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Few studies have explored the relative strength of ecogeographic versus lineage-specific effects on a global scale, particularly for poikilotherms, those organisms whose internal temperature varies with their environment. Here, we compile a global dataset of life history traits in Daphnia, at the species-and population-level, and use those data to parse the relative influences of lineage-specific effects and climate. We also compare the thermal response (plasticity) of life history traits and their dependence on climate, temperature, precipitation, and latitude. We found that the mode of evolution for life history traits varies but that the thermal response of life history traits most often follows a random walk model of evolution. We conclude that life history trait evolution in Daphnia is not strongly species-specific but is ecogeographically distinct, suggesting that life history evolution should be understood at the population level for Daphnia and possibly for other poikilotherms. [ABSTRACT FROM AUTHOR]

Simple sequence repeats (SSRs) are rare (approximately 1%) in most genomes and are generally considered to have no function. However, penaeid shrimp genomes have a high proportion of SSRs (>23%), raising the question of whether these SSRs play important functional and evolutionary roles in these SSR-rich species. Here, we show that SSRs drive genome plasticity and adaptive evolution in two penaeid shrimp species, Fenneropenaeus chinensis and Litopenaeus vannamei. Assembly and comparison of genomes of these two shrimp species at the chromosome-level revealed that transposable elements serve as carriers for SSR expansion, which is still occurring. The remarkable genome plasticity identified herein might have been shaped by significant SSR expansions. SSRs were also found to regulate gene expression by multi-omics analyses, and be responsible for driving adaptive evolution, such as the variable osmoregulatory capacities of these shrimp under low-salinity stress. These data provide strong evidence that SSRs are an important driver of the adaptive evolution in penaeid shrimp. This study focuses on the role of simple sequence repeats (SSRs) in the evolution of the genomes of two penaeid shrimp species, Fenneropenaeus chinensis and Litopenaeus vannamei. They observed a significant expansion in SSRs in the genomes of these species (~23%) compared what is seen in other animal genomes (~1%) and suggest a possible mechanistic relationship between SSRs and transposable elements. [ABSTRACT FROM AUTHOR]

Abstract: Removing individuals from a wild population can affect the availability of prospective mates and the outcome of competitive interactions, with subsequent effects on mating patterns and sexual selection. Consequently, the rate of harvest‐induced evolution is predicted to be strongly dependent on the strength and dynamics of sexual selection, yet there is limited empirical knowledge on the interplay between selective harvesting and the mating systems of exploited species. In this study, we used genetic parentage assignment to compare mating patterns of the highly valued and overexploited European lobster (Homarus gammarus) in a designated lobster reserve and nearby fished area in southern Norway. In the area open to fishing, the fishery is regulated by a closed season, a minimum legal size and a ban on the harvest of egg‐bearing females. Due to the differences in size and sex‐specific fishing mortality between the two areas, males and females are of approximately equal average size in the fished area, whereas males tend to be larger in the reserve. Our results show that females would mate with males larger than their own body size, but the relative size difference was significantly larger in the reserve. Sexual selection acted positively on both body size and claw size in males in the reserve, while it was nonsignificant in fished areas. This strongly suggests that size truncation of males by fishing reduces the variability of traits that sexual selection acts upon. If fisheries continue to target large individuals (particularly males) with higher relative reproductive success, the weakening of sexual selection will likely accelerate fisheries‐induced evolution towards smaller body size. [ABSTRACT FROM AUTHOR]

The gradual increase of CO 2 concentration in the atmosphere, absorbed by the ocean surface water through air to sea equilibration termed ocean acidification (OA), leads to the decline of pH in seawater. It is not clear so far how the composition of fatty acids, particular the immune-related, in marine crustacean and the subsequent energy supply in marine ecosystem are affected by OA. The brine shrimp Artemia sinica is an open and common feed that provide essential fatty acids for mariculture. In this study, the fatty acids profiles of brine shrimp cultured under different lower pH levels of CO 2 driven seawater were investigated. The results showed a significant reduction of the proportion of total saturated fatty acids under the pH7.6 within one week. Meanwhile, the percentage of total monounsaturated fatty acids was significantly decreased at day 14 under pH7.8, and this percentage gave a significant increase of proportion within one week under pH7.6. Furthermore, the relative content of total polyunsaturated fatty acids (PUFAs) was found to be clearly increased with exposure to different seawater acidification at day 1, suggesting that the brine shrimp immune response was likely to be affected by acidified seawater as the PUFAs have been well known to be involved in immunomodulatory effects through alterations on cell membrane fluidity/lipid mediators and gene expression of cell signaling pathways. Notably, eicosapentaenoic acid and docosahexaenoic acid, which have essential effect on various physiological processes such as inflammatory cytokines production and cell structural stability, were strongly increased under two lower pH treatments within one week and with the significant increase at day 1 under pH7.6. These data clearly supported the hypothesis that OA might affect fatty acids composition, likely also the innate immunity, in crustacean and the subsequent energy transfer by food-chain system in the marine ecosystem. [ABSTRACT FROM AUTHOR]

