Agonistic interactions between invasive green crabs, Carcinus maenas (Linnaeus), and sub-adult American lobsters, Homarus americanus (Milne Edwards)

The invasive green crab, Carcinus maenas, has recently expanded its range into the Southern Gulf of St. Lawrence, where there is potential for substantial niche overlap with juvenile American lobsters, Homarus americanus. We used two experiments to elicit, record and analyze the agonistic interactions of adult green crabs (carapace width of 63-75 mm) and sub-adult (carapace length of 55-70 mm) lobsters. The first experiment gave each animal equal access to a limited food resource. The green crabs were first to the food in significantly more trials, spent a significantly greater proportion of time with the food, and were able to successfully defend the food from attacks by the heavier lobsters. In the second experiment, we allowed the lobsters to gain possession and initiate feeding on the food before releasing the green crabs. In these trials, the lobsters spent significantly more time with the food, and were able to defend the food from the green crabs. The results of both experiments are discussed in the context of game theory. The different behaviour of the crustaceans in the two experiments is consistent with the “bourgeois” strategy in a hawk and dove game simulation. With this strategy, an animal acts like a hawk if in possession of a resource, but acts like a dove if the other animal is in possession of the resource. The fact that the green crabs were able to physically compete with, and in many cases dominate the larger, heavier lobsters supports the potential for competitive impacts of green crabs on sub-adult lobsters.     

Trophic interactions between two introduced suspension-feeders, Crepidula fornicata and Crassostrea gigas, are influenced by seasonal effects and qualitative selection capacity

The effects of season and qualitative selection capacity on trophic relationships between two sympatric invasive suspension-feeders, Crepidula fornicata and Crassostrea gigas, were investigated in Bourgneuf Bay (France) from January 2003 to June 2004. Carbon and nitrogen stable isotopic deviations, δ¹³C and δ¹⁵N, of common Atlantic slippersnails and Pacific oysters were analysed relative to isotopic composition and availability of end-members.Slippersnail deviations were less variable over the sampling period compared with those of oysters. Significant differences between δ¹³C and δ¹⁵N of C. fornicata and C. gigas were found from winter to early summer, and linked to major isotopic changes in oysters. We identified three distinct seasonal periods: January to March when oysters were ¹⁵N-enriched compared to slippersnails and to themselves at other times of the year, April to June-July when oysters showed a ¹⁵N-depletion and a more marked ¹³C-depletion compared to slippersnails and to themselves at other times of the year, and July-August to December when both species presented similar carbon and nitrogen deviations. Species-specific differences in qualitative selection capability may explain these seasonal differences in isotopic deviations. Whereas the isotopic composition of the indiscriminate suspension-feeding slippersnails reflects the composition of the seston throughout the year, the oyster is capable of qualitative selection. The oyster isotopic compositions are consistent with a facultative activation of selection mechanisms under conditions of qualitative and quantitative food limitation, notably the preferential ingestion and assimilation of the dominant organic source in the suspended pool.We conclude that C. fornicata and C. gigas are trophic competitors only in winter and spring at this site, where detrital end-members are major POM components. These results underscore (1) the importance of long-term (annual) studies in the evaluation of potential trophic competition, and (2) the necessity to include the qualitative selection capacities of suspension-feeders in future interpretations of trophic relationships in marine coastal ecosystems.     

Agonistic interactions between the invasive green crab, Carcinus maenas (Linnaeus) and juvenile American lobster, Homarus americanus (Milne Edwards)

