Crustaceans are major constituents to aquatic ecosystems that provide a variety of ecological and economic services. Individual crustacean species are adept at occupying diverse niches and their success, in part, stems from neuro-endocrine signaling cascades that regulate physiology in response to environmental and internal cues. Peptide hormones are major signal transducers in crustaceans. The crustacean hyperglycemic hormone family of peptides regulates various aspects of growth, reproduction, and metabolism. These peptides may function as the terminal hormone to regulate some physiological activities or may function as intermediates in a signaling cascade. Ecdysteroids and terpenoids are two major classes of terminal signaling molecules in these cascades. Hormones from these two classes function independently or in concert to regulate various processes. Ecdysteroid signaling is subject to toxicological disruption through disturbances in ecdysteroid synthesis or binding of toxicants to the ecdysteroid receptor. Methyl farnesoate is the major terpenoid hormone of crustaceans and also is susceptible to disruption by environmental chemicals. However, the methyl farnesoate signaling pathway is poorly understood and only limited mechanistic confirmation for disruption of this endocrine signaling pathway exists. Disruption of the ecdysteroid/terpenoid signaling pathways in crustaceans has been associated with aberrations in growth, metamorphosis, reproductive maturation, sex determination, and sex differentiation. Population studies have revealed disruptions in crustacean growth, molting, sexual development, and recruitment that are indicative of environmental endocrine disruption. However, environmental factors other that pollution (i.e., temperature, parasitism) also can elicit these effects and definitive causal relationships between endocrine disruption in field populations of crustaceans and chemical pollution is generally lacking.

Crustacean endocrine toxicology: a review

Elementary Statistics with Applications in Medicine and the Biological Sciences. By Frederick E. Croxton. Pp. vii, 376. $1.95. 1959 (Dover Publications, Inc., New York.)

1. General considerations 221 2. Origin of vitellogenin 222 3. Vitellogenin uptake by vitellogenic ovaries 223 a) Transformation and role of the follicle envelope 223 b) Vitellogenic oocyte and endocytosis mechanism 224 4. From vitellogenin to vitellin: a processing? 224 5. Vitellogenin synthesis and vitellogenin level in haemolymph as means for monitoring vitellogenesis 226 6. Timing of the reproductive cycle: duration and relation with the molting cycle 227 B. Vitellogenesis control 229 1. Inhibitory control by VIH (Vitellogenesis Inhibiting Hormone) 229 a) The X organ-sinus gland complex 229 Eyestalked species Eyestalkless species b) Ways of action 230 Control of vitellogenin synthesis Control of vitellogenin uptake by the oocytes c) Extraction and purification of VIH 231 d) Latest data on VIH 231 2. Stimulatory control 233 a) Neurohumoral factors 234 b) Vitellogenin Stimulating Ovarian Hormone (VSOH) 234 c) Ecdysteroids 234 d) Juvenoids 235 e) Ovary-stimulating factor from males 237

Female reproduction in Malacostracan Crustacea.

Steroid molecules are present in all invertebrates, and some of them have established hormonal roles: this is the case for ecdysteroids in arthropods and, to a lesser extent, for vertebrate-type steroids in molluscs. Steroids are not only hormones, they may also fulfill many other functions in chemical communication, chemical defense or even digestive physiology. The increasing occurrence of endocrine disruption problems caused by environmental pollutants, which interfere in particular with reproductive physiology of vertebrates but also of invertebrates has made necessary to better understand the endocrine physiology of the latter and the role of steroids in these processes. So many attempts are being made to better understand the endocrine roles of steroids in arthropods and molluscs, and to establish whether they also fulfill similar functions in other invertebrate phyla. At the moment, both the precise identification of these steroids, the determination of their origin (endogenous versus exogenous) and of their mechanism of action are under active investigation. This research takes profit of the development of genome sequencing programs on many invertebrate species, which allow the identification of receptors and/or biosynthetic enzymes, when related to their vertebrate counterparts, but the story is not so simple, as will be exemplified by estrogen receptors of molluscs.

Steroids in aquatic invertebrates.

The molting process in arthropods is regulated by steroid hormones acting via nuclear receptor proteins. The most common molting hormone is the ecdysteroid, 20-hydroxyecdysone. The receptors of 20-hydroxyecdysone have also been identified in many arthropod species, and the amino acid sequences determined. The functional molting hormone receptors consist of two members of the nuclear receptor superfamily, namely the ecdysone receptor and the ultraspiracle, although the ecdysone receptor may be functional, in some instances, without the ultraspiracle. Generally, the ecdysone receptor/ultraspiracle heterodimer binds to a number of ecdysone response elements, sequence motifs that reside in the promoter of various ecdysteroid-responsive genes. In the ensuing transcriptional induction, the ecdysone receptor/ultraspiracle complex binds to 20-hydroxyecdysone or to a cognate ligand that, in turn, leads to the release of a corepressor and the recruitment of coactivators. 3D structures of the ligand-binding domains of the ecdysone receptor and the ultraspiracle have been solved for a few insect species. Ecdysone agonists bind to ecdysone receptors specifically, and ligand-ecdysone receptor binding is enhanced in the presence of the ultraspiracle in insects. The basic mode of ecdysteroid receptor action is highly conserved, but substantial functional differences exist among the receptors of individual species. Even though the transcriptional effects are apparently similar for ecdysteroids and nonsteroidal compounds such as diacylhydrazines, the binding shapes are different between them. The compounds having the strongest binding affinity to receptors ordinarily have strong molting hormone activity. The ability of the ecdysone receptor/ultraspiracle complex to manifest the effects of small lipophilic agonists has led to their use as gene switches for medical and agricultural applications.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1742-4658.2009.07347.x

Arthropod nuclear receptors and their role in molting.