There is growing evidence of rapid genetic adaptation of natural populations to environmental change, opening the perspective that evolutionary trait change may subsequently impact ecological processes such as population dynamics, community composition, and ecosystem functioning. To study such eco-evolutionary feedbacks in natural populations, however, requires samples across time. Here, we capitalize on a resurrection ecology study that documented rapid and adaptive evolution in a natural population of the water flea Daphnia magna in response to strong changes in predation pressure by fish, and carry out a follow-up mesocosm experiment to test whether the observed genetic changes influence population dynamics and top-down control of phytoplankton. We inoculated populations of the water flea D. magna derived from three time periods of the same natural population known to have genetically adapted to changes in predation pressure in replicate mesocosms and monitored both Daphnia population densities and phytoplankton biomass in the presence and absence of fish. Our results revealed differences in population dynamics and top-down control of algae between mesocosms harboring populations from the time period before, during, and after a peak in fish predation pressure caused by human fish stocking. The differences, however, deviated from our a priori expectations. An S-map approach on time series revealed that the interactions between adults and juveniles strongly impacted the dynamics of populations and their top-down control on algae in the mesocosms, and that the strength of these interactions was modulated by rapid evolution as it occurred in nature. Our study provides an example of an evolutionary response that fundamentally alters the processes structuring population dynamics and impacts ecosystem features. [ABSTRACT FROM AUTHOR]

Male sexual differentiation in crustaceans is controlled by the androgenic gland (AG), a unique male endocrine organ that, in decapods, is located at the base of the 5th pereiopod. In these animals, the insulin-like androgenic gland hormone (IAG) is the major factor secreted from the AG to induce masculinization and maintain male characteristics. It has, however, recently been proposed that this hormone also plays a role in growth and ovarian development in females. In this study, we tested such a possibility by searching for the IAG gene in the marbled crayfish, a parthenogenetic animal that reproduces asexually to form an all-female genetic clone. Based on the phylogenetic relationship between the marbled crayfish and Procambarus fallax, a gonochoristic species of the same North American Cambaridae family, we searched for the IAG gene in the marbled crayfish and then fully sequenced it. The open reading frame of the gene was found to be completely identical in the two species, and their introns shared over 94% identity. It was also found that, in addition to its expression at the base of the 5th pereiopod and in the testes of male P. fallax crayfish, IAG was expressed in the muscle tissue of P. fallax males and females and even of the parthenogenetic marbled crayfish. These findings provide new insight into possible functions of IAG, in addition to its role as a masculinization-inducing factor, and also constitute the basis for a discussion of the evolutionary relationship between the above two species. [ABSTRACT FROM AUTHOR]

With 104 endemic species family Candonidae is one of the most diverse crustacean groups in Lake Baikal, yet their phylogenetic relationships and position in the family have not been addressed so far. Here, we study the phylogenetic position of Baikal candonids within the family and their evolutionary history using molecular markers for the first time since their original description. We choose 10 Baikal and 28 species from around the world, and three ribosomal RNA-s (18S, 28S, and 16S), and analyze individual and concatenated datasets using Bayesian Inference in MrBayes and BEAST. For molecular divergence time estimates, four fossil records are used to calibrate the root and three internal nodes. The 28S dataset is tested under the strict molecular clock, while for other data we use relaxed clocks. Resulting trees show incongruence between molecular and fossil divergence time estimates, with the former suggesting older ages. Strict molecular clock analysis results in narrower node age confidence intervals and younger time estimates than other analysis. All trees support at least two candonid lineages in Baikal, with two independent colonization events, and 28S suggests a major radiation between 12 and 5 Mya. This divergence time estimate mostly agrees with another, unrelated, ostracod group in the lake and other lake animals as well. Baikal candonid clades show a close phylogenetic relationship with Palearctic lineages, but their deep divergence is indicative of separate genera. Results also suggest a monophyly of tribes that today live exclusively in subterranean waters, and we offer several hypotheses of their evolutionary history. [ABSTRACT FROM AUTHOR]