Invasive organisms have the potential for competition with native organisms. In the Southern Gulf of St. Lawrence, juvenile American lobsters have a potential spatial overlap with adult green crabs. Crustaceans use agonistic behaviour to settle disputes, with the larger organism often winning contests for limited resources such as food and shelter. Two experiments were carried out using adult green crabs (53-76 mm carapace width) and juvenile American lobsters (28-57 mm carapace length). The first experiment used a limited food resource. We found that green crabs were the first to the food in all trials, fed in significantly more trials than lobsters and spent a significantly greater proportion of time with the food. The lobsters were only able to displace the green crabs from the food in 2 of 65 attempts. The second experiment was designed to examine shelter competition; unexpectedly some predation by green crabs on lobsters occurred, which allowed us to test hypotheses about how relative size and shelter use affect predation. Green crabs captured and consumed juvenile lobsters in 6 of 11 trials. The lobsters that survived spent significantly more time in shelter. There was no clear relationship between shelter use and size of lobster. The lobsters that were larger in relation to the green crabs suffered a higher rate of predation, which we believe was due to more conspicuous activity and less use of shelter. It appears that green crabs have the potential to negatively impact native juvenile lobster.     

Habitat selection of two gobies (Microgobius gulosus, Gobiosoma robustum): influence of structural complexity, competitive interactions, and presence of a predator

Herein I compare the relative importance of preference for structurally complex habitat against avoidance of competitors and predators in two benthic fishes common in the Gulf of Mexico. The code goby Gobiosoma robustum Ginsburg and clown goby Microgobius gulosus (Girard) are common, ecologically similar fishes found throughout the Gulf of Mexico and in the southeastern Atlantic Ocean. In Florida Bay, these fishes exhibit habitat partitioning: G. robustum is most abundant in seagrass-dominated areas while M. gulosus is most abundant in sparsely vegetated habitats. In a small-scale field survey, I documented the microhabitat use of these species where their distributions overlap. In a series of laboratory experiments, I presented each species with structured (artificial seagrass) versus nonstructured (bare sand) habitats and measured their frequency of choosing either habitat type. I then examined the use of structured versus nonstructured habitats when the two species were placed together in a mixed group. Finally, I placed a predator (Opsanus beta) in the experimental aquaria to determine how its presence influenced habitat selection. In the field, G. robustum was more abundant in seagrass and M. gulosus was more abundant in bare mud. In the laboratory, both species selected grass over sand in allopatry. However, in sympatry, M. gulosus occupied sand more often when paired with G. robustum than when alone. G. robustum appears to directly influence the habitat choice of M. gulosus: It seems that M. gulosus is pushed out of the structured habitat that is the preferred habitat of G. robustum. Thus, competition appears to modify the habitat selection of these species when they occur in sympatry. Additionally, the presence of the toadfish was a sufficient stimulus to provoke both M. gulosus and G. robustum to increase their selection for sand (compared to single-species treatments). Distribution patterns of M. gulosus and G. robustum likely result from a synthesis of various biotic and abiotic filters, including physiological tolerances to environmental factors, dispersal ability of larvae, and availability of food. Selection for structural complexity, competition, and presence of predators may further define the resulting pattern of distribution observed in the field.     

Effects of salinity on larval stages of the rhizocephalan barnacle Loxothylacus texanus: survival and metamorphosis in response to the host, Callinectes sapidus

It is known that the rhizocephalan barnacle Loxothylacus texanus infects the greater blue crab, Callinectes sapidus, in the Gulf of Mexico and adjacent waters, however, factors that affect the prevalence and distribution of this parasite, particularly the dispersive larval stages of this organism, are not well understood. In the current study, the effects of salinity on larval survival and the metamorphosis of L. texanus in response to postmolt host exoskeleton were examined. Acute and acclimated responses were similar. Larval survival was highest in the 20-35‰ range, with 100% mortality of nauplii at all salinities <20‰ and >50‰. L. texanus cyprids were able to metamorphose over a broad range of salinities (15-60‰). In several cases, metamorphosis was actually greatest at high salinities (40-50‰). These data predict that L. texanus larvae would be concentrated in portions of Gulf of Mexico waters with salinities >20‰ such as the mouths of estuaries and bays. Conversely, upper regions of estuaries may be inhospitable to the dispersive (naupliar) stage of the parasite and may serve as a refuge from infection for host crabs.     

