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The single and synergistic effects of man-made changes to the environment, such as habitat destruction, climate change, introduction of novel, long-lived chemicals into the environment, transport of exotic species and pathogens into new geographical areas, and other factors are predicted to cause widespread population declines and species extinctions of plants and animals in this century. From its inception, physiology has dealt with organismal capacities to deal with environmental change. This essay argues that physiologists, their methods and concepts can make more substantial contributions to Conservation Biology than they have to date. A few of the many ways in which physiologists can participate in Conservation Biology include formulating standards for proof of cause-and-effect relations and providing information about how environmental change could affect organismal energetics, host-pathogen relations, immune defenses, and others.
Field endocrinology techniques allow the collection of samples (i.e., blood, urine, feces, tissues) from free-living animals for analysis of hormones, receptors, enzymes, etc. These data reveal mechanisms by which individuals respond to environmental challenges, breed, migrate and regulate all aspects of their life cycles. Field endocrinology techniques can also be used to address many issues in conservation biology. We briefly review past and current ways in which endocrine methods are used to monitor threatened species, identify potential stressors and record responses to environmental disturbance. We then focus on one important aspect of conservation: how free-living populations respond to human disturbance, particularly in relation to ecotourism. Breeding adult Magellanic penguins, Spheniscus magellanicus, appear to habituate well to tourists, and breed in an area where about 70,000 people visit during the season. Baseline levels of corticosterone return to normal after exposure of naïve birds to humans. However, penguin chicks appear to show a heightened adrenocortical response to handling stress in nests exposed to tourists, compared to chicks living in areas isolated from human intrusions. Given that developmental exposure to stress can have profound influences on how individuals cope with stress as adults, this potential effect of tourists on chicks could have long-term consequences. This field endocrine approach identified a stressor not observed through monitoring behavior alone.
The last three decades have brought clear recognition that many populations of animals are experiencing severe declines or local and global extinctions. Many examples have become common knowledge to the general public, such as worldwide declines in amphibian populations and extensive loss of coral reefs. The mechanisms underlying these and other changes are poorly understood. However, a growing literature indicates that a wide array of chemical contaminants have the potential to disrupt normal cell-to-cell signaling mechanisms. A global pollutant of most aquatic systems, nitrate has the potential to be an endocrine disrupting contaminant. This paper reviews studies performed on vertebrates demonstrating that nitrate and/or nitrite have the potential to alter endocrine function. Further, a retrospective study of our work on alligators from various lakes in Florida suggests that nitrate could contribute to some of the altered endocrine parameters previously reported in juvenile animals. We propose hypotheses suggesting that nitrate could alter steroidogenesis by 1) conversion to nitrite and nitric oxide in the mitochondria, the site of initial steroid synthesis, 2) altering Cl− ion concentrations in the cell by substituting for Cl− in the membrane transport pump or 3) binding to the heme region of various P450 enzymes associated with steroidogenesis and altering enzymatic action. Future studies are needed to examine the endocrine disruptive action of this ubiquitous pollutant. A growing literature indicates that all biologists studying natural systems, whether they choose to or not, must now consider contaminant exposure as a direct influence on their studies. That is, ubiquitous global contamination has the potential to alter the endocrine, nervous and immune systems of all organisms with resulting changes in gene expression and phenotypes.
The goal of this study was to further investigate the role of endogenous APGWamide levels in imposex induction in snails. APGWamide is a common neurotransmittor/neuromodulator peptide found in many species of molluscs, and is often related to sex organ growth or reproductive behavior. Mud snails (Ilyanassa obsoleta) were collected from the Rachel Carson Estuarine Reserve near Beaufort, NC, and were dosed with the environmental contaminant tributyltin (TBT), testosterone (T), or solvent vehicle (EtOH/ saline) controls. Both TBT and T have been shown previously to induce female snails to grow penises (a condition termed imposex), and to increase male penis size. Male normalized penis length was correlated to endogenous APGWamide levels (as measured by Western blotting of whole animal homogenates, r2 = 0.475), and control males had significantly higher APGWamide levels than control females. All TBT-treated animals, (male, female, and imposex) had levels of APGWamide similar to control males and significantly higher than control females. In testosterone treated animals, APGWamide levels were the same as controls and it is likely that testosterone interferes with a downstream signaling event to induce imposex. In addition, immunohistochemistry for APGWamide expression in abdominal areas was done on female, male and imposex snails collected from the wild. The pattern of APGWamide in imposex snails was similar to male snails, showing large patches of immuno-reactive areas in the top portion of the visceral mass. In female snails, no areas of cross-reactivity were found.
