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\DOI{10.5802/crchim.354}
\datereceived{2024-10-11}
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\dateposted{2024-11-19}
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\makeatletter
\def\TITREspecial{\relax}
\def\cdr@specialtitle@english{Chemical Ecology -- Chemical Mediation in the Environment}
\def\cdr@specialtitle@french{\'Ecologie chimique -- M\'ediation chimique dans l'environnement}
\makeatother

\CDRsetmeta{articletype}{foreword}

\title{Foreword: chemical mediation in the environment -- Chemical
ecology and the French GDR MediatEC}

\alttitle{Avant-propos : M\'ediation chimique dans l'environnement --
L'\'ecologie chimique et le GDR MediatEC}

\author{\firstname{Anne-Genevi\`{e}ve} \lastname{Bagn\`{e}res}\CDRorcid{0000-0002-1729-379X}}
\address{Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), CNRS --
University of Montpellier - EPHE -- IRD, 1919 route de Mende, 34293
Montpellier Cedex 5, France}
\email[A.-G. Bagn\`{e}res]{ag.bagneres@cefe.cnrs.fr}

\author{\firstname{Olivier P.} \lastname{Thomas}\CDRorcid{0000-0002-5708-1409}}
\address{School of Biological and Chemical Sciences, Ryan Institute,
University of Galway, H91TK33 Galway, Ireland}

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\xsection{}
Chemical mediation refers to the process by which chemicals, both
natural and synthetic, influence the interactions and behaviours of
living organisms within ecosystems. These molecules usually affect
various biological processes, including growth, reproduction,
communication, and defence mechanisms among plants, animals, and
microorganisms. The concept is at the core of the scientific field of
chemical ecology and it encompasses the study of how these chemicals
are produced, released, transported, and transformed in the
environment, as well as their ecological and health impacts. 

Historically, chemical ecology has first focused on plants and their
chemically mediated interactions, with other living organisms such as
insects, microbes but also other plants and animals. Such chemical cues
have been identified as end products of secondary or specialised
metabolic pathways finely tuned through a long evolutionary history and
leading to a structurally unique and inspiring chemical diversity of
bioactive metabolites. With the expansion of microbiology, close
associations between plants and microbes such as bacteria or fungi were
also identified as being mediated by chemical cues. Then, plant--plant
communication was also evidenced to be mediated by volatile metabolites
through the concept of allelopathy. While plants remain a major
subfield of chemical ecology, interactions between other living
organisms soon became of huge interest for the broader community. With
the discovery of additional sources of chemical diversity in the marine
environment and in the microbial world, it soon became evident that
chemical interactions are ubiquitous and would benefit from the
creation of a scientific consortium. With the development of always
greener practices, chemical ecology is now offering new opportunities
in diverse fields, for example through the natural biocontrol for the
proliferation of invasive species or pests.

By nature, chemical ecology is multi- and interdisciplinary and the
endeavour to build a large research group around chemical ecology was
mainly supported and funded by the CNRS in France. The GDR MediatEC
(CNRS 3658) was launched in 2014 from the merger of two similar and
previous actions centred on chemical ecology in the terrestrial
environment and marine biologists and chemists. The benefits of
positive interactions between these communities were evident very early
and resulted in a long list of positive collaborations and interactions
between scientists of different backgrounds and centres of interest.
For instance, the natural product chemists with deep knowledge
especially when working on complex marine natural products brought
their \mbox{expertise} to the (micro)biologists \mbox{working} on terrestrial models.
A key component of the success of the GDR MediatEC was the creation and
optimal use of shared facilities and expensive equipment by both
communities in the terrestrial and aquatic fields. In addition to the
yearly friendly meetings of the GDR organised all across France since
2014, we must mention the financial support for attending conferences
or projects and the publication of a special issue entitled Aquatic
Chemical Ecology in the journal Aquatic Ecology~\cite{1} and also a
co-authoring book on Chemical Ecology in 2016~\cite{2} translated
afterwards in French (2017) and Spanish (2020) languages. Based on all
these successes of this programme that also helped to build an
international recognition of the French community working in chemical
ecology, this collaborative network was renewed in 2018 for an
additional 4 years and was terminated in 2022. Further actions are
ongoing to maintain links between all members of this community such as
creating a Thematic network (CNRS-RT).

The main thematic areas of research supported during these 8 years were:
\begin{itemize}
\item Chemical ecology and evolution
\item Chemical diversity and biosynthesis
\item Chemical mediation
\item Chemical ecology in a changing environment
\item Applied chemical ecology
\end{itemize}
These research themes were led by two to three researchers from
different institutions and background to foster positive interactions.
They were supported by technological platforms and infrastructures
dedicated to the study of chemical interactions including the
development of new tools in metabolomics. 

