Species recognition in social amoebae

Aggregative multicellularity requires the ability of cells to recognise conspecifics. Social amoebae are among the best studied of such organisms, but the mechanism and evolutionary background of species recognition remained to be investigated. Here we show that heterologous expression of a single Dictyostelium purpureum gene is sufficient for D. discoideum cells to efficiently make chimaeric fruiting bodies with D. purpureum cells. This gene forms a bidirectional pair with another gene on the D. purpureum genome, and they are both highly polymorphic among independent wild isolates of the same mating group that do not form chimaeric fruiting bodies with each other. These paired genes are both structurally similar to D. discoideum tgrB1/C1 pair, which is responsible for clonal discrimination within that species, suggesting that these tgr genes constitute the species recognition system that has attained a level of precision capable of discriminating between clones within a species. Analysis of the available genome sequences of social amoebae revealed that such gene pairs exist only within the clade composed of species that produce precursors of sterile stalk cells (prestalk cells), suggesting concurrent evolution of a precise allorecognition system and a new ‘worker’ cell-type dedicated to transporting and supporting the reproductive cells.     

Folic Acid as Second Chemotactic Substance in the Cellular Slime Moulds

IT has been known for some time that in certain species of cellular slime moulds acrasin, the substance which attracts the amoebae to central collection points during the aggregation phase, is cyclic AMP^1–4. We were also able to show that E. coli gave off another substance besides cyclic AMP (henceforth referred to as bacterial factor, or BF) which attracted the vegetative amoebae of Dictyostelium discoideum⁵. Here we demonstrate that this second attractant has the properties of folic acid or one of its derivatives. We also show that folic acid and related compounds not only attract the vegetative amoebae of D. discoideum (No. NC-4H) but also the amoebae of six other species (Dictyostelium rosarium No. CC-7; D. mucoroides No. 11; D. purpureum No. 2; D. minutum No. V-3; Polysphondylium violaceum No. 1; P. pallidum No. 2). For the latter three species cyclic AMP is not the aggregative attractant (ref. 6 and J. T. B., E. M. H., S. Noller, F. B. Oleson and A. B. Roberts, in preparation) which raises the interesting question of whether their acrasin might be related to the folates.     

Comparative genomics of the social amoebae <Emphasis Type="Italic">Dictyostelium discoideum</Emphasis> and <Emphasis Type="Italic">Dictyostelium purpureum</Emphasis>

Background

The social amoebae (Dictyostelia) are a diverse group of Amoebozoa that achieve multicellularity by aggregation and undergo morphogenesis into fruiting bodies with terminally differentiated spores and stalk cells. There are four groups of dictyostelids, with the most derived being a group that contains the model species Dictyostelium discoideum.

Results

We have produced a draft genome sequence of another group dictyostelid, Dictyostelium purpureum, and compare it to the D. discoideum genome. The assembly (8.41 × coverage) comprises 799 scaffolds totaling 33.0 Mb, comparable to the D. discoideum genome size. Sequence comparisons suggest that these two dictyostelids shared a common ancestor approximately 400 million years ago. In spite of this divergence, most orthologs reside in small clusters of conserved synteny. Comparative analyses revealed a core set of orthologous genes that illuminate dictyostelid physiology, as well as differences in gene family content. Interesting patterns of gene conservation and divergence are also evident, suggesting function differences; some protein families, such as the histidine kinases, have undergone little functional change, whereas others, such as the polyketide synthases, have undergone extensive diversification. The abundant amino acid homopolymers encoded in both genomes are generally not found in homologous positions within proteins, so they are unlikely to derive from ancestral DNA triplet repeats. Genes involved in the social stage evolved more rapidly than others, consistent with either relaxed selection or accelerated evolution due to social conflict.

Conclusions

The findings from this new genome sequence and comparative analysis shed light on the biology and evolution of the Dictyostelia.