Aquatic pollution has led to the accumulation of various xenobiotics in crustaceans. A number of these environmental chemicals have been found to interfere with molting of crustaceans. Results of initial mechanistic studies with Uca pugilator suggest that the disruption of molting results from the disturbance to the Y-organ-ecdysteroid receptor (EcR) axis by xenobiotics. Such disturbance to the Y-organ-EcR axis can be caused by interference with epidermal ecdysteroid signaling and/or alterations in ecdysteroidogenesis and/or ecdysteroid disposition. Because the adverse impacts on crustacean molting cannot be readily seen in the wild, the disruption of molting represents an invisible form of endocrine disruption.
To clarify the effect of environmental endocrine disruptors on the induction of secondary sexual characteristics in wild animals, we observed 1,527 male and 1,847 female specimens of sexually mature Japanese freshwater crabs, Geothelphusa dehaani, collected at 12 sample points from 10 rivers in Sasebo City, Nagasaki Prefecture, Japan. The results obtained were as follows:
Abnormal males, with external appearance of a complete male, but having female genital openings, were observed at frequencies of 8–32% of males collected at all sample points. In contrast to this, all females collected were normal.
The frequency of abnormal males increased significantly with the increase in individual carapace width.
This species inhabits mountain streams in Japan, which are free from tributyltin that is known to induce the sexual mosaic phenomenon in mollusks. The streams are most likely polluted by some agricultural chemicals and chemicals present in waste gases from cars and especially particulate materials from diesel engines. The clear relationship of the frequencies of abnormal males to size (or age) suggests that the sexual mosaic phenomenon is induced not only at early stages of male development but after sexual maturation, in response to long-term exposure to chemical(s) during the whole life cycle of males. The definitive causal factors and mechanisms inducing sexual mosaics in this species are still unclear.
Organisms in natural habitats must frequently respond to changes in their environments through various physiological mechanisms. My laboratory has developed several methods for the quantification of stress in crustaceans. An ELISA was developed for the crustacean hyperglycemic hormone (CHH) from the American lobster (Homarus americanus). It is sensitive to as little as 0.2 fmol of peptide. Increases in hemolymph CHH were observed under conditions of acute hypoxia, elevated temperature, and altered salinity. In addition, elevated CHH concentrations were observed in Norway lobsters (Nephrops norvegicus) that were parasitized with the dinoflagellate Hematodinium sp.
Stress proteins, also known as heat-shock proteins (HSPs), comprise a highly conserved class of proteins that display elevated transcription during periods of stress. Using homologous molecular probes, my collaborators and I have examined the influence of heat-shock, osmotic stress, and the molt cycle upon HSP expression at the protein and mRNA levels. We observed a significant elevation in HSP mRNA expression after 1 hr of heat-shock or after 0.5 hr of osmotic stress. When comparing claw and abdominal muscles during molting, we observed a tissue-specific HSP response. Quantification of these different stress responses may serve as early indicators of the degradation of environmental health.
