Both morph‐ and species‐dependent asymmetries affect reproductive barriers between heterostylous species

The interaction between floral traits and reproductive isolation is crucial to explaining the extraordinary diversity of angiosperms. Heterostyly, a complex floral polymorphism that optimizes outcrossing, evolved repeatedly and has been shown to accelerate diversification in primroses, yet its potential influence on isolating mechanisms remains unexplored. Furthermore, the relative contribution of pre‐ versus postmating barriers to reproductive isolation is still debated. No experimental study has yet evaluated the possible effects of heterostyly on pre‐ and postmating reproductive mechanisms. We quantify multiple reproductive barriers between the heterostylous Primula elatior (oxlip) and P. vulgaris (primrose), which readily hybridize when co‐occurring, and test whether traits of heterostyly contribute to reproductive barriers in unique ways. We find that premating isolation is key for both species, while postmating isolation is considerable only for P. vulgaris; ecogeographic isolation is crucial for both species, while phenological, seed developmental, and hybrid sterility barriers are also important in P. vulgaris, implicating sympatrically higher gene flow into P. elatior. We document for the first time that, in addition to the aforementioned species‐dependent asymmetries, morph‐dependent asymmetries affect reproductive barriers between heterostylous species. Indeed, the interspecific decrease of reciprocity between high sexual organs of complementary floral morphs limits interspecific pollen transfer from anthers of short‐styled flowers to stigmas of long‐styled flowers, while higher reciprocity between low sexual organs favors introgression over isolation from anthers of long‐styled flowers to stigmas of short‐styled flowers. Finally, intramorph incompatibility persists across species boundaries, but is weakened in long‐styled flowers of P. elatior, opening a possible backdoor to gene flow through intramorph pollen transfer between species. Therefore, patterns of gene flow across species boundaries are likely affected by floral morph composition of adjacent populations. To summarize, our study highlights the general importance of premating isolation and newly illustrates that both morph‐ and species‐dependent asymmetries shape boundaries between heterostylous species.     

Identification of insect cell lines and cell‐line cross‐contaminations by nuclear ribosomal ITS sequences

This report shows how the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (rDNA) can be used to determine the species identity of insect cell lines and to distinguish between cell lines derived from closely related insect species. A PCR‐RFLP method with the endonucleases HincII and PstI produces restriction fragment profiles that could distinguish between insect cell lines at the species level. Another PCR‐based method used three species‐specific primer sets, Ly‐ITS1/Ly‐ITS2, ITS1‐1/Ld‐ITS1 and Sf9‐F2/ITS4, to identify the cell lines from Lymantria xylina, L. dispar and Spodoptera frugiperda, respectively. This method also detected cell‐line cross‐contaminations (CLCC) with contamination levels as low as 1% (10 cells in a population of 1000 cells) even when the contaminating cells were from a closely related species. Compared with conventional methods used for cell‐line identification and CLCC detection, the methods presented here are fast and sensitive and could easily be applied to other cell culture laboratories.     

Rapid identification and characterization of Vibrio species using whole‐cell MALDI‐TOF mass spectrometry

Aims: Vibrio identification by means of traditional microbiological methods is time consuming because of the many biochemical tests that have to be performed to distinguish closely related species. This work aimed at evaluating the use of MALDI‐TOF mass spectrometry for the rapid identification of Vibrio (V.) spp. as an advantageous application to rapidly discriminate the most important Vibrio spp. and distinguish Vibrio spp. from closely related bacterial species like Photobacterium damselae and Grimontia hollisae and other aquatic bacteria like Aeromonas spp. Methods and Results: Starting from sub‐colony amounts of pure cultures grown on agar plates, a very simple sample preparation procedure was established and combined with a rapid and automated measurement protocol that allowed species identification within minutes. Closely related species like Vibrio alginolyticus and Vibrio parahaemolyticus or Vibrio cholerae and Vibrio mimicus could thus be differentiated by defining signatures of species‐identifying biomarker ions (SIBIs). As a reference method for species designation and for determination of relationships between strains with molecular markers, partial rpoB gene sequencing was applied. Conclusions: The MALDI‐TOF MS‐based method as well as the rpoB sequence‐based approach for Vibrio identification described in this study produced comparable classification results. The construction of phylogenetic trees from MALDI‐TOF MS and rpoB sequences revealed a very good congruence of both methods. Significance and Impact of the Study: Our results suggest that whole‐cell MALDI‐TOF MS‐based proteometric characterization represents a powerful tool for rapid and accurate classification and identification of Vibrio spp. and related species.     