     

Effects of Host Interspecific Interaction in the <Emphasis Type="Italic">Maculinea</Emphasis>–<Emphasis Type="Italic">Myrmica</Emphasis> Parasite–Host System

A model of interspecific host competition in a system with one parasite (butterfly—Maculinea) and multiple potential hosts (ants—Myrmica) is presented. Results indicate that host interspecific competition increases the occurrence of multiple host behaviour in Maculinea natural populations but decreases the ability of the parasite populations to adapt to the most abundant host species. These qualitative predictions were compared with data on host specificity, with good agreement. Analysis of the data also indicates that Maculinea teleius and Maculinea arion respond differently to changes in relative host abundances. Maculinea teleius shows a larger fraction of sites where it displays multiple host behaviour and a larger fraction of sites where the niches of the hosts overlap. In some instances, Maculinea teleius is adapted to Myrmica hosts that are present in lower frequencies. Maculinea arion is locally more host-specific and occurs at sites where host interspecific competition is unlikely and is more frequently adapted to the most abundant host species.     

Bacterial resistance to arsenic protects against protist killing

Protists kill their bacterial prey using toxic metals such as copper. Here we hypothesize that the metalloid arsenic has a similar role. To test this hypothesis, we examined intracellular survival of Escherichia coli (E. coli) in the amoeba Dictyostelium discoideum (D. discoideum). Deletion of the E. coli ars operon led to significantly lower intracellular survival compared to wild type E. coli. This suggests that protists use arsenic to poison bacterial cells in the phagosome, similar to their use of copper. In response to copper and arsenic poisoning by protists, there is selection for acquisition of arsenic and copper resistance genes in the bacterial prey to avoid killing. In agreement with this hypothesis, both copper and arsenic resistance determinants are widespread in many bacterial taxa and environments, and they are often found together on plasmids. A role for heavy metals and arsenic in the ancient predator–prey relationship between protists and bacteria could explain the widespread presence of metal resistance determinants in pristine environments.     

The mitochondrial DNA of <Emphasis Type="Italic">Dictyostelium discoideum</Emphasis>: complete sequence,gene content and genome organization

We present an overview of the gene content and organization of the mitochondrial genome of Dictyostelium discoideum. The mitochondria genome consists of 55,564?bp with an A + T content of 72.6%. The identified genes include those for two ribosomal RNAs (rnl and rns), 18 tRNAs, ten subunits of the NADH dehydrogenase complex (nad1, 2, 3, 4, 4L, 5, 6, 7, 9 and 11), apocytochrome b (cytb), three subunits of the cytochrome oxidase (cox1/2 and 3), four subunits of the ATP synthase complex (atp1, 6, 8 and 9), 15 ribosomal proteins, and five other ORFs, excluding intronic ORFs. Notable features of D. discoideum mtDNA include the following. (1) All genes are encoded on the same strand of the DNA and a universal genetic code is used. (2) The cox1 gene has no termination codon and is fused to the downstream cox2 gene. The 13 genes for ribosomal proteins and four ORF genes form a cluster 15.4?kb long with several gene overlaps. (3) The number of tRNAs encoded in the genome is not sufficient to support the synthesis of mitochondrial protein. (4) In total, five group I introns reside in rnl and cox1/2, and three of those in cox1/2 contain four free-standing ORFs. We compare the genome to other sequenced mitochondrial genomes, particularly that of Acanthamoeba castellanii.     

<Emphasis Type="Italic">qRfg3</Emphasis>, a novel quantitative resistance locus against <Emphasis Type="Italic">Gibberella</Emphasis> stalk rot in maize

Key message

A quantitative trait locus  qRfg3 imparts recessive resistance to maize Gibberella stalk rot. qRfg3 has been mapped into a 350-kb interval and could reduce the disease severity index by ~26.6%.

Abstract

Gibberella stalk rot, caused by the fungal pathogen Fusarium graminearum, severely affects maize yield and grain quality worldwide. To identify more resistance quantitative trait loci (QTLs) against this disease, we analyzed a recombinant inbred line (RIL) population derived from a cross between resistant H127R and susceptible C7-2 inbred lines. Within this population, maize resistance to Gibberella stalk rot had high broad-sense heritability. A major QTL, qRfg3, on chromosome 3 was consistently detected across three field trials, accounting for 10.7–19.4% of the total phenotypic variation. Using a progeny-based sequential fine-mapping strategy, we narrowed qRfg3 down to an interval of ~350 kb. We further demonstrated that qRfg3 is a recessive resistance locus to Gibberella stalk rot that reduced the disease severity index by ~26.6%. Both the gene location and recessive genetic mode distinguish qRfg3 from other stalk rot resistance loci. Hence, qRfg3 is valuable as a complement to existing resistance QTLs to improve maize resistance to Gibberella stalk rot.

