Biological species problems in some Tetramesa (Hymenoptera, Eurytomidae)

Using horizontal starch gel electrophoresis, ten enzyme systems were surveyed in ten populations of Tetramesa reared from eight species of grass collected from different sites in Britain. Eight species of Tetramesa were recognized on the basis of the number and relative mobilities of electromorph bands for larvae, pupae and adults. No differences were found between populations of T. hyalipennis (Walk.) reared from Elymus repens (L.) and E.farctus (Viv.) or between populations of T. eximia (Gir.) reared from Calamagrostis epigejos (L.) Roth and Ammophila arenaria (L.) Link. Experiments on mate-choice and host preference also supported the electrophoretic results for populations of T. hyalipennis and T. eximia.     

Multiple independent formations of Tragopogon tetraploids (Asteraceae): evidence from RAPD markers

Polyploidy is widely recognized as a significant force leading to the formation of new plant species. Estimates of the number of angiosperm species with polyploid origins are as high as ≈ 50%; however, in spite of this prevalence, many aspects of polyploid evolution remain poorly understood. Recent studies have suggested that recurrent origins of polyploid species are the rule rather than the exception. The present study is one of only a few designed to quantify the number of independent origins of a polyploid species. The two tetraploid species Tragopogon mirus and T. miscellus (Asteraceae) arose within the past 50 years in the Palouse region of eastern Washington and adjacent northern Idaho. Previous work using morphology, cpDNA and rDNA restriction site analyses, allozymes, cytology, and flavonoid chemistry established that T. mirus had arisen at least five times, and T. miscellus at least twice, on the Palouse. To assess the frequency of multiple origins of these species more rigorously, seven populations of T. mirus and three populations of T. miscellus that were indistinguishable based on previous markers were surveyed using random amplified polymorphic DNA (RAPD) markers; populations of the diploid progenitor species from the same sites were also analysed. Each tetraploid population had a unique RAPD marker profile, suggesting that each population surveyed originated independently of the other populations in the region. Only two of the tetraploid populations combined the RAPD marker profiles of the diploid progenitors occurring at the same site. Both polyploid species, whose ranges and numbers have greatly increased since their formation in the early part of the twentieth century, have formed repeatedly on a local geographical scale and during a short time frame. Furthermore, each tetraploid species is spreading not primarily by dispersal of propagules from a single population of origin, but through repeated, independent polyploidization events that recreate the polyploid taxa.     

Molecular characterisation of inter and intra-specific somatic hybrids of potato using randomly amplified polymorphic DNA (RAPD) markers

Summary Protoplast fusion allows the transfer of both mono- and polygenic traits between species that are sexually incompatible. This approach has particular relevance for potato, and somatic hybridisation has been used to introduce a range of disease resistance genes from sexually incompatible wild species into the cultivated potato gene pool. In addition, protoplast fusion allows the resynthesis of tetraploid genotypes from pre-selected diploid or dihaploid donor parents. A limiting factor for the efficient exploitation of this technology in potato breeding is the difficulty of unequivocally identifying nuclear hybrids (heterokaryons). In order to facilitate the identification of hybrids at an early stage following fusion, Randomly Amplified Polymorphic DNA markers (RAPDs) have been used to characterise molecularly both inter- and intra-specific somatic hybrids of potato. RAPD markers detect naturally occurring polymorphism in the donor genotypes and utilise short oligonucleotide primers of arbitrary nucleotide sequence in combination with the polymerase chain reaction (PCR). The exploitation of RAPDs in the characterisation of both somatic and sexual hybrids is discussed.     

Evaluation of the extent of genetic variation in mahoganies (Meliaceae) using RAPD markers

Despite the economic importance of mahoganies (Meliaceae) little is known of the pattern of genetic variation within this family of tropical trees. We describe the application of a polymerase chain reaction (PCR)-based polymorphic DNA assay procedure random amplified polymorphic DNAs (RAPDs) to assess the extent of genetic variation between eight mahogany species from four genera. Pronounced genetic differentiation was found between the species and genera. There was a clear separation of Cedrela odorata from the other species, with 95% of the variable amplification products differing, whereas Lovoa trichilioides, Khaya spp. and Swietenia spp. were more closely grouped. These results are consistent with the current taxonomic viewpoint. A number of markers were found to be diagnostic for particular species, which could be of value in determining the status of putative hybrids. The application of RAPDs to the study of genetic variation in mahoganies is discussed in the context of developing genetic conservation and improvement strategies for these species.     

