European Congeners Research Articles

Interspecific differences in swimming performance, behavior and survival between native Italian gudgeon (Gobio benacensis Pollini, 1816) and non-native European gudgeon (Gobio gobio Linnaeus, 1758)

Introduction of non-native species is an important cause of biodiversity decline in rivers. Separated by mountains and salt water, the freshwater fish fauna in Italy has experienced a natural isolation from fish in continental Europe. As a consequence, several Italian fish species have diverged from their European sister species, likely with unique adaptations to the local environment. Relatedly, the region is also susceptible to the invasion of non-native fish, and today almost half the fish species present are of non-native origin. Several of these non-native species have Italian congeners susceptible to competition and hybridizations, and, in the long run, displacements and extinctions. One such example is the Italian gudgeon (Gobio benacensis) and its European congener European gudgeon (Gobio gobio). During the last few decades the European gudgeon was introduced in Italian waters and has since spread rapidly, causing progressive declines in the Italian species. As for several other similar species pairs, little is known about potential differences in ecology and behavior. Here we study differences between Italian and European gudgeons in a controlled laboratory environment, using a combined open field and provoked escape response test, as well as tracking their sympatric survival over time in the hatchery. The smaller Italian gudgeon displayed a lower maximum swimming speed compared to the larger European gudgeon. The Italian gudgeon also experienced substantially higher sympatric mortality, resulting in only European gudgeon surviving to the end of the experiment. Contrary to expectations, no difference was seen in boldness and the Italian gudgeon displayed a higher movement activity, moving a larger distance in an open field test, compared to its European sister species. The reported differences could play a role in the replacement process, and may also have impacts on the surrounding ecosystem, and the prey and predators that have coevolved with the Italian species.

The first Paleogene record of Hyperisus Mulsant and Rey (Coleoptera: Ptinidae) with description of a new species and an attempt of biogeographic analysis of ptinid assemblage in Baltic amber

ABSTRACT Based on an inclusion in Baltic amber, the first extinct species of the genus Hyperisus Mulsant and Rey, 1863 (Ptinidae: Ernobiinae: Xestobiini), namely H. carstengroehni sp. nov. is described. This new fossil Eocene species differs from extant European congeners in having the dorsal pubescence of two types; the lesser body size; the abdominal ventrite 5 punctate; the dorsal pubescence evenly dense; the antennal club longer than antennomeres 1–8 combined; and in the details of dorsal punctation. Provisional biogeographical affinities of the described Baltic amber Ptinidae (as of July 2023) are briefly analysed. All 20 extant genera known in Baltic amber (100% of analysed assemblage) still inhabit Holarctic of Recent. The ptinid assemblage of Baltic amber is almost twice closer in the composition of genera to the extant fauna of Palearctic or Nearctic than to other regions. Possible explanations are proposed for the abundance of death-watch beetles in Baltic amber.

First records of Eresus moravicus Řezáč, 2008 (Araneae: Eresidae) from Romania

In this paper, we report the first records of Eresus moravicus Řezáč, 2008 from Romania. The collected specimens from the new localities are described with phenological and ecological data. The new records are also confirmed by the first molecular data (mitochondrial gene fragments COI and ND1) for E. moravicus from Romania and compared with other European congeners. The distribution and possible occurrence of other Eresus species in Romania is discussed on the basis of sampling bias, past taxonomic confusion and habitat suitability. This work highlights the need for revision of this cryptic spider family in the light of new data on its taxonomy and for the preservation of fragile rocky steppes in southern Romania, which constitute an important refuge for invertebrate biodiversity.

Hydrodroma angelieri (Acari, Hydrachnidia: Hydrodromidae) a new water mite species from Corsica based on morphological and DNA barcode evidence

In the present study we used morphological data and DNA barcodes to describe a new species, Hydrodroma angelieri sp. nov. from Corsica, France. A high genetic distance of 17.3±0.017% K2P from its molecularly most closely related European congener, H. despiciens (Müller, 1776), supports H. angelieri sp. nov. as a distinct species. Morphologically the new species can be identified on the basis of relatively small leg claws, the presence of only one swimming seta on II-L-5 and 4-6 swimming setae on the anterior surface of IV-L-5. An updated key for the European species of Hydrodroma is provided.

A new species of Stylicletodes Lang, 1936 (Copepoda: Harpacticoida: Cletodidae) from the East China Sea, including an updated key to species and synopsis of distribution records.