     

Property nouns with -<Emphasis Type="Italic">ité</Emphasis> and -<Emphasis Type="Italic">itude</Emphasis>: formal alternation and morphopragmatics or the sad-itude of the A<Emphasis Type="Italic">ité</Emphasis><Subscript>N</Subscript>

Adjectival nominalisation in French involves a range of suffixes, among them -ité and -itude (e.g. banal ‘banal’ > banalité ‘banality’, ample ‘wide’ > amplitude ‘amplitude’). These suffixes show similarities in terms of their historical development, form, and meaning of the derived nouns. The competition between the two has contributed to the unavailability of -itude in active derivation in favour of -ité suffixation. Only a handful of newly coined -itude nouns have been recorded in dictionaries since the 16th century, compared to hundreds of -ité nouns that have been formed over the same period. However, more recently there has been an explosion of -itude derivations, particularly online. In this article, we examine the various criteria that may affect the selection and distribution of both affixes, aiming to determine the specific properties of each suffix as well as the reasons for the retention of -itude as an active suffix. Our study is based on a corpus of attested data consisting of 2,642 deadjectival nouns from a range of sources.     

Cyclic AMP Phosphodiesterase and its Inhibitor in Slime Mould Development

CYCLIC adenosine-3′,5′-monophosphate (cyclic AMP) acts as a chemotactic factor causing cell aggregation in the slime mould, Dtctyosteltum discoideum^1,2. Aggregation in this organism is the link between the growth phase and the second phase of development, in which cells cooperate and differentiate to form a multicellular fruiting body. The finding that cyclic AMP also mediates developmental functions other than chemotaxis³ suggests that regulation of cyclic AMP synthesis and destruction is important in the control of morphogenesis in D. discoideum.     

Diversity and community patterns of testate amoebae in Bau Sen and Bau Trang lakes in Binh Thuan Province,Vietnam

The species composition and distribution of testate amoebae in Bau Sen and Bau Trang lakes (Binh Thuan Province, Vietnam) were investigated. Fifty-three species, varieties and forms have been identified from the water column and sediments. Twenty-seven species, varieties and forms from the genera Arcella, Centropyxis, Cyclopyxis, Difflugia and Pyxidicula were found in Vietnam for the first time. The updated list of testate amoebae in Vietnam now includes 286 taxa. The genera Arcella, Centropyxis and Difflugia are characterized by the highest frequency of occurrence. The species diversity of Arcella, Centropyxis, Difflugia was the highest. Centropyxis aculeata, Arcella discoides, Difflugia schurmanni, Netzelia oviformis and Difflugia limnetica were the most common species. Many species have shown restricted distribution, some species have been found only in one lake and not been found in another lake. The number of observed species, varieties, and forms in each lake is 34. The average number of the species per sample on the shores of the lakes subjected to human agricultural activity was significantly higher than in the samples from the shores of the lakes with less anthropogenic disturbance. The curves of “cumulative species number vs. sampling effort” are well fitted by equations S = 7.60 N ^0.69 for Bau Sen lake and S = 12.52 N ^0.46 for Bau Trang. The curves are unsaturated, which indicates that more intensive investigations of testate amoebae should be expected to reveal more species.     

A SNP in the promoter region of the<Emphasis Type="Italic">VvmybA1</Emphasis> gene is responsible for differences in grape berry color between two related bud sports of grape

The VvmybA1 gene in grape (Vitis vinifera) plays a key role in the biosynthesis of anthocyanin. The grape cultivars, ‘Benitaka’ (red color) and ‘Brazil’ (black color) were the result of a bud mutation. ‘Benetika’ was derived from ‘Italia’ (green color) and ‘Brazil’ was developed from ‘Benetika’. Single sequence repeat (SSR) molecular marker analysis was performed in order to demonstrate that the three cultivars have a common pedigree. A sequence analysis of the promoter region and coding sequence of VvmybA1 revealed a base substitution between ‘Benitaka’ and ‘Brazil’ in the promoter region and a deletion of a large DNA fragment in the promoter region of ‘Italia’. Anthocyanin content and expression of the VvmybA1 and UFGT genes in ‘Brazil’ were higher than in ‘Benitaka’ and barely detectable in ‘Italia’. A transient expression system was used to introduce VvmybA1 driven by the three different promoters present in ‘Italia’, ‘Brazil’, and ‘Benitaka’ into somatic embryos of ‘Centennial Seedless’ (Vitis vinifera L.) by Agrobacterium-mediated transformation. This resulted in the production of red cells in the embryos transformed with the constructs of VvmybA1 from ‘Brazil’ and ‘Benitaka’ and no color production in embryos transformed with the VvmybA1 construct from ‘Italia’. In addition, the embryos transformed with the ‘Brazil’ construct had more red color than the embryos transformed with the ‘Benitaka’ construct. These results suggested that a SNP mutation in the promoter region of VvmybA1 in ‘Benitaka’ (red color) was responsible for the color change displayed by ‘Brazil’ (black color).     