A sympatric sibling species complex of Petrotilapia Trewavas from Lake Malawi analysed by enzyme electrophoresis (Pisces: Cichlidae)

The protein electromorphs of three taxa of Petrotilapia , referred to in earlier works as sibling species, were examined by starch-gel electrophoresis. The results indicated that, for the three taxa, no alternative fixed alleles occurred for any of the 25 loci (enzymes) examined. However, heterogeneous gene frequencies were indicated at seven polymorphic loci. This suggests that either the taxa are isolated 'sibling' species which recently diverged, or that they are 'incipient' species with minimal gene flow between morphs. The genetic and field data lend support to the hypothesis that sympatric splitting of morphs could be important in the explosive radiation of the cichlidae.     

Delimitation of sympatric Palaemon (Decapoda,Palaemonidae) species of the Laguna Madre,Mexico

Grass shrimps Palaemon mundusnovus, P. pugio and P. vulgaris sympatrically inhabit in the Laguna Madre, Mexico. They exhibit very close morphological similarity and overlap in their diagnostic characteristics, which has hindered certainty in their identification and has raised doubt regarding their taxonomic validity. In this work, we analyse intra‐ and interspecific morphometric and meristic variability through a multivariate analysis, and we determine the molecular variation using mitochondrial sequences of the 12S, 16S and COX1 genes to confirm the validity of the three taxa as having distinct lineages or to recognize a smaller number of species with phenotypic plasticity. Our results corroborate the taxonomic validity of the three species; however, there is intraspecific plasticity, interspecific overlap of characteristics and greater morphological and molecular similarity between the species P. mundusnovus and P. pugio, whereas P. vulgaris was better delimited. These species form a monophyletic group but the phylogenetic relationship obtained is discussed. Telson length was the primary variable in the principal components analysis, whereas the length of the propodus of the second pereiopod was the best discriminant. The range of variation reported in the characteristics linked to the rostrum is extended, and its influence on the separation of these species is recognized. The joint application of multivariate analysis from morphological variables and molecular tools is recommended to clarify the taxonomic status of species featuring close morphological similarity and sympatric distribution.     

Hybridization among sympatric species of Rhododendron (Ericaceae) in Turkey: morphological and molecular evidence

Rhododendron (Ericaceae) is a large genus in which barriers to hybridization are especially weak, but many species are maintained in sympatry. Hybridization among four species of Rhododendron subsect. Pontica, which occur in sympatry in Turkey, was investigated. Material of R. ponticum, R. smirnovii, R. ungernii, and R. caucasicum and their putative hybrids was collected from the wild. Based on morphology, chloroplast DNA and nuclear ribosomal DNA restriction fragment length polymorphism (RFLP) profiles, each accession was identified as a species or hybrid combination. Five of the six possible hybrid combinations among the four species were detected. Rhododendron ponticum × R. smirnovii was represented by a single individual and R. caucasicum × R. smirnovii by one small group of hybrid plants. The combinations R. ponticum × R. ungernii and R. ungernii × R. smirnovii showed evidence of frequent backcrossing, while R. ponticum × R. caucasicum appeared unusual in that an intermediate hybrid type was abundant, whereas hybrids with phenotypes approaching either parent were rare. Possible explanations of this latter situation are discussed. The results suggest that natural hybridization among Rhododendron species is common and that ecological factors are important in maintaining integrity when species occur in sympatry.     

Lack of genetic variability in the rare and endangered Limonium cavanillesii (Plumbaginaceae) using RAPD markers

Limonium cavanillesii is an extremely endangered plant species endemic to the east Mediterranean region of Spain. Regarded as extinct for several years, the recent discovery of a small population (only 29 individuals) has prompted the adoption of measures for its conservation by official agencies. As part of this effort, we have analysed genetic variation in this population by means of random amplified polymorphic DNA (RAPDs). The analysis of 29 individuals with 11 different primers produced 131 monomorphic bands. To our knowledge, this is the lowest level of genetic variation detected in plants using RAPD markers. This result could be explained both by the apomictic reproductive system of this species and by the passage through a severe bottleneck in recent times, after which there has been no chance for mutation to restore detectable genetic variation.     

