Biology subjects

Hardege, J. D.

Publications and source records attributed to Hardege, J. D..

4 recordsLinked to original sources

bioRxiv2026

Adult Marine Annelid Platynereis dumerilii Chemically Stunt the Growth of Juveniles

Within species, individuals of the same age can differ in size. Previously, parental genetics, nutrition, space, and social interactions have been suggested to explain different growth rates. However, direct effects of larger individuals on the physiology and growth of smaller individuals are poorly understood. In this study, we investigated how larger individuals of the marine worm Platynereis dumerilii can impact the growth of smaller conspecifics. Comparing growth distributions in communally and individually reared worms, we show that larger worms suppress the growth of smaller ones. Furthermore, we were able to demonstrate that this suppression is chemically mediated. The chemical cue does not originate from faeces but is water soluble, stable for several days and smaller than 3 kDa. Our findings highlight the importance of non-reproduction related chemical signalling, showing evidence that dominant individuals can chemically suppress the growth of their conspecifics. This study provides new insights into how hierarchy can be established and maintained in a population and is particularly relevant for the growing community studying this model species.

animal behavior and cognition↗

bioRxiv2024

The molecular arsenal of the key coastal bioturbator Hediste diversicolor faced with changing oceans

The importance of infaunal bioturbators for the functioning of marine ecosystems cannot be overstated. Inhabitants of estuarine and coastal habitats are expected to show resilience to fluctuations in seawater temperature and pH, which adds complexity to our understanding of the effects of global change drivers. Further, stress responses may be propagated through chemical cues within and across species, which may amplify the costs of life and alter species interactions. Research into the molecular mechanisms underlying this resilience has been limited by a lack of annotated genomes and associated molecular tools. In this study, we present the first chromosome-level, annotated draft genome of the marine ragworm Hediste diversicolor, specifically mapping genes important for chemical communication, sensing and pH homeostasis. Using these resources, we then evaluate the transcriptomic and behavioural responses of two distinct populations -- one field-sampled from Portugal (Ria Formosa) and one laboratory-acclimated and -bred from the United Kingdom (Humber) -- to changes in seawater pH, temperature, and odour cues from a low pH-stressed predator. Both populations displayed adaptive responses to future oceanic conditions, with targeted acid-base regulation in the Ria Formosa population experiment, and broader changes in metabolism and growth genes in the Humber population experiment. Chemical cues from stressed fish predators induced genes related to Schreckstoff biosynthesis in ragworms. Additionally, under future ocean conditions including increased temperature, the Humber population exhibited signs of cellular stress and damage. Our findings using the new annotated genome offer novel insights into the molecular arsenal of acid-base regulation which aids in predicting the impacts of an increasingly acidified and unstable ocean, and to transfer this knowledge to investigate these mechanisms in species with less tolerance.

genomics↗

bioRxiv2020

Ocean Acidification Amplifies the Olfactory Response to 2-Phenylethylamine: Altered Cue Reception as a Mechanistic Pathway?

With carbon dioxide (CO2) levels rising dramatically, climate change threatens marine environments. Due to increasing CO2 concentrations in the ocean, pH levels are expected to drop by 0.4 units by the end of the century. There is an urgent need to understand the impact of ocean acidification on chemical-ecological processes. To date, the extent and mechanisms by which the decreasing ocean pH influences chemical communication are unclear. Combining behaviour assays with computational chemistry, we explore the function of the predator related cue 2-phenylethylamine (PEA) for hermit crabs (Pagurus bernhardus) in current and end-of-the-century oceanic pH. We demonstrate that this dietary predator cue for mammals and sea lampreys is an attractant for hermit crabs. Furthermore, we show that the potency of the cue increases at pH levels expected for the year 2100. In order to explain this increased potency, we assess changes to PEAs conformational and charge-related properties as one potential mechanistic pathway. Using quantum chemical calculations validated by NMR spectroscopy, we characterise the different protonation states of PEA in water. We show how protonation of PEA could affect receptor-ligand binding, using a possible model receptor for PEA (human TAAR1). Investigating potential mechanisms of pH dependent effects on olfactory perception of PEA and the respective behavioural response, our study advances the understanding of how ocean acidification interferes with the sense of smell and thereby might impact essential ecological interactions in marine ecosystems.

ecology↗

bioRxiv2019

Saxitoxin and tetrodotoxin bioavailability increases in future oceans

Increasing atmospheric levels of carbon dioxide are largely absorbed by the worlds oceans, decreasing surface water pH1. In combination with increasing ocean temperatures, these changes have been identified as a major sustainability threat to future marine life2. Interactions between marine organisms are known to depend on biomolecules, but the influence of oceanic pH on their bioavailability and functionality remains unexplored. Here we show that global change significantly impacts two ecological keystone molecules3 in the ocean, the paralytic toxins saxitoxin (STX) and tetrodotoxin (TTX). Increasing temperatures and declining pH increase the abundance of the toxic forms of these two neurotoxins in the water. Our geospatial global model highlights where this increased toxicity could intensify the devastating impact of harmful algal blooms on ecosystems in the future, for example through an increased incidence of paralytic shellfish poisoning (PSP). We also use these results to calculate future saxitoxin toxicity levels in Alaskan clams, Saxidomus gigantea, showing critical exceedance of limits save for consumption. Our findings for TTX and STX exemplarily highlight potential consequences of changing pH and temperature on chemicals dissolved in the sea. This reveals major implications not only for ecotoxicology, but also for chemical signals mediating species interactions such as foraging, reproduction, or predation in the ocean with unexplored consequences for ecosystem stability and ecosystem services.

pharmacology and toxicology↗