The role of hemiparasitic plants: influencing tallgrass prairie quality,diversity, and structure

Wood betony, Orobanchaceae (Pedicularis canadensis) and bastard toadflax, Santalaceae (Comandra umbellata) are two root‐hemiparasitic plant species found in tallgrass prairie communities. Natural resource managers are interested in utilizing these species as “pseudograzers” in grasslands to reduce competitively dominant grasses and thereby increase ecological diversity and quality in prairie restorations and urban plantings. We performed an observational field study at 5 tallgrass prairie sites to investigate the association of hemiparasite abundance with metrics of phylogenetic and ecological diversity, as well as floristic quality. Although no reduction in C₄ grasses was detected, there was a significant association between hemiparasite abundance and increased floristic quality at all 5 sites. Hemiparasite abundance and species richness were positively correlated at one restoration site. In a greenhouse mesocosm experiment, we investigated response to parasitism by P. canadensis in 6 species representing different plant functional groups of the tallgrass prairie. The annual legume partridge pea, Fabaceae (Chamaecrista fasciculata) had the greatest significant dry biomass reduction among 6 host species, but the C₄ grass big bluestem, Poaceae (Andropogon gerardii) had significantly greater aboveground biomass when grown with the hemiparasite. Overall, host species biomass as a total community was significantly reduced in mesocosms, consistent with other investigations that demonstrate influence on community structure by hemiparasitic plant species. Although hemiparasites were not acting as pseudograzers, they have the potential to influence community structure in grassland restorations and remnants.     

Relationships of Plant Parasitic Nematodes to Sites in Native Iowa Prairies

Soil samples were collected from three native Iowa prairies and analyzed for plant paiasitic nematodes and selected soil properties. Sites or nematodes were clustered with similarities related to habitat by a cluster analysis of site by nematode species and of nematodes by site. Some nematodes occurred in a wide range of prairie habitats, whereas others were more restricted. For example, greater numbers of Xiphinema americanum were in the low, well-drained sites than in the low wet sites or upland dry sites. Wet sites contained fewer nematodes than well-drained sites. Well-drained sites contained mainly Tylenchorhynchus maximus, Helicotylenchus pseudorobustus, and X. americanum. Wetter sites contained almost exclusively X. chambersi, H. hydrophilus, Telylenchus joctus, and an undescribed species of Tylenchorhynchus.     

Tamarin polyspecific associations: Forest utilization and stability of mixed-species groups

Niche separation is likely to play a key role in the formation of mixed-species groups. Saddle-backed tamarins (Saguinus fuscicollis) were studied at three sites with different primate communities in northern Bolivia: (1) with red-bellied tamarins,S. labiatus; (2) with emperor tamarins,S. imperator; and (3) without a congeneric species. The degree of association is higher betweenS. labiatus andS. fuscicollis than betweenS. imperator andS. fuscicollis and is related to differences in forest utilization between associating pairs. Niche separation is found to be greater betweenS. labiatus andS. fuscicollis than betweenS. fuscicollis andS. imperator. The mean height and habitat utilization ofS. fuscicollis does not differ greatly across the three sites, nor does the height of tamarins in and out of association. It is concluded that combined with differences in body size and dietary overlap, vertical segregation plays an important role in tamarin polyspecific associations (increasing the potential of both foraging and anti-predatory benefits) and that this is not a consequence of vertical displacement ofS. fuscicollis by its dominant congeners.     

Comparative Analyses of Plastid Sequences between Native and Introduced Populations of Aquatic Weeds Elodea canadensis and E. nuttallii

Non-indigenous species (NIS) are species living outside their historic or native range. Invasive NIS often cause severe environmental impacts, and may have large economical and social consequences. Elodea (Hydrocharitaceae) is a New World genus with at least five submerged aquatic angiosperm species living in fresh water environments. Our aim was to survey the geographical distribution of cpDNA haplotypes within the native and introduced ranges of invasive aquatic weeds Elodea canadensis and E. nuttallii and to reconstruct the spreading histories of these invasive species. In order to reveal informative chloroplast (cp) genome regions for phylogeographic analyses, we compared the plastid sequences of native and introduced individuals of E. canadensis. In total, we found 235 variable sites (186 SNPs, 47 indels and two inversions) between the two plastid sequences consisting of 112,193 bp and developed primers flanking the most variable genomic areas. These 29 primer pairs were used to compare the level and pattern of intraspecific variation within E. canadensis to interspecific variation between E. canadensis and E. nuttallii. Nine potentially informative primer pairs were used to analyze the phylogeographic structure of both Elodea species, based on 70 E. canadensis and 25 E. nuttallii individuals covering native and introduced distributions. On the whole, the level of variation between the two Elodea species was 53% higher than that within E. canadensis. In our phylogeographic analysis, only a single haplotype was found in the introduced range in both species. These haplotypes H1 (E. canadensis) and A (E. nuttallii) were also widespread in the native range, covering the majority of native populations analyzed. Therefore, we were not able to identify either the geographic origin of the introduced populations or test the hypothesis of single versus multiple introductions. The divergence between E. canadensis haplotypes was surprisingly high, and future research may clarify mechanisms that structure native E. canadensis populations.     