Certain anthropogenic chemicals, most notably xeno-oestrogens, are known to have the potential to disrupt vertebrate endocrine systems. For example, induction of the female-specific protein, vitellogenin, in male fish is a well-known effect of exposure to xeno-oestrogens and serves as a biomarker of such exposure. There have been few comparable studies of putative biomarkers of endocrine disruption in invertebrates. An exception is the upregulation of vitellin-like larval storage protein (LSP) expression in the barnacle cypris larva following exposure to oestrogenic chemicals. The current study aimed to establish whether larvae of the glass prawn, Palaemon elegans, are likewise susceptible to xeno-oestrogen exposure. Using a polyclonal antiserum to P. elegans apolipovitellin, an 86 kDa polypeptide was detected by western blotting in the larval and early postlarval stages of this species. An indirect ELISA applied to the soluble protein fraction of larval homogenates determined that the titre of this putative LSP ranged, depending on larval stage, from 0.48–0.67 ng μg−1. Exposure of P. elegans larvae to the xeno-oestrogen 4-n-nonylphenol (4-NP), at 0.2–20 μg L−1, resulted in a significant, concentration-independent increase in putative LSP levels of 5–18%. Conversely, exposure to the natural oestrogen, 17β-oestradiol (E2), at 0.2 and 20 μg L−1, led to a significant concentration-independent decline (up to 11%) in LSP levels. Whether the effect of 4-NP results from endocrine disruption is not known, however, an oestrogen receptor-mediated effect is unlikely. Other than a slight increase in larval mortality when exposed to 4-NP at 2 μg L−1, neither 4-NP nor E2 significantly affected development, growth or survival of P. elegans larvae.
To gain basic understanding of the reproductive and developmental effects of endocrine disrupting chemicals in invertebrates, we have used C. elegans as an animal model. The completion of the C. elegans genome sequence brings to bear microarray analysis as a tool for these studies. We previously showed that the C. elegans genome was responsive to vertebrate steroid hormones, and changes in gene expression of traditional biomarkers used in environmental studies were detected; i.e., vitellogenin (vtg), cytochrome P450 (cyp450), glutathione-S-transferase (gst) and heat shock proteins (hsp). The data were interpreted to suggest that exogenous lipophilic compounds can be metabolized via cytochrome P450 proteins, and that the resulting metabolites can bind to members of the Nuclear Receptor (NR) class of proteins and regulate gene expression. In the present study, using DNA microarrays, we examined the pattern of gene expression after progesterone (10−5, 10−7 M), estradiol (10−5 M), cholesterol (10−9 M) and cadmium (0.1, 1 and 10 μM) exposure, with special attention to the members of NRs. Of approximately 284 NRs in C. elegans, expression of 25 NR genes (representing 9% of the total NRs in C. elegans) was altered after exposure to steroids. Of note, each steroid activated or inhibited different subsets of NR genes, and only estradiol regulated NR genes implicated in neurogenesis. These results suggest that NRs respond to a variety of exogenous steroids, which regulate important metabolic and developmental pathways. The response of the C. elegans genome to cholesterol and cadmium was analyzed in more detail. Cholesterol is a probable precursor to signaling molecules that may interact with NRs and we focused on expression of genes related to lipid metabolism (cyp450), transport and storage (i.e., vitellogenin). Worms exposed to cadmium respond principally by activating the expression of genes encoding stress-responsive proteins, such as mtl-2 and cdr-1, and no significant changes in expression of NRs or vtg genes were observed. The possible implications of these results with regard to the evolution of steroid receptors, endocrine disruption and the role of vitellogenin as a lipid transporter are discussed.
Freshwater mussels, Elliptio complanata were collected from a reference and pollutant-impacted pond on Cape Cod, MA. Glutathione-S-transferase (GST) activity was measured in gill, hepatopancreas and foot. In addition, content of seven heavy metals were measured in whole bodies. GST activity was significantly elevated in hepatopancreas and foot, as was whole body cadmium level in animals from the contaminated site suggesting that these animals have been exposed to organic and inorganic contaminants. Sodium dodecyl acrylamide gel electrophoresis (SDS-PAGE) analysis showed putative vitellogenins with molecular weight 180 and 205 kDa bands only in the ovary. In non-denatured gel electrophoresis ovarian extracts revealed two higher molecular weight bands at 550 and 700 kDa, which were reproductive stage specific. Western blotting of SDS-PAGE and non-denatured gels using the anti-scallop yolk-protein antibody confirmed the presence of cross-reacting bands of the same molecular weights in the ovary but not other tissues. Although several experiments involving steroid hormone exposure were done, no significant changes in vitellogenin protein levels were observed. However, using an anti-human ERβ antibody, ERβ positive bands were observed both in female foot, and the ovary. No cross reactivity with the antibody was observed in hepatopancreas. Additional studies are required to resolve questions of vitellogenin regulation and the role of (xeno)estrogens in bivalve molluscs.