Both sexes of a new species, Stylicletodes wellsi sp. nov. (Harpacticoida: Cletodidae), are described from material collected from sediments in the East China Sea. The new species belongs to a species group whose members are characterized by an anal operculum that has a backwardly directed, median linguiform process and fifth legs that display naked or sparsely pinnate armature elements in both sexes. Within this group, S. wellsi sp. nov. is morphologically closest to S. reductus Wells, 1965 but differs primarily from its European congener in the armature pattern of P4 (both rami) and the female P5. Distribution records of all species are summarized and an updated identification key to the seven valid species in the genus is presented. Taxonomic issues related to the type species S. longicaudatus (Brady, 1880) are briefly discussed.

New records of Pseudotachidiidae from South Korea, including a key to species of the Pseudomesochrinae (Copepoda: Harpacticoida).

Two species of the marine harpacticoid family Pseudotachidiidae (Copepoda) are reported from subtidal sediments in the Southern Sea of Korea. Psammis wellsi sp. nov. (Danielsseniinae) is most closely related to P. longisetosa Sars, 1910 but differs from its European congener in the ventral ornamentation of the female genital double-somite, the dorsal ornamentation of the second abdominal somite in the male, the armature of the proximal endite of the maxillary syncoxa, the relative setal lengths and general shape of the female P5, and the relative length of the inner seta of the male P5 endopodal lobe and P6. The female of Pseudomesochra tatianae Drzycimski, 1968 is redescribed in detail, constituting the only other record of the species since its discovery at the type locality in western Norway. East Asian records of members of the four subfamilies currently recognized in the Pseudotachidiidae are summarized. Published and other records of the 23 described species in the Pseudomesochrinae are collated and their armature patterns of P1P5 are tabulated and corrected where necessary. Pseudomesochra affinis (Sars, 1920) is removed from its synonymy with P. longifurcata T. Scott, 1902 and formally reinstated as a valid species. An updated female-based key to the 19 valid species of Pseudomesochra T. Scott, 1902 and four species of Keraia Willen Dittmar, 2009 is presented.

Metabolic and Transcriptional Profiling of Fraxinus chinensis var. rhynchophylla Unravels Possible Constitutive Resistance against Agrilus planipennis

The emerald ash borer (EAB, Agrilus planipennis), an ash-tree wood-boring beetle, has caused widespread mortality of ash. Asian ash, which coevolved with EAB, is considered more resistant than its North American and European congeners. Although some compounds and proteins related to resistance to EAB have been identified, the underlying ash resistance mechanism to EAB still needs further study. The Asian ash species, Fraxinus chinensis var. rhynchophylla, is highly resistant to EAB. In this study, metabolic and transcriptional profiling of the phloem of this species was investigated, and differentially expressed metabolites and genes were analyzed by comparing them with those of the susceptible F. pennsylvanica. Four hundred and twenty-eight metabolites were detected in both species, and several coumarins and lignans, which were exclusive to F. chinensis var. rhynchophylla, were identified. Compared with susceptible F. pennsylvanica, genes related to phenylpropanoid biosynthesis, ethylene (ET), and jasmonic acid (JA) biosynthesis and signaling in F. chinensis var. rhynchophylla were found to be up-regulated. It was hypothesized that coumarins, lignans, and ET and JA signaling might contribute to greater resistance to EAB in F. chinensis var. rhynchophylla. This study suggests candidate metabolites and genes for biomarker development in future ash-breeding programs.

A Messinian (latest Miocene) occurrence for Albanerpeton Estes & Hoffstetter, 1976 (Lissamphibia: Albanerpetontidae) at Moncucco Torinese, Piedmont Basin, northwestern Italy, and a review of the European Cenozoic record for albanerpetontids

Albanerpetontids are an extinct clade of superficially salamander-like lissamphibians that range from the Middle Jurassic (Bathonian)-Early Pleistocene and have a primarily Laurasian distribution. The best Cenozoic record for the clade is in Europe, where two species in the type genus AlbanerpetonEstes & Hoffstetter, 1976 occur in over 40 localities of early Oligocene-Early Pleistocene age in Austria, Czech Republic, France, Germany, Hungary, Italy, and Serbia. From the post-evaporitic Messinian (5.41-5.33 Ma or latest Miocene) succession at Moncucco Torinese, in the Piedmont Basin, northwestern Italy, here we describe isolated albanerpetontid jaws and vertebrae referable to A. pannonicumVenczel & Gardner, 2005. This Italian occurrence extends the temporal record for A. pannonicum from the Early Pleistocene and Pliocene back into the latest Miocene and it narrows the temporal gap between that species and its European congener, A. inexpectatumEstes & Hoffstetter, 1976 (early Oligocene-late Miocene).