Segmented organisms and structures have fascinated biologists since William Bateson first described homeotic transformation and recognized the fundamental evolutionary significance of segmental organization. On evolutionary time scales, segments may be lost or gained during major morphological transitions. But how segment loss compares to gain on developmental time scales remains mysterious. Here, we examine the ease of reverse development (opposite to normal growth) by comparing developmentally plastic leg segment loss versus gain in individual barnacles transplanted between different water flow conditions. Plastic segment addition occurred rapidly (one to two molts) and exclusively near the limb base. In contrast, developmentally plastic segment loss-the first observation in any arthropod-took much longer (>10 molts) and, remarkably, occurred throughout the leg (23% of losses occurred mid-limb). Segment loss was not a simple reversal of segment addition. Intersegmental membranes fused first, followed by elimination of duplicate tendons and gradual shortening (but not loss) of duplicate setae. Setal loss, in particular, may impose a severe developmental constraint on arthropod segment fusion. This asymmetric developmental potential (time lag of phenotypic response)-plastic segment addition (amplified normal development) is faster and more orderly than segment loss (reverse development)-adds a new dimension to models of developmental plasticity because the cost of making a developmental mistake in one direction will be greater than in the other. [ABSTRACT FROM AUTHOR]

Salinity is the primary driver of osmoregulatory evolution in decapods, and may have influenced their diversification into different osmotic niches. In semi-terrestrial crabs, hyper-osmoregulatory ability favors sojourns into burrows and dilute media, and provides a safeguard against hemolymph dilution; hypo-osmoregulatory ability underlies emersion capability and a life more removed from water sources. However, most comparative studies have neglected the roles of the phylogenetic and environmental components of inter-specific physiological variation, hindering evaluation of phylogenetic patterns and the adaptive nature of osmoregulatory evolution. Semi-terrestrial fiddler crabs (Uca) inhabit fresh to hyper-saline waters, with species from the Americas occupying higher intertidal habitats than Indo-west Pacific species mainly found in the low intertidal zone. Here, we characterize numerous osmoregulatory traits in all ten fiddler crabs found along the Atlantic coast of Brazil, and we employ phylogenetic comparative methods using 24 species to test for: (i) similarities of osmoregulatory ability among closely related species; (ii) salinity as a driver of osmoregulatory evolution; (iii) correlation between salt uptake and secretion; and (iv) adaptive peaks in osmoregulatory ability in the high intertidal American lineages. Our findings reveal that osmoregulation in Uca exhibits strong phylogenetic patterns in salt uptake traits. Salinity does not correlate with hyper/hypo-regulatory abilities, but drives hemolymph osmolality at ambient salinities. Osmoregulatory traits have evolved towards three adaptive peaks, revealing a significant contribution of hyper/hypo-regulatory ability in the American clades. Thus, during the evolutionary history of fiddler crabs, salinity has driven some of the osmoregulatory transformations that underpin habitat diversification, although others are apparently constrained phylogenetically. [ABSTRACT FROM AUTHOR]

Conspicuous asymmetries seen in many animals and plants offer diverse opportunities to test how the development of a similar morphological feature has evolved in wildly different types of organisms. One key question is: do common rules govern how direction of asymmetry is determined (symmetry is broken) during ontogeny to yield an asymmetrical individual? Examples fromnumerous organisms illustrate howdiverse thisprocess is. These examples also provide some surprising answers to related questions. Is direction of asymmetry in an individual determined by genes, environment or chance? Is direction of asymmetry determined locally (structure by structure) or globally (at the level of the whole body)? Does direction of asymmetry persist when an asymmetrical structure regenerates following autotomy? The answers vary greatly for asymmetries as diverse as gastropod coiling direction, flatfish eye side, crossbill finch bill crossing, asymmetrical claws in shrimp, lobsters and crabs, katydid sound-producing structures, earwig penises and various plant asymmetries. Several examples also reveal how stochastic asymmetry in mollusc and crustacean early cleavage, in Drosophila oogenesis, and in Caenorhabditis elegans epidermal blast cell movement, is a normal component of deterministic development. Collectively, these examples shed light on the role of genes as leaders or followers in evolution. [ABSTRACT FROM AUTHOR]