Genetic mapping of the female mimic morph locus in the ruff

Background

Ruffs (Aves: Philomachus pugnax) possess a genetic polymorphism for male mating behaviour resulting in three permanent alternative male reproductive morphs: (i) territorial ‘Independents’, (ii) non-territorial ‘Satellites’, and (iii) female-mimicking ‘Faeders’. Development into independent or satellite morphs has previously been shown to be due to a single-locus, two-allele autosomal Mendelian mode of inheritance at the Satellite locus. Here, we use linkage analysis to map the chromosomal location of the Faeder locus, which controls development into the Faeder morph, and draw further conclusions about candidate genes, assuming shared synteny with other birds.

Results

Segregation data on the Faeder locus were obtained from captive-bred pedigrees comprising 64 multi-generation families (N?=?381). There was no evidence that the Faeder locus was linked to the Satellite locus, but it was linked with microsatellite marker Ppu020. Comparative mapping of ruff microsatellite markers against the chicken (Gallus gallus) and zebra finch (Taeniopygia guttata) genomes places the Ppu020 and Faeder loci on a region of chromosome 11 that includes the Melanocortin-1 receptor (MC1R) gene, which regulates colour polymorphisms in numerous birds and other vertebrates. Melanin-based colouration varies with life-history strategies in ruffs and other species, thus the MC1R gene is a strong candidate to play a role in alternative male morph determination.

Conclusion

Two unlinked loci appear to control behavioural development in ruffs. The Faeder locus is linked to Ppu020, which, assuming synteny, is located on avian chromosome 11. MC1R is a candidate gene involved in alternative male morph determination in ruffs.

     

Susceptibility of germinating cruciferous seeds to <Emphasis Type="Italic">Bagrada hilaris</Emphasis> (Hemiptera: Pentatomidae) feeding injury

Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is a serious pest that attacks both germinating and seedling stages of a variety of cruciferous crops grown in the Central Coast of California. B. hilaris feeding on germinating seeds can cause severe stunting and plant mortality, and little is known about the feeding preference of B. hilaris for germinating seeds of major cruciferous hosts and varieties of hosts. No-choice and choice experiments were conducted in which germinating seeds in soilless and soil settings were exposed to B. hilaris adults for 7 days. Susceptibility scores were developed using B. hilaris feeding injury sites, distorted leaves, and deformed and dead plants to determine the overall B. hilaris preference for germinating host seeds. Based on the scores, the order of preference was arugula (Eruca sativa L.)?>?turnip (B. rapa L. var. rapa)?>?mizuna (B. rapa L. nipposinica)?>?kale (B. oleracea L. acephala)?>?choi (Brassica rapa L. var. chinensis)?>?broccoli (B. oleracea var. italica Plenck)?>?cauliflower (B. oleracea L. var. botrytis)?>?lettuce (Lactuca sativa L.)?>?sweet alyssum (Lobularia maritima [L.] Desv.). The lowest feeding injury was recorded on germinating lettuce and sweet alyssum seeds. Furthermore, no-choice and choice experiments were conducted with four varieties each of arugula and mizuna, twelve varieties each of kale and choi, and nine varieties/types of leafy Asian greens. The arugula varieties ‘Wild Rocket’ and ‘Spirit’ were more damaged by B. hilaris than other varieties tested. Among mizuna varieties, ‘Beira F1’ was more attractive to B. hilaris than ‘Scarlet’ or ‘Starbor F1.’ The choi varieties ‘Tokyo Bekana,’ ‘Feng Qing Choi F1,’ ‘Joi Choi F1,’ and ‘Win-Win Choi F1’ were more attractive than ‘Rosie F1.’ The leafy Asian greens variety ‘Carlton F1’ was more attractive to B. hilaris than ‘Yukina Savon,’ ‘Tatsoi OG,’ ‘Komatsuna Summerfest F1,’ ‘Red Rain F1,’ and ‘Shungiku.’ Therefore, the results suggest that not all varieties were equally susceptible to B. hilaris feeding and possibly be utilized for further field evaluation as a trap crop or developing more resistant varieties to B. hilaris.     