Mideopsis milankovici sp. nov. a new water mite from Montenegro based on morphological and molecular data (Acariformes, Hydrachnidia, Mideopsidae)

Water mite species of the genus Mideopsis Neuman, 1880 are common in running and standing waters in the Palaearctic. In the present study we used an integrative taxonomic approach by applying partial COI sequences (DNA-barcodes) and morphological characteristics to describe a new species, Mideopsis milankovici sp. nov. from the Mediterranean region of Montenegro. A high genetic distance (18.8-26% K2P) from three other known European congeners, M. crassipes Soar, 1904, M. orbicularis (Müller, 1776), and M. roztoczensis Biesiadka and Kowalik, 1979, support M. milankovici sp. nov. as a distinct species. From M. persicus Pešić and Saboori, 2015, a species known from South Iran, which resembles the new species in the shape of the ejaculatory complex, M. milankovici sp. nov. differs by the morphology of dorsal shield.

Coast to coast: High genomic connectivity in North American scoters.

Dispersal shapes demographic processes and therefore is fundamental to understanding biological, ecological, and evolutionary processes acting within populations. However, assessing population connectivity in scoters (Melanitta sp.) is challenging as these species have large spatial distributions that span remote landscapes, have varying nesting distributions (disjunct vs. continuous), exhibit unknown levels of dispersal, and vary in the timing of the formation of pair bonds (winter vs. fall/spring migration) that may influence the distribution of genetic diversity. Here, we used double‐digest restriction‐associated DNA sequence (ddRAD) and microsatellite genotype data to assess population structure within the three North American species of scoter (black scoter, M. americana; white‐winged scoter, M. deglandi; surf scoter, M. perspicillata), and between their European congeners (common scoter, M. nigra; velvet scoter, M. fusca). We uncovered no or weak genomic structure (ddRAD Φ ST < 0.019; microsatellite F ST < 0.004) within North America but high levels of structure among European congeners (ddRAD Φ ST > 0.155, microsatellite F ST > 0.086). The pattern of limited genomic structure within North America is shared with other sea duck species and is often attributed to male‐biased dispersal. Further, migratory tendencies (east vs. west) of female surf and white‐winged scoters in central Canada are known to vary across years, providing additional opportunities for intracontinental dispersal and a mechanism for the maintenance of genomic connectivity across North America. In contrast, the black scoter had relatively elevated levels of divergence between Alaska and Atlantic sites and a second genetic cluster found in Alaska at ddRAD loci was concordant with its disjunct breeding distribution suggestive of a dispersal barrier (behavioral or physical). Although scoter populations appear to be connected through a dispersal network, a small percentage (<4%) of ddRAD loci had elevated divergence which may be useful in linking areas (nesting, molting, staging, and wintering) throughout the annual cycle.

Will climate change increase hybridization risk between potential plant invaders and their congeners in Europe?

AimInterspecific hybridization can promote invasiveness of alien species. In many regions of the world, public and domestic gardens contain a huge pool of non‐native plants. Climate change may relax constraints on their naturalization and hence facilitate hybridization with related species in the resident flora. Here, we evaluate this possible increase in hybridization risk by predicting changes in the overlap of climatically suitable ranges between a set of garden plants and their congeners in the resident flora.LocationEurope.MethodsFrom the pool of alien garden plants, we selected those which (1) are not naturalized in Europe, but established outside their native range elsewhere in the world; (2) belong to a genus where interspecific hybridization has been previously reported; and (3) have congeners in the native and naturalized flora of Europe. For the resulting set of 34 alien ornamentals as well as for 173 of their European congeners, we fitted species distribution models and projected suitable ranges under the current climate and three future climate scenarios. Changes in range overlap between garden plants and congeners were then assessed by means of the true skill statistic.ResultsProjections suggest that under a warming climate, suitable ranges of garden plants will increase, on average, while those of their congeners will remain constant or shrink, at least under the more severe climate scenarios. The mean overlap in ranges among congeners of the two groups will decrease. Variation among genera is pronounced; however, and for some congeners, range overlap is predicted to increase significantly.Main conclusionsAveraged across all modelled species, our results do not indicate that hybrids between potential future invaders and resident species will emerge more frequently in Europe when climate warms. These average trends do not preclude, however, that hybridization risk may considerably increase in particular genera.

