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serotonin (i.e., 5-hydroxytryptamine) tends to enhance gametogenesis in decapod species,
whereas dopamine tends to inhibit it (reviewed by Mazurová et al. 2008).
20-Hydroecdysone is known to be the most active form of ecdysteroid. Commonly called
molting hormone, it enhances the molting process such as apolysis and new cuticle secre-
tion, which are essential for the growth and development of crustaceans (Lachaise et al.
1993). Because of the close relationship between molt and reproduction cycles in female
organisms, this hormone certainly plays a key role in vitellogenesis regulation (Charniaux-
Cotton 1973; Subramoniam 2000). Ecdysteroids trigger their regulatory activity through
interaction with the ecdysteroid receptor (EcR). To regulate transcription, EcR needs to
dimerize with the orphan retinoid X receptor (RXR). EcR and RXR belong to the super-
family of nuclear receptors. However, although EcR structure and functioning in insects is
well documented, our knowledge of EcR in crustaceans remains limited (Verhaegen et al.
2010). Similarly, the natural ligand(s) for invertebrate RXRs is still under debate.
The sesquiterpenoid methyl farnesoate (MF) is the equivalent of the juvenile hormone of
insects. MF is involved as a morphogen in the postembryonic larval stage of development,
in the positive regulation of the molt cycle, as well as in stimulation of reproductive matu-
ration in female decapods (Laufer and Biggers 2001; Nagaraju et al. 2003). Experimental
evidence also suggests that MF is a male sex determinant in cladocerans in which cyclical
parthenogenesis occurs (Olmstead and LeBlanc 2001). Insect RXRs are capable of binding
terpenoid hormones (reviewed by LeBlanc 2007). However, the regulatory activity of MF
by binding to RXR or the EcR-RXR complex has not yet been demonstrated in crustaceans.
In malacostracans, the wider taxon that includes decapods, AGH positively regulates
sexual differentiation and the maintenance of the male reproductive system, spermato-
genetic activity, and differentiation of secondary sexual characteristics (Charniaux-
Cotton 1965; Charniaux-Cotton and Payen 1988). In females, the androgenic glands do not
develop, and the sexual differentiation of ovaries is spontaneously induced and oogenesis
is directly regulated by a gonad-inhibiting neurohormone.
8.5.2 Impact of EDCs on Crustaceans
By analogy to the
in vivo
approaches used for aquatic vertebrates, in particular in fish,
the measurements of hormone levels, associated receptor quantities and/or activities of
enzymes involved in hormone metabolism should also constitute relevant approaches to
assess the endocrine-disrupting potential of a compound and/or a natural matrix. However,
studies reporting such measurements in crustaceans have been mainly conducted in the
framework of ecophysiological research and on large species such as decapods with poten-
tial applications in aquaculture (LeBlanc 2007). As regards ecotoxicologically relevant spe-
cies (i.e., with a short life cycle and easy to use in laboratory and
in situ
experiments)
such as branchiopods, copepods, isopods, amphipods, and mysids, the characterization of
hormone regulation remains limited or even largely unknown. The study of ecotoxicologi-
cally relevant species is burdened with (1) a lack of detailed knowledge concerning their
life cycle (e.g., description of reproductive and molt cycles), which is essential to under-
stand and to interpret the evolution of hormone levels, and (2) analytical limitations owing
to small amounts of biological material available.
Impact assessment of EDCs on invertebrates has received particular attention over the
past 10 years (Verslycke et al. 2007; Mazurová et al. 2008). Crustacean studies have been
structured around two main axes. The first concerns the toxicity assessment of com-
pounds known or suspected to be ED in vertebrate species, such as 17α-ethinylestradiol,
bisphenol A, nonylphenols, diethylstilbestrol, and polychlorobiphenyls in a context of risk
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