Parasite community structure within and across host populations of a marine pelagic fish: how repeatable is it?

The geographical variation in parasite community structure among populations of the same host species remains one of the least understood aspects of parasite community ecology. Why are parasite communities clearly structured in some host populations, and randomly assembled in others? Here, we address this fundamental question using data on the metazoan parasite communities of different host size-classes of four distinct populations of a small pelagic fish, the Argentine anchovy, Engraulis anchoita, from the South West Atlantic. Within each fish sample, fish length was correlated with both the total intensity of parasites and species richness among infracommunities. More importantly, average fish length correlated with mean infracommunity richness and mean total intensity across the fish samples, indicating that the characteristics of parasite assemblages in a fish population are strongly influenced by the size of its fish in relation to those in other populations. Nested subset patterns were observed in about half of the fish samples. This means that the presence or absence of parasite species among fish individuals is often not random; however, no repeatability of nestedness among component communities was observed. Average fish length did not influence directly the likelihood that a parasite assemblage was significantly nested. However, variables influenced by average fish length, namely mean infracommunity richness and mean total intensity, determine the probability that a nested hierarchy will be observed; host size may thus indirectly affect parasite community structure either itself or via its influence on host movement and feeding patterns. To some extent, this apparent link may be due to the sensitivity of nestedness analyses to the proportion of presence in a presence/absence matrix; this in itself is a biological feature of the parasite community, however, which is associated with mean host length.     

Where are they all from? – sources and sustainability in the ornamental freshwater fish trade

The global trade in ornamental fish involves c. 125 countries worldwide and is worth c. US $15–30 billion each year. This total is dominated (90%) by freshwater fishes, most of which are sourced from breeding facilities located in developing countries, typically in Asia or South America, but also in Israel, USA and Europe. Some fish are still obtained from natural (wild) sources, but the exact percentage of wild-caught fish is difficult to quantify given a lack of reliable data. Although c. 1000 species of freshwater fishes are widely available (from a total of > 5300 on sale), the most dominant freshwater fishes in the market comprise only 30 species from the orders Cyprinodontiformes, Perciformes, Characiformes and Siluriformes. In this perspectives review paper, illustrative example case studies of wild-fish collecting (Barcelos and Rio Xingu, Brazil) and breeding projects (Java, Indonesia) are described. In addition, wild-collecting expeditions to West Papua, Indonesia are discussed, focused on discovering novel species of rainbowfish (Melanotaeniidae) for breeding in captivity. Sustainability of the aquarium industry is considered in its broadest sense. The aquarium industry has been portrayed as both a major threat to natural ecosystems, but also as being part of the solution in terms of helping to maintain species when they have gone extinct in the wild or offering an income to impoverished citizens who might otherwise engage in much more destructive practices.     

Mitochondria: are they the seat of senescence?

The frequently quoted figure for the fractional univalent reduction of oxygen to superoxide in mitochondria is certainly too high by at least one order of magnitude. This is so because the higher number (2%) was derived from mitochondria whose cytochrome c oxidase was blocked with cyanide. Nevertheless, even the more correct number (0.1%) means that the production of O(2)(-) and H(2)O(2) in mitochondria is large and apt to result in damage to macromolecules in spite of such defensive enzymes as superoxide dismutases and glutathione peroxidase. The data available for nematodes and flies provide a compelling case for the view that the accumulation of oxidative damage to specific mitochondrial proteins leads to the progressive dysfunction that we see as senescence. The data available from work with mammals are much weaker and do not yet allow a strong position to be taken.     

Planning the next fishing trip: where are the gaps in knowledge about freshwater fish assemblages in Argentina?

Hydrobiologia - In this study, we present a new method to compare the distribution of knowledge regarding the biodiversity of a taxa with the distribution of environments inhabited by that taxa, in...     

Vetulicolians—are they deuterostomes? chordates?

A recent paper by Shu et al.(1) reinterprets the fossil Vetulicola and related forms, all from the Lower Cambrian, as basal deuterostomes, assigning them their own phylum, Vetulicolia. Their conclusion is based on the presence of structures resembling gill slits and a trunk-like region that shows evidence of segmentation. This report summarizes the fossil evidence for their interpretation and evaluates a possible alternative, that vetulicolians may instead be tunicate-like chordates. Implications for our understanding of the nature of the primitive deuterostome (and chordate) body plan are discussed. .     

Parasites of the superorganism: are they indicators of ecosystem health?