Progress and gaps in understanding mechanisms of ash tree resistance to emerald ash borer, a model for wood-boring insects that kill angiosperms.

We review the literature on host resistance of ash to emerald ash borer (EAB, Agrilus planipennis), an invasive species that causes widespread mortality of ash. Manchurian ash (Fraxinus mandshurica), which coevolved with EAB, is more resistant than evolutionarily naïve North American and European congeners. Manchurian ash was less preferred for adult feeding and oviposition than susceptible hosts, more resistant to larval feeding, had higher constitutive concentrations of bark lignans, coumarins, proline, tyramine and defensive proteins, and was characterized by faster oxidation of phenolics. Consistent with EAB being a secondary colonizer of coevolved hosts, drought stress decreased the resistance of Manchurian ash, but had no effect on constitutive bark phenolics, suggesting that they do not contribute to increased susceptibility in response to drought stress. The induced resistance of North American species to EAB in response to the exogenous application of methyl jasmonate was associated with increased bark concentrations of verbascoside, lignin and/or trypsin inhibitors, which decreased larval survival and/or growth in bioassays. This finding suggests that these inherently susceptible species possess latent defenses that are not induced naturally by larval colonization, perhaps because they fail to recognize larval cues or respond quickly enough. Finally, we propose future research directions that would address some critical knowledge gaps.

Trilobodrilus itoi sp. nov., with a Re-Description of T. nipponicus (Annelida: Dinophilidae) and a Molecular Phylogeny of the Genus.

The marine interstitial annelid Trilobodrilus itoi sp. nov., the sixth member of the genus, is described on the basis of specimens collected intertidally at Ishikari Beach, Hokkaido, Japan; this is the second species in the genus described from the Pacific Rim. In addition, T. nipponicus Uchida and Okuda, 1943 is re-described based on fresh topotypic material from Akkeshi, Hokkaido, Japan. From both species, we determined sequences of the nuclear 18S and 28S rRNA genes, and the mitochondrial cytochrome c oxidase subunit I (COI) gene. Molecular phylogenetic trees based on concatenated sequences of the three genes showed that T. itoi and T. nipponicus form a clade, which was the sister group to a clade containing the two European congeners T. axi Westheide, 1967 and T. heideri Remane, 1925. The Kimura two-parameter distance for COI was 22.5-22.7% between T. itoi and T. nipponicus, comparable with interspecific values in other polychaete genera. We assessed the taxonomic utility of epidermal inclusions and found that the known six species can be classified into three groups.

The Euro-American genus Eopelobates, and a re-definition of the family Pelobatidae (Amphibia, Anura)

The extinct Eopelobates (Eocene of western North America; Eocene–Pliocene of Europe) and Pelobates (Oligocene–Recent of Europe; Recent of northern Africa and the Middle East) are superficially toad-like anurans that are united within the family Pelobatidae mainly on the basis of a unique, tripartite frontoparietal complex. Both genera have a relatively good fossil record consisting of isolated bones, skeletons, and developmental series of tadpoles through adults, all of which are potentially informative for tracing the evolutionary history of the family. Eopelobates is of interest for several reasons. Of the two pelobatid genera, Eopelobates appears earlier in the fossil record (early Eocene vs. late Oligocene) and it is more primitive in lacking many of the features associated with fossoriality in extant Pelobates. The taxonomic composition of Eopelobates has been contentious and at least one putative new species has long been recognised, but never formally named. Here, we provide updated taxonomic accounts for Pelobatoidea, Pelobatidae, Pelobates, and Eopelobates and document development within a series of tadpoles and juveniles of E. bayeri from Bechlejovice (late Oligocene in age), Czech Republic. We also provide updated accounts for the five previously named and currently accepted species of Eopelobates. For the European congeners, E. anthracinus (late Oligocene) and E. bayeri (early Oligocene–middle Miocene) can confidently be regarded as separate species; although the distinction between E. hinschei and E. wagneri (both middle Eocene) is less certain, we provisionally maintain them as separate species. Micro-CT scans for the holotype skeleton of E. grandis (latest Eocene, USA) help resolve some problematic features, most notably showing that the cranial sculpture is of the pit-and-ridge style that is typical for Eopelobates. A sixth congener is named and described based on two skeletons from the middle Eocene portion of the Green River Formation, in Wyoming, USA. We caution that reports of Eopelobates-like anurans from the pre-Eocene of western North America and the early Eocene of India are based on isolated bones that cannot be assigned with confidence to that genus. The presence of Eopelobates in both North America and Europe may be explained by dispersal via the high latitude land bridge that connected those two continents during the late Paleocene through Eocene. The pelobatid fossil record is informative for documenting the nature and timing of changes in cranial features (e.g. ornament patterns, shape of nasals, pattern of frontoparietal–squamosal contact) from the inferred primitive condition seen in most Eopelobates to the more derived condition seen in extant Pelobates, but it is less informative for tracing the evolution of fossoriality, which is a key attribute of extant Pelobates.