Contrasting patterns of X‐chromosome divergence underlie multiple sex‐ratio polymorphisms in stalk‐eyed flies

Sex‐linked segregation distorters cause offspring sex ratios to differ from equality. Theory predicts that such selfish alleles may either go to fixation and cause extinction, reach a stable polymorphism or initiate an evolutionary arms race with genetic modifiers. The extent to which a sex ratio distorter follows any of these trajectories in nature is poorly known. Here, we used X‐linked sequence and simple tandem repeat data for three sympatric species of stalk‐eyed flies (Teleopsis whitei and two cryptic species of T. dalmanni) to infer the evolution of distorting X chromosomes. By screening large numbers of field and recently laboratory‐bred flies, we found no evidence of males with strongly female‐biased sex ratio phenotypes (SR) in one species but high frequencies of SR males in the other two species. In the two species with SR males, we find contrasting patterns of X‐chromosome evolution. T. dalmanni‐1 shows chromosome‐wide differences between sex‐ratio (X^SR) and standard (X^ST) X chromosomes consistent with a relatively old sex‐ratio haplotype based on evidence including genetic divergence, an inversion polymorphism and reduced recombination among X^SR chromosomes relative to X^ST chromosomes. In contrast, we found no evidence of genetic divergence on the X between males with female‐biased and nonbiased sex ratios in T. whitei. Taken with previous studies that found evidence of genetic suppression of sex ratio distortion in this clade, our results illustrate that sex ratio modification in these flies is undergoing recurrent evolution with diverse genomic consequences.     

Microsatellite primers for the African mole‐rat genus Cryptomys and cross‐species amplification within the family Bathyergidae

We report 11 microsatellite loci for the African mole‐rat genus Cryptomys (Rodentia: Bathyergidae), isolated from the Damaraland mole‐rat (Cryptomys damarensis) and the Common mole‐rat (C. hottentotus hottentotus). All loci are highly polymorphic in the source species, with between six and 13 alleles and observed heterozygosity ranging from 0.54 to 0.86. Two C. damarensis loci (DMR1 and 6) may be located on the X‐chromosome. Cross‐species amplification was investigated in 10 Bathyergid species, representative of the five genera. The majority of loci amplified polymorphic product in all Cryptomys species tested. Amplification was also widespread in the other genera, except in Heterocephalus.     

Female‐ and male‐specific signals of quality in the barn owl

Most bird studies of female signalling have been confined to species in which females display a male‐ornament in a vestigial form. However, a great deal of benefit may be gained from considering phenotypic traits that are specific to females. This is because (1) sex‐specific traits may signal sex‐specific qualities and (2) females may develop a male‐ornament not because they are selected to do so, but because fathers transmit to daughters the underlying genes for its expression (genetic correlation between the sexes). We investigated these two propositions in the barn owl Tyto alba, a species in which male plumage is lighter in colour and less marked with black spots than that of females. Firstly, we present published evidence that female plumage spottiness reflects parasite resistance ability. We also show that male plumage coloration is correlated with reproductive success, male feeding rate and heart mass. Secondly, cross‐fostering experiments demonstrate that plumage coloration and spottiness are genetically correlated between the sexes. This implies that if a given trait value is selected in one sex, the other sex will indirectly evolve towards a similar value. This prediction is supported by the observation that female plumage coloration and spottiness resembled that of males, in comparisons at the level of Tyto alba alba populations, Tyto alba subspecies and Tyto species. Our results therefore support the hypothesis that sex‐specific traits signal sex‐specific qualities and that a gene for a sex‐specific trait can be expressed in the other sex as the consequence of a genetic correlation between the sexes.     