Occurrence,Parasitism, and Pathogenicity of Nematodes Associated with Sycamore (Platanus occidentalis L.)

Ten species of stylet-bearing nematodes were recovered in a survey of sycamore (Platanus occidentalis L. ) stands in Georgia. Helicotylenchus, Xiphinema, and Criconemoides were the genera found most frequently. Populations of Hoplolaimus galeatus, Scutellonema brachyurum, Helicotylenchus dihystera and H. pseudorobustus increased on greenhouse-grown sycamore, but Trichodorus christiei, Xiphinema americanum, Meloidogyne hapla, M. arenaria and M. incognita did not. Hoplolaimus galeatus and S. brachyurum are semi-endoparasites; H. dihystera and H. pseudorobustus are migratory endoparasites. Hoplolaimus galeatus caused extensive root necrosis and marked decrease of fresh weights of seedling roots and tops. Helicotylenchus dihystera and S. brachyurum produced only qualitatively different sparse and unhealthy root growth. Helicotylenchus pseudorobustus caused only a reduction in root surface area.     

Interaction of sauger Sander canadensis and walleye Sander vitreus in a large,shallow northern river

The objectives of this study were to: (1) determine the relative abundance of sauger Sander canadensis and walleye S. vitreus within the Rainy River using a standardized index netting technique; (2) assess the life-history characteristics of the two species in a northern river; (3) examine the spatial distribution of the two species; (4) assess year-class synchrony. At a larger scale, relative abundance of S. canadensis and S. vitreus were similar among sections of the river. However, at a finer scale, S. canadensis were the dominant species over more area (24%) of the river than S. vitreus (12%). Life-history traits for both species were within the range reported for North American. Mortality rates were similar, suggesting that anglers were not affecting one species more than the other. Year-class strengths were not synchronous between S. canadensis and S. vitreus (r = 0.07). There was evidence of S. canadensis potentially outcompeting S. vitreus with a strong year class of S. canadensis followed by a very weak class of S. vitreus. Additionally, S. canadensis were larger than S. vitreus in most sections of the river when adjusted for mean size. However, the potential interspecific competition was not to the exclusion of S. vitreus. Turbidity was probably the factor that enable S. canadensis to survive sympatrically with S. vitreus given their inability to segregate by depth within the river.     

Susceptibility of three lepidopteran pests to five entomopathogenic nematodes and in vivo mass production of these nematodes

Abstract

An investigation was conducted in pots to access the susceptibility of three lepidopteran pests, namely, gram pod borer, Helicoverpa armigera, greater wax moth, Galleria mellonella, and rice moth, Corcyra cephalonica, to two recently described species, Steinernema masoodi, S. seemae, and three indigenous S. carpocapsae, S. glaseri and S. thermophilum entomopathogenic nematodes (EPN). The suitability of these lepidopterans for the in vivo mass production of the nematodes was also estimated. Among the five species of EPN, S. masoodi, S. seemae and S. carpocapsae were found most pathogenic to C. cephalonica, bringing about mortality within 24 h, followed by H. armigera (36, 38 and 48 h, respectively) and G. mellonella (30, 36 and 48 h, respectively). The other species of EPN, viz., S. glaseri and S. thermophilum was the least pathogenic, which killed the larvae of C. cephalonica in 29 and 36 h, respectively, G. mellonella in 48 h, and H. armigera in 38 and 56 h, respectively. Galleria mellonella was found the most suitable host for the mass production of infective juveniles (IJs) of S. seemae, which yielded higher IJs than S. carpocapsae. Helicoverpa armigera was the next best suitable alternate host, which produced maximum IJs in case of S. seemae followed by S. masoodi, S. carpocapsae, S. glaseri and S. thermophilum. Rice moth, Corcyra cephalonica was the least suitable host. The susceptibility of H. armigera to five tested EPN species and susceptibility of G. mellonella and C. cephalonica to S. masoodi and S. seemae are new records.     