Does land use change affect the interactions between two dry grassland species?

Over the last 20 years, a change in traditional land use practices has taken place in central Germany. Formerly species-rich dry grassland communities have been converted into communities with greatly reduced diversity in many places. Whereas grass species have expanded, several forbs have declined in abundance. For the present study, plant-plant interactions were assessed between the expanding grass Festuca rupicola and the forb Dianthus carthusianorum - two typical, companion grassland species - to ascertain any associated effects of land use change. A competition experiment was set up with replacement design, in which pots were placed in the open field and monitored over two consecutive years. In order to assess the performance of both species in monoculture (D9, F9) and mixture (D3F6, D6F3) the parameters biomass, length of flowering stems, number of flowering stems and number of flowers per individual, or length of panicles, were analyzed. Positive and negative interactions were evaluated using the “Relative Neighbour Effect” index (RNE). To simulate land use by grazing or mowing, individuals in half of the pots were clipped in the first year after sowing. At this time, performance of D. carthusianorum - in terms of length of flowering stems, number of flowering stems and number of flowers - was significantly affected: whereas the first parameter increased, both of the other parameters decreased with increasing presence of the grass species. However, RNE indicated facilitation with a low number of F. rupicola individuals, and competition with a high number of F. rupicola individuals. In contrast, F. rupicola did not show any significant differences in performance with increasing presence of D. carthusianorum, and the RNE switched from neutral interaction to facilitation. In the second year after sowing, the performance of D. carthusianorum in the various treatments did not differ, except for the length of the flowering stems. The simulation of land use practices did not affect the performance of D. carthusianorum, but F. rupicola showed significant differences in biomass and in length of the panicles, as was the case also between monocultures and mixtures. The performance of the grass species was clearly improved in the unclipped treatments. The RNE reflected competition against D. carthusianorum which became reduced in unclipped treatments, while F. rupicola became facilitated. There were no interactions between the different treatments (monocultures and mixtures) and the simulated land use change (clipped and unclipped). Our data suggest that although traditional land use practices, i.e. grazing and mowing, do not affect the development of D. carthusianorum, the abandonment of these practices has improved F. rupicola performance, which has led to the increasingly invasive character of this grass species over the last 20 years.     

Effects of temperature, salinity, and irradiance on the growth of the dinoflagellate Akashiwo sanguinea

The effects of temperature, salinity, and irradiance on the growth of the dinoflagellate Akashiwo sanguinea were examined in the laboratory. The irradiance at the light compensation point (I₀) was 14.40 μmol m^− 2 s^− 1 and the irradiance at growth saturation (I_s) was 114 μmol m^− 2 s^− 1. We exposed A. sanguinea to 48 combinations of temperature (5-30 °C) and salinity (5-40) under saturating irradiance; it exhibited its maximum growth rate of 1.13 divisions/day at a combination of 25 °C and salinity of 20. A. sanguinea was able to grow at temperatures from 10 to 30 °C and salinities from 10 to 40. This study revealed that A. sanguinea was a eurythermal and euryhaline organism; in Japan it should have formed blooms in early summer, when salinity was relatively low. In addition, it was noteworthy that A. sanguinea had markedly cold-durability, retaining the motile form of vegetative cells for more than 50 days at 5 °C and at salinities of 25-30.     

Effects of hydrological regimes on competitive interactions of Schoenoplectus fluviatilis and two co-occurring wetland plants