Over the past thirty years, a global occurrence of sexual aberration has occurred whereby females among populations of prosobranch snails exhibit male sex characteristics. This condition, called imposex, has been causally associated with exposure to the biocide tributyltin. Tributyltin-exposed, imposex snails typically have elevated levels of testosterone which have led to the postulate that this endocrine dysfunction is responsible for imposex. This overview describes recent evidence that supports this postulate. Gastropods maintain circulating testosterone levels and administration of testosterone to females or castrates stimulates male sex differentiation in several snail species. Studies in the mud snail (Ilyanassa obsoleta) have shown that gastropods utilize a unique strategy for regulating free testosterone levels. Excess testosterone is converted to fatty acid esters by the action of a testosterone-inducible, high capacity/low affinity enzyme, acyl-CoA:testosterone acyl transferase, and stored within the organisms. Free testosterone levels are regulated during the reproductive cycle apparently due to changes in esterification/desterification suggesting that testosterone functions in the reproductive cycle of the organisms. Testosterone esterification provides a unique target in the testosterone regulatory machinery of snails that is altered by tributyltin. Indeed, imposex and free testosterone levels were elevated in field collected snails containing high tin levels, while testosterone-fatty acid ester pools were reduced in these organisms. These observations indicate that tributyltin elevates free testosterone by reducing the retention of testosterone as fatty acid-esters. This endocrine effect of tributyltin may be responsible for imposex.
There is a growing body of literature describing the actions of endocrine disruptors on annelids. These pollutants cause decreases in growth and reproductive output, delay sexual maturation, and inhibit the immune system in annelids. More studies are needed to determine the mechanisms that underlie these responses. Most invertebrate endocrine disruptor research focuses on steroids. In recent years many new invertebrate peptide hormones including those related to the molluscan peptide FMRFamide have been identified. Since the storage of these peptides can be inhibited by steroids during insect metamorphosis, they may be affected by endocrine disruptors. Therefore, it is worthwhile to give a brief overview of this peptide family to those studying endocrine disruption in invertebrates with the hope that they may begin to consider these peptides in their future research. In 1977 Price and Greenberg isolated FMRFamide from the cerebral ganglia of the clam, Macrocallista nimbosa. Since then researchers have used bioassays and immunoassays to identify a large number of FMRFamide-related peptides (FaRPs) from many invertebrate phyla. Even more peptides are predicted by the FaRP genes that have been sequenced. FaRPs have a variety of functions and act as neurotransmitters, neuromodulators, or neurohormones. Each function is species and tissue specific. Most FaRP receptors are linked to a second messenger system. However, at least one is a ligand gated sodium channel. On going studies are examining FaRPs from the molecular to organismal level.
Comparative developmental and reproductive studies were performed on several species of estuarine crustaceans in response to three juvenile hormone agonists (pyriproxyfen, methoprene and fenoxycarb). Larval development of the grass shrimp, Palaemonetes pugio, was greater than two orders of magnitude more sensitive to disruption by methoprene and fenoxycarb than was embryonic development. Developing larvae of the mud crab, Rhithropanopeus harrisii, exhibited reduced metamorphic success at lower concentrations of methoprene and pyriproxyfen than grass shrimp larvae. These responses suggest that the more rigidly controlled metamorphic process in crabs is more sensitive to compounds acting as endocrine disruptors than is the more flexible metamorphic pattern in shrimp. The final crab larval stage, the megalopa, was more sensitive to methoprene and fenoxycarb exposure than earlier zoeal stages. Mud crab larvae exposed to fenoxycarb had reduced biomass and lipid content, particularly triglycerides and sterols. Concentrations of fenoxycarb which reduced the reproductive capacity in single life-cycle exposures of the estuarine mysid, Americamysis bahia, were similar to those concentrations which inhibited metamorphosis in grass shrimp. Juvenile mysids released by exposed adults and reared through maturation without further exposure produced fewer young and had altered sex ratios (lower percentages of males) at lower parental-exposure concentrations than directly affected parental reproduction. These transgenerational responses may well be a product of irreversible effects during developmental exposures which become apparent following maturation and initiation of reproduction. These findings support using a functional approach as an appropriate screening procedure to evaluate potential environmental endocrine-disrupting chemicals in aquatic environments.