Variation in dormancy and germination in three co-occurring perennial forest herbs

Mesic deciduous forest herbs often disperse seed with morphophysiological dormancy (MPD) that prevents germination during unfavorable periods for seedling survival. However, for seeds of some species with MPD, seasonal separation of root and shoot emergence and variation in dormancy levels can complicate interpretation of seedling emergence timing in the field. We tested whether dormancy-break and germination requirements differed among co-occurring perennial forest herbs, Actaea racemosa, Hydrastis canadensis, and Sanguinaria canadensis, which are wild-harvested for their medicinal properties and known to have MPD. Seeds of all species exhibited a summer → autumn → winter requirement for seedling emergence in spring. However, species differed in seed-bank persistence due to variation in primary dormancy levels and stratification requirement of seeds. A. racemosa and H. canadensis can form short-term persistent seed bank, whereas S. canadensis can form a long-term persistent seed-bank, regardless of whether elaiosomes were removed from seeds prior to burial. A. racemosa seeds are dispersed in autumn with weak physiological dormancy, as seeds germinated to high rates at 15/6°C after 8 weeks. In contrast, most seeds of the summer dispersed species, H. canadensis and S. canadensis, require summer temperatures to overcome physiological dormancy. Consequently, seedling emergence is reduced and delayed by 1 year if seeds are not sown immediately following the period of natural dispersal. Seedling emergence was much lower in the field than in controlled conditions for all species, especially in the small-seeded A. racemosa. Interspecific variation in dormancy levels and germination traits must be considered when establishing populations for conservation purposes and in understanding recruitment limitation in perennial forest herbs.     

Sexual Behaviour in the Slave-making Ant,Harpagoxenus canadensis M. R. Smith,and Sexual Pheromone Experiments with H. canadensis,H. americanus (Emery), and H. sublaevis (Nylander) (Hymenoptera; Formicidae)

The sexual behaviour of Harpagoxenus canadensis closely resembles that of European H. sublaevis. Young ♀♀ of both species exhibit a sexual-calling behaviour (Locksterzeln) during which they attract the ♂♂ by poison gland secretion. The sexual pheromones of both species seem to be identical, but interspecific mating is prevented by various behavioural mechanisms of the ♀♀. A third species, H. americanus, seems to be less closely related to H. canadensis and H. sublaevis: Its ♂♂ are not sensitive to the pheromones of these two species.     

Nuclear DNA content of <Emphasis Type="Italic">Hydrastis canadensis</Emphasis> L. and genome size stability of in vitro regenerated plantlets

Knowing the genome size is an important step towards deciding and planning for genome sequencing of a given species. Using flow cytometry, nuclear DNA content of Hydrastis canadensis was estimated, and genome size stability of its in vitro regenerated plantlets were assessed. The nuclear DNA content of H. canadensis was estimated to be 2.62 ± 0.020 pg/2C. This is the first report to estimate nuclear DNA content of H. canadensis; therefore this study provides valuable information that will facilitate genome sequencing and subsequent molecular studies of this economically important medicinal plant. Comparison of genome size between in vitro regenerated (explant source was from wild plants) and wild plants of H. canadensis did not reveal any significant difference (P ≤ 0.05) in nuclear DNA content. This suggests that micropropagation of H. canadensis, even after numerous sub-culturing and long-term culture periods produced in vitro plantlets with a stable genome size. These results provide further evidence that micropropagation techniques have the potential to be used as a source of planting stock, along with seeds, for restoring locally threatened H. canadensis wild populations and for commercial cultivation to supply the growing herbal market.     

Genetic differentiation of the Iberian tree frogs Hyla arborea molleri and Hyla meridionalis (Amphibia: Anura)

Genetic differentiation of Hyla arborea molleri and H. meridionalis was studied through allozyme electrophoresis and through essays of artificial hybridization. Samples were taken at several localities in Portugal, where these species occur either in sympatry or allopatry, and at one locality in France. Of the 21 presumptive loci analyzed, 6 were monoallelic, while 9 loci were discriminative between both species. A relatively high level of genetic differentiation was found between the two species (NEI's D = 0.725), contrasting with their morphological similarity. Remarkably low levels of genetic variability were found within species, with greater differentiation found among samples of H. meridionalis than of H. a. molleri. Although the capacity for interspecific hybridization was low, hybrid embryos resulted from both reciprocal crosses, but with much greater success in the cross ♂H. a. molleri x δH. meridionalis. Hybrids showed greater similarity with the male parent, and showed heterozygote allozymic phenotypes for discriminative loci. Results are compared with those of similar studies on the same and different species of Hyla, and differentiation of H. a. molleri and H. meridionalis is discussed in relation to their taxonomic status and origin.     

