Biogeography of free-living soil nematodes from the perspective of plate tectonics.

In this first biogeographical synthesis based on the morphology and known distribution of a group of free-living soil nematodes, data indicate a pre-Jurassic origin followed by West Gondwanaland radiation for some genera and Laurasian radiation for others.

A new species and new synonym in Heptagenia walsh (Ephemeroptera: Heptageniidae: Heptageniinae) based on molecular and morphological evidence.

A new mayfly species, Heptagenia whitingi Webb & McCafferty n.sp. is described from larvae, a male subimago, a female adult, and eggs collected from large rivers in the west-central portion of North America. Larvae are differentiated from other North American Heptagenia Walsh by a pair of large, rectangular pale markings on abdominal tergum 4, and the combination of having the posterior margin of the abdominal terga with bluntly pointed spines less than half the length of the fine setae, small blunt spines on the posterior margin of the caudal filaments, and numerous rows of setae laterally on the ventral surface of the labrum. A 630 bp partial sequence of the mitochondrial gene cytochrome oxidase 1 (COI) from three specimens of H. whitingi n.sp. was compared with those of 12 specimens representing eight other North American species of Heptagenia. Intraspecific sequence divergences based on Kimura-2-parameter (K2P) distance ranged from 0-1.1%. Interspecific sequence divergence based on K2P distance ranged from 8.9-20.0%. Heptagenia whitingi n.sp. differed from its sister taxon H. flavescens (Walsh) by 11.7%. Heptagenia diabasia Burks and H. elegantula (Eaton) differed from each other by only 1.1%; these two alleged species show a clinal pattern in larval abdominal coloration and there are no structural differences between the semaphorants. On this basis, H. diabasia is placed as a junior subjective synonym of H. elegantula, n.syn.

Assessing Heterodera glycines-Resistant and Susceptible Cultivar Yield Response.

The soybean cyst nematode Heterodera glycines (SCN) is of major economic importance and widely distributed throughout soybean production regions of the United States where different maturity groups with the same sources of SCN resistance are grown. The objective of this study was to assess SCN-resistant and -susceptible soybean yield responses in infested soils across the north-central region. In 1994 and 1995, eight SCN-resistant and eight SCN-susceptible public soybean cultivars representing maturity groups (MG) I to IV were planted in 63 fields, either infested or noninfested, in 10 states in the north-central United States. Soil samples were taken to determine initial SCN population density and race, and soil classification. Data were grouped for analysis by adaptation based on MG zones. Soybean yields were 658 to 3,840 kg/ha across the sites. Soybean cyst nematode-resistant cultivars yielded better at SCN-infested sites but lost this superiority to susceptible soybean cultivars at noninfested sites. Interactions were observed among initial SCN population density, cultivar, and location. This study showed that no region-wide predictive equations could be developed for yield loss based on initial nematode populations in the soil and that yield loss due to SCN in our region was greatly confounded by other stress factors, which included temperature and moisture extremes.

Species concepts do matter in nematology.

Nematology is a taxon-based science, and a correct understanding of species and their relationships is basic to all nematological research. Modern methods of systematic analysis have reshaped issues concerning species recognition.

Why ecologists need systematics: importance of systematics to ecological research.

Ecologists are concerned with population dynamics of organisms and with the spatial patterns of single or multiple populations. The goal of the ecologist is usually to explain the observed patterns in terms of processes. Field samples of nematodes from different habitats may contain similar but not identical specimens of a nominal taxon, and the systematist can help the ecologist decide whether the specimens are ecophenotypes of a single taxon or represent distinct species. A correct decision may be important or trivial, depending on the parameters and goals of the ecological study. When a precise identification is crucial to the success of the study, new biochemical methodologies of systematists may provide rapid and accurate diagnoses. Systematists can provide additional help in the assignment of taxa to trophic groups. For clarifying host-parasite associations, often a goal in ecological investigations, modern analytical methods of systematists can facilitate the ordering of systematic relationships.

Phylogenetic analyses in dorylaimida using data from 2-d protein patterns.

Data from two-dimensional protein patterns for nine dorylaimid isolates were analyzed using PAUP, a computer program for inferring phylogenies under the principle of maximum parsimony. With a variety of available options, including branch swapping and rooting, essentially the same tree was obtained. When isolates of the genus Labronema were analyzed alone, all trees obtained had the same topology, although tree length varied considerably, depending on whether a hypothetical ancestral taxon was included.

Funaria maryanneae n. sp. and Proleptonchus weischeri n. sp. (Nematoda: Dorylaimida) from Europe and new synonyms in Leptonchoidea.

Funaria maryanneae n. sp., distinguished by its large size and long prerectum, is described from specimens collected in Bad Sooden, Germany, D. B. R. This nematode was collected also from Fräkmüntegg (Mt. Pilatus), Switzerland. Proleptonchus weischeri n. sp., with short hemispheroid female tail and relatively anterior vulva, is described from specimens collected in Kaufunger Wald near Kassel, Germany, D. B. R. This is the first report of either genus from the continent of Europe. Leptonchus parisii Zullini, 1973, from Chiapas, Mexico, becomes a junior synonym of Funaria obtusa (Thorne, 1939) Goseco, Ferris and Ferris, 1974. Leptonchus acutus Zulliui, 1973 becomes Funaria acuta n. comb., and Funaria rothi Goseco, Ferris and Ferris, 1974 becomes a junior synonym of Funaria acuta.

ss-tubulin Paralogs Provide a Qualitative Test for a Phylogeny of Cyst Nematodes.