We investigated the effects of different hydrological regimes (wet [flooded at a constant water depth for duration of the study], cycle [reflooded at eight weeks following natural drying], and wet–dry [initially flooded and allowed to naturally dry for duration of the study]) on the competitive ability of Schoenoplectus fluviatilis (Torr.) M. T. Strong with an annual, native wetland plant (Polygonum pensylvanicum L.) and a perennial, wetland plant (Schoenoplectus tabernaemontani [C. C. Gmel.] Palla). To assess competitive response of the plants, we used a greenhouse target-neighbor study with neighbor plants planted at varying densities (0 [control], 1, 10, and 15 plants pot⁻¹). Our results suggest that S. fluviatilis is competitively superior to S. tabernaemontani and P. pensylvanicum. S. tabernaemontani and P. pensylvanicum biomass declined by 90% and 75% in presence of S. fluviatilis, respectively. However, the competitive ability of S. fluviatilis was generally not enhanced by flooding regime. The competitive coefficients of S. fluviatilis were similar among the three hydrological regimes under intraspecific competition and interspecific competition with S. tabernaemontani, but for interspecific competition with P. pensylvanicum, the competitive coefficient for S. fluviatilis was higher for the cycle treatment compared to the wet–dry and dry treatments. Interestingly, S. tabernaemontani was a strong competitor against S. fluviatilis in the wet and cycle treatments, indicating that maintaining longer hydroperiods could be used as a management tool to encourage growth of S. tabernaemontani and reduce encroachment of S. fluviatilis.     

Effects of salinity on leaf growth and survival of the Mediterranean seagrass Posidonia oceanica (L.) Delile

The main aim of this study was to estimate the effects of salinity variation on the Mediterranean seagrass Posidonia oceanica (L.) Delile and its attached epiphytes. Leaf growth and survival of this plant were tested in several short-term (15 days) mesocosms experiments under controlled conditions between February 2001 and November 2001. Plants collected from shallow meadows at Alicante (SE Spain), with an ambient salinity of 36.8-38.0 psu, were placed in tanks of 300 L with an additional overhead light and exposed to different salinity treatments (ranging from 25 to 57 psu) during 15 days. To estimate the mortality and growth recuperation, in some experiments shoots were returned to control salinity (38 psu). Leaf growth was measured in the laboratory where epiphytic fauna and flora were removed from leaves, with a razor blade, to determine their biomass.P. oceanica was negatively influenced by increased salinity. Shoots showed a significant decrease in growth and survival, whereas epiphyte biomass did not show a clear response because of their high variability. Maximum leaf growth occurred between 25 and 39 psu. In addition, plants suffered considerable mortality at salinities above 42 psu and below 29 psu, with 100% mortality at 50 psu. In salinities between 39 and 46 psu, surviving plants were able to regain their original growth rate when returned to normal seawater salinity (38 psu). These results suggest that P. oceanica is one of the most sensitive seagrasses to salinity increments it is more tolerant to salinity reductions (25.0-36.4 psu), perhaps due to the terrestrial origin of seagrasses.     

Molecular and morphological relationships between two closely related species, Turbinaria ornata and T. conoides (Sargassaceae,Phaeophyceae)

We employed four markers (two chloroplastic, one mitochondrial and one nuclear) to investigate whether Turbinaria ornata and Turbinaria conoides, two morphologically similar brown algae, are distinct species. The molecular data revealed reciprocal monophyly, thus confirming the two algae as discrete species. Nevertheless, taxonomical ambiguities remain. T. conoides is more morphologically variable than T. ornata. We identified an atypical T. conoides morphotype whose blade possesses intramarginal teeth, a morphological characteristic of the T. ornata group that is normally absent within T. conoides. The molecular data indicate, nonetheless, that this morphotype belongs genetically to the T. conoides group. Thus, the results cast doubt upon the validity of using intramarginal teeth for species diagnosis.     

Allozymatic divergence between border populations of two cryptic species of the Drosophila buzzatii cluster species (Diptera: Drosophilidae)

Drosophila antonietae and Drosophila gouveai are allopatric, cactophilic, cryptic and endemic of South America species, which aedeagus morphology is considered the main diagnostic character. In this work, single close populations from the edge distributions of each species, located in an “introgressive corridor”, were analyzed regarding temporal isozenzymatic genetic variability. Isocitrate dehydrogenase (Idh) appeared as a diagnostic locus between D. antonieate and D. gouveai because each population was fixed for different alleles. Moreover, several polymorphic loci showed accentuated divergence in the allele frequency, as evidenced by Nei’s I (0.3188) and D (1.1432), and also by Reynolds’ genetic distance and identity (1.3207 and 0.7331, respectively). Our results showed that, in spite of the very similar external morphology, related evolutionary histories, close distributions, and events of introgression in the studied area, these cryptic species have high allozymatic differentiation, and this is discussed here.     

