SUMMARY Parasites are known to affect the predatory behaviour or diet of their hosts. In relation to biological invasions, parasites may significantly influence the invasiveness of the host population and/or mediate the relationships between the invader and the invaded community. Dikerogammarus villosus, a recently introduced species, has had a major impact in European rivers. Notably, its high position in trophic web and high predatory behaviour, have both facilitated its invasive success, and affected other macroinvertebrate taxa in colonized habitats. The intracellular parasite Cucumispora dikerogammari, specific to D. villosus, has successfully dispersed together with this amphipod. Data presented here have shown that D. villosus infected by this parasite have a reduced predatory behaviour compared with healthy individuals, and are much more active suggesting that the co-invasive parasite may diminish the predatory pressure of D. villosus on newly colonized communities.
Some larval helminths alter the behavior of their intermediate hosts in ways that favor the predation of infected hosts, thus enhancing trophic transmission. Gammarids (Crustacea: Amphipoda) offer unique advantages for the study of the proximate factors mediating parasite-induced behavioral changes. Indeed, amphipods infected by distantly related worms (acanthocephalans, cestodes and trematodes) encysted in different microhabitats within their hosts (hemocoel, brain) present comparable, chronic, behavioral pathologies. In order to evaluate the potential connection between behavioral disturbances and immune responses in parasitized gammarids, this Review surveys the literature bearing on sensorimotor pathway dysfunctions in infected hosts, on the involvement of the neuromodulator serotonin in altered responses to environmental stimuli, and on systemic and neural innate immunity in arthropods. Hemocyte concentration and phenoloxidase activity associated with melanotic encapsulation are depressed in acanthocephalan-manipulated gammarids. However, other components of the arsenal deployed by crustaceans against pathogens have not yet been investigated in helminth-infected gammarids. Members of the Toll family of receptors, cytokines such as tumor necrosis factors (TNFs), and the free radical nitric oxide are all implicated in neuroimmune responses in crustaceans. Across animal phyla, these molecules and their neuroinflammatory signaling pathways are touted for their dual beneficial and deleterious properties. Thus, it is argued that neuroinflammation might mediate the biochemical events upstream of the serotonergic dysfunction observed in manipulated gammarids - a parsimonious hypothesis that could explain the common behavioral pathology induced by distantly related parasites, both hemocoelian and cerebral.
The mesopelagic habitat is a vast space that lacks physical landmarks and is structured by depth, light penetration, and horizontal currents. Solar illumination is visible in the upper 1,000 m of the ocean, becoming dimmer and spectrally filtered with depth-generating a nearly monochromatic blue light field . The struggle to perceive dim downwelling light and bioluminescent sources and the need to remain unseen generate contrasting selective pressures on the eyes of mesopelagic inhabitants . Hyperiid amphipods are cosmopolitan members of the mesopelagic fauna with at least ten different eye configurations across the family-ranging from absent eyes in deep-living species to four enlarged eyes in mesopelagic individuals [3-7]. The hyperiid amphipod Paraphronima gracilis has a pair of bi-lobed apposition compound eyes, each with a large upward-looking portion and a small lateral-looking portion. The most unusual feature of the P. gracilis eye is that its upward-looking portion is resolved into a discontinuous retina with 12 distinct groups, each serving one transverse row of continuously spaced facets. On the basis of eye morphology, we estimated spatial acuity (2.5° ± 0.11°, SEM; n = 25) and optical sensitivity (30 ± 3.4 μm(2) ⋅ sr, SEM; n = 25). Microspectrophotometry showed that spectral sensitivity of the eye peaked at 516 nm (±3.9 nm, SEM; n = 6), significantly offset from the peak of downwelling irradiance in the mesopelagic realm (480 nm). Modeling of spatial summation within the linear retinal groups showed that it boosts sensitivity with less cost to spatial acuity than more typical configurations.
BACKGROUND: Gammarus minus, a freshwater amphipod living in the cave and surface streams in the eastern USA, is a premier candidate for studying the evolution of troglomorphic traits such as pigmentation loss, elongated appendages, and reduced eyes. In G. minus, multiple pairs of genetically related, physically proximate cave and surface populations exist which exhibit a high degree of intraspecific morphological divergence. The morphology, ecology, and genetic structure of these sister populations are well characterized, yet the genetic basis of their morphological divergence remains unknown. RESULTS: We used degenerate PCR primers designed to amplify opsin genes within the subphylum Crustacea and discovered two distinct opsin paralogs (average inter-paralog protein divergence [almost equal to] 20%) in the genome of three independently derived pairs of G. minus cave and surface populations. Both opsin paralogs were found to be related to other crustacean middle wavelength sensitive opsins. Low levels of nucleotide sequence variation (< 1% within populations) were detected in both opsin genes, regardless of habitat, and dN/dS ratios did not indicate a relaxation of functional constraint in the cave populations with reduced or absent eyes. Maximum likelihood analyses using codon-based models also did not detect a relaxation of functional constraint in the cave lineages. We quantified expression level of both opsin genes and found that the expression of both paralogs was significantly reduced in all three cave populations relative to their sister surface populations. CONCLUSIONS: The concordantly lowered expression level of both opsin genes in cave populations of G. minus compared to sister surface populations, combined with evidence for persistent purifying selection in the cave populations, is consistent with an unspecified pleiotropic function of opsin proteins. Our results indicate that phototransduction proteins such as opsins may have retained their function in cave-adapted organisms because they may play a pleiotropic role in other important processes that are unrelated to vision.
Increasing sea surface temperatures are predicted to alter marine plant-herbivore interactions and, thus, the structure and function of algal and seagrass communities. Given the fundamental role of host plant quality in determining herbivore fitness, predicting the effects of increased temperatures requires an understanding of how temperature may interact with diet quality. We used an herbivorous marine amphipod, Sunamphitoe parmerong, to test how temperature and diet interact to alter herbivore growth, feeding rates, survival, and fecundity in short- and long-term assays. In short-term thermal stress assays, S. parmerong was tolerant to the range of temperatures that it currently experiences in nature (20-26 °C), with mortality at temperatures > 27 °C. In longer term experiments, two generations of S. parmerong were reared in nine combinations of temperature (ambient, + 2, + 4 °C) and diet (two high- and one low-quality algal species) treatments. Temperature and diet interacted to determine total numbers of amphipods in the F1 generation and the potential F2 population size (sum of brooded eggs and newly hatched juveniles). The size and development rate of F1 individuals were affected by diet, but not temperature. Consumption rates per capita were highest at intermediate temperatures but could not explain the observed differences in survival. Our results show that predicting the effects of increasing temperature on marine herbivores will be complicated by variation in host plant quality, and that climate-driven changes to plant availability will affect herbivore performance, and thus the strength of plant-herbivore interactions.
Due to its sensitivity to many environmental and anthropogenic stressors, including a wide range of chemical compounds, Hyalella azteca, a freshwater amphipod, has emerged as one of the most commonly used invertebrates for ecotoxicological assessment.Peptidergic signaling systems are key components in the control of organism-environment interactions, and there is a growing literature suggesting that they are targets of a number of aquatic toxicants.Interestingly, and despite its model species status in the field of ecotoxicology, little is known about the peptide hormones of H. azteca.Here, a transcriptome was produced for this species using the de novo assembler Trinity and mined for sequences encoding putative peptide precursors; the transcriptome was assembled from 460,291,636 raw reads and consists of 133,486 unique transcripts.Seventy-six sequences encoding peptide pre/preprohormones were identified from this transcriptome, allowing for the prediction of 202 distinct peptides, which included members of the allatostatin A, allatostatin B, allatostatin C, allatotropin, bursicon, CCHamide, corazonin, crustacean cardioactive peptide, crustacean hyperglycemic hormone/molt-inhibiting hormone, ecdysis-triggering hormone, eclosion hormone, elevenin, FMRFamide-like peptide, glycoprotein hormone, GSEFLamide, inotocin, leucokinin, myosuppressin, neuropeptide F, orcokinin, orcomyotropin, pigment dispersing hormone, proctolin, pyrokinin, red pigment concentrating hormone, RYamide, short neuropeptide F, SIFamide, sulfakinin, tachykinin-related peptide and trissin families.These peptides expand the known peptidome for H. azteca approximately nine-fold, forming a strong foundation for future studies of peptidergic control, including disruption by aquatic toxicants, in this important ecotoxicological model.
In the ancient Lake Baikal, Russia, amphipod crustaceans have undergone a spectacular adaptive radiation, resulting in a diverse community of species. A survey of microsporidian parasites inhabiting endemic and non-endemic amphipod host species at the margins of Lake Baikal indicates that the endemic amphipods harbour many microsporidian parasite groups associated with amphipods elsewhere in Eurasia. While these parasites may have undergone a degree of adaptive radiation within the lake, there is little evidence of host specificity. Furthermore, a lack of reciprocal monophyly indicates that exchanges of microsporidia between Baikalian and non-Baikalian hosts have occurred frequently in the past and may be ongoing. Conversely, limitations to parasite exchange between Baikalian and non-Baikalian host populations at the margins of the lake are implied by differences in parasite prevalence and lack of shared microsporidian haplotypes between the two host communities. While amphipod hosts have speciated sympatrically within Lake Baikal, the parasites appear instead to have accumulated, moving into the lake from external amphipod populations on multiple occasions to exploit the large and diverse community of endemic amphipods in Lake Baikal.
Groundwater is an extreme environment due to its absence of light, resource scarcity and highly fragmentary nature. Successful groundwater colonizers underwent major evolutionary changes and exhibit eye and pigment loss (troglomorphies). Consequently, their chances of dispersal and survival in the well-connected surface waters are greatly decreased, resulting in significant endemism. The West Palaearctic subterranean amphipod genus Niphargus comprises hundreds of narrowly endemic and troglomorphic species. Nevertheless, a few are known to occur in surface waters, two of which, N. hrabei and N. valachicus, have extremely large ranges that even exceed those of many surface-water amphipods. We studied whether this pattern results from a secondary colonization of the relatively well-connected epigean environment, and that this ecological shift promoted the large-scale dispersal of these species. Results showed that despite their ecological and zoogeographic similarities, N. hrabei and N. valachicus are not closely related and independently colonized surface waters. Their phylogeographic patterns indicate Middle to Late Pleistocene dispersal episodes throughout the Danube lowlands, and relatively modest yet significant genetic differentiation among populations. Clustering based on morphology revealed that the two species are phenotypically closer to each other than they are to most other epigean congeners. We presume that the ecological shift to surface environments was facilitated by their ability to thrive in hypoxic waters where rheophilic competitors from the family Gammaridae cannot survive. In conclusion, our results indicate that adaptation to groundwater is not a one-way evolutionary path and that troglomorphic species can occasionally recolonize and widely disperse in surface waters.
There is a lack of suitable tropical marine species for ecotoxicity tests. An attractive model organism for ecotoxicology is the marine amphipod Parhyale hawaiensis, which is already a model for genetic and developmental studies. This species is widespread, can tolerate changes in salinity, is easy to handle and is representative of circumtropical regions. The aim of this work was to describe standardized procedures for laboratory husbandry, define conditions for acute toxicity tests, and to provide acute toxicity test results for some reference toxicants. Culturing conditions for the organism in the laboratory were established in reconstituted seawater (30 ± 2 salinity), 24 ± 2 °C, photoperiod 12/12 h light/dark. Acute toxicity test procedures were developed for 96 h-exposure time, and organisms at ages <7 days. The miniaturized version of the test, based on 96-well microplates and 200 µL of exposure media provided consistent results compared to larger exposure volumes (80-mL vials protocol). Acute toxicity of Ag, Cd, Cu, Zn and ammonia determined for P. hawaiensis were consistent to previous results for other marine amphipods. We conclude that P. hawaiensis can be successfully cultured in standardized conditions and be effectively used in acute toxicity testing. Further development and use of this model will enable standardized and reproducible ecotoxicology investigations in understudied and vulnerable tropical marine ecosystems.
In an effort to broaden our understanding of the biodiversity and distribution of gregarines infecting crustaceans, this study describes two new species of gregarines, Thiriotia hyperdolphinae n. sp. and Cephaloidophora oradareae n. sp., parasitizing a deep sea amphipod (Oradarea sp.). Amphipods were collected using the ROV Hyper-Dolphin at a depth of 855 m while on a cruise in Sagami Bay, Japan. Gregarine trophozoites and gamonts were isolated from the gut of the amphipod and studied with light and scanning electron microscopy, and phylogenetic analysis of 18S rDNA. T. hyperdolphinae n. sp. was distinguished from existing species based on morphology, phylogenetic position, as well as host niche and geographic locality. While Cephaloidophora oradareae n. sp. distinguished itself from existing Cephaloidophora, based on a difference in host (Oradarea sp.), geographic location, and to a certain extent morphology. We established this new species with the understanding that a more comprehensive examination of diversity at the molecular level is necessary within Cephaloidophora. Results from the 18S rDNA molecular phylogeny showed that T. hyperdolphinae n. sp. was positioned within a clade consisting of Thiriotia spp., while C. oradareae n. sp. grouped within the Cephaloidophoridae. Still, supplemental genetic information from gregarines infecting crustaceans will be needed to better understand relationships within this group of apicomplexans. This article is protected by copyright. All rights reserved.