{\advance\baselineskip by .06pt

A diversity of authors forms different backgrounds and disciplines have
contributed to this special issue as a reflection of the
interdisciplinarity of the consortium. The erudite and fine analysis of
Beniddir and Poupon~\cite{3} starts with a brief and meaningful history
of natural product chemistry and its importance for pharmacy and drug
discovery. The point-of-view article then gives some insights on the
importance of synthetic biology and bioinformatics for the future
development of the field of pharmacognosy and the positive inclusion of
metabolites of diverse origin including the marine \mbox{environment} and
microbes. As a confirmation that the marine \mbox{environment} is becoming of
growing interest for the society, Rousseau et~al.~\cite{4} present a
review on the chemical interplay that takes place within the seaweed
holobiont. This fundamental knowledge is bringing key contributions in
the context of the ``seaweed revolution'' and the blue bioeconomy. The
following article shows how dynamic the research on microbes of marine
origin is in the French scientific community. Bertrand and 
coworkers~\cite{5} studied the change in metabolome and lipidome of a
fungus of marine origin when grown in different conditions. This study
highlights the importance of new tools developed in bioinformatics for
the annotation of metabolites present in minute quantities. Allelopathy
has been studied by Tison-Rosebery et~al.~\cite{6} between a
proliferative macrophyte in Aquitaine lakes and blooms of the
cyanobacteria \textit{Microcystis aeruginosa} using also a metabolomics
approach by LC-HRMS. The presence of metabolites downregulating the
growth of the cyanobacteria could help mitigating the negative effects
of its blooms. As presented by Eparvier and coworkers~\cite{7},
molecular networking using t-SNE available in the newly developed
software MetGem has been used to annotate the antimicrobial and defence
metabolites produced by a bacterial strain present in a termite. A
subsequent study by Touboul and coworkers~\cite{8} applies similar
bioinformatics tools to the GC-MS data obtained on the volatile organic
compounds (VOCs) released by a South American plant in order to
identify antifungal metabolites. The soil is an example of medium where
complex interactions mediated by chemical cues between organisms take
place. In the study by Chauvat and coworkers~\cite{9}, the impact of
the presence of an insect in the vicinity of plant roots induced a
change in the metabolome of the soil. As nicely illustrated by Mondet
et~al.~\cite{10}, pheromones are essential metabolites for insects and
especially for honeybees. A seasonal change in the metabolome of the
brood has been observed and needs now to be better analysed and
understood. Plant--insect interactions are still full of surprises as
exemplified by the identification by Gibernau  et~al.~\cite{11} of an
unusual VOC from the Mediterranean plant \textit{Arum pictum}
that can play a role in the attraction of a diversity of insects.
Chemical emissions of the almond tree were for the first time
investigated under changing conditions by Leconte et~al.~\cite{12}.
Identification of some VOCs \mbox{involved} in the positive interaction with
the almond wasp could serve as a natural biocontrol of its
proliferation. As demonstrated by Richard and coworkers~\cite{13}, the
presence of endosymbionts in the male terrestrial isopode known as
potato bug modifies the metabolome composition of its cuticle while
becoming feminised. Despite this change in reproductive behaviour,
these individuals remain less attractive to males, which could be
linked to this change in the metabolomics profile. Insects continue to
be an important source of chemical diversity as exemplified by the
discovery of new alkaloids of the azamacrolide family found in several
species of ladybirds by Magro et~al.~\cite{14}. The presence of major
families of specialised metabolites should be included into the
integrative approaches used in phylogenetics studies of plants and
animals. Contact and distance interactions are the two modes of actions
of chemically mediated interactions and they are usually difficult to
tell apart in chemical ecology. Menacer et~al.~\cite{15} were able to
show that, for the cabbage root fly, VOCs act mainly when in mixtures,
and have effects either at distance or at contact, but not both. In a
changing environment, trees represent nutritional resources for bumble
bees and flowering species are crucial to sustain colony initiation
through chemical mediation. Geki\`{e}re et~al.~\cite{16} showed that
orchards are good candidates to offset the ongoing decline of early
flowering willows. Therefore, conservation strategies should consider
specialised metabolite profiles, especially flavonoids, when designing
agri-environmental schemes to support wild bee. The identification of
pheromones in invasive species of insects such as hornets in Europe is
highly relevant for biocontrol. To this end, Darrouzet and
coworkers~\cite{17} have characterised the chemical profiles of the
putative pheromones contained in the venom glands of four types of
female hornets.

}

Overall, this special issue presents a broad overview of the evolving
field of chemical ecology in France developed through the GDR MediatEC,
spanning from the historical plant--insect interaction to the more
recent marine and microbial environments. It highlights how dynamic the
field is through the different disciplines and environments involved,
and the valuable inputs it gives to both basic and applied science
especially in a time of drastic global change.

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