Gastrointestinal parasites of the Samango monkey,Cercopithecus mitis,in Natal,South Africa

Eight gastro-intestinal tracts of Cercopithecus mitis labiatus from Karkloof, Natal, and 121 fecal samples from C. m. erythrarchus from Cape Vidal, Natal, were examined for helminth parasites and/or their eggs. Fecal samples from six of the C. m. labiatus were examined for protozoan cysts. Five protozoon and six helminth species were identified from C.m labiatus. Most adult worms occurred in the caecum and colon, gut regions which also contained the highest volatile fatty acid levels. The eggs of nine helminth species were recovered from C. m. erythrarchus fecal samples; protozoans were not looked for in these samples.     

Predicting invasive success of Hydrilla verticillata (L.f.) Royle in flowing water

Alien aquatic plant species have had spectacular success in invading New Zealand’s freshwaters. Their continued introduction has resulted in few water bodies retaining their natural or original indigenous aquatic vegetation, and associated adverse changes, such as reduced biodiversity and amenity values are well known. This highlights the need to accurately assess aquatic plant species that are already in the country and those outside for their potential to have a negative impact on New Zealand’s lakes and waterways. The study presented in this paper describes an approach to evaluating the invasive weed potential of Hydrilla verticillata (L.f.) Royle compared with Elodea canadensis Michx. under flowing water conditions. The two species were planted in combination and alone, and in a sheltered or exposed position relative to the direction of the water flow. Over the 2-year study, two different waterflow rates were used (0.1 and 0.2 m/s) which represented the gauged flows from a stream of interest that contains E. canadensis and flows from a H. verticillata infested lake. H. verticillata was competitive compared with E. canadensis and able to persist and thrive in the presence of E. canadensis in both exposed and sheltered habitats. These results corroborate observations from other countries of H. verticillata growing in flowing waters and highlight the significant threat posed by H. verticillata to streams and waterways in New Zealand.     

Host Range Assessment of Helicotylenchus pseudorobustus (Tylenchida: Hoplolaimidae) on Pasture Species

The host status of 15 commonly occurring pasture species for Helicotylenchus pseudorobustus was tested in a greenhouse trial. Only tall fescue, with and without Neotyphodium endophyte infection, was a good host (Pf/Pi = final/initial population > 1). Inoculation survival was tested in a second trial, which showed that only 10% of the H. pseudorobustus nematodes survived the first 7 days after inoculation. When the Pf/Pi was adjusted to account for a 10% survival, all of the grass and clover hosts tested had a Pf/Pi > 1. Both trials showed a positive correlation between increased numbers of H. pseudorobustus and free-living nematodes.     

Phenology and common garden and reciprocal transplant studies of Polymnia canadensis (Asteraceae), a monocarpic species of the North American Temperate Deciduous Forest

Polymnia canadensis, an herbaceous plant species ofthe North American Temperate Deciduous Forest heretofore reported as beingperennial, is shown to be primarily monocarpic. In common garden experiments,the majority of plants grown from seeds or seedlings collected in Kentucky,Alabama, Virginia, Ohio, and Missouri were monocarpic, but some were dicarpic,tricarpic or polycarpic. Observations in natural populations of P.canadensis suggested that there is variation in the life history ofthis species throughout its geographic range. Anthesis date and height ofplantsat anthesis were significantly different between mesic and dry field sites incentral Kentucky populations, but common garden and reciprocal transplantexperiments showed that these were due mainly to environmental (and not togenetic) effects. The latter was also true for age of maturity and rate ofchange in plant height. Lack of significant site × source interaction forthese characters indicated that plants did not differ in their plasticresponsesbetween sources at each site. Winter annual, biennial, triennial, and dicarpicand tricarpic perennial life histories occurred within populations in bothcommon garden and reciprocal transplant experiments. In the latter experiments,most matured plants were either biennials (most common) or winter annuals(second most common), with the order reversed in the former experiments due toamore benign environment favoring earlier maturity. The extensive phenotypicplasticity displayed by P. canadensis for phenology andlife history enables the species to inhabit a wide range of environments.     

Taxonomic and ecological notes on Hexarthra bulgarica from high mountain lakes and ponds in the Sierra Nevada (Spain)

Hexarthra bulgarica was found in 16 of the 37 high mountain lakes (over 2500 m) studied in the Sierra Nevada (Southern Spain). These populations resemble closely the subspecies H. b. canadensis. Data on the morphology and ecology of the Sierra Nevada populations are given, and these are compared to published information on the three other subspecies of H. bulgarica.Research supported by CAICYT Project No. 3069/83.     