Ecogeographical Variation in Skull Shape of South-American Canids: Abiotic or Biotic Processes?

Species morphological changes can be mutually influenced by environmental or biotic factors, such as competition. South American canids represent a quite recent radiation of taxa that evolved forms very disparate in phenotype, ecology and behaviour. Today, in the central part of South America there is one dominant large species (the maned wolf, Chrysocyon brachyurus) that directly influence sympatric smaller taxa via interspecific killing. Further south, three species of similar sized foxes (Lycalopex spp.) share the same habitats. Such unique combination of taxa and geographic distribution makes South American dogs an ideal group to test for the simultaneous impact of climate and competition on phenotypic variation. Using geometric morphometrics, we quantified skull size and shape of 431 specimens belonging to the eight extant South American canid species: Atelocynus microtis, Cerdocyon thous, Ch. brachyurus, Lycalopex culpaeus, L. griseus, L. gymnocercus, L. vetulus and Speothos venaticus. South American canids are significantly different in both skull size and shape. The hypercarnivorous bush dog is mostly distinct in shape from all the other taxa while a degree of overlap in shape—but not size—occurs between species of the genus Lycalopex. Both climate and competition impacts interspecific morphological variation. We identified climatic adaptations as the main driving force of diversification for the South American canids. Competition has a lower degree of impact on their skull morphology although it might have played a role in the past, when canid community was richer in morphotypes.     

Chemosensory cues of predators and competitors influence search for refuge in fruit by the coconut mite <Emphasis Type="Italic">Aceria guerreronis</Emphasis>

Organisms are adapted to recognize environmental cues that can provide information about predation risk or competition. Non-vagrant eriophyoid mites mainly avoid predation by using habitats that are difficult for predators to access (galls or confined spaces in plants) such as the meristematic region of the coconut fruit, which is inhabited by the phytophagous mites Aceria guerreronis and Steneotarsonemus concavuscutum. The objective of this study was to investigate the response of A. guerreronis to cues from the predators Neoseiulus baraki and Amblyseius largoensis in coconut fruits, cues from conspecifics (A. guerreronis injured) and cues from the phytophage S. concavuscutum. The test was carried out through the release of about 300 A. guerreronis on coconut fruits previously treated with cues from predators, conspecific or heterospecific phytophagous. We also observed the walking behaviour of A. guerreronis exposed to the same chemical cues using a video tracking system. The infestation of fruits by A. guerreronis was greater in the presence of predator cues and reduced in the presence of S. concavuscutum cues, but cues from injured conspecifics did not interfere in the infestation process. In addition, the cues also altered the walking parameters of A. guerreronis: it walked more in response to cues from predators and the heterospecific phytophage. Aceria guerreronis spent more time in activity in the treatments with clues than in the control treatment. These results suggest that A. guerreronis recognizes cues from predators and competitors and modifies its behaviour to increase its fitness.     

Pistil-function breakdown in a new <Emphasis Type="Italic">S</Emphasis>-allele of European pear, <Emphasis Type="Italic">S</Emphasis><Subscript><Emphasis Type="Italic">21</Emphasis></Subscript>°, confers self-compatibility