Molecular genetic evidence for reproductive isolation between sympatric populations of smelt Osmerus in Lake Utopia, south-western New Brunswick, Canada

Two morphologically and ecologically distinct forms of smelt, Osmerus, reside sympatrically in Lake Utopia, south-western New Brunswick, Canada. The ‘normal-sized’ form matures at greater than 200 mm standard length, averages about 31–33 gill rakers, and spawns in lake outlets. By contrast, the ‘dwarf-sized’ form matures at less than 150 mm standard length, averages 34–36 gill rakers, and spawns in small streams 3–5 weeks later than the normal form. We tested whether these sympatric forms represented ecological polymorphism within a single population or two reproductively isolated demes by assaying variation within and between forms by mitochondrial DNA (mtDNA) restriction site and nuclear minisatellite DNA analyses. Analysis of smelt mtDNA with twelve restriction enzymes resolved ten composite genotypes (differing by an average 0.27% sequence divergence) which differed markedly in frequency between the forms. Net percentage sequence divergence between the forms was O.l6%. A Wagner parsimony/ bootstrapping analysis of the restriction site presence/absence matrix, however, suggested that there were no significant distinctions between dwarf and normal smelt based on the phylogeny of composite genotypes. Hybridization studies of genomic DNA digests with a minisatellite probe indicated both that nuclear restriction fragment differentiation and the frequency of specific fragments differed significantly between the forms. Significant genetic differentiation between the sympatric forms demonstrates that they are distinct gene pools and reproductively isolated. Our molecular evidence for reproductive isolation between dwarf and normal smelt in Lake Utopia, coupled with the persistent morphological and ecological differentiation between them, argues strongly that they are behaving as distinct species. The Lake Utopia Osmerus populations provide further illustration of the potential for rapid differentiation to the level of biological species in postglacial environments.     

Genetic patterns and pollination in Ophrys iricolor and O. mesaritica (Orchidaceae): sympatric evolution by pollinator shift

Ophrys iricolor and O. mesaritica are a pair of morphologically similar, closely related sexually deceptive orchids from the eastern Mediterranean. Ophrys iricolor is known to be pollinated by Andrena morio males and the specific pollinator of Ophrys mesaritica is determined as Andrena nigroaenea. Amplified fragment length polymorphism revealed O. iricolor and O. mesaritica to be genetically intermixed on the whole, although populations of O. iricolor and O. mesaritica in geographical proximity are strongly differentiated, suggesting that specific pollinators locally differentiate these taxa. Based on the available biological data and the system of pollinator attraction operative in Ophrys, we hypothesize that O. mesaritica may have arisen from O. iricolor by pollinator shift and that this is more probable than scenarios invoking hybridization as a result of mispollination by rare, non‐specific flower visitors or specifically attracted insects. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 583–598.     

Two new cryptic and sympatric species of the king crab parasite Briarosaccus (Cirripedia: Rhizocephala) in the North Pacific

Rhizocephalan barnacles have been reported to parasitize a wide range of king crab species (Lithodidae). So far all these parasites have been assigned to a single species, Briarosaccus callosus Boschma, 1930, which is assumed to have a global distribution. Here we investigate Briarosaccus specimens from three different king crab hosts from the fjord systems of Southeastern Alaska: Lithodes aequispinus Benedict, 1895, Paralithodes camtschaticus (Tilesius, 1815), and Paralithodes platypus (Brandt, 1850). Using molecular markers and by morphological comparison we show that Briarosaccus specimens from these three commercial exploited king crabs are in fact morphologically distinct from B. callosus, and further represent two separate species which we describe. The two new species, Briarosaccus auratum n. sp. and B. regalis n. sp., are cryptic by morphological means and were identified as distinct species by the use of genetic markers (COI and 16S). They occur sympatrically, yet no overlap in king crab hosts occurs, with B. auratum n. sp. only found on L. aequispinus, and B. regalis n. sp. as parasite of the two Paralithodes hosts. © 2015 The Authors. Zoological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London     

Phylogenetic and molecular evidence for allochronic speciation in gall-forming aphids (Pemphigus)

Sympatric populations can diverge when variation in phenology or life cycle causes them to mate at distinctly different times. We report patterns consistent with this process (allochronic speciation) in North American gall-forming aphids, in the absence of a host or habitat shift. Pemphigus populi-transversus Riley and P. obesinymphae Aoki form a monophyletic clade within the North American Pemphigus group. They are sympatric on the eastern cottonwood, Populus deltoides (Salicaceae), but have distinctly different life cycles, with sexual stages offset by approximately six months. Field evidence indicates that intermediate phenotypes do not commonly occur, and mitochondrial and bacterial endosymbiont DNA sequences show no maternal gene flow between the two species. Because a genetically distinct population of P. obesinymphae occurs in the southwestern United States on Populus fremontii, we consider the possibility of an initial allopatric phase in the divergence. We discuss the likely origins of the host use patterns in P. obesinymphae, and the larger sequence of evolutionary changes that likely led to the sympatric divergence of P. populi-transversus and P. obesinymphae. A plausible interpretation at this stage of investigation is that a shift in timing of the life cycle in an ancestral population, correlated with an underlying phenological complexity in its host plant, spurred divergence between the incipient species.     