High‐throughput SNP‐genotyping analysis of the relationships among Ponto‐Caspian sturgeon species

Legally certified sturgeon fisheries require population protection and conservation methods, including DNA tests to identify the source of valuable sturgeon roe. However, the available genetic data are insufficient to distinguish between different sturgeon populations, and are even unable to distinguish between some species. We performed high‐throughput single‐nucleotide polymorphism (SNP)‐genotyping analysis on different populations of Russian (Acipenser gueldenstaedtii), Persian (A. persicus), and Siberian (A. baerii) sturgeon species from the Caspian Sea region (Volga and Ural Rivers), the Azov Sea, and two Siberian rivers. We found that Russian sturgeons from the Volga and Ural Rivers were essentially indistinguishable, but they differed from Russian sturgeons in the Azov Sea, and from Persian and Siberian sturgeons. We identified eight SNPs that were sufficient to distinguish these sturgeon populations with 80% confidence, and allowed the development of markers to distinguish sturgeon species. Finally, on the basis of our SNP data, we propose that the A. baerii‐like mitochondrial DNA found in some Russian sturgeons from the Caspian Sea arose via an introgression event during the Pleistocene glaciation.     

Asymmetric and frequency‐dependent pollinator‐mediated interactions may influence competitive displacement in two vernal pool plants

A plant species immigrating into a community may experience a rarity disadvantage due to competition for the services of pollinators. These negative reproductive interactions have the potential to lead to competitive displacement or exclusion of a species from a site. In this study, we used one‐ and two‐species arrays of potted plants to test for density and frequency dependence in pollinator‐mediated and above‐ground intraspecific and interspecific competition between two species of Limnanthes that have overlapping ranges, but rarely occur in close sympatry. There were asymmetric competitive effects; the species responded differently to their frequency within 16‐plant replacement series arrays. Limnanthes douglasii rosea experienced stronger reductions in lifetime and per‐flower fertility, likely due to pollinator‐mediated competition with Limnanthes alba. This effect may be linked to asymmetrical competition through heterospecific pollen transfer. This study demonstrates that pollinator‐mediated competition may discourage establishment of L. d. rosea in sites already occupied by its congener.     

Development of EST‐SSRs from the Alpine Lady‐fern,Athyrium distentifolium

The utility of EST‐simple sequence repeats (EST‐SSRs) was evaluated in the fern Athyrium distentifolium. From 1152 frond cDNA clones, 165 microsatellites, including di‐, tri‐, tetra and penta‐nucleotide repeat motifs, were identified. Primer design was possible for 74 of the SSRs; subsequent screening of 10 loci on 186 individuals from six natural populations revealed between two and seven alleles per locus and expected heterozygosity (H_E) estimates ranging from 0.027 to 0.809. Eight of these loci were further examined for cross‐species and cross‐generic amplification in other Woodsiaceae species, and polymorphic products were detected. EST‐derived SSRs provide robust, informative and potentially transferable polymorphic markers suitable for biodiversity research.     

Ultraviolet‐B‐driven pigmentation and genetic diversity of benthic macroinvertebrates from high‐altitude Andean streams

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Fine‐ and Broad‐Scale Approaches to Understanding the Evolution of Aggression in Crickets