高榕榕果内Eupristina属两种榕小蜂的遗传进化关系

对生长在福州地区的高榕进行长期追踪观察,发现高榕榕果内仅生活着Eupristina altissima和Eupristina sp.榕小蜂,前者为高榕的传粉小蜂,后者无传粉行为,两者雌蜂之间在体色、触角、花粉袋和花粉刷等部位存在细微的差异,而两者雄蜂之间无形态差异。通过克隆福建地区5个样地的高榕榕果内收集到的E. altissima和Eupristina sp.榕小蜂,以及细叶榕的传粉小蜂Eupristina verticillata(外群)的Cytb及COI基因,并进行碱基组成及遗传距离分析,用邻接法构建系统发育树,分析两榕小蜂群体之间的遗传进化关系,结果显示:(1)榕小蜂COI及Cytb序列碱基组成中A+T的含量(Cytb序列中A+T=75.3%,COI序列中A+T=75.5%)显著高于G+C,符合膜翅目昆虫线粒体基因碱基组成特征。(2)对两群体小蜂进行遗传距离分析显示,Cytb序列中E. altissima和Eupristina sp. 群体内各样本之间的平均遗传距离分别为0.0092和0.0030,而E. altissima与Eupristina sp. 群体间的平均距离为0.1588;COI序列中E. altissima 与Eupristina sp. 群体内各样本之间的平均遗传距离分别为0.0065和0.0205,而二者群体间的平均遗传距离为0.1043,表明两者群体间的遗传距离明显大于各自群体内各样本间的遗传距离。统计GenBank中下载的6个属34种榕小蜂Cytb序列的种间遗传距离为0.0811-0.1723,6个属28种榕小蜂COI序列的种间遗传距离为0.0939-0.1986。由此认为E. altissima和Eupristina sp.之间的遗传距离差异已经达到了种间水平,即E. altissima与Eupristina sp.为两个不同的种。(3)在形态上,两种小蜂的雌蜂之间有微小差异,而二者雄蜂之间无差异,但Cytb与COI序列分析结果一致表明:E. altissima与Eupristina sp.雄蜂之间,以及二者雌蜂之间的遗传距离均差异显著,表明形态变异滞后于基因变异。雌蜂在表型上进化快于雄蜂,可能是由于雌蜂羽化后从榕果出飞,受到外界环境因素的影响较大,且两种雌蜂在传粉功能上存在差异,故二者之间的形态差异较大,而雄蜂寿命短,又终生生活在黑暗封闭、环境变化相对恒定的榕果内,两种雄蜂在行为上不存在差异,故二者表型变异较为缓慢。E. altissima和Eupristina sp.小蜂对宿主的专一性不强,在榕-蜂协同进化过程中,可能发生过宿主转移事件。     

Comparison of low salinity tolerance in Callinectes sapidus Rathbun and Callinectes similis Williams postlarvae upon entry into an estuary