Molecular characterization of eight Indian Snakehead species (Pisces: Perciformes Channidae) using RAPD markers

Murrels (Perciformes; Channidei; Channidae) are unique group of freshwater air breathing fishes having a confined distribution to African and Asian continents. The phylogenetic relationship among eight Channid species viz. Channa aurantimaculata, Channa bleheri, Channa diplogramma, Channa gachua, Channa marulius, Channa punctatus, Channa stewartii and Channa striatus were investigated using RAPD markers. Eight random oligodecamers viz. OPAC03, OPAC05, OPAC07, OPAC09, OPAC19, OPA10, OPA11 and OPA16 were used to generate the RAPD profile. Estimates of Nei’s (Genetics, 89:583–590, 1978) unbiased genetic distance (D) demonstrated sufficient genetic divergence to discriminate the samples of different species and the values ranged from 0.3292 to 0.800 The present RAPD analyses strongly substantiate the view of earlier morphological and osteological studies of Channid species, the closer association among species in “gachua” and “marulius” groups.     

Detection of genetic diversity and selective gene introgression in coffee using RAPD markers

RAPD (randomly amplified polymorphic DNA) markers generated by arbitary decamers have been successfully employed to detect genetic polymorphisms between coffee species and between Coffea arabica genotypes. The RAPD profiles were used to construct dendrograms and these were consistent with the known history and evolution of Coffea arabica. Material originating from Ethiopia and the arabica sub-groups — C. arabica var. typica and C. arabica var. bourbon — were clearly distinguished. RAPD analysis therefore reflects morphological differences between the sub-groups and the geographical origin of the coffee material. Species-specific amplification products were also identified, but, more importantly, amplification products specific to C. canephora were identified in two C. arabica genotypes, Rume Sudan and Catimor 5175. This diagnostic product is therefore indicative of interspecific gene flow in coffee and has biological implications for selective introgressive hybridisation in coffee. Our study demonstrates the power of the polymerase chain reaction technology for the generation of genetic markers for long-lived perennial tree and bush crops.On study leave from: Universidad de San Carlos de Guatemala, Facultad de Agronomia, Ciudad Universitaria, Zona 12, Apartado Postal No. 1545, Guatemala, Central America     

No barriers to fertilization between sympatric colour morphs in the marine species flock Hypoplectrus (Serranidae)

Assortative mate choice is, so far, the only demonstrated isolating barrier between colour morphs in fish species flocks, such as freshwater cichlids and marine hamlets, suggesting an important role for sexual selection in speciation. However, there has been little consideration of post-copulatory mechanisms that are known to influence reproductive isolation in other taxa. Selective pressures through a cost to hybrid matings, or genetic drift, may lead to the evolution of fertilization barriers through gamete incompatability. In cases of incipient speciation, such as the hamlets, complete fertilization blocks may not have evolved. Instead, differential fertilization between species may reduce the success of interspecific fertilizations. We examined the fertilization dynamics of sympatric Hypoplectrus nigricans (black hamlet) and Hypoplectrus puella (barred hamlet). Experimental crosses were performed to score fertilization success in within-morph and between-morph crosses. Fertilization success did not differ between self-fertilized, within-morph or between-morph crosses. We therefore found no evidence of post-mating barriers through sperm:egg incompatibilities and potential for self-fertilization. Our results are consistent with a mechanism of colour morph divergence based on sexually selected morph mating preferences.     

Phylogeography and demography of sympatric sister surfperch species, Embiotoca jacksoni and E. lateralis along the California coast: historical versus ecological factors

With 18 closely related endemic species that radiated in a diversity of ecological niches, the California surfperches (Embiotocidae) species flock is a good candidate for the study of sympatric speciation. Resource partitioning has been suggested as an important driving force in the radiation of the surfperch family. Within the family, two congeneric sister species, Embiotoca jacksoni and E. lateralis, are known to compete strongly for a preferred single food resource and may be used as a model of ecological interactions for the family. Along the California coast, the distribution of the two species differs. Embiotoca jacksoni has a continuous range, whereas E. lateralis shows a disjunction with a distribution gap in the Southern California Bight. Two hypotheses may explain this disjunct distribution. Ecological competition may have displaced E. lateralis in favor of E. jacksoni. Alternatively, a common vicariant event may have separated the species into northern and southern populations, followed by secondary contact in E. jacksoni but not in E. lateralis. The two hypotheses predict different phylogeographic and demographic signatures. Using a combined phylogeographic and coalescent approach based on mitochondrial control region data, we show that vicariance can only account for a portion of the observed divergences. Our results are compatible with a significant role played by ecological competition in the southern range of the species.     