Male field crickets frequently engage in agonistic contests to establish dominance in social interactions and gain access to mate attraction territories. Crickets (Orthoptera: Gryllidae) are often used as a model taxon to study aggression, but limited documentation of aggression in some cricket species hinders our understanding of its evolutionary costs and benefits. Our study investigated cricket aggression at two scales: the within‐species scale for two cricket species, Gryllus assimilis and G. veletis, whose aggression had not been adequately documented and the among‐species scale to detect evolutionary patterns in species’ levels of aggression. In both G. veletis and G. assimilis, winners spent more time being aggressive than losers, but they were not larger or heavier. Collectively, our results reveal that G. veletis males are more aggressive than G. assimilis. Male G. veletis had higher aggression scores that male G. assimilis. The majority of G. veletis contests escalated to grappling (a highly aggressive behavior), while less than one quarter of G. assimilis contests escalated to grappling. Further, G. veletis males transitioned between two of the most aggressive behaviors most often while G. assimilis transitioned between two of the least aggressive behaviors most often. We integrate this new information on aggression for G. assimilis and G. veletis with previously documented aggression data for many cricket species to investigate aggression in a broader evolutionary context than previously possible. Within a phylogenetic context, we test the hypothesis that species whose males use burrows from which to call and attract females are more aggressive than species with non‐burrowing males. We found evidence consistent with this hypothesis; species with burrowing males tended to be more aggressive than species with non‐burrowing males. Together, our study provides fine‐scale understanding of aggression in two cricket species and broad‐scale evolutionary context for aggression across cricket species.     

Antagonistic interactions subdue inter‐species green‐beard cooperation in bacteria

Cooperation can be favoured through the green‐beard mechanism, where a set of linked genes encodes both a cooperative trait and a phenotypic marker (green beard), which allows carriers of the trait to selectively direct cooperative acts to other carriers. In theory, the green‐beard mechanism should favour cooperation even when interacting partners are totally unrelated at the genome level. Here, we explore such an extreme green‐beard scenario between two unrelated bacterial species—Pseudomonas aeruginosa and Burkholderia cenocepacia, which share a cooperative locus encoding the public good pyochelin (an iron‐scavenging siderophore) and its cognate receptor (green beard) required for iron–pyochelin uptake. We show that pyochelin, when provided in cell‐free supernatants, can be mutually exchanged between species and provide fitness benefits under iron limitation. However, in co‐culture we observed that these cooperative benefits vanished and communities were dominated by P. aeruginosa, regardless of strain background and species starting frequencies. Our results further suggest that P. aeruginosa engages in interference competition to suppress B. cenocepacia, indicating that inter‐species conflict arising from dissimilarities at the genome level overrule the aligned cooperative interests at the pyochelin locus. Thus, green‐beard cooperation is subdued by competition, indicating that interspecific siderophore cooperation is difficult to evolve and to be maintained.     

Succession during the re‐creation of a flood‐meadow 1985‐1999

Abstract. The study site, Somerford Mead, is located on the river Thames floodplain and was a species‐rich flood‐meadow in the 1950s. In the 1960s and 1970s it was subjected to intensive grassland management with regular NPK additions and occasional herbicide treatment. In 1981 Somerford Mead was ploughed for the first time and converted to arable land. Seeds of an Alopecuruspratensis‐Sanguisorba officinalis flood‐meadow community (MG4; Rodwell 1992) were sown onto prepared soil in the autumn of 1986, and botanical records were made from 1985 to 1999. From 1989 to 1999, three replicates of three treatments: cow‐grazing, sheep‐grazing and no‐grazing were introduced after hay‐cutting. Analysis successfully separated the establishment phase from the experimental phase and showed a significant difference between the grazed and ungrazed treatments. Abiotic and biotic factors which might contribute to successional trends are discussed. A convoluted pattern for each treatment could be attributed in part to intrinsic‘cycles’of perennial hemicryptophytes behaving as short‐lived species and in part to the percentage frequency of many species which was reduced in 1990 and 1995/1996, years of drought. After the initial inoculation of MG4 seed and the disappearance of arable therophytes, recruitment of new species was very slow. Coefficients for Somerford Mead matched against MG4 (Rodwell 1992) produced an equilibrium within three years. It subsequently fluctuated over a 10‐yr period well below the level of Oxey Mead, the donor site. Land managers should ensure that their proposed site has the right soils and hydrology for MG4 grassland and that traditional management of hay‐cutting and aftermath grazing is practised. Only one cut a year in July could lead to a reduction in percentage frequency of most species except Arrhenatherum elatius.     