The mitochondrial genomes of three North American stygobiont amphipodsStygobromus tenuis potomacus,S. foliatusandS. indentatuscollected from Caroline County, VA, were sequenced using a shotgun sequencing approach on an Illumina NextSeq500 (Illumina Inc., San Diego, CA). All three mitogenomes displayed 13 protein-coding genes, 22 tRNAs and two rRNAs typical of metazoans. WhileS. tenuisandS. indentatusdisplayed identical gene orders similar to the pancrustacean ground pattern,S. foliatusdisplayed a transposition of thetrnL2-cox2genes to afteratp8-atp6. In addition, a shortatp8gene, longerrrnLgene and large inverted repeat within the Control Region distinguishedS. foliatusfromS. tenuis potomacusandS. indentatus. Overall, it appears that gene order varies considerably among amphipods, and the addition of theseStygobromusmitogenomes to the existing sequenced amphipod mitogenomes will prove useful for characterizing evolutionary relationships among various amphipod taxa, as well as investigations of the evolutionary dynamics of the mitogenome in general. [ABSTRACT FROM PUBLISHER]

Malacostracan crustaceans of the fossil order Pygocephalomorpha are conspicuous elements in brackish to freshwater faunas in the upper Carboniferous of Laurentia and lower Permian of Gondwana. A pronounced sexual dimorphism is recognizable within its members, with Pygocephalomorpha females bearing oöstegites: modified epipodites that hold a brood pouch where the eggs develop until juvenile stage, with no planktonic dispersal of larvae. The preservation of oöstegites is quite rare and is described here for the first time from the American continents. The specimens, ventrally preserved Liocaris huenei females bearing oöstegites, come from the Irati Formation, a lower Permian sequence of the Paraná Basin, from an outcrop in southern Brazil. The oöstegites are similar to those previously described for Pygocephalomorpha, displaying seven pairs of overlapping epipodites that cover the whole cephalothorax. The scarcity of these structures in the fossil record may be explained by taphonomic bias (it requires ventrally preserved crustaceans) but more likely by palaeobiological aspects, such as preservation of an ovigerous moult. The record from the Irati Formation suggests that pygocephalomorphs had seasonal reproduction, with females maturing at the same time and acquiring oöstegites that would be lost after the release of juveniles. This record confirms the relationship of the Brazilian Liocaris Beurlen to the English Pygocephalus Huxley and South African Notocaris Broom pygocephalomorphs and provides an insight into its palaeoecological significance. [ABSTRACT FROM AUTHOR]

Most barnacles are sessile, simultaneous hermaphrodites that reproduce by copulation. This is achieved through the extension of a muscular penis, famous for being the proportionally largest in the animal kingdom. The penis is a long cylindrical or conical organ, composed of a series of folded rings, allowing it to stretch to great lengths. The penises are covered with chemosensory setae allowing them to seek out receptive neighbors. For many species, the condition of the penis changes seasonally. In the most extreme circumstances, it degenerates and is shed during the first post-mating molt and is re-grown for the next mating season. Barnacle penises have been shown to exhibit phenotypic plasticity in response to many different challenges. When exposed to heavy waves, diameter is increased by thickening both the cuticle and muscles. When mates are far, length increases by adding ringed annulations. Experiments have shown that these plastic traits are modular, capable of changing independently from each other and that they improve mating ability. Alternate strategies to increase reproductive ability by barnacles include the production of dwarf and complemental males, sperm casting and sperm leakage, and aerial copulation. All of these mating strategies may have important implications for the study of reproductive biology, life history, and sex allocation theory. [ABSTRACT FROM AUTHOR]

The habitat of cave-adapted organisms is characterized by complete darkness and in some instances, an apparent lack of environmental distinction between day and night. It is unclear if cave-adapted organisms retain circadian rhythms that can be light-entrained. Stygobromus allegheniensis (Allegheny Cave Amphipod) is an eyeless troglobitic crustacean found in caves located in the Northeastern region of the United States. Two cave populations were examined for evidence of light-entrained circadian rhythms. The first population inhabits a small tectonic cave (Ice Caves, Sam's Point Preserve, NY) and the second (Clarksville Cave, Clarksville, NY) inhabits a long cave system in limestone rock. Experiments conducted in both the field and the laboratory suggest that the capacity to exhibit motor rhythms has been conserved in at least some individuals of both populations. Nonetheless, their motor activity rhythms have high variability of period length between individuals and do not appear to be light-entrainable. It is thus proposed that in this species, light-entrainable circadian rhythms controlling motor activity have undergone incipient regressive evolution. [ABSTRACT FROM AUTHOR]