Planktonic larvae of estuarine crabs are commonly exported to the continental shelf for development and then return to coastal and estuarine areas as postlarvae (megalopae). Megalopae returning to estuaries must be adapted to survive in brackish water whereas those of coastally distributed species should not need such adaptations. We investigated 1) whether megalopae of the estuarine crab Callinectes sapidus and the coastal crab Callinectes similis undergo changes in salinity tolerance upon entry into an estuary and 2) what factors induce those changes. Megalopae were collected at a coastal site and a nearby estuarine site and exposed to a range of salinities (5, 10, 15, 20 and 30) for 6 h. Percent survival was determined after 24 h reintroduction to the collection site water. We also investigated 1) whether increased salinity tolerance was induced by reduced salinity or estuarine chemical cues, 2) the time to acclimation and 3) the salinity necessary for acclimation. C. sapidus megalopae from the estuarine site were more likely to survive exposure to low salinities than those from the coastal site. C. sapidus megalopae from the coastal site exhibited increased survival after acclimation to salinities of 27 and 23 for 12 h. Estuarine chemical cues had no effect on salinity tolerance. C. similis megalopae were less likely to survive at low salinities and did not exhibit an acclimation response upon exposure to reduced salinities. These results suggest that megalopae of C. sapidus are physiologically adapted to recruit to estuaries whereas megalopae of C. similis are unable to acclimate to low salinity conditions.     

Competition and facilitation between the alien mussel Mytilus galloprovincialis and indigenous species: Moderation by wave action

As the alien species that most dominates space along the South African coast, the Mediterranean mussel Mytilus galloprovincialis has radically altered community composition on invaded shores. We experimentally assessed interspecific interactions between this invasive species and dominant indigenous species in conjunction with considering how wave action moderates such interactions. The density of both M. galloprovincialis and the limpet Scutellastra granularis increased with wave action. Conversely, the tube-building polycheate Gunnarea capensis was negatively affected by wave exposure, being most abundant on sheltered shores. The influence of wave action on the indigenous mussel Aulacomya ater, however, remains unclear. M. galloprovincialis outcompeted both G. capensis and A. ater at moderate to high exposure levels, whereas it had both positive and negative effects on S. granularis. It outcompeted adult limpets on primary rock space on semi-exposed and exposed shores, reducing densities of this portion of the population. However, recruitment of S. granularis was facilitated by M. galloprovincialis, as greater numbers recruited to the secondary substratum offered by mussel shells. Again this interaction intensified with wave action. Due to the extremely high density of recruits on secondary space, the net effect of M. galloprovincialis on S. granularis was positive. Thus, wave action not only influences the abundance of individual species, but also mediates both positive and negative interspecific interactions in rocky shore communities, including the impact of alien species such as M. galloprovincialis.     

Effects of salinity, temperature and pH on the survival of the nemertean Procephalothrix simulus Iwata, 1952

The salinity, temperature and pH tolerance of Procephalothrix simulus Iwata, 1952, were experimentally studied. In hypo-media, the nemerteans could survive 96 h in 3.3‰ solution at 10 °C (median lethal salinity [LS₅₀] was not determined at this temperature), and 96 h LS₅₀ were 7.3‰ and 13.5‰ at 20 °C and 30 °C, respectively. In hyper-media, 96 h LS₅₀ values were 53.9‰, 47.1‰ and 41.4‰ at 10 °C, 20 °C and 30 °C, respectively. The trend of body weight changes in diluted media indicated that this nemertean is a volume regulator. During a 96-h exposure in media at 0 °C, worms were thanatoid but could recover if the temperature was gradually elevated to 20 °C. In thermal tolerance experiments, the nemertean survived 96 h in seawater of 30 °C, and worms suffered high mortalities when the temperature exceeded 32 °C. Present results suggest that the interaction of temperature and salinity on the lethal effects on P. simulus is significant (P < 0.05). Elevated temperature (range 10-30 °C) decreased the worm's solute tolerance, and elevated salinity (range 18-38‰) decreased the worm's thermal tolerance. The survival pH level for this nemertean ranged from 5.00 to 9.20.     

