The less amorous Gammarus: predation risk affects mating decisions in Gammarus duebeni (Amphipoda)

We examined the trade-off between the behaviours associated with predator avoidance and mate acquisition in the mate-guarding amphipod crustacean Gammarus duebeni. We used laboratory experiments to investigate the impact of olfactory predator cues on activity, mate choice and mate-guarding behaviour of males and females. Pair formation declined under perceived risk of predation, reflecting reduced activity of both males and females and hence a reduced likelihood of encountering a mate. We also observed a reduction in the choosiness of both males and females. Under increased perceived predation risk, assessment of the female by the male was more likely to be followed by pair formation, and males showed a nonsignificant trend towards reduced discrimination in favour of large females and were less tenacious in their pair bond when they paired during exposure to predator cues. Females also showed less resistance behaviour, suggesting that both males and females trade off the costs of maximizing current reproductive success against the benefits of predator avoidance for survival and reproduction in the future. We discuss the implications of such context-dependent mating behaviours for ecological interactions between species and suggest that predators, via the effects of perceived predation risk on mate choice and mate guarding in the prey species, induce trait-mediated indirect effects with the potential to influence population dynamics and community structure. (C) 2008 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

A keystone effect for parasites in intraguild predation?

Intraguild predation (IGP) is common in communities, yet theory suggests it should not often persist and coexistence of participating species should be rare. As parasitism can play keystone roles in interactions between competitors, and between predators and prey, here we examine the role of parasites in maintaining IGP. We used numerical exploration of population dynamic equations to determine coexistence and exclusion zones for two species engaged in IGP with shared parasitism. We demonstrate that parasitism increases the range of conditions leading to coexistence when the parasite exerts a greater deleterious effect on the 'stronger' species in terms of the combined effects of competition and predation. Such a parasite can enable an inferior competitor that is also the less predatory to persist, and may actually lead to numerical dominance of this species.

The replacement of a native freshwater amphipod by an invader: roles for environmental degradation and intraguild predation

We assessed the extent to which an invader, Gammarus pulex (Crustacea: Amphipoda), has replaced a native, Gammarus duebeni celticus, over a 13-year period in a European river system and some of the abiotic and biotic factors that could account for this. Between 1988 and 2001, 56% of mixed-species sites had become invader-only sites, whereas no mixed sites had become native only again. The native dominated areas of higher dissolved oxygen and water quality, with the reciprocal true for the invader. Field transplant experiments revealed that native survivorship was lower in areas where it had been replaced than in areas where the invader does not yet occur. In invader-only areas, native survivorship was lower than that of the invader when kept separately and lowest when both species were kept together. We also observed predation of the native by the invader. Laboratory oxygen manipulation experiments revealed that at 30% saturation, the native's survivorship was two thirds that of the invader. We conclude that decreasing water quality favours replacement of the native by the invader.

Lethal and sublethal toxicity of ammonia to native, invasive, and parasitised freshwater amphipods

In lethal and sublethal ammonia toxicity tests, we examined differences in tolerance of three species of freshwater amphipods, one native and two invasive in Ireland. The native Gammarus duebeni celticus was slightly less tolerant to ammonia than the invasive G. pulex (96h LC50 = 1.155 and 1.544 mg l(-1), respectively), while another invader, Crangonyx pseudograeilis, had the lowest tolerance (LC50 = 0.36 mg l(-1)). Parasitism of G. pulex by the acanthocephalan Echinorhynchus truttae greatly reduced the tolerance of the invader to ammonia (LC50 = 0.381 mg l(-1)). Further, precopula pair disruption tests indicated that G. d. celticus was more sensitive to ammonia than G. pulex at sublethal levels. We discuss these results in the context of the ecological replacements of native by invader amphipods. (C) 2004 Elsevier Ltd. All rights reserved.