The concept of ecosystem health is derived from analogies with human health, which subsequently leads to the implication that the ecosystem has organismal properties, a 'superorganism' in the Clementsian sense. Its application and usefulness has been the subject of a contentious debate; yet, the term 'ecosystem health' has captured the public's imagination and woven its way into the current lexicon, even incorporated into public policy. However, the application of parasites as bioindicators of ecosystem health poses a curious conundrum. Perceptions of parasites range from mild distaste to sheer disgust among the general public, the media, environmental managers and non-parasitologists in the scientific community. Nevertheless, the biological nature of parasitism incorporates natural characteristics that are informative and useful for environmental management. The helminths in particular have evolved elegant means to ensure their transmission, often relying on complex life cycle interactions that include a variety of invertebrate and vertebrate hosts. The assemblage of these diverse parasites within a host organism potentially reflect that host's trophic position within the food web as well as the presence in the ecosystem of any other organisms that participate in the various parasite life cycles. Perturbations in ecosystem structure and function that affect food web topology will also impact upon parasite transmission, thus affecting parasite species abundance and composition. As such, parasite populations and communities are useful indicators of environmental stress, food web structure and biodiversity. In addition, there may be useful other means to utilise parasitic organisms based on their biology and life histories such as suites or guilds that may be effective bioindicators of particular forms of environmental degradation. The challenge for parasitology is to convince resource managers and fellow scientists that parasites are a natural part of all ecosystems, each species being a potentially useful information unit, and that healthy ecosystems have healthy parasites.     

C and Q bands in long arm of Y chromosomes; are they identical?

Summary A phenotypically normal male has a small Y chromosome with no Yq fluorescence, but displays constitutive heterochromatin on the end of Yq. C and Q bands on Yq therefore need not be necessarily identical.     

Ectoparasites: are they the proximate cause of cleaning interactions?

We tested the importance of ectoparasites in cleaning symbioses by comparing the activity of Caribbean cleaning gobies ( Elacatinus evelynae ) and of their clients during three daily periods (early morning, midday and late afternoon) in which ectoparasite availability varied naturally. Emergence from the benthos of gnathiid isopod larvae, the main target of cleaning goby predation, was higher at night, when cleaners are inactive, than during the day. Overall ectoparasite loads also tended to be higher on clients in the morning. This coincided with higher rates of visits to cleaning stations by client fish in the morning than at midday, but high rates of client visits were also recorded in the late afternoon. Clients were more likely to adopt stereotypical incitation poses, which increase the likelihood of being cleaned, in the morning than later in the day. Inspection bouts by cleaning gobies were longest in the morning. Cleaner and client behaviours therefore change predictably in response to natural diurnal variation in ectoparasite availability. These results add to a growing number of studies supporting the idea that cleaning symbioses are mutualisms dependent on ectoparasite removal.     

Bacterial EPIYA effectors – Where do they come from? What are they? Where are they going?

Recent studies have revealed a distinct class of bacterial effectors defined by the presence of EPIYA or EPIYA‐related motif. These bacterial EPIYA effectors are delivered into host cells via type III or IV secretion, where they undergo tyrosine phosphorylation at the EPIYA motif and thereby manipulate host signalling by promiscuously interacting with multiple SH2 domain‐containing proteins. Up to now, nine EPIYA effectors have been identified from various bacteria. These effectors do not share sequence homology outside the EPIYA motif, arguing against the idea that they have common ancestors. A search of mammalian proteomes revealed the presence of a mammalian EPIYA‐containing protein, Pragmin, which potentiates Src family kinase (SFK) activity by binding and sequestrating the SFK inhibitor Csk upon EPIYA phosphorylation. As several bacterial EPIYA effectors also target Csk, they may have evolved through generation of sequences that mimic the Pragmin EPIYA motif. EPIYA motifs are often diverged through multiple duplications in each bacterial effector. Such a structural plasticity appears to be due to intrinsic disorder of the EPIYA‐containing region, which enables the bacterial effectors to undergo efficient phosphorylation and mediate promiscuous interaction with multiple host proteins. Given the functional versatility of the EPIYA motif, many more bacterial EPIYA effectors will soon be emerging.     

Resveratrol and rapamycin: are they anti‐aging drugs?

Studies of the basic biology of aging have advanced to the point where anti‐aging interventions, identified from experiments in model organisms, are beginning to be tested in people. Resveratrol and rapamycin, two compounds that target conserved longevity pathways and may mimic some aspects of dietary restriction, represent the first such interventions. Both compounds have been reported to slow aging in yeast and invertebrate species, and rapamycin has also recently been found to increase life span in rodents. In addition, both compounds also show impressive effects in rodent models of age‐associated diseases. Clinical trials are underway to assess whether resveratrol is useful as an anti‐cancer treatment, and rapamycin is already approved for use in human patients. Compounds such as these, identified from longevity studies in model organisms, hold great promise as therapies to target multiple age‐related diseases by modulating the molecular causes of aging.     

Effect of zinc salts on the structure–function of actomyosin from pelagic fish

The effect of zinc salts, zinc chloride and zinc sulfate on the structure and ATPase enzyme activity of actomyosin from pelagic fish (Sardinella longiceps) has been investigated. ATPase enzyme activity decreased in the presence of both the zinc salts. The inhibitory effect is present in both pH of 7.0 and 9.0. At concentration of 1 × 10^?3 M of zinc salts, complete inhibition of ATPase enzyme activity is observed. With the increase in temperature from 25 °C to 45 °C the ATPase activity decreased by nearly 80%. The solubility profile of actomyosin in the presence of zinc salts shows a sigmoid pattern as the concentration of both the zinc salts increases. Free SH content of actomyosin decreased with the increase in concentration of zinc salts. Intrinsic fluorescence indicated significant decrease in relative fluorescence intensity of actomyosin. This indicates significant alterations in the structure of actomyosin. Analysis of secondary structure also indicates significant alteration in the α-helical content upon binding of both zinc salts.     