The combined influence of sub-optimal temperature and salinity on the in vitro viability of Perkinsus marinus, a protistan parasite of the eastern oyster Crassostrea virginica

Perkinsus marinus is a major cause of mortality in eastern oysters along the Gulf of Mexico and Atlantic coasts. It is also well documented that temperature and salinity are the primary environmental factors affecting P. marinus viability and proliferation. However, little is known about the effects of combined sub-optimal temperatures and salinities on P. marinus viability. This in vitro study examined those effects by acclimating P. marinus at three salinities (7, 15, 25 ppt) to 10 °C to represent the lowest temperatures generally reached in the Gulf of Mexico, and to 2 °C to represent the lowest temperatures reached along the mid-Atlantic coasts and by measuring changes in cell viability and density on days 1, 30, 60 and 90 following acclimation. Cell viability and density were also measured in 7 ppt cultures acclimated to each temperature and then transferred to 3.5 ppt. The largest decreases in cell viability occurred only with combined low temperature and salinity, indicating that there is clearly a synergistic effect. The largest decreases in cell viability occurred only with both low temperature and salinity after 30 days (3.5 ppt, 2 °C: 0% viability), 60 days (3.5 ppt, 10 °C: 0% viability) and 90 days (7 ppt, 2 °C: 0.6 ± 0.7%; 7 ppt, 10 °C: 0.2 ± 0.2%).     

Competition between Salvinia minima and Spirodela polyrhiza mediated by nutrient levels and herbivory

We investigated the effects of initial biomass, nutrients, herbivory, and competition with Spirodela polyrhiza (L.) Schleid on Salvinia minima Baker biomass and density. S. minima populations were subjected to two levels of herbivory (control vs. two adults per plant) from the weevil Cyrtobagous salviniae Calder and Sands and eight levels of competition from S. polyrhiza, while growing in high (5 mg N l⁻¹) or low (0.5 mg N l⁻¹) nutrient conditions. Herbivory was the most important factor in S. minima biomass production while competition or fertility had no measurable impact. In contrast, S. polyrhiza biomass was mediated primarily by nutrients, not competition. There was no herbivory treatment for this plant. S. polyrhiza was superior to S. minima at converting nutrients to biomass but this did not give it a competitive advantage since S. minima biomass was unchanged when herbivory was absent. S. minima can generally overtop S. polyrhiza which, in turn, can form multiple layers within its mat. These characteristics may act to lessen competition between these species, thereby permitting their habitat sharing.     

Hebeloma species associated with Cistus

The genus Hebeloma has a number of species highly specific to Cistus and others that occur with several host genera. This paper discusses the species of Hebeloma that appear to be ectomycorrhizal with Cistus, judging from their occurrence when Cistus is the only available host. The previously unknown species H. plesiocistum spec. nov. is described. We also provide a key to the known Hebeloma associates of Cistus. Molecular analyses based on ITS sequence data further illustrate the distinctness of the newly described species and difficulties in the species delimitation with view to H. erumpens. Specific associations with Cistus may have evolved more than once within the genus Hebeloma.     

RPB2 sequences reveal a close phylogenetic relationship between tetraploid Hordelymus and diploid Hordeum species in Triticeae (Poaceae)

The origin of Hordelymus genome has been debated for years, and no consensus conclusion was reached. In this study, we sequenced and analyzed the RPB2 (RNA polymerase subunit II) gene from Hordelymus europaeus (L.) Harz, and its potential diploid ancestor species those were suggested in previous studies. The focus of this study was to examine the phylogenetic relationship of Hordelymus genomes with its potential donor Hordeum, Psathyrostachys, and Taeniatherum species. Two distinguishable copies of sequences were obtained from H. europaeus. The obvious difference between the two copies of sequences is a 24 bp indel (insertion/deletion). Phylogenetic analysis showed a strong affinity between Hordeum genome and Hordelymus with 85% bootstrap support. These results suggested that one genome in tetraploid H. europaeus closely related to the genome in Hordeum species. Another genome in H. europaeus is sister to the genomes in Triticeae species examined here, which corresponds well with the recently published EF-G data. No obvious relationship was found between Hordelymus and either Ta genome donor, Taeniatherum caput-medusae or Ns genome donor, Psathyrostachys juncea. Our data does not support the presence of Ta and Ns genome in H. europaeus, and further confirms that H. europaeus is allopolyploid.