Fenoxycarb and pyriproxyfen are insecticides that gain their toxicity by specifically acting as insect juvenile hormone agonists (JHA), and so are endocrine disruptors by design and effectively prevent larvae from maturing into adults. Efforts to assess the environmental effects of JHAs on nontarget populations of invertebrates have resulted in the utilization of several established estuarine crustacean models. This work was conducted to test the hypothesis that the mortality, inhibition of development and decreased fecundity reported previously in these animals from JHA exposure coincides with abnormal circulating titers of ecdysteroids. Gravid female grass shrimp (Palaemonetes pugio) and mud crabs (Rhithropanopeus harrisii), species with different developmental plasticity and JHA tolerances, were collected and held at wet lab conditions (20 ppt salinity, 25°C) until larval release. Larvae were collected <12 hr after hatch and exposed to JHAs during a static renewal test through end of development with seawater or nominal concentrations of JHA previously shown to induce significant developmental delays and/or decreased body weights. Larvae were subsampled (10 larvae/sample, n = 2 to 8) at each developmental stage, lyophilized, and ecdysteroids extracted by homogenization in 80% methanol and elution from C18 Sep-Pak cartridges with 25%, 60% and 100% methanol to capture the polar, free, and apolar conjugates, respectively, and then quantified by ELISA. As was expected significant differences in successful completion of development (larval survival), developmental duration, and growth (dry weight) were observed. These physiological perturbations were linked with significantly altered ecdysteroid titers, supporting a newly emerging theory that juvenoids possibly act as anti-ecdysteroids through a novel molecular mechanism involving inhibition of ecdysteroid signaling.
Methoprene is a pesticide that acts as a juvenile hormone agonist. Although developed initially against insects, it has since been shown to have toxic effects on larval and adult crustaceans. Methoprene was one of several pesticides applied to the Western Long Island Sound (WLIS) watershed area during the summer of 1999; the other pesticides were malathion, resmethrin, and sumethrin. These pesticides were applied as part of a county-by-county effort to control the mosquito vector of West Nile Virus. Subsequently, the seasonal lobster catches from the WLIS have decreased dramatically. The lethality of the pesticides to lobsters had been unknown. We studied the effects of methoprene while other investigators studied effects of the other pesticides. We questioned whether methoprene, through its effects on larvae, adults or both, could have contributed to this decline. We found that low levels of methoprene had adverse effects on lobster larvae. It was toxic to stage II larvae at 1 ppb. Stage IV larvae were more resistant, but did exhibit significant increases in molt frequency beginning at exposures of 5 ppb. Juvenile lobsters exhibited variations in tissue susceptibility to methoprene: hepatopancreas appeared to be the most vulnerable, reflected by environmental concentrations of methoprene inhibiting almost all protein synthesis in this organ.
Our results indicated that methoprene concentrates in the hepatopancreas, nervous tissue and epidermal cells of the adult lobster. Methoprene altered the synthesis and incorporation of chitoproteins (cuticle proteins) into adult postmolt lobster explant shells. SDS PAGE analyses of adult post–molt shell extracts revealed changes in the synthesis of chitoproteins in the methoprene-treated specimens, suggesting that methoprene affects the normal pathway of lobster cuticle synthesis and the quality of the post-molt shell. Although it is likely that a combination of factors led to the reduced lobster population in WLIS, methoprene may have contributed both by direct toxic effects and by disrupting homeostatic events under endocrine control.