European pear exhibits RNase-based gametophytic self-incompatibility controlled by the polymorphic S-locus. S-allele diversity of cultivars has been extensively investigated; however, no mutant alleles conferring self-compatibility have been reported. In this study, two European pear cultivars, ‘Abugo’ and ‘Ceremeño’, were classified as self-compatible after fruit/seed setting and pollen tube growth examination. S-genotyping through S-PCR and sequencing identified a new S-RNase allele in the two cultivars, with identical deduced amino acid sequence as S ₂₁ , but differing at the nucleotide level. Test-pollinations and analysis of descendants suggested that the new allele is a self-compatible pistil-mutated variant of S ₂₁ , so it was named S ₂₁ °. S-genotypes assigned to ‘Abugo’ and ‘Ceremeño’ were S ₁₀ S ₂₁ ° and S ₂₁ °S ₂₅ respectively, of which S ₂₅ is a new functional S-allele of European pear. Reciprocal crosses between cultivars bearing S ₂₁ and S ₂₁ ° indicated that both alleles exhibit the same pollen function; however, cultivars bearing S ₂₁ ° had impaired pistil-S function as they failed to reject either S ₂₁ or S ₂₁ ° pollen. RT-PCR analysis showed absence of S ₂₁ °-RNase gene expression in styles of ‘Abugo’ and ‘Ceremeño’, suggesting a possible origin for S ₂₁ ° pistil dysfunction. Two polymorphisms found within the S-RNase genomic region (a retrotransposon insertion within the intron of S ₂₁ ° and indels at the 3′UTR) might explain the different pattern of expression between S ₂₁ and S ₂₁ °. Evaluation of cultivars with unknown S-genotype identified another cultivar ‘Azucar Verde’ bearing S ₂₁ °, and pollen tube growth examination confirmed self-compatibility for this cultivar as well. This is the first report of a mutated S-allele conferring self-compatibility in European pear.     

Improved Feedstock Option or Invasive Risk? Comparing Establishment and Productivity of Fertile <Emphasis Type="Italic">Miscanthus × giganteus</Emphasis> to <Emphasis Type="Italic">Miscanthus sinensis</Emphasis>

The perennial grass genus Miscanthus has great promise as biomass feedstock, but there are concerns about potential invasion outside production fields. While the sterile hybrid Miscanthus × giganteus is currently one of the leading feedstock options due to its low invasive potential, fertile varieties are being developed to reduce establishment costs, and their invasive risks need to be further assessed. We performed seed addition experiments in Ohio and Iowa, USA to examine the establishment, flowering, persistence, and shoot biomass per plot of a fertile M. × giganteus biotype (‘PowerCane’) and two Miscanthus sinensis biotypes, one feral, and one ornamental. Seeds were added to small, replicated plots in each of the 2 years under two seeding densities and two competition treatments, and plots were monitored for 2–3 years. The ‘PowerCane’ biotype established better, survived better, and produced greater amounts of biomass per plot than both M. sinensis biotypes. All three biotypes flowered by the second or third year after establishment, with inflorescences more numerous in ‘PowerCane’ and the Ornamental M. sinensis biotypes. Effects of seeding density and competition on these patterns were minor in most cases. Our research suggests that ‘PowerCane’ exhibits many traits shared by both biomass crops and invasive species: multi-year persistence, high biomass potential, and fertility. We suggest that the benefits of a seeded M. × giganteus should be carefully weighed against its increased invasive risk prior to deployment across the landscape.     

Conspecific tolerance and heterospecific competition as mechanisms for overcoming resistance to invasion by an intertidal crab

The success of the invasive Asian shore crab, Hemigrapsus sanguineus, stems partly from its ability to exclude established crab species from preferred rocky and cobble intertidal habitat. Here, we assessed preference and competition for habitat types (cobble vs. sand) for H. sanguineus and two competitor species; the previous invasive green crab, Carcinus maenas, and the native rock crab, Cancer irroratus, in New England. In simple laboratory experiments, we paired similarly sized heterospecifics and conspecifics from each species, and also grouped combinations of C. maenas and H. sanguineus in a series of four-individual sets in order to dissect the outcome of intra- and inter-specific competition at different densities. Individually, all three species preferred cobble substrate. With paired conspecifics, H. sanguineus individuals would cohabitate in cobble, whereas C. maenas and C. irroratus individuals each excluded conspecifics from cobble. In heterospecific pairs, H. sanguineus excluded both C. maenas and C. irroratus from cobble. C. maenas and C. irroratus, were equally likely to exclude the other species, but rarely excluded H. sanguineus. In larger assemblages, H. sanguineus preferentially grouped under cobble, whereas C. maenas were more evenly distributed among habitat types. These observations demonstrate that conspecific tolerance and heterospecific competition can be effective, complementary mechanisms for overcoming invasion resistance. Such mechanisms help explain the well-studied success of H. sanguineus following its introduction into New England coastal habitats, and the resulting exclusion of preexisting crab species.