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ABSTRACT: The current consensus is that Microsporidia belong to a select group of parasites capable of causing both intersexuality and complete sex reversal in their hosts. Indeed, species such as Nosema granulosis and Dictyocoela duebenum, which infect amphipod crustaceans, are regularly referred to as 'feminising microsporidians'. This categorisation is based on a combination of findings: that these species are vertically transmitted and occur at a high prevalence of infection in intersex and female amphipods, that infected amphipod populations are female-biased, and that infected females have significantly female-biased broods with no concurrent increase in mortality. In this study, we report on a population of the amphipod Echinogammarus marinus presenting both female bias and high levels of intersexuality, which are infected with D. deubenum. In keeping with its feminising classification, infection is prevalent in animals presenting female and intersex phenotypes. However, a further screen revealed the presence of a previously unknown paramyxean parasite related to organisms of the genus Marteilia, a group known to cause catastrophic sexual dysfunction in bivalves. We found that the paramyxean parasite was also vertically transmitted, with infections being more prevalent in females and intersex animals. Critically, every animal infected with D. deubenum was also co-infected with the paramyxean, with few animals presenting an independent paramyxean infection. In contrast, co-infection of E. marinus with a paramyxean and the non-feminising microsporidian Dictyocoela berillonum rarely occurred. These observations raise a new hypothesis, namely, that D. duebenum and other feminising microsporidians are not actually capable of host feminisation but instead 'hitch-hike' together with a feminising paramyxean parasite.
International journal for parasitology 05/2012; 42(7):683-91. · 3.39 Impact Factor
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ABSTRACT: A notable body of research has established a clear link between intersexuality and the feminising influence of microsporidia
infection in amphipods. In this study, we investigated the relationship between microsporidia infection and intersexuality
in the amphipod Echinogammarus marinus (Leach) from Portsmouth, southern England. The analysis revealed a male-biased population (~2:1) harbouring both Dictyocoela berillonum and Dictyocoela duebenum microsporidia, with ~38 and 6% of animals displaying ‘high’ levels of infection, respectively. We also reveal the presence
of several intersex phenotypes: intersex females (1%) that possess genital papillae. Two male intersex phenotypes—internal
intersex (8.2%), possessing an oviduct structure on their testes, and external intersex males (4.4%), which possess external
brood plates. We found a statistically significant relationship between D. berillonum infection and the external intersex male phenotype; however, the male-biased population and low levels of female infection
suggest that the correlation may not be the result of incomplete feminisation. In addition, we found that the internal and
external intersex characteristics are rarely seen on the same specimen, suggesting that the male intersex phenotypes are caused
by distinct mechanisms. In combination, these findings are suggestive of a more complex relationship between amphipod intersexuality
and their microsporidia than had previously been recognised.
Marine Biology 04/2012; 158(2):461-470. · 2.28 Impact Factor
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ABSTRACT: The antifouling agent tributyltin (TBT) is a highly toxic pollutant present in many aquatic ecosystems. Despite of regulations on the usage of TBT, it remains in high concentrations in sediments both in harbors and in off-shore sites. The toxicity of TBT in mollusks is well documented. However, adverse effects in other aquatic organisms, such as crustaceans, are less well known. This study is an effort to assess the effects of environmentally realistic concentrations of TBT on an ecologically important species in Swedish fresh and brackish water ecosystems, the benthic amphipod Monoporeia affinis. Field collected animals were exposed during gonad maturation to TBT (70 and 170 ng/g sediment d wt) for five weeks in static microcosms with natural sediment. Exposure concentrations were chosen to reflect effects at concentrations found in Swedish coastal sediment, but below expected effects on survival. TBT exposure resulted in a statistically significant adverse effect on oocyte viability and a doubling of the prevalence of microsporidian parasites in females, from 17% in the control to 34% in the 170 ng TBT/g sediment d wt exposure. No effects on survival were observed. Borderline significant effects were observed on male sexual maturation in the 70 ng TBT/g d wt exposure and on ecdysteroid levels in the 170 ng/g sediment d wt exposure. Both reproduction and parasite infection effects are of ecological importance since they have the potential to affect population viability in the field. This study gives further evidence to the connection between low dose contaminant exposure and increases in microsporidian parasite infection.
Aquatic toxicology (Amsterdam, Netherlands) 09/2010; 101(1):72-7. · 3.12 Impact Factor
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ABSTRACT: Perfluorooctane sulfonate (PFOS) is the focus of intense toxicity research due to its persistence and widespread occurrence in biota. Studies on benthic invertebrates have shown them to be subjects of high PFOS exposure. However, effects on benthic invertebrates exposed to PFOS in the field are still far from elucidated. To fill a knowledge gap on concentrations and effects in benthic invertebrates, a microcosm study on the benthic amphipod Monoporeia affinis was performed. Field collected M. affinis were analysed for PFOS and showed average background concentrations 39 and 58 ng/g (wet weight) in two different samplings. The field collected animals were exposed to three concentrations of PFOS (50, 200 and 5000 microg PFOS/L water) for 3 weeks during gonad development. Body burdens of PFOS were determined after experiment termination. Results showed negative effects on survival and reproduction effects such as decreased sexual maturation and decreased oocyte viability caused by PFOS exposure. Additionally, a follow-up experiment demonstrated a significant increase in the infection incidence by a microsporidian muscle parasite in animals exposed to PFOS at tissue concentrations in the range of concentrations found in field collected benthic amphipods. This is the first study to demonstrate increased microsporidian infection with pollutant exposure and it suggests that ecologically relevant PFOS concentrations could be sufficient to elicit these effects.
Aquatic toxicology (Amsterdam, Netherlands) 02/2010; 98(1):99-106. · 3.12 Impact Factor
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ABSTRACT: Invertebrate infertility has been under-explored as a potential ecological issue or biomarker of stress within ecotoxicology. To date, the majority of studies focussing on contaminant induced infertility have centred on vertebrate groups. This study aimed to address the question whether industrial pollution has the ability to influence the sperm counts and testicular morphology of male amphipod, Echinogammarus marinus (Leach). In addition, the sperm counts of normal and intersex specimens were compared to assess the potential impact of a crustacean with a disrupted endocrine system. Specimens of E. marinus were collected at one industrially impacted (Inverkeithing) and two reference (Thurso and Loch Fleet) sites along the north and eastern coasts of Scotland. Significantly higher sperm counts ( approximately 20%) were observed from normal males collected from reference sites compared to the industrially impacted site. Higher proportions (30%) of intersex specimens were observed at the industrially impacted site compared to 17 and 6% male intersexuality observed at Thurso and Loch Fleet, respectively. Intersex male specimens from Thurso had lower mean sperm counts ( approximately 15%) than normal male specimens, however, this result was not significant (P=0.089). No significant differences in sperm counts were observed between normal and intersex males at Inverkeithing. Our results indicate that industrial pollution does have the potential to affect the sperm counts of male crustaceans. Whether the quality of sperm in Crustacea from contaminated sites is also compromised or whether this is an endocrine mediated effect is yet to be confirmed. To date, many of the studies of endocrine disruption in crustaceans have, surprisingly, focussed on female fecundity parameters, growth and moulting despite many of the vertebrate studies initially focussing on the male gender. Whether this could be an ecological issue needs to be addressed through further field and laboratory based studies. It is recommended that, strategically, considerable information regarding developing methodologies could be gained from scientists working in the crustacean aquaculture industries and crustacean taxonomists.
Aquatic Toxicology 07/2008; 88(1):81-7. · 3.76 Impact Factor