Synthetic insecticides have been used intensively for the past 50 years in many parts of the world. Insect populations, both target and nontarget, have responded by evolving resistance. One of the nontarget insects is Drosophila melanogaster, which is well-suited for genetic analysis and has been particularly well-studied in both laboratory and field populations. Resistance to several insecticides, including two for which significant resistance in field populations has not been found, has been generated in susceptible laboratory strains following mutagenesis, allowing comprehensive study of the resistance genes. Field populations of D. melanogaster have evolved resistance to many, but not all, insecticides in use today. Both the genetic and biochemical mechanisms that underlie resistance in this insect are similar to those in other insects. Therefore, D. melanogaster can be a sentinel organism for long-term release of toxicants into the environment. While it remains useful for genetic analysis of resistance, a better understanding of the movement and population structures of this insect will be a prerequisite for its sentinel utilization at specific locales.
One of the most urgent problems in conservation biology today is the continuing loss of amphibian populations on a global scale. Recent amphibian population declines in Australia, Central America, the western United States, Europe, and Africa have been linked to a pathogenic chytrid fungus, Batrachochytrium dendrobatidis, which infects the skin. The skin of amphibians is critical for fluid balance, respiration, and transport of essential ions; and the immune defense of the skin must be integrated with these physiological responses. One of the natural defenses of the skin is production of antimicrobial peptides in granular glands. Discharge of the granular glands is initiated by stimulation of sympathetic nerves. To determine whether antimicrobial skin peptides play a role in protection from invasive pathogens, purified antimicrobial peptides and natural peptide mixtures recovered from the skin secretions of a number of species have been assayed for growth inhibition of the chytrid fungus. The general findings are that most species tested have one or more antimicrobial peptides with potent activity against the chytrid fungus, and natural mixtures of peptides are also effective inhibitors of chytrid growth. This supports the hypothesis that antimicrobial peptides produced in the skin are an important defense against skin pathogens and may affect survival of populations. We also report on initial studies of peptide depletion using norepinephrine and the kinetics of peptide recovery following induction. Approximately 80 nmoles/g of norepinephrine is required to deplete peptides, and peptide stores are not fully recovered at three weeks following this treatment. Because many species have defensive peptides and yet suffer chytrid-associated population declines, it is likely that other factors (temperature, conditions of hydration, “stress,” or pesticides) may alter normal defenses and allow for uncontrolled infection.
Rising concern over pesticide usage near estuarine systems and evidence of physical and physiological impacts on estuarine organisms have strengthened the need to better identify the ecological effects of nonpoint source runoff. Grass shrimp, Palaemonetesspp., are ecologically important and abundant marsh inhabitants that may be impacted by anthropogenic contamination. Populations of grass shrimp were sampled monthly, over a period of ten years, at four sites in South Carolina with varying upland land use characteristics. Spatial and temporal trends in grass shrimp densities were noted over time and between sites. Agricultural and golf course land usage corresponded with decreased grass shrimp population levels, overall shrimp size, and percentage of gravid females. Conservation methods, such as the use of best management practices (BMPs) and integrated pesticide management (IPM) at agricultural fields, corresponded with increased grass shrimp population density.
To fully understand the implications of a chemical's effect on the conservation of a species, effects observed at the physiological or individual level must be expressed in terms of the population. Since long-term field experiments are typically not feasible, vital rates such as survival and reproduction of individual organisms are measured in life table response experiments (LTRE) and employed to extrapolate the effects of a pollutant on the population. The population-level response of the mysid, Americamysis bahia, to varying concentrations of methoprene (0, 4, 8, 16, 31, 62 μg/L) was determined using age-structured population models. Models were parameterized from the results of an LTRE conducted throughout the entire mysid life cycle. A density-independent matrix model with time invariant demographic parameters was developed to measure the change in population growth rate, λ, with change in methoprene concentration. The values of λ were greater than one for all methoprene concentrations, indicating that populations exposed to the concentrations reported here would not become extinct. However, a general decrease in λ occurred with increasing methoprene concentration and would result in reduced population sizes. Sensitivity and decomposition analyses were conducted to determined the relative roles of the vital rates on altered population growth rates and determined that impaired reproduction was the primary influence on the observed decrease in λ. The model constructed was a useful tool for linking the individual-level effects to the population-level consequences of methoprene exposure on mysids, as well as defining the mechanism (reduced reproduction) responsible for the observed effects on population.