Differential drift and parasitism in invading and native Gammarus spp. (Crustacea : Amphipoda)

Invading and native species often interact directly, such as by predation, producing patterns of exclusion and coexistence. Less direct factors, such as interactions with the broader abiotic and biotic environment, may also contribute to such patterns, but these have received less recognition. In Northern Ireland, the North American Gammarus tigrinus has invaded freshwaters populated with the native Gammarus duebeni celticus, with intraguild predation between the two implicated in their relative success. However, these species also engage in day and night

Differential physico-chemical tolerances and intraguild predation among native and invasive amphipods (Crustacea); a field study

We used field surveys and transplant experiments to elucidate the relative roles of physico-chemical regime and intraguild predation in determining the generally mutually exclusive distributions of native and invader freshwater amphipod species. Field surveys showed that the native Gammarus duebeni celticus dominates the shoreline of Lough Neagh, N. Ireland, with some co-occurrence with the N. American invader G. tigrinus. However, the latter species dominates the deeper areas of the mid-Lough. Transplant experiments showed no difference in survival of the native and invader in single species 'bioassay tubes' placed along the shoreline. However, there was significantly higher survival of the invader compared with the native in single species tubes placed in the mid-Lough. In mixed species tubes on the shoreline, the native killed and ate the invader, with no reciprocal interaction, leading to significant reductions of the invader. However, the invader had significantly higher survival than the native in mixed species tubes in the mid-Lough, with no evidence. of predation between the two species. These results indicate that, whereas differential intraguild predation may determine domination of the shoreline by the native, differential physico-chemical tolerances may be major determinants of the domination of the mid-Lough by the invader. This study emphasises the need to consider the habitat template in conjunction with biotic interactions before attempting to draw conclusions about mechanisms determining relative distribution patterns of native and invasive species.

Temporal changes in the distribution of native and introduced freshwater amphipods in Lough Neagh, Northern Ireland

Studies of invasion scenarios over long time periods are important to refine explanations and predictions of invasion success and impact. We used data from surveys in 1958 and 1999 of the macroinvertebrates of Lough Neagh, Northern Ireland, to assess changes in the distribution of native and introduced amphipods in relation to the wider assemblage. In 1958, the invader G. tigrinus dominated the shoreline fauna, with the native G. d. celticus present in very low numbers, whereas in 1999 the reverse was evident. In both surveys, G. tigrinus was the only amphipod present in the mid-Lough. G. tigrinus thus seems to have become established within L. Neagh, perhaps overshot and then senesced, with the native species re-establishing on the shoreline, with the invader mostly restricted to the deep mid-Lough. The non-amphipod macroinvertebrate assemblage was similar between the two surveys, in terms of Bray-Curtis community similarity, assemblage diversity, dominance and the taxa based ASPT water quality index. However, the mean density of macroinvertebrates (all taxa combined) was lower in 1999 compared to 1958, largely accounted for by a decline in oligochaete numbers. Since Gammarus species may be predators of other macroinvertebrates and influence their distribution and abundance, we investigated this trophic link in staged laboratory encounters. Both G. tigrinus and G. d. celticus preyed on isopods, alderflies, mayflies, chironomids and mysids, however, the native G. d. celticus had a significantly greater predatory impact on isopods and chironomids than did the invader G. tigrinus. While we cannot definitively ascribe cause and effect in the present scenario, we discuss how replacement of one amphipod species by another may have impacts on the wider macroinvertebrate assemblage.

An acanthocephalan parasite mediates intraguild predation between invasive and native freshwater amphipods (Crustacea)

1. The balance of predation between closely related invasive and native species can be an important determinant of the success or failure of biological invasions. In Irish freshwaters, the introduced amphipod Gammarus pulex has replaced the native G. duebeni celticus, possibly through differential mutual intraguild predation (IGP). Theoretically, parasitism could mediate such predation and hence the invasion outcome. However, this idea remains poorly studied.