Habitat characteristics of an alien species <Emphasis Type="Italic">Elodea canadensis</Emphasis> in Slovenian watercourses

The distribution, abundance and habitat characteristics of an alien species, Elodea canadensis, were surveyed in watercourses in Slovenia. The accompanying plant community was also examined. Distribution and abundance of macrophytes were assessed in reaches of different length, and habitat assessment is based on 12 parameters of the Riparian, Channel, and Environmental (RCE) Inventory. E. canadensis thrived in 132 out of 1,227 reaches examined and in 12 of the 39 watercourses surveyed. It grew in the company of a variety of species, most frequently with different species of Potamogeton. It was rarely found as the prevailing, and never as the only species in any reach. Canonical correspondence analysis (CCA) of reaches with E. canadensis revealed that the presence of detritus, retention structures and properties of the riparian zone explained most of the variance in community composition. Habitat analysis of well-established stands of E. canadensis showed that its preferred habitats were watercourses flowing through agricultural landscape, with a narrow, more or less disturbed riparian zone, with moderate presence of retention structures, and with sediment that was a mixture of gravel, sand and silt with either coarse or fine organic matter. It was not found in the parts of streams with the most dynamic flow, and was absent from watercourses in the karst region, due to the frequent and extreme water level fluctuations. The alien species E. canadensis did not express its invasive character in heterogeneous watercourses with rich macrophyte communities.     

Light reduction predicts widespread patterns of dominance between asters and goldenrods

Here we investigate the long-cited pattern that throughout the eastern United States, Solidago species (goldenrods), and in particular S. canadensis displace Aster species and dominate old-field communities. Theory predicts that such a ubiquitous pattern of repeated dominance should be linked to competitive ability for a limiting resource. However, no one has investigated this possibility in old-fields, representing a potentially significant gap in our understanding of a common human-altered environment. We tested the hypothesis that S. canadensis is the superior competitor for light compared to other common co-occurring goldenrod species, and that the goldenrods in general are the superior competitors for light compared to coexisting aster species, which are typically less abundant. We tested this hypothesis by comparing the light attenuation abilities of four goldenrod species, S. canadensis, S. rugosa, S. gigantea, and Euthamia graminifolia, and three aster species, Aster novae-angliae, A. pilosus, and A. prenanthoides. Consistent with our hypothesis, S. canadensis had a greater ability to attenuate light than any of the other goldenrods at higher densities, and the goldenrods overall had a greater ability to attenuate light than the asters. By conducting a census in our study area, we verified that S. canadensis is locally the most abundant goldenrod and that goldenrods are more locally abundant than asters. Furthermore, by conducting a literature survey we found evidence that S. canadensis replaces A. pilosus through time. Thus we found a close correspondence between relative abundance in the field and light attenuation ability in field experiments. These results are consistent with theory predicting that competition for limiting resources, in this case light, explains patterns of dominance and relative abundance in old-field plant communities.     

Dietary Differences Among Sympatric Callitrichinae in Northern Bolivia: Callimico goeldii,Saguinus fuscicollis and S. labiatus

Studies of sympatric species can provide important data to define how dietary and habitat requirements differ among them. I collected dietary data during a first yearlong comparative study of wild groups of Callimico goeldii, Saguinus labiatus and S. fuscicollis. Dietary overlap was highest between Saguinus fuscicollis and Saguinus labiatus throughout the year, and lowest between Saguinus labiatus and Callimico goeldii. All three species had high dietary overlap in February and March when a few abundant fruit species dominated their diets. Although all three species rely heavily on many of the same fruits and arthropods, there are several important distinctions among their diets. Surprisingly, Callimico goeldii consume large quantities of fungus throughout the year: 29% of annual feeding records. Mycophagy is more frequent in the dry season when fruits are scarce. In contrast, Saguinus labiatus rarely eat fungus during the period of fruit scarcity, and instead rely on nectar, a resource never exploited by Callimico goeldii. Saguinus fuscicollis also rely on nectar during periods of low fruit availability and increase their intake of arthropods and exudates. During April, a period of fruit scarcity, exudates comprise >50% of the feeding records of Saguinus fuscicollis. The use of different food resources during fruit scarcity, and differences in the heights at which each species feeds and forages appear to define a distinct ecological niche for each of them and allow them to maintain long-term associations throughout the year. Furthermore, I hypothesize that the limited distribution of Callimico goeldii may result from their restriction to forests that have high disturbance rates, where microhabitats appropriate for fungal growth are abundant, but which also contain abundant fruit and insects.