THE TROPHIC ECOLOGY OF FRESHWATER GAMMARUS SPP. (CRUSTACEA:AMPHIPODA): PROBLEMS AND PERSPECTIVES CONCERNING THE FUNCTIONAL FEEDING GROUP CONCEPT

Gammarus spp. are widespread throughout a diverse range of freshwater habitats and can be the dominant part of many benthic macroinvertebrate assemblages, in terms of both numbers and/or biomass. Although the vast majority of studies have emphasized the herbivorous nature of Gammarus spp. and their ‘shredder’ functional feeding group (FFG) classification, we show that a far wider food base is exploited than has been previously acknowledged. This ‘plasticity’ as herbivore/predator is linked to the success of Gammarus spp. in persisting in and colonizing/invading disturbance-prone ecosystems. Intraguild predation and cannibalism are more common than previously realized. This behaviour appears to be a causal mechanism in many amphipod species replacements. Additionally, Gammarus spp. are major predators of other members of the macroinvertebrate community. Furthermore, while many studies have emphasized fish predation on Gammarus spp., we illustrate how this fish: amphipod, predator: prey interaction may be a two-way process, with Gammarus spp. themselves preying upon juvenile and wounded/trapped fish. We urge that a new realism be adopted towards the trophic ecology of Gammarus spp. and their role as predators and prey and that previously established FFG assumptions of both the food and the feeder be questioned critically.     

Activation of Tyrosinase Reduces the Cytotoxic Effects of the Superoxide Anion in B16 Mouse Melanoma Cells

Tyrosinase may protect against oxidative stress by using the superoxide anion (O^?₂) in the production of melanin. We have examined this by comparing its cytotoxic effects in B16/F10 and B16/F10-differential deficient (-DD) mouse melanoma cells that express high and low levels of tyrosinase activity respectively. Xanthine oxidase (XO) was used to generate O^?₂ and cytotoxicity assessed by measuring cell survival. XO increased O^?₂ concentrations and 3 h later dose related decreases in cell survival were seen. F10 cells were more resistant to these cytotoxic effects than the F10-DD cells. [Nle⁴,DPhe⁷]MSH increased tyrosinase activity and melanin content, reduced O^?₂ concentration and increased the resistance of F10 cells to the cytotoxic effects of O^?₂. No such effects were seen in F10-DD cells. The effect of [Nle⁴,DPhe⁷]MSH on the resistance of the F10 cells was time-dependent and noticeable when tyrosinase activity but not melanin was increased. This suggests that it was the activation of tyrosinase rather than the increase in the melanin that provided the protection against O^?₂. In support of this, inhibition of tyrosinase with phenylthiocarbamide reduced the increased resistance induced by [Nle⁴,DPhe⁷]MSH. Moreover, although melanin was capable of scavenging O^?₂ it had little effect at concentrations comparable to those in the activated F10 cells. XO also increased the melanin content of F10 but not F10-DD cells. We conclude that tyrosinase is able to utilise O^?₂ to produce melanin and this provides pigment cells with a unique anti-oxidant mechanism.     

Tamoxifen Inhibition of Ocular Melanoma Cell Attachment to Matrix Proteins

Tamoxifen plays a major role in the management of breast cancer in women and is currently used to a lesser extent in other neoplasias. Many of the pharmacological properties of tamoxifen are consistent with anti-estrogen activity, but it also has significant, although lesser, benefit in patients whose tumours are estrogen-receptor negative. We recently reported that murine B16 melanoma cell attachment to extracellular matrix proteins can be inhibited by calmodulin antagonists. In seeking a calmodulin antagonist that could be used clinically, we investigated tamoxifen, which is known to have calmodulin antagonist activity in vitro, and confirmed that it will inhibit murine melanoma cell attachment in vitro. In the current study, we examined the effect of tamoxifen on the attachment of human ocular melanoma cell lines to a range of extracellular matrix substrates to evaluate the potential relevance of calmodulin antagonists, including tamoxifen, to reducing metastatic spread of these tumours. We report that six ocular melanoma cell lines established from choroidal melanoma tumours showed rapid attachment to a range of substrates and that this attachment can be significantly reduced by an experimental calmodulin antagonist (J8) and by tamoxifen. In summary, we conclude that the ability of calmodulin antagonists, including tamoxifen, to inhibit ocular melanoma cell attachment to matrix proteins in vitro merits further investigation as it may offer another approach to reducing metastatic spread of these tumours.     