VIM‐1 carbapenemase‐producing Escherichia coli in gulls from southern France

Acquired carbapenemases currently pose one of the most worrying public health threats related to antimicrobial resistance. A NDM‐1‐producing Salmonella Corvallis was reported in 2013 in a wild raptor. Further research was needed to understand the role of wild birds in the transmission of bacteria resistant to carbapenems. Our aim was to investigate the presence of carbapenem‐resistant Escherichia coli in gulls from southern France. In 2012, we collected 158 cloacal swabs samples from two gull species: yellow‐legged gulls (Larus michahellis) that live in close contact with humans and slender‐billed gulls (Chroicocephalus genei) that feed at sea. We molecularly compared the carbapenem‐resistant bacteria we isolated through culture on selective media with the carbapenem‐susceptible strains sampled from both gull species and from stool samples of humans hospitalized in the study area. The genes coding for carbapenemases were tested by multiplex PCR. We isolated 22 carbapenem‐resistant E. coli strains from yellow‐legged gulls while none were isolated from slender‐billed gulls. All carbapenem‐resistant isolates were positive for bla_VIM‐1 gene. VIM‐1‐producing E. coli were closely related to carbapenem‐susceptible strains isolated from the two gull species but also to human strains. Our results are alarming enough to make it urgently necessary to determine the contamination source of the bacteria we identified. More generally, our work highlights the need to develop more bridges between studies focusing on wildlife and humans in order to improve our knowledge of resistant bacteria transmission routes.     

Wing shape,wing size,and sexual dimorphism in eye‐span in stalk‐eyed flies (Diopsidae)

The eyes of stalk‐eyed flies (Diopsidae) are positioned at the end of rigid peduncles (‘stalks’) protruding laterally from the head. Eye‐stalk length varies within the family and, in some species, varies between males and females. Larger eye‐stalks in males result from sexual selection for longer stalks, a trait that increases male reproductive success. In the present study, we examined whether an increase in eye‐stalk length results in an adjustment of wing size and shape to deal with the burden of bearing an exaggerated ‘ornament’. We compared wing morphology among ten species of stalk‐eyed flies that differ in eye‐span and the degree of sexual dimorphism. Mass‐specific wing length differed between males and females in seven out of the ten species. Nondimensional wing shape parameters differed between the species (P < 0.001), but mostly did not differ between males and females of the same species. Dimorphism in eye‐span closely correlated with dimorphism in wing length (r = 0.89, P < 0.001) and the correlation remained significant (r = 0.81, P = 0.006) after correcting for phylogenetic relationships. Once corrected for phylogenetic relatedness, the mass‐specific wing length of males (but not females) was weakly correlated with mass‐specific eye‐span (r = 0.66, P = 0.042). We propose that the observed proportional increase in wing length associated with increased eye‐span can facilitate aerial manoeuverability, which would otherwise be handicapped by the elevated moment of inertia imposed by the wider head. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 860–871.     

Dispersal and recruitment limitation in native versus exotic tree species: life‐history strategies and Janzen‐Connell effects