Characterization of crab EcR and RXR homologs and expression during limb regeneration and oocyte maturation.

In the brachyuran crab Metopograpsus messor mating occurs only among "hard" (intermolt) individuals. Our present light and electron microscopic studies reveal that the spermatophores received by the females during coitus are discernible within the spermathecae until 24 h postmating. The study demonstrates time-dependent dissolution of the spermatophores of M. messor within the spermathecal lumen. The spermatozoa of M. messor were subjected to electron microscopic analysis. In addition to decapod and brachyuran features, the spermatozoa of M. messor display characters typical of the heterotreme-thoracotreme assemblage crabs, such as acrosomal length : width ratio (1.2), and the concentric arrangement of the acrosomal zones around the perforatorium. While the "onion ring" lamellation of the outer acrosome zone represents a typical thoracotreme character, the occurrence of the accessory opercular ring is indicative of its affinity to the GrapsinaeSesarminae subfamilies within the Grapsidae.

/pdf/spermatophore-transfer-and-sperm-structure-in-the-brachyuran-3ruia3pre8.pdf

Spermatophore transfer and sperm structure in the brachyuran crab Metopograpsus messor (Decapoda: Grapsidae)

The annual cycle of a Metopograpsus population (Muzhupilangad estuary) had three distinct periods: (1) growth-reproduction (January–May), when crabs were involved in moult and reproduction; (2) inactive period (June–July), and (3) reproductive period (August–December). Usually, spawning was immediately followed by another vitellogenic cycle, paralleled by the embryogenesis of prehatch eggs in the brood. Moulting was seemingly an annual event. In the programming of moult and reproduction, the species deviated from the common brachyuran pattern, inasmuch as the postmoult females engaged in active vitellogenesis. The synchrony in the stages of maturation and spawning, and the precision with which the physiological events are programmed, make this highly fecund species an ideal model for an integrated study of the physiology of growth and reproduction.

Seasonal growth and reproduction in a highly fecund brachyuran crab, Metopograpsus messor (Forskal) (Grapsidae)

In Calicut populations of P. hydrodromous, the ovary is not refractory during September—November of the prebreeding season; it is inhibited from developing apparently by a gonad-inhibiting hormone(s) contained in the eyestalks. The prevalent tendency in Paratelphusa during the prebreeding season is to reproduce, and not to moult. The precocious ovarian growth induced by eyestalk removal during this season is biochemically impoverished, possibly due to uneven oocyte development, which in turn may be caused by the unpreparedness of a section of the population of oocytes for vitellogenesis. The ovary appears to have to pass through a period of oogonial proliferation under the influence of the moult-precipitating hormones during the moulting season, and subsequently through a period of oocyte differentiation during the prebreeding season, for normal vitellogenesis during the breeding season.

Ovarian growth, induced by eyestalk ablation during the prebreeding season, is not normal in the crab, Paratelphusa hydrodromous (Herbst)

The presently reported study investigated seasonal fluctuations in the prevalence in four species of Nerocila infesting commercially exploited marine fishes representing the families Engraulidae, Clupeidae and Ambassidae, from the Malabar coast (Kerala, India). Seven of 56 fish species belonging to 23 families were infested by either one or two species of Nerocila. All the collected Nerocila species showed significant seasonal fluctuations in the prevalence of infestation, reaching maximum from October through April and minimum (or total absence of the parasites) from May through September. Such fluctuations were analyzed based on environmental parameters. Body surface, postero-ventral side of the head and the lateral line of the host fish form the major infestation site for the recovered Nerocila species. Skin lesion and hemorrhages were observed on the fish parasitized with these cymothoids.

Seasonal fluctuation of the prevalence of cymothoids representing the genus Nerocila (Crustacea, Isopoda), parasitizing commercially exploited marine fishes from the Malabar Coast, India

Gopinathan Anilkumar

Papers

Characterization of crab EcR and RXR homologs and expression during limb regeneration and oocyte maturation.

Spermatophore transfer and sperm structure in the brachyuran crab Metopograpsus messor (Decapoda: Grapsidae)

Seasonal growth and reproduction in a highly fecund brachyuran crab, Metopograpsus messor (Forskal) (Grapsidae)

Ovarian growth, induced by eyestalk ablation during the prebreeding season, is not normal in the crab, Paratelphusa hydrodromous (Herbst)

Seasonal fluctuation of the prevalence of cymothoids representing the genus Nerocila (Crustacea, Isopoda), parasitizing commercially exploited marine fishes from the Malabar Coast, India