Transcriptome analyses of a Chinese hazelnut species Corylus mandshurica.

BackgroundCorylus was renowned for its production of hazelnut and taxol. To understand the local adaptation of Chinese species and speed up breeding efforts in China, we analyzed the leaf transcriptome of Corylus mandshurica, which had a high tolerance to fungal infections and cold.ResultsA total of 12,255,030 clean pair-end reads were generated and then assembled into 37,846 Expressed Sequence Tag (EST) sequences. During functional annotation, 26,565 ESTs were annotated with Gene Ontology (GO) terms using Blast2go and 11,056 ESTs were grouped into the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways using KEGG Automatic Annotation Server (KAAS). We identified 45 ESTs that were homologous to enzymes and transcription factors responsible for taxol synthesis. The most differentiated orthologs between C. mandshurica and a European congener, C. avellana, were enriched in stress tolerance to fungal resistance and cold.ConclusionsIn this study, we detected a set of genes related to taxol synthesis in a taxol-producing angiosperm species for the first time and found a close relationship between most differentiated genes and different adaptations to fungal infection and cold in C. mandshurica and C. avellana. These findings provided tools to improve our understanding of local adaptation, genetic breeding and taxol production in hazelnut.

Molecular Characterization of Glossiphonia elegans (Verrill, 1872) (Glossiphoniidae: Hirudinida) from its type locality, West River, New Haven County, Connecticut, USA

Clepsine elegans Verrill, 1872 was described based on material collected from the West River, New Haven, New Haven County, Connecticut, USA (Verrill, 1872). Moore (1901) synonymized C. elegans with the European congener Glossiphonia complanata (Linnaeus, 1758) in view of the morphological similarities of the two species. Subsequently, all North American leeches bearing 6 eyespots and a pair of paramedial lines were considered Glossiphonia complanata. Using specimens collected from Ontario and Michigan, Siddall et al. (2005) resurrected Glossiphonia elgans (Verrill, 1872), because specimens collected from Ontario, Canada and Michigan, USA showed considerable genetic distinction from, and did not form monophyletic group with, European specimens of G. complanata.

Seed germination ecophysiology of two western North American species of Sambucus (Caprifoliaceae sensu lato), and comparisons with eastern North American and European congeners

AbstractSeeds of the western North American (wNA) species Sambucus caerulea in the Sambucus nigra species complex and Sambucus callicarpa in the Sambucus racemosa complex contain embryos that are 70–75% fully developed when freshly matured. These embryos must elongate approximately 15–25% before radicle emergence occurs. Embryos in seeds of both species grew better at 5°C than at 25/15°C. Dormancy was broken by cold stratification at 5°C, which was also the optimal temperature for germination. Gibberellic acid substituted for cold stratification in both species. Thus, seeds of both species have intermediate complex morphophysiological dormancy (MPD). The seed dormancy characteristics of both species differ from those of congeners in eastern North America (eNA). In contrast, dormancy break in S. callicarpa is similar to its European congeners, but is unclear in S. caerulea. Our study represents the first to compare seed dormancy among wNA, eNA and European congeners. In North America, the geographic pattern of dormancy break for Sambucus is similar to that of Osmorhiza (Apiaceae) and Erythronium (Liliaceae): cold stratification is required in wNA taxa and warm + cold stratification is required in eNA taxa. Moreover, the pattern in S. callicarpa is similar to that in some species of Sanicula (Apiaceae): cold stratification in Europe and warm + cold stratification in eNA. The evolution of seed dormancy in these groups might have occurred under similar environmental circumstances, resulting in the sharing of dormancy‐breaking mechanisms within geographical regions.