Summary Crustaceans possess a diverse array of specialized limbs. Although shifts in Hox gene expression domains have been postulated to play a role in generating this limb diversity, little functional data have been provided to understand the precise roles of Hox genes during crustacean development. We used a combination of CRISPR/Cas9-targeted mutagenesis and RNAi knockdown to decipher the function of the six Hox genes expressed in the developing mouth and trunk of the amphipod Parhyale hawaiensis . These experimentally manipulated animals display specific and striking homeotic transformations. We found that abdominal-A ( abd-A ) and Abdominal-B ( Abd-B ) are required for proper posterior patterning, with knockout of Abd-B resulting in an animal with thoracic type legs along what would have been an abdomen, and abd-A disruption generating a simplified body plan characterized by a loss of specialization in both abdominal and thoracic appendages. In the thorax, Ubx is necessary for gill development and for repression of gnathal fate, and Antp dictates claw morphology. In the mouth, Scr and Antp confer the part-gnathal, part-thoracic hybrid identity of the maxilliped, and Scr and Dfd prevent antennal identity in posterior head segments. Our results allow us to define the role Hox genes play in specifying each appendage type in Parhyale , including the modular nature by which some appendages are patterned by Hox gene inputs. In addition, we define how changes in Hox gene expression have generated morphological differences between crustacean species. Finally, we also highlight the utility of CRISPR/Cas9-based somatic mutagenesis in emerging model organisms. [ABSTRACT FROM AUTHOR]

Molting is one of the most important biological processes in shrimp growth and development. All shrimp undergo cyclic molting periodically to shed and replace their exoskeletons. This process is essential for growth, metamorphosis, and reproduction in shrimp. However, the molecular mechanisms underlying shrimp molting remain poorly understood. In this study, we investigated global expression changes in the transcriptomes of the Pacific white shrimp, Litopenaeus vannamei, the most commonly cultured shrimp species worldwide. The transcriptome of whole L. vannamei was investigated by RNA-sequencing (RNA-seq) throughout the molting cycle, including the inter-molt (C), pre-molt (D0, D1, D2, D3, D4), and post-molt (P1 and P2) stages, and 93,756 unigenes were identified. Among these genes, we identified 5,117 genes differentially expressed (log2ratio ≥1 and FDR ≤0.001) in adjacent molt stages. The results were compared against the National Center for Biotechnology Information (NCBI) non-redundant protein/nucleotide sequence database, Swiss-Prot, PFAM database, the Gene Ontology database, and the Kyoto Encyclopedia of Genes and Genomes database in order to annotate gene descriptions, associate them with gene ontology terms, and assign them to pathways. The expression patterns for genes involved in several molecular events critical for molting, such as hormone regulation, triggering events, implementation phases, skelemin, immune responses were characterized and considered as mechanisms underlying molting in L. vannamei. Comparisons with transcriptomic analyses in other arthropods were also performed. The characterization of major transcriptional changes in genes involved in the molting cycle provides candidates for future investigation of the molecular mechanisms. The data generated in this study will serve as an important transcriptomic resource for the shrimp research community to facilitate gene and genome annotation and to characterize key molecular processes underlying shrimp development. [ABSTRACT FROM AUTHOR]

We determined the mitogenome sequence ofMunida gregaria(Fabricius 1793) (Anomura, Galatheoidea, Munididae), which is the first complete mitogenome sequence in the family Munididae Ahyong et al., 2010. The mitogenome ofM. gregariais 16 326 bp in length and contains 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs) and two control regions (CRs). Mitogenome analysis ofM. gregariashowed an extra copy of the CR and rearrangements of two PCGs (nad2andnad3) compared to the arthropod ground pattern. Additionally, it contains a tRNA (trnY) inversion and rearrangements of two PCGs (nad1andnad3) when compared with that ofNeopetrolisthes maculatusandShinkaia crosnieri, respectively. The phylogenetic tree confirmed thatM. gregariabelongs to the superfamily Galatheoidea within Anomura. Our results will be useful for the detailed study of mitogenome evolution and the phylogenetic relationships among the superfamily in the infraorder Anomura. [ABSTRACT FROM PUBLISHER]

