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Microscopic plastic items (microplastics) are ubiquitously present in aquatic ecosystems. With decreasing size their availability and potential to accumulate throughout food webs increase. However, little is known on the uptake of microplastics by freshwater invertebrates. To address this, we exposed species with different feeding strategies to 1, 10 and 90 µm fluorescent polystyrene spheres (3–3 000 particles mL −1 ). Additionally, we investigated how developmental stages and a co-exposure to natural particles (e.g., food) modulate microplastic ingestion. All species ingested microplastics in a concentration-dependent manner with Daphnia magna consuming up to 6 180 particles h −1 , followed by Chironomus riparius (226 particles h −1 ), Physella acuta (118 particles h −1 ), Gammarus pulex (10 particles h −1 ) and Lumbriculus variegatus (8 particles h −1 ). D. magna did not ingest 90 µm microplastics whereas the other species preferred larger microplastics over 1 µm in size. In C. riparius and D. magna , size preference depended on the life stage with larger specimens ingesting more and larger microplastics. The presence of natural particles generally reduced the microplastics uptake. Our results demonstrate that freshwater invertebrates have the capacity to ingest microplastics. However, the quantity of uptake depends on their feeding type and morphology as well as on the availability of microplastics.

Cryptic species complexes-genetically divergent lineages with similar phenotypes may appear cryptic not due to true similarity, but because high within-species morphological variation masks interspecies differences, particularly in heterogeneous environments. This study tests whether such lineages exhibit morphological convergence across similar environmental gradients or context-dependent divergence, challenging their cryptic status. We propose a theoretical framework to assess phenotypic differentiation and apply it using the amphipod complex Gammarus roeselii , which diversified in the Balkan Peninsula before one lineage expanded into Central Europe. We examined five lineages across similar environmental gradients to evaluate their phenotypic divergence. Our findings confirmed their cryptic status. However, phenotypic differentiation along environmental gradients revealed MOTU-specific adaptive trajectories: traits under strong selection (e.g., anti-predator defences) showed convergent responses, while morphological (e.g., body length) and physiological traits (e.g., gill area) diverged, likely due to local selection. Some MOTUs exhibited distinct, partially divergent sexual dimorphism, suggesting varied reproductive or ecological strategies within cryptic lineages. Phenotypic variation was greater within than between MOTUs, reinforcing their cryptic status and revealing strong local adaptive responses. This complex exemplifies how adaptive divergence and biogeographic history jointly shape biodiversity, with morphological stasis despite genetic and ecological differentiation exposing hidden speciation and environmental responses.

Adaptive radiations are bursts of evolutionary species diversification that have contributed to much of the species diversity on Earth. An exception is modern Europe, where descendants of ancient adaptive radiations went extinct, and extant adaptive radiations are small, recent and narrowly confined. However, not all legacy of old radiations has been lost. Subterranean environments, which are dark and food-deprived, yet buffered from climate change, have preserved ancient lineages. Here we provide evidence of an entirely subterranean adaptive radiation of the amphipod genus Niphargus , counting hundreds of species. Our modelling of lineage diversification and evolution of morphological and ecological traits using a time-calibrated multilocus phylogeny suggests a major adaptive radiation, comprised of multiple subordinate adaptive radiations. Their spatio-temporal origin coincides with the uplift of carbonate massifs in South-Eastern Europe 15 million years ago. Emerging subterranean environments likely provided unoccupied, predator-free space, constituting ecological opportunity, a key trigger of adaptive radiation. This discovery sheds new light on the biodiversity of Europe. There are relatively few known extant adaptive radiations in Europe that predate the Pleistocene. Here, Borko et al. characterize the diversity and diversification of the subterranean amphipod genus Niphargus , showing evidence for a large adaptive radiation associated with massif uplift 15 million years ago.

Regenerating animals have the ability to reproduce body parts that were originally made in the embryo and subsequently lost due to injury. Understanding whether regeneration mirrors development is an open question in most regenerative species. Here, we take a transcriptomics approach to examine whether leg regeneration shows similar temporal patterns of gene expression as leg development in the embryo, in the crustacean Parhyale hawaiensis . We find that leg development in the embryo shows stereotypic temporal patterns of gene expression. In contrast, the dynamics of gene expression during leg regeneration show a higher degree of variation related to the physiology of individual animals. A major driver of this variation is the molting cycle. We dissect the transcriptional signals of individual physiology and regeneration to obtain clearer temporal signals marking distinct phases of leg regeneration. Comparing the transcriptional dynamics of development and regeneration we find that, although the two processes use similar sets of genes, the temporal patterns in which these genes are deployed are different and cannot be systematically aligned.