Chemical communication in mating behaviour of the slave-making ant Polyergus rufescens (Hymenoptera, Formicidae): 3-ethyl-4-methylpentanol as a critical component of the queen sex pheromone

The aim of the research reported here was to determine whether 3-ethyl-4-methylpentanol, a minor but crucial component of the sex pheromone of the North American slave-making ant species Polyergus breviceps, was also a component of the sex pheromone of the European congener Polyergus rufescens. Thus, the contents of mandibular glands of P. rufescens virgin queen were extracted and analysed. The main component of the extracts was methyl 6-methylsalicylate and 3-ethyl-4-methylpentanol was identified as one of several minor components. Further analyses showed that the insects produce mainly the (R)-enantiomer of the alcohol. Males’ responses to various blends of methyl 6-methylsalicylate with the racemate or the pure enantiomers of 3-ethyl-4- methylpentanol were tested in field behavioural bioassays. The data showed that blends of methyl 6- methylsalicylate and 3-ethyl-4-methylpentanol were strongly synergistic, with the most active ratios being biased toward the first component. The addition of other minor components to the binary blend neither increased nor decreased responses by males. Only the (R)-enantiomer of the alcohol was biologically active; its antipode did not inhibit attraction. The results are discussed in terms of the evolution of signals, and are compared with the results previously obtained for the allopatric species Polyergus breviceps.

A review of Palaearctic Teuchophorus, with a new species from Bulgaria (Diptera: Dolichopodidae)

The Palaearctic species of Teuchophorus are reviewed and a key provided to males. T. chaetifemoratus is described as new from Bulgaria. The male of this species is easily recognized by the ventral and posteroventral rows of strong curved bristles on the hind femur and, in contrast to all other Palaearctic species, its hind tibia does not show any peculiar chaetotaxy. It shares the same habitat preference as most of its Western European congeners, whereas Mediterranean species occur in more open habitats. T. simplex Mik is recorded for the first time from Bulgaria. T. bisetus Loew is reinstated as a distinct species, whereas T. tenuemarginatus Strobl most probably does not belong to Teuchophorus and is regarded as nomen dubium. In contrast to the literature, European, African and some Oriental Teuchophorus species have 6 dorsocentral bristles instead of 5, and the entire generic range encompasses 4 to 6 dorsocentral bristles. Two morphological features are found in both sexes of all Teuchophorus species and are the only reliable characters to separate this genus from Sympycnus (sensu lato): the oblique position of crossvein dm-cu and the anterior bend at the base of the distal section of vein M 1 .

A REASSESSMENT OF SPECIES BOUNDARIES IN CYSTOSEIRA AND HALIDRYS (PHAEOPHYCEAE, FUCALES) ALONG THE NORTH AMERICAN WEST COAST1

Application of phylogenetic species recognition to morphologically recognized species in the genera Cystoseira Agardh and Halidrys Lyngbye on North American west coasts revealed little genetic variation despite a remarkable degree of morphological variation currently used to recognize and delineate species. Whereas morphological characteristics allow recognition of two genera, four morphological species and three informal forms, maximum genetic variation among them was similar to that characteristic of the intraspecific level in European congeners and other Fucales. Among morphological species and forms, nucleotide variation in a combined 26S (large subunit (LSU)) and internal transcribed spacer (ITS) ribosomal DNA analysis was below 3% while it was 1% or less for the RUBISCO spacer of the chloroplast DNA. Comparison of the LSU data to available data for European congeners showed that the genera Cystoseira and Halidrys are not monophyletic and that the previously recognized Cystoseiraceae should be included within the family Sargassaceae. These observations suggest that the current taxonomy for the Sargassaceae fails to reflect evolutionary history because Atlantic and Pacific Cystoseira and Halidrys appear to have arrived at similar morphologies independently. Our results indicate a comparatively recent establishment on the west coast of North America of a sargassacean progenitor whose descendant taxa have experienced limited genetic divergence and are characterized by a high capacity for phenotypic variation despite their overall genetic similarity.