The polarization of light provides information that is used by many animals for a number of different visually guided behaviours. Several marine species, such as stomatopod crustaceans and cephalopod molluscs, communicate using visual signals that contain polarized information, content that is often part of a more complex multidimensional visual signal. In this work, we investigate the evolution of polarized signals in species of Haptosquilla, a widespread genus of stomatopod, as well as related protosquillids. We present evidence for a pre-existing bias towards horizontally polarized signal content and demonstrate that the properties of the polarization vision system in these animals increase the signal-to-noise ratio of the signal. Combining these results with the increase in efficacy that polarization provides over intensity and hue in a shallow marine environment, we propose a joint framework for the evolution of the polarized form of these complex signals based on both efficacy-driven (proximate) and content-driven (ultimate) selection pressures. [ABSTRACT FROM AUTHOR]

Mechanical redundancy within a biomechanical system (e.g., many-to-one mapping) allows morphologically divergent organisms to maintain equivalent mechanical outputs. However, most organisms depend on the integration of more than one biomechanical system. Here, we test whether coupled mechanical systems follow a pattern of amplification (mechanical changes are congruent and evolve toward the same functional extreme) or independence (mechanisms evolve independently). We examined the correlated evolution and evolutionary pathways of the coupled four-bar linkage and lever systems in mantis shrimp (Stomatopoda) ultrafast raptorial appendages. We examined models of character evolution in the framework of two divergent groups of stomatopods-'smashers' (hammer-shaped appendages) and 'spearers' (bladed appendages). Smashers tended to evolve toward force amplification, whereas spearers evolved toward displacement amplification. These findings show that coupled biomechanical systems can evolve synergistically, thereby resulting in functional amplification rather than mechanical redundancy. [ABSTRACT FROM AUTHOR]

The water flea Daphnia magna has been used as an animal model in ecology, evolution, and environmental sciences. Thanks to the recent progress in Daphnia genomics, genetic information such as the draft genome sequence and expressed sequence tags (ESTs) is now available. To investigate the relationship between phenotypes and the available genetic information about Daphnia, some gene manipulation methods have been developed. However, a technique to induce targeted mutagenesis into Daphnia genome remains elusive. To overcome this problem, we focused on an emerging genome editing technique mediated by the clustered regularly interspaced short palindromic repeats/CRISPR-associated (CRISPR/Cas) system to introduce genomic mutations. In this study, we targeted a functionally conserved regulator of eye development, the eyeless gene in D. magna. When we injected Cas9 mRNAs and eyeless-targeting guide RNAs into eggs, 18–47% of the survived juveniles exhibited abnormal eye morphology. After maturation, up to 8.2% of the adults produced progenies with deformed eyes, which carried mutations in the eyeless loci. These results showed that CRISPR/Cas system could introduce heritable mutations into the endogenous eyeless gene in D. magna. This is the first report of a targeted gene knockout technique in Daphnia and will be useful in uncovering Daphnia gene functions. [ABSTRACT FROM AUTHOR]

The water flea Daphnia magna has been used as an animal model in ecology, evolution, and environmental sciences. Thanks to the recent progress in Daphnia genomics, genetic information such as the draft genome sequence and expressed sequence tags (ESTs) is now available. To investigate the relationship between phenotypes and the available genetic information about Daphnia, some gene manipulation methods have been developed. However, a technique to induce targeted mutagenesis into Daphnia genome remains elusive. To overcome this problem, we focused on an emerging genome editing technique mediated by the clustered regularly interspaced short palindromic repeats/CRISPR-associated (CRISPR/Cas) system to introduce genomic mutations. In this study, we targeted a functionally conserved regulator of eye development, the eyeless gene in D. magna. When we injected Cas9 mRNAs and eyeless-targeting guide RNAs into eggs, 18–47% of the survived juveniles exhibited abnormal eye morphology. After maturation, up to 8.2% of the adults produced progenies with deformed eyes, which carried mutations in the eyeless loci. These results showed that CRISPR/Cas system could introduce heritable mutations into the endogenous eyeless gene in D. magna. This is the first report of a targeted gene knockout technique in Daphnia and will be useful in uncovering Daphnia gene functions. [ABSTRACT FROM AUTHOR]

