorbed and accumulated onto the surface of microplastics on marine organisms is understudied. This study sought to (I) investigate whether plastic leachate has an effect on the respiration rate of hermit crabs and, (II) investigate whether plastic leachate has an effect on the foraging behaviour of hermit crabs. We found that within repeated measures design hermit crabs exposed to plastic leachate had different levels of oxygen consumption when compared to their control; with there being an increase or decrease dependent on the leachate type. This is potentially problematic due to high concentrations of microplastics along coastlines which may lead to impaired filtration within crustaceans resulting in lethality and reduced food intake.</p>