This review briefly summarizes the latest findings on reproductive endocrinology of Atlantic hagfish (Myxine glutinosa) and implications for fisheries management. In response to a major decline or collapse of the fisheries (groundfish and anadromous species) industry in the Northeast, species that were once considered alternative or underutilized have and are being identified that may be suitable for commercial harvest, one such example is the hagfish. Hagfish in recent years have been sought after as valuable fish not only for their flesh, but also their skin. Currently, there are no regulations governing the harvesting of hagfish along the East Coast. There has been little to no information of the life history of hagfish including growth rate, age determination, reproductive biology, life span, and larval size at hatching. Thus, the level at which a sustainable fisheries for this species can be maintained is unknown. In some parts of the world, hagfish stocks are being depleted due to overfishing. In order for fisheries management to manage its hagfish stocks and develop a sustainable commercial hagfish fishery, critical information is needed to assist in determining the optimal use of this valuable resource.
Key elements of the reproductive system have not been elucidated in hagfish. However, there is new evidence from recent reproductive studies that Atlantic hagfish may have a seasonal reproductive cycle. These data include seasonal changes in gonadotropin-releasing hormone (GnRH), gonadal steroids, estradiol and progesterone, corresponding to gonadal reproductive stages along with the putative identity of a functional corpus luteum. This newly acquired data may provide important information to fisheries managers of the East Coast.
Bering Sea snow crabs (Chionoecetes opilio) are a commercially important crab harvested in the Bering Sea. Optimal management of this species requires an understanding of the biology of this crab that is currently incomplete. Fisheries managers apply a continuous growth model in their management of snow crab, which assumes that male crabs increase in size throughout their lifespan. Male snow crabs undergo a morphometric molt that leads to a disproportionate increase in chelae size and it is still debated whether this molt is associated with a terminal molt. This study was conducted to determine whether adult male C. opilio are anecdysic. Using current knowledge of the hormonal regulation of crustacean growth, snow crab physiology was manipulated to induce an increase in molting hormones (ecdysteroids). Since female snow crabs are known to undergo a terminal molt after attaining reproductive maturity, we compared ecdysteroid levels in eyestalk-ablated terminally molted females, small-clawed males and large-clawed males. Snow crabs were collected from the Bering Sea and maintained in circulating seawater at approximately 6°C. Animals were either eyestalk-ablated or left intact. Ecdysteroid levels in hemolymph were quantified using an enzyme-linked immunosorbant assay (ELISA). Circulating ecdysteroids were significantly higher in small-clawed male crabs when compared to large-clawed males or terminally molted females. Eyestalk-ablation increased circulating ecdysteroids in small-clawed males, but had no significant effect on circulating ecdysteroids in large-clawed males or in terminally molted females.
Multicellular animals, which evolved about 700 to 1,000 myr ago, contain many of the genes found in yeast. Important for the evolution of multicellular animals were new pathways for intercellular signaling that regulated more complex physiological responses. Here we focus on the contribution to this process of lipophilic molecules that interact with nuclear receptors and the aryl hydrocarbon receptor, as well as enzymes that regulate the concentrations of these molecules. Both nuclear receptors and the aryl hydrocarbon receptor are found in invertebrates and vertebrates. We propose that environmental chemicals (xenobiotics) have been an important influence on the evolution of multicellular animals through a process involving the co-evolution of ligand-activated transcription factors and enzymes that detoxify xenobiotics. Indeed, this conversion of “xenobiotic swords” into “adaptive plowshares” contributed to the diverse physiology found in multicelluar animals. An important implication of this analysis is that enzymes as well as hormone receptors are vulnerable targets for endocrine disruptors. That is, some toxic chemicals act by inhibiting the enzymes that catalyze the formation or degradation of lipophilic signals, such as steroids, thus, disrupting hormone action.