The supralittoral environment, at the transition between sea and land, is characterized by harsh conditions for life. Nonetheless, evolution of terrestrial isopods (Oniscidea), the only group of Crustacea fully adapted to live on land, appears to have involved a transitional step within the supralittoral. The two most basal oniscidean lineages (Ligiidae and Tylidae) have representatives that successfully colonized the supralittoral. One of them is the genus Tylos, which is found exclusively in supralittoral sandy beaches from tropical and subtropical coasts around the world. Comprehensive phylogenetic hypotheses for this genus are lacking, which are necessary for understanding the evolution and biogeography of a lineage that successfully diversified in the harsh sea-land interface. Herein, we studied the phylogenetic relationships among 17 of the 21 currently recognized species of the genus Tylos, based on sequences from four mitochondrial genes (Cytochrome Oxidase I, Cytochrome b, 16S rDNA, and 12S rDNA). Maximum Likelihood and Bayesian phylogenetic analyses identified several lineages with deep divergences and discrete geographic distributions. Phylogenetic and distributional patterns of Tylos provide important clues on the biogeography and evolution of this group. Large divergences among the most basal clades are consistent with ancient splits. Due to the biological characteristics of Tylos, which likely prevent dispersal of these isopods across vast oceanic scales, we argue that tectonic events rather than trans-oceanic dispersal explain the distribution of Tylos in different continents. Overwater dispersal, however, likely enabled range expansions within some basins, and explains the colonization of volcanic oceanic islands. Present-day distributions were also likely influenced by sea level and climate changes. High levels of allopatric cryptic genetic differentiation are observed in different regions of the world, implying that the dispersal abilities of Tylos isopods are more limited than previously thought. Our results indicate that a taxonomic revision of this group is necessary. [ABSTRACT FROM AUTHOR]

Recent scientific interest following the “discovery” of lithodid crabs around Antarctica has centred on a hypothesis that these crabs might be poised to invade the Antarctic shelf if the recent warming trend continues, potentially decimating its native fauna. This “invasion hypothesis” suggests that decapod crabs were driven out of Antarctica 40–15 million years ago and are only now returning as “warm” enough habitats become available. The hypothesis is based on a geographically and spatially poor fossil record of a different group of crabs (Brachyura), and examination of relatively few Recent lithodid samples from the Antarctic slope. In this paper, we examine the existing lithodid fossil record and present the distribution and biogeographic patterns derived from over 16,000 records of Recent Southern Hemisphere crabs and lobsters. Globally, the lithodid fossil record consists of only two known specimens, neither of which comes from the Antarctic. Recent records show that 22 species of crabs and lobsters have been reported from the Southern Ocean, with 12 species found south of 60°S. All are restricted to waters warmer than 0°C, with their Antarctic distribution limited to the areas of seafloor dominated by Circumpolar Deep Water (CDW). Currently, CDW extends further and shallower onto the West Antarctic shelf than the known distribution ranges of most lithodid species examined. Geological evidence suggests that West Antarctic shelf could have been available for colonisation during the last 9,000 years. Distribution patterns, species richness, and levels of endemism all suggest that, rather than becoming extinct and recently re-invading from outside Antarctica, the lithodid crabs have likely persisted, and even radiated, on or near to Antarctic slope. We conclude there is no evidence for a modern-day “crab invasion”. We recommend a repeated targeted lithodid sampling program along the West Antarctic shelf to fully test the validity of the “invasion hypothesis”. [ABSTRACT FROM AUTHOR]

Background: The Chinese mitten crab, Eriocheir sinensis, is one of the most studied and economically important crustaceans in China. Its transition from a swimming to a crawling method of movement during early development, anadromous migration during growth, and catadromous migration during breeding have been attractive features for research. However, knowledge of the underlying molecular mechanisms that regulate these processes is still very limited. Findings: A total of 258.8 gigabases (Gb) of raw reads from whole-genome sequencing of the crab were generated by the Illumina HiSeq2000 platform. The final genome assembly (1.12 Gb), about 67.5 % of the estimated genome size (1.66 Gb), is composed of 17,553 scaffolds (>2 kb) with an N50 of 224 kb. We identified 14,436 genes using AUGUSTUS, of which 7,549 were shown to have significant supporting evidence using the GLEAN pipeline. This gene number is much greater than that of the horseshoe crab, and the annotation completeness, as evaluated by CEGMA, reached 66.9 %. Conclusions: We report the first genome sequencing, assembly, and annotation of the Chinese mitten crab. The assembled draft genome will provide a valuable resource for the study of essential developmental processes and genetic determination of important traits of the Chinese mitten crab, and also for investigating crustacean evolution. [ABSTRACT FROM AUTHOR]