Resolution of a taxonomic conundrum: an ultrastructural and molecular description of the life cycle of Pleistophora mulleri (Pfeiffer 1895; Georgevitch 1929)

The classification of a microsporidian parasite observed in the abdominal muscles of amphipod hosts has been repeatedly revised but still remains inconclusive. This parasite has variable spore numbers within a sporophorous vesicle and has been assigned to the genera Glugea, Pleistophora, Stempellia, and Thelohania. We used electron microscopy and molecular evidence to resolve the previous taxonomic confusion and confirm its identification as Pleistophora mulleri. The life cycle of P. mulleri is described from the freshwater amphipod host Gammarus duebeni celticus. Infection appeared as white tubular masses within the abdominal muscle of the host. Light and transmission electron microscope examination revealed the presence of an active microsporidian infection that was diffuse within the muscle block with no evidence of xenoma formation. Paucinucleate merogonial plasmodia were surrounded by an amorphous coat immediately external to the plasmalemma. The amorphous coat developed into a merontogenetic sporophorous vesicle that was present throughout sporulation. Sporogony was polysporous resulting in uninucleate spores, with a bipartite polaroplast, an anisofilar polar filament and a large posterior vacuole. SSU rDNA analysis supported the ultrastructural evidence clearly placing this parasite within the genus Pleistophora. This paper indicates that Pleistophora species are not restricted to vertebrate hosts.

Parasitism may enhance rather than reduce the predatory impact of an invader

Invasive species can have profound impacts on communities and it is increasingly recognized that such effects may be mediated by parasitism. The 'enemy release' hypothesis posits that invaders may be successful and have high impacts owing to escape from parasitism. Alternatively, we hypothesize that parasites may increase host feeding rates and hence parasitized invaders may have increased community impacts. Here, we investigate the influence of parasitism on the predatory impact of the invasive freshwater amphipod Gammarus pulex. Up to 70 per cent of individuals are infected with the acanthoce- phalan parasite Echinorhynchus truttae, but parasitized individuals were no different in body condition to those unparasitized. Parasitized individuals consumed significantly more prey (Asellus aquaticus; Isopoda) than did unparasitized individuals. Both parasitized and unparasitized individuals displayed Type-II functional responses (FRs), with the FR for parasitized individuals rising more steeply, with a higher asymptote, compared with unparasi- tized individuals. While the parasite reduced the fitness of individual females, we predict a minor effect on population recruitment because of low parasite prevalence in the peak reproductive period. The parasite thus has a large per capita effect on predatory rate but a low population fitness effect, and thus may enhance rather than reduce the impact of this invader.

Stratification and Monitoring of Juvenile Idiopathic Arthritis Patients by Synovial Proteome Analysis

Juvenile idiopathic arthritis (JIA) comprises a poorly understood group of chronic, childhood onset, autoimmune diseases with variable clinical outcomes. We investigated whether profiling of the synovial fluid (SF) proteome by a fluorescent dye based, two-dimensional gel (DIGE) approach could distinguish patients in whom inflammation extends to affect a large number of joints, early in the disease process. SF samples from 22 JIA patients were analyzed: 10 with oligoarticular arthritis, 5 extended oligoarticular and 7 polyarticular disease. SF samples were labeled with Cy dyes and separated by two-dimensional electrophoresis. Multivariate analyses were used to isolate a panel of proteins which distinguish patient subgroups. Proteins were identified using MALDI-TOF mass spectrometry with expression further verified by Western immunoblotting and immunohistochemistry. Hierarchical clustering based on the expression levels of a set of 40 proteins segregated the extended oligoarticular from the oligoarticular patients (p <0.05). Expression patterns of the isolated protein panel have also been observed over time, as disease spreads to multiple joints. The data indicates that synovial fluid proteome profiles could be used to stratify patients based on risk of disease extension. These protein profiles may also assist in monitoring therapeutic responses over time and help predict joint damage. © 2009 American Chemical Society.