Impact of the biological control agent Tetramesa romana (Hymenoptera: Eurytomidae) on Arundo donax (Poaceae: Arundinoideae) along the Rio Grande River in Texas

Five years post-release of the arundo gall wasp, Tetramesa romana, into the riparian habitats of the lower Rio Grande River, changes in the health of the invasive weed, Arundo donax, or giant reed, have been documented. These changes in plant attributes are fairly consistent along the study area of 558 river miles between Del Rio and Brownsville, TX, and support the hypothesis that the arundo wasp has had a significant impact as a biological control agent. Plant attributes were measured prior to release in 10 quadrats at each of 10 field sites in 2007, and measured again at the same undisturbed sites, 5 years after the release of T. romana, in 2014. Above ground biomass of A. donax decreased on average by 22% across the 10 sites. This decline in biomass was negatively correlated to increased total numbers of T. romana exit holes in main and lateral shoots per site in 2014 compared to 2007. Changes in biomass, live shoot density and shoot lengths, especially the positive effect of galling on main and lateral shoot mortality, appear to be leading to a consistent decline of A. donax. Economically, this reduction in A. donax biomass is estimated to be saving 4.4 million dollars per year in agricultural water. Additional impacts are expected as populations of the wasp increase and as other biological control agents such as the arundo scale, Rhizaspidiotus donacis, become more widespread.     

Molecular evidence of a peripatric origin for two sympatric species of field crickets (Gryllus rubens and G. texensis) revealed from coalescent simulations and population genetic tests

Species pairs that differ primarily in characters involved in mating interactions and are largely sympatric raise intriguing questions about the mode of speciation. When species divergence is relatively recent, the footprint of the demographic history during speciation might be preserved and used to reconstruct the biogeography of species divergence. In this study, patterns of genetic variation were examined throughout the geographical range of two cryptic sister taxa of field crickets, Gryllus texensis and G. rubens; mitochondrial cytochrome oxidase I (COI) was sequenced in 365 individuals sampled from 48 localities. Despite significant molecular divergence between the species, they were not reciprocally monophyletic. We devised several analyses to statistically explore what historical processes might have given rise to this genealogical structure. The analyses indicated that the biogeographical pattern of genetic variation does not support a model of recent gene flow between species. Instead, coalescent simulations suggested that the genealogical structure within G. texensis, namely a deep split between two geographically overlapping clades, reflects historical substructure within G. texensis. Additional tests that consider the concentration of G. rubens haplotypes in one of the two G. texensis genetic clusters suggest a model of speciation in which G. rubens was derived from one lineage of a geographically subdivided ancestor. These results indicate that, despite the contemporary sympatry of G. texensis and G. rubens, the data are indicative of an peripatric origin in which G. rubens was derived from one of the two historical partitions in the species currently recognized as G. texensis. This proposed model of species divergence suggests how the interplay of geography and selection may give rise to new species, although this requires testing with multilocus data. Specifically, the model highlights how that geographical partitioning of ancestral variation in the past may augment the selectively driven divergence of characters involved in the reproductive isolation of the species today.     

No host‐associated differentiation in the gall wasp Diplolepis rosae (Hymenoptera: Cynipidae) on three dog rose species

Differences in quality and quantity of secondary compounds, as well as in leaf traits of host plants, may influence the host choice of herbivores. Different host preferences could lead to host‐associated differentiation, the first step of sympatric speciation. In the present study, we investigated whether the rose gall wasp Diplolepis rosae L. (Hymenoptera: Cynipidae) shows genetic differentiation related to its host plants (Rosa canina L., Rosa corymbifera Borkh., and Rosa rubiginosa L.). These three host species radiated recently and subsequently expanded their range. Therefore, we expected a diversification within the closely‐associated phytophagous insects. The process of genetic differentiation should be intensified in D. rosae by its close relationship to the host plant, as well as by its parthenogenetic reproduction (infection rate by Wolbachia sp. of almost 100%). However, using 106 polymorphic amplified fragment length polymorphism markers, we found no genetic differentiation among the wasps from different host plants. The population structuring between geographical localities was also low, suggesting considerable gene flow between sites. In part, the low genetic differentiation between sites is explained by the wide distribution of host species and hybrids between host plants. Hybrids with intermediate traits may facilitate the gene flow between wasp populations exploiting different host species. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 369–377.