Understanding the processes that shaped the strikingly irregular distribution of species richness across the Tree of Life is a major research agenda. Changes in ecology may go some way to explain the often strongly asymmetrical fates of sister clades, and we test this in the caridean shrimps. First appearing in the Lower Jurassic, there are now ~3500 species worldwide. Carideans experienced several independent transitions to freshwater from marine habitats, while many of the marine species have also evolved a symbiotic lifestyle. Here we use diversification rate analyses to test whether these ecological traits promote or inhibit diversity within a phylogenetic framework. We demonstrate that speciation rates are more than twice as high in freshwater clades, whilst symbiotic ecologies are associated with lower speciation rates. These lower rates amongst symbiotic species are of concern given that symbioses often occur in some of the most diverse, delicately balanced and threatened marine ecosystems. Katie Davis et al. test the hypothesis that ecological traits are linked to diversification in caridean shrimps. They find that transitions from marine to freshwater habitats contributed to higher diversification rates, whereas symbiosis is associated with a slight decrease in diversification rates. [ABSTRACT FROM AUTHOR]

Summary How do stunning functional innovations evolve from unspecialized progenitors? This puzzle is particularly acute for ultrafast movements of appendages in arthropods as diverse as shrimps [ 1 ], stomatopods [ 2 ], insects [ 3–6 ], and spiders [ 7 ]. For example, the spectacular snapping claws of alpheid shrimps close so fast (∼0.5 ms) that jetted water creates a cavitation bubble and an immensely powerful snap upon bubble collapse [ 1 ]. Such extreme movements depend on (1) an energy-storage mechanism (e.g., some kind of spring) and (2) a latching mechanism to release stored energy quickly [ 8 ]. Clearly, rapid claw closure must have evolved before the ability to snap, but its evolutionary origins are unknown. Unearthing the functional mechanics of transitional stages is therefore essential to understand how such radical novel abilities arise [ 9–11 ]. We reconstructed the evolutionary history of shrimp claw form and function by sampling 114 species from 19 families, including two unrelated families within which snapping evolved independently (Alpheidae and Palaemonidae) [ 12, 13 ]. Our comparative analyses, using micro-computed tomography (microCT) and confocal imaging, high-speed video, and kinematic experiments with select 3D-printed scale models, revealed a previously unrecognized “slip joint” in non-snapping shrimp claws. This slip joint facilitated the parallel evolution of a novel energy-storage and cocking mechanism—a torque-reversal joint—an apparent precondition for snapping. Remarkably, these key functional transitions between ancestral (simple pinching) and derived (snapping) claws were achieved by minute differences in joint structure. Therefore, subtle changes in form appear to have facilitated wholly novel functional change in a saltational manner. Video Abstract [ABSTRACT FROM AUTHOR]

Many organisms have geographical distributions extending from the tropics to near polar regions or can experience up to 30°C temperature variation within the lifespan of an individual. Two forms of evolutionary adaptation to such wide ranges in ambient temperatures are frequently discussed: local adaptation and phenotypic plasticity. The freshwater planktonic crustacean Daphnia magna, whose range extends from South Africa to near arctic sites, shows strong phenotypic and genotypic variation in response to temperature. In this study, we use D. magna clones from 22 populations (one clone per population) ranging from latitude 0° (Kenya) to 66° North (White Sea) to explore the contributions of phenotypic plasticity and local adaptation to high temperature tolerance. Temperature tolerance was studied as knockout time (time until immobilization, T[sub imm]) at 37°C in clones acclimatized to either 20°C or 28°C. Acclimatization to 28°C strongly increased T[sub imm], testifying to adaptive phenotypic plasticity. At the same time, T[sub imm] significantly correlated with average high temperature at the clones' sites of origin, suggesting local adaptation. As earlier studies have found that haemoglobin expression contributes to temperature tolerance, we also quantified haemoglobin concentration in experimental animals and found that both acclimatization temperature (AccT) and temperature at the site of origin are positively correlated with haemoglobin concentration. Furthermore, Daphnia from warmer climates upregulate haemoglobin much more strongly in response to AccT, suggesting local adaptation for plasticity in haemoglobin expression. Our results show that both local adaptation and phenotypic plasticity contribute to temperature tolerance, and elucidate a possible role of haemoglobin in mediating these effects that differs along a cold-warm gradient. [ABSTRACT FROM AUTHOR]