Life‐history traits of invasive exotic plants are typically considered to be exceptional vis‐à‐vis native species. In particular, hyper‐fecundity and long range dispersal are regarded as invasive traits, but direct comparisons with native species are needed to identify the life‐history stages behind invasiveness. Until recently, this task was particularly problematic in forests as tree fecundity and dispersal were difficult to characterize in closed stands. We used inverse modelling to parameterize fecundity, seed dispersal and seedling dispersion functions for two exotic and eight native tree species in closed‐canopy forests in Connecticut, USA. Interannual variation in seed production was dramatic for all species, with complete seed crop failures in at least one year for six native species. However, the average per capita seed production of the exotic Ailanthus altissima was extraordinary: > 40 times higher than the next highest species. Seed production of the shade tolerant exotic Acer platanoides was average, but much higher than the native shade tolerant species, and the density of its established seedlings (≥ 3 years) was higher than any other species. Overall, the data supported a model in which adults of native and exotic species must reach a minimum size before seed production occurred. Once reached, the relationship between tree diameter and seed production was fairly flat for seven species, including both exotics. Seed dispersal was highly localized and usually showed a steep decline with increasing distance from parent trees: only Ailanthus altissima and Fraxinus americana had mean dispersal distances > 10 m. Janzen‐Connell patterns were clearly evident for both native and exotic species, as the mode and mean dispersion distance of seedlings were further from potential parent trees than seeds. The comparable intensity of Janzen‐Connell effects between native and exotic species suggests that the enemy escape hypothesis alone cannot explain the invasiveness of these exotics. Our study confirms the general importance of colonization processes in invasions, yet demonstrates how invasiveness can occur via divergent colonization strategies. Dispersal limitation of Acer platanoides and recruitment limitation of Ailanthus altissima will likely constitute some limit on their invasiveness in closed‐canopy forests.     

A novel genome‐wide microsatellite resource for species of Eucalyptus with linkage‐to‐physical correspondence on the reference genome sequence

Keystone species in their native ranges, eucalypts, are ecologically and genetically very diverse, growing naturally along extensive latitudinal and altitudinal ranges and variable environments. Besides their ecological importance, eucalypts are also the most widely planted trees for sustainable forestry in the world. We report the development of a novel collection of 535 microsatellites for species of Eucalyptus, 494 designed from ESTs and 41 from genomic libraries. A selected subset of 223 was evaluated for individual identification, parentage testing, and ancestral information content in the two most extensively studied species, Eucalyptus grandis and Eucalyptus globulus. Microsatellites showed high transferability and overlapping allele size range, suggesting they have arisen still in their common ancestor and confirming the extensive genome conservation between these two species. A consensus linkage map with 437 microsatellites, the most comprehensive microsatellite‐only genetic map for Eucalyptus, was built by assembling segregation data from three mapping populations and anchored to the Eucalyptus genome. An overall colinearity between recombination‐based and physical positioning of 84% of the mapped microsatellites was observed, with some ordering discrepancies and sporadic locus duplications, consistent with the recently described whole genome duplication events in Eucalyptus. The linkage map covered 95.2% of the 605.8‐Mbp assembled genome sequence, placing one microsatellite every 1.55 Mbp on average, and an overall estimate of physical to recombination distance of 618 kbp/cM. The genetic parameters estimates together with linkage and physical position data for this large set of microsatellites should assist marker choice for genome‐wide population genetics and comparative mapping in Eucalyptus.     

Long‐term seed bank dynamics in a temperate forest under conversion from coppice‐with‐standards to high forest management

Questions: How do changes in forest management, i.e. in disturbance type and frequency, influence species diversity, abundance and composition of the seed bank? How does the relationship between seed bank and vegetation change? What are the implications for seed bank dynamics? Location: An ancient Quercus petraea — Carpinus betulus forest in conversion from coppice‐with‐standards to regular Quercus high forest near Montargis, France. Methods: Seed bank and vegetation were sampled in six replicated stand types, forming a chronosequence along the conversion pathway. The stand types represented mid‐successional stages of stands in transition from coppice‐with‐standards (to high forest (16 plots) and early‐ and mid‐successional high forest stands (32 plots). Results: Seed bank density and species richness decreased with time since last disturbance. Adjusting for seed density effects obscured species richness differences between stand types, but species of later seres were nested subsets of earlier seres, implying concomitant shifts in species richness and composition with time since disturbance. Later seres were characterized by species with low seed weight and high seed longevity. Seed banks of early seres were more similar to vegetation than to later seres. Conclusions: Abandonment of the coppice‐with‐standards regime altered the seed bank characteristics, as well as its relationship with vegetation. Longer management cycles under high forest yield impoverished seed banks. For their persistence, seed bank species will increasingly rely on management of permanently open areas in the forest landscape. Thus, revegetation at the beginning of new high‐forest cycles may increasingly depend on inflow from seed sources.