Evolutionary relationships among cyst nematodes based on predicted ss-tubulin amino acid and DNA sequence data were compared with phylogenies inferred from ribosomal DNA (ITS1, 5.8S gene, ITS2). The ss-tubulin amino acid data were highly conserved and not useful for phylogenetic inference at the taxonomic level of genus and species. Phylogenetic trees based on ss-tubulin DNA sequence data were better resolved, but the relationships at lower taxonomic levels could not be inferred with confidence. Sequences from single species often appeared in more than one monophyletic clade, indicating the presence of ss-tubulin paralogs (confirmed by Southern blot analysis). For a subset of taxa, good congruence between the two data sets was revealed by the presence of the same putative ss-tubulin gene paralogs in monophyletic groups on the rDNA tree, corroborating the taxon relationships inferred from ribosomal DNA data.

Crop rotation effects on population densities of ectoparasitic nematodes.

The influence of rotation crop species on population densities of ectoparasitic nematode species common to soybean and corn fields of the North-Central region of the USA was studied for 5 years in 16 field blocks rotated to corn, soybeans, oats, wheat, and forage mixtures. Each block was sampled each year between mid-July and mid-August. High populations of Helicotylenchus pseudorobustus were maintained in all crops, especially corn. Tylenchorhynchus martini and Xiphinema americanum also developed with all crops, but a second year of corn depressed densities of both species. Paratylenchus projectus densities were high on soybeans and on forage consisting primarily of legumes.

Effect of soil type on population densities of nematodes in soybean rotation fields.

The effect of soil type on population densities of plant parasitic nematode species in 17 field blocks of four different soil types rotated to corn, soybeans, wheat, and forage mixtures was investigated during a generally droughty 5-year period. High densities of Helicotylenchus pseudorobustus were found in dark silty clay loams. Highest densities of Tylenchorhynchus acutus were also in one of the dark-colored silty clay loams. Light-colored silt loams favored development of Paratylenchus projectus, which developed poorly in the darker soils. Comparable densities of Xiphinema americanum were found in all soils and on all crops, regardless of soil type. Tylenchorhynchus martini, although present, did not build up in any of the soils. Populations of Pratylenchus species were generally low in the rotated blocks of all soil types.

Heterodera glycines in Indiana: I. Reproduction of Geographical Isolates on Soybean Differentials.

Four of five geographical isolates of Heterodera glycines from Indiana classified as Race 3 using standard differentials showed many differences when classified using another group of differentials comprised of five soybean breeding lines and cultivars. Two isolates from northern Indiana produced cysts on more of the differentials tested than did three isolates from southern Indiana, suggesting that potential resistant lines should be tested on a range of H. glycines populations originating from the areas for which cultivars are being developed.

Heterodera glycines in Indiana: II. Morphology of Geographical Isolates.

Although much morphometric overlap occurs among five geographical isolates of Heterodera glycines in Indiana, significant differences in means exist among the isolates for various comparisons of second-stage juveniles. By using combinations of means, most of the isolates can be distinguished from the rest: e.g., the Vanderburgh County isolate (southern Indiana) has the longest esophagus, tail, and tail terminus; the Vigo County isolate (also from the south) has the shortest esophagus; the White County isolate (northern Indiana) has the shortest tail and tail terminus and the greatest total length; the Benton County isolate (north) is the shortest. Morphological similarities and differences do not appear to be coordinated with reproductive behavioral patterns we observed in the northern versus the southern isolates.

Population Development of Pratylenchus hexincisus in Eight Corn Inbreds.

Of eight corn inbreds tested in the greenhouse and field, three (H60, H95, and H84) supported lower populations of Pratylenchus hexincisus than other inbreds included in this study. No apparent differences existed among inbreds in nematode invasion or development in the roots, or in population structure. Differences in population were therefore attributed to differential reproduction.

Dispersion and Distribution of Pratylenchus scribneri and Hoplolaimus galeatus in Soybean Fields.

Examination of dispersional characteristics of Pratylenchus scribneri and Hoplolaimus galeatus indicated that there were patches within soybean fields in which both survival and reproduction wexe enhanced in spite of apparent homogeneity of soil type and topography. Treatment with carbofuran reduced the patchiness (or increased the dispersion) for H. galeatus while it had the opposite effect for P. scribneri. P. scribneri was less highly dispersed in conventional tillage plots than in the zero tillage plots. Populations from quadrats contained entirely within the patches could be described by the normal distribution (in the case of P. scribneri) or by the Poisson distribution (in the case of H. galeatus), while populations from quadrats contained entirely outside the patches could be described by the Poisson distribution for both nematodes. None of the distributions tested (Poisson, normal, negative binomial, Neyman's) gave an adequate fit when populations from both inside and outside the patches were considered together. In all instances, log and ln transformations reduced the goodness of fit of the data to all of the distributions tested. Even with logarithmic transformations, parametric statistics were not appropriate for analysis of data in most instances.

Phylogenetic relationships based on ribosomal DNA data for four species of cyst nematodes from Italy and one from syria.

Phylogenetic analysis of new ribosomal DNA (rDNA) data for Heterodera mediterranea, H. hordecalis, H. carotae, and H. fici from Italy and H. ciceri from Syria, along with published data for other species, showed high bootstrap support for the following relationships: (((((H. carotae H. cruciferae) H. goettingiana) (((H. trifolii H. ciceri) H. mediterranea) ((H. avenae H. latipons) H. fici))) (Cactodera betulae H. hordecalis)) (Globodera rostochiensis G. pallida)). The rDNA sequence data were for the two internal transcribed spacers (ITS1 and ITS2) plus the 5.8S gene between them. These inferred relationships support the classic ''Goettingiana Group'' of H. carotae