Do invasive freshwater fish species grow better when they are invasive?

A frequent assumption in invasion ecology is that invasive species have enhanced growth rates in their invasive ranges. However, invasions frequently occur in sub‐tropical and tropical environments where growth could be higher simply due to climatic conditions rather than novel habitat. In this study, a meta‐analysis of growth rates (length‐at‐age data) was completed for six invasive freshwater fish species: common carp Cyprinus carpio, largemouth bass Micropterus salmoides, brown trout Salmo trutta, brown bullhead Ictalurus nebulosus, flathead catfish Pylodictis olivaris and northern snakehead Channa argus. Significant effects of climate on growth were observed for all species except common carp, and following normalization of growth for climate effects, a range of growth responses between native and invasive populations were revealed. Two species (brown trout, flathead catfish) showed significantly increased growth rates in invasive compared to native ranges, but two species (common carp, largemouth bass) showed significantly faster growth in native ranges, and two other species (northern snakehead, brown bullhead) showed no difference in growth rates. No species showed both significantly enhanced growth rates and initial sizes in invasive compared to native ranges. Using the comparative method, countergradient growth variations were apparent for all species within their native ranges and for all but one species in invasive ranges. Invasive populations of freshwater fish do not always grow faster when invasive and future studies need to consider growth covariates (e.g. climate and countergradient growth) prior to comparing life‐history differences between invasive and native populations.     

Evidence of opposing fitness effects of parental heterozygosity and relatedness in a critically endangered marine turtle?

How individual genetic variability relates to fitness is important in understanding evolution and the processes affecting populations of conservation concern. Heterozygosity–fitness correlations (HFCs) have been widely used to study this link in wild populations, where key parameters that affect both variability and fitness, such as inbreeding, can be difficult to measure. We used estimates of parental heterozygosity and genetic similarity (‘relatedness’) derived from 32 microsatellite markers to explore the relationship between genetic variability and fitness in a population of the critically endangered hawksbill turtle, Eretmochelys imbricata. We found no effect of maternal MLH (multilocus heterozygosity) on clutch size or egg success rate, and no single‐locus effects. However, we found effects of paternal MLH and parental relatedness on egg success rate that interacted in a way that may result in both positive and negative effects of genetic variability. Multicollinearity in these tests was within safe limits, and null simulations suggested that the effect was not an artefact of using paternal genotypes reconstructed from large samples of offspring. Our results could imply a tension between inbreeding and outbreeding depression in this system, which is biologically feasible in turtles: female‐biased natal philopatry may elevate inbreeding risk and local adaptation, and both processes may be disrupted by male‐biased dispersal. Although this conclusion should be treated with caution due to a lack of significant identity disequilibrium, our study shows the importance of considering both positive and negative effects when assessing how variation in genetic variability affects fitness in wild systems.     

Genetic and karyotypic structure in the shrews of the Sorex araneus group: are they independent?

The species of the common shrew (Sorex araneus) group are morphologically very similar but exhibit high levels of karyotypic variation. Here we used genetic variation at 10 microsatellite markers in a data set of 212 individuals mostly sampled in the western Alps and composed of five karyotypic taxa (Sorex coronatus, Sorex antinorii and the S. araneus chromosome races Cordon, Bretolet and Vaud) to investigate the concordance between genetic and karyotypic structure. Bayesian analysis confirmed the taxonomic status of the three sampled species since individuals consistently grouped according to their taxonomical status. However, introgression can still be detected between S. antinorii and the race Cordon of S. araneus. This observation is consistent with the expected low karyotypic complexity of hybrids between these two taxa. Geographically based cryptic substructure was discovered within S. antinorii, a pattern consistent with the different postglaciation recolonization routes of this species. Additionally, we detected two genetic groups within S. araneus notwithstanding the presence of three chromosome races. This pattern can be explained by the probable hybrid status of the Bretolet race but also suggests a relatively low impact of chromosomal differences on genetic structure compared to historical factors. Finally, we propose that the current data set (available at http://www.unil.ch/dee/page7010_en.html#1) could be used as a reference by those wanting to identify Sorex individuals sampled in the western Alps.     

The effects of fishing on the diversity,biomass and trophic structure of Seychelles’ reef fish communities

A fishery independent underwater visual census technique was used to assess the effects of fishing on the diversity, biomass and trophic structure of the diurnally active non-cryptic reef-associated fish communities of the Seychelles. One hundred and thirty four species associated with three significantly different types of reef habitat were censused at one unfished ground and in six fishing grounds subject to different fishing intensity and the biomass of several species targeted by the fishery. The diversity of families containing target species (lutjanidae, lethrinidae) was significantly higher at unfished and lightly fished sites as was the total biomass of the fish community and the biomass of piscivorous, piscivorous/invertebrate feeding and herbivorous trophic groups. However, there was no indication that the biomass of non-target species increased in response to the removal of their predators by fishing. The findings of this study are significant for fishery managers because they suggest that the intensive differential cropping of top predators will not necessarily lead to increases in the biomass and productivity of their prey.