The topic of endocrine disruption and the broad range of physiological effects caused by endocrine disrupting chemicals (EDCs) can only be meaningfully framed within an ecological and evolutionary context. Environmental pollutants and EDCs operate by disrupting the “chemical communication” that coordinates signaling within an organism. Here we discuss how EDCs are also able to disrupt the chemical communication between plants and soil bacteria necessary for initiating nitrogen-fixing symbiosis. We also examine, through examples of pollutant-related impacts on a wide range of invertebrates, the need for identifying emerging targets of EDCs. We suggest broadening the defined field of endocrine disruption to encompass the effects of synthetic chemicals that interfere with signaling and communication, not only within an organism, but also between organisms and linking ecosystems. The ecological consequences of failing to recognize novel targets of chemical pollutants and EDCs may be a net loss of biological diversity and a further imbalance of the global nitrogen cycle.
Nereis succinea and Platynereis dumerilii (Annelida, Polychaeta) are broadcast spawners and reproduce semelparously. The final events in reproduction, swarming and spawning are co-ordinated by sex pheromones.
A water-soluble fraction of crude oil, the volatile fraction (C9—C16) of EKO FISK crude oil was found to induce release of gametes in male nereids at levels <0.3 ppm.
Using vacuum distillation, column chromatography, preparative GC and GC-MS analysis we showed that C5-alkylated benzenes were most potent in inducing sperm release, of those n-butyl-4-methylbenzene and 1,4-diethyl-2-methylbenzene were found to induce release of gametes at concentrations ≥4 nM. This threshold is lower than those reported for natural pheromones (nereithione: 60 nM, uric acid: 600 nM) but higher than background levels of aromatic compounds of 0.05 nM and below.
Other oil fractions showed additional effects, blocking pheromone reception or narcotising and intoxicating animals. Part of these effects could be assigned to naphthalenes at levels down to approx. 320 nM. In the original mixtures, their action was modified or compensated by the presence of gamete release inducing alkylated benzenes. Other highly paralysing substances remained elusive.
Over the last decade, evidence has mounted demonstrating that human-made compounds released into the environment are disrupting endocrine systems of animals. Research has centered largely on direct steroidogenic or antisteroidogenic effects of these compounds with a recent focus on development of rapid in vitro assays employing estrogen receptors. A literature search and analysis confirms attention placed on estrogen and anti-estrogen-like aspects of endocrine disruption at the receptor level. Non-steroidal components of the hypothalamic-pituitary-end gland axes have received much less attention in the published endocrine disruption literature. Furthermore, aspects of endocrine physiology, such as the ability of animals to cope with stress or communicate chemically, have also received relatively less literature attention when compared to disruption of development and reproduction. As researchers continue to investigate complex mixes of human-synthesized compounds in the environment, it is critical to broaden the spectrum of hormonal disruption investigated beyond estrogenic and androgenic actions and to determine how exposure to mixes affects physiological function beyond reproduction. Last, in the field of endocrine disruption, it also important to begin to use data on individuals for development of hypotheses regarding fitness risks, changes in population dynamics, and the potential for ecosystem level disruption.
The vertebrate endocrine system is well-characterized, with many reports of disruption by environmental chemicals. In contrast, cnidarians are less compartmentalized, physiological regulation is poorly understood, and the potential for disruption is unknown. Endocrine-like activity has not been systematically studied in cnidarians, but several classical vertebrate hormones (e.g., steroids, iodinated organic compounds, neuropeptides, and indoleamines) have been identified in cnidarian tissues. Investigators have made progress in identifying putative bioregulatory molecules in cnidarians, and testing the effects of these individual compounds. Less progress has been made in elucidating signaling pathways. For example, putative gonadotropin-releasing hormone and sex steroids have been identified in cnidarian tissues, but it is unknown whether these compounds are components of a larger signal cascade comparable to the vertebrate hypothalamic-pituitary-gonadal axis. Further, while sex steroids and iodinated organic compounds may help to regulate cnidarian physiology, the mechanisms of action are unknown. Homologs to the vertebrate steroid and thyroid receptors have not been identified in cnidarians, so more research is needed to understand the mechanisms of endocrine-like signaling in cnidarians. Elucidation of cnidarian regulatory pathways will provide insight into evolution of hormonal signaling. These studies will also improve understanding of how cnidarians respond to environmental cues and will provide a basis to investigate disruption of physiological processes by physical and chemical stressors.