Potential effects of the invasive ‘killer shrimp’ (Dikerogammarus villosus) on macroinvertebrate assemblages and biomonitoring indices

1. Water quality monitoring data from 10 watercourses and laboratory mesocosm studies were used to assess the potential impacts of the crustacean amphipod invader Dikerogammarus villosus on resident macroinvertebrate assemblage structure in Central European fresh waters. 2. The presence of D. villosus was associated with a decline in the prevalence of many native species, pollution sensitive as well as pollution tolerant, and changes in biotic indices, despite the trends of improved water quality coinciding with the invasion period. A general increase in the prevalence of other invaders was also noted. The potential impacts of D. villosus were substratum dependent, differing between stone, concrete and sand‐dominated sites. 3. Mean Multimetric Macroinvertebrate Index Flanders (MMIF) values were marginally lower when D. villosus was present (P < 0.06), as opposed to when other amphipod species or no amphipods were present, despite the improved water quality. Mesocosm studies showed that several macroinvertebrate taxa were completely eliminated in treatments with D. villosus, oligochaete worms, Caenidae mayfly, chironomids and tipulids being particularly vulnerable to D. villosus predation. Biological Monitoring Working Party (BMWP) scores were lower in mesocosms with D. villosus as opposed to the native Gammarus pulex or no amphipods at all. 4. We predict that resident macroinvertebrate assemblages in both Central Europe and Britain will come under increasing pressure as D. villosus invasions progress. Consequently, macroinvertebrate biotic indices, such as the MMIF or BMWP, may need to be revised to account for changes in taxa sensitivities to water quality as well as increased predation and competition.     

α-MSH and Melanogenesis in Normal Human Adult Melanocytes

Normal human skin melanocytes do not pigment consistently to α-melanocyte stimulating hormone (α-MSH) in culture. The aim of this study was to establish media conditions in which to obtain a reproducible melanogenic response to α-MSH in these cells. Twenty-five media of varying mitogen composition were examined. As previously noted by other workers, melanocyte morphology and proliferation are greatly affected by media composition. However, under the majority of media conditions that supported melanocyte survival and proliferation, cells did not respond to α-MSH with any consistent increase in dopa oxidase activity or melanin content. In only one medium condition, where basic fibroblast growth factor (bFGF) was the sole mitogen present, α-MSH induced both an increase in dopa oxidase activity (at 48%) and in melanin content (of 283%).     

The dynamics of predation on Gammarus spp. (Crustacea: Amphipoda)

Gammarus spp. (Crustacea: Amphipoda) are widespread throughout a diverse range of marine, freshwater and estuarine/brackish habitats, often dominating benthic macroinvertebrate communities in terms of both numbers and/or biomass. Gammarus spp. are the dominant macroinvertebrate prey items of many fish, whether as a seasonal food source or a year-round staple. Selective predation by fish on Gammarus spp. is often linked to parasitism and the body size of the prey. Gammarus spp. populations are under increasing threat from both pollution and replacement/displacement by introduced species. Loss of populations and species invasions/replacements could have significant impacts on native predator species if the predator(s) cannot successfully adapt their feeding patterns to cope with non-indigenous Gammarus prey species. Despite this, many fish predation studies do not identify Gammarus prey to species level. This lack of precision could be important, as Gammarus spp. exhibit wide variations in physiochemical tolerances, habitat requirements, abilities to invade and susceptibility to replacement. Although rarely acknowledged, the impacts of nonpiscean predators (particularly macroinvertebrates) on Gammarus prey species may frequently be stronger than those exerted by fish. A major aim of this review is to ascertain the current importance of Gammarus as a prey species, such that the implications of changes in Gammarus spp. populations can be more accurately assessed by interested groups such as ecologists and fisheries managers. We also review the dynamics of Gammarus spp. as prey to a diverse array of mammals, birds, amphibians, insects, flatworms, other crustaceans such as crabs and crayfish and, perhaps most importantly, other Gammarus spp.     

Human Melanoma Cell Lines Show Little Relationship Between Expression of Pigmentation Genes and Pigmentary Behaviour In Vitro

Several laboratories are pursuing the question of whether the expression of pigment genes can be used as a useful marker for tumour progression. However, many melanoma tumours are amelanotic in vivo. The purpose of this study was to examine the relationship between the expression of tyrosinase-related genes [tyrosinase, tyrosinase-related protein-1 (TRP-1) and tyrosinase-related protein-2 (TRP-2)] and pigmentation of melanoma cells. Fourteen cutaneous melanoma cell lines were examined for visible pigment, melanin content, and dopa oxidase activity and findings were related to the previously determined expression of the three tyrosinase-related genes in these cells in culture. Four of the cell lines were also stimulated with α-MSH, isobutylmethylxanthine, and forskolin to examine the relationship between induced pigmentation and upregulation of pigmentation genes. There was no simple correlation between pigmentation gene expression and dopa oxidase activity or total melanin content of the 14 melanoma cell lines in culture. In the majority of cells, there was no appreciable pigment, whereas, in contrast, half of the cells showed significant dopa oxidase activity. Upregulation of dopa oxidase activity was achieved by α-MSH in two out of four cell lines examined in detail and with IBMX in three out of four of these cell lines. IBMX increased tyrosinase gene expression in all four cell lines; α-MSH was without effect; and TRP-1 and TRP-2 expression were largely unaffected by IBMX or α-MSH. Modest changes in morphology were noted in response to IBMX. Overall, however, human melanoma cell lines were, with two exceptions, amelanotic in culture despite the fact that 10 out of the 14 lines expressed tyrosinaserelated genes. We conclude that measurable pigmentation is not a necessary consequence of the expression of pigmentation genes. An implication of this work is that amelanotic tumours in vivo may nevertheless be positive for tyrosinase-related genes.