The amphipod crustacean Parhyale hawaiensis is a blossoming model system for studies of developmental mechanisms and more recently regeneration. We have sequenced the genome allowing annotation of all key signaling pathways, transcription factors, and non-coding RNAs that will enhance ongoing functional studies. Parhyale is a member of the Malacostraca clade, which includes crustacean food crop species. We analysed the immunity related genes of Parhyale as an important comparative system for these species, where immunity related aquaculture problems have increased as farming has intensified. We also find that Parhyale and other species within Multicrustacea contain the enzyme sets necessary to perform lignocellulose digestion ('wood eating'), suggesting this ability may predate the diversification of this lineage. Our data provide an essential resource for further development of Parhyale as an experimental model. The first malacostracan genome will underpin ongoing comparative work in food crop species and research investigating lignocellulose as an energy source. The marine crustacean known as Parhyale hawaiensis is related to prawns, shrimps and crabs and is found at tropical coastlines around the world. This species has recently attracted scientific interest as a possible new model to study how animal embryos develop before birth and, because Parhyale can rapidly regrow lost limbs, how tissues and organs regenerate. Indeed, Parhyale has many characteristics that make it a good model organism, being small, fast-growing and easy to keep and care for in the laboratory. Several research tools have already been developed to make it easier to study Parhyale. This includes the creation of a system for using the popular gene editing technology, CRISPR, in this animal. However, one critical resource that is available for most model organisms was missing; the complete sequence of all the genetic information of this crustacean, also known as its genome, was not available. Kao, Lai, Stamataki et al. have now compiled the Parhyale genome – which is slightly larger than the human genome – and studied its genetics. Analysis revealed that Parhyale has genes that allow it to fully digest plant material. This is unusual because most animals that do this rely upon the help of bacteria. Kao, Lai, Stamataki et al. also identified genes that provide some of the first insights into the immune system of crustaceans, which protects these creatures from diseases. Kao, Lai, Stamataki et al. have provided a resource and findings that could help to establish Parhyale as a popular model organism for studying several ideas in biology, including organ regeneration and embryonic development. Understanding how Parhyale digests plant matter, for example, could progress the biofuel industry towards efficient production of greener energy. Insights from its immune system could also be adapted to make farmed shrimp and prawns more resistant to infections, boosting seafood production.

Research on the uptake and effects of bioplastics by aquatic organisms is still in its infancy. Here, we aim to advance the field by comparing uptake and effects of microplastic particles (MPP) of a biodegradable bioMPP (polyhydroxybutyrate (PHB)) and petroleum-based MPP (polymethylmethacrylate (PMMA)) in the freshwater amphipod Gammarus fossarum. Ingestion of both MPP in different particle sizes (32–250 µm) occurred after 24 h, with highest ingestion of particles in the range 32–63 µm and almost complete egestion after 64 h. A four-week effect-experiment showed a significant decrease of the assimilation efficiency in amphipods exposed to the petroleum-based MPP from week two onwards. The petroleum-based PMMA affected assimilation efficiency significantly in contrast to the biodegradable PHB, but overall differences in direct comparison of MPP types were small. Both MPP types led to a significantly lower wet weight gain relative to the control treatments. After four weeks, differences between both MPP types and silica, used as a natural particle control, were detected. In summary, these results suggest that both MPP types provoke digestive constraints on the amphipods, which go beyond those of natural non-palatable particles. This highlights the need for more detailed research comparing environmental effects of biodegradable and petroleum-based MPP and testing those against naturally occurring particle loads.

The environmental drivers that effect the pelagic amphipod communities in the neritic province have received little attention worldwide. This study analyzed the influence of fluvial discharges and wind regime on the pelagic amphipods in neritic waters of the southern Gulf of Mexico during two contrasting seasons: May (dry, lower discharges and wind speeds) and November (nortes, higher discharges and wind speeds). Zooplankton samples were collected at five depth levels of the water column (0-6, 6-12, 12-18, 45-55, and 95-105 m) using a stratified opening-closing net system. Environmental gradients were assessed by defining three horizontal assemblages ('coastal', 'neritic', 'slope') and two vertical assemblages ('surface': 0-18 m; 'deep': 45-105 m). Seasonally, the greater volume of nutrient-rich discharges during nortes resulted in a higher amphipod density. Spatially, low salinity waters off river mouths corresponded to the lowest amphipod density and diversity. The horizontal and vertical assemblages showed significant differences during the dry (ANOSIM test, p < 0.05); during nortes, the structure of horizontal and vertical assemblages showed a lower heterogeneity, probably due to wind strength. Differences within the assemblages defined in the horizontal and vertical planes were only evident when Lestrigonus bengalensis was considered in the analysis; however, without this species, the amphipod community showed more homogeneity across the two seasons. Anchylomera blossevillei, Tetrathyrus forcipatus, and the juveniles of Eupronoidae were ecologically relevant in the characterization of the assemblages due to their specific environmental requirements. Diversity, evaluated using the completeness method, increased from the coast to the ocean in both seasons; vertically, diversity was highest in the 'deep' assemblage during the dry, but no differences were observed between assemblages in nortes. The greater similarity of the assemblages during nortes was associated with a higher homogeneity in hydrological conditions due to the strong winds that dominate this season. These findings contribute to a deeper ecological understanding of the effects of hydro-meteorological conditions on the structure of pelagic amphipod communities.

Background Lake Baikal is one of the oldest freshwater lakes and has constituted a stable environment for millions of years, in stark contrast to small, transient bodies of water in its immediate vicinity. A highly diverse endemic endemic amphipod fauna is found in one, but not the other habitat. We ask here whether differences in stress response can explain the immiscibility barrier between Lake Baikal and non-Baikal faunas. To this end, we conducted exposure experiments to increased temperature and the toxic heavy metal cadmium as stressors. Results Here we obtained high-quality de novo transcriptome assemblies, covering mutiple conditions, of three amphipod species, and compared their transcriptomic stress responses. Two of these species, Eulimnogammarus verrucosus and E. cyaneus , are endemic to Lake Baikal, while the Holarctic Gammarus lacustris is a potential invader. Conclusions Both Baikal species possess intact stress response systems and respond to elevated temperature with relatively similar changes in their expression profiles. G. lacustris reacts less strongly to the same stressors, possibly because its transcriptome is already perturbed by acclimation conditions.

It has been suggested that giant Antarctic marine invertebrates will be particularly vulnerable to declining O2 levels as our ocean warms in line with current climate change predictions. Our study provides some support for this oxygen limitation hypothesis, with larger body sizes being generally more sensitive to O2 reductions than smaller body sizes. However, it also suggests that the overall picture is a little more complex. We tested predictions from three different, but overlapping, O2-related hypotheses accounting for gigantism, using four Antarctic amphipod species encompassing a wide range of body sizes. We found a significant effect of body size, but also of species, in their respiratory responses to acutely declining O2 tensions. The more active lifestyle of intermediate-sized Prostebbingia brevicornis was supported by a better respiratory performance than predicted by the oxygen limitation hypothesis alone, but consistent with the symmorphosis hypothesis. We suggest that giant polar amphipods are likely to be some of the first to fare badly in an O2-poor ocean. However, the products of past evolutionary innovation, such as respiratory pigments that enhance O2-transport and novel gas exchange structures, may in some species offset any respiratory disadvantages of either large or small body size. This article is part of the theme issue ‘Physiological diversity, biodiversity patterns and global climate change: testing key hypotheses involving temperature and oxygen’.

We explore the delayed consequences of parental exposure to environmentally relevant cadmium concentrations on the life-history traits throughout generations of the freshwater crustaceanGammarus fossarum. We report the preliminary results obtained during a challenging one-year laboratory experiment in this environmental species and propose the use of population modeling to interpret the changes in offspring life-history traits regarding their potential demographic impacts. The main outcome of this first long-term transgenerational assay is that the exposure of spawners during a single gametogenesis cycle (3 weeks) could result in severe cascading effects on the life-history traits along three unexposed offspring generations (one year). Indeed, we observed a decrease in F1 reproductive success, an early onset of F2 offspring puberty with reduced investment in egg yolk reserves, and finally a decrease in the growth rate of F3 juveniles. However, the analysis of these major transgenerational effects by means of a Lefkovitch matrix population model revealed only weak demographic impacts. Population compensatory processes mitigating the demographic consequences of parental exposure seem to drive the modification of life-history traits in offspring generations. This exploratory study sheds light on the role of population mechanisms involved in the demographic regulation of the delayed effects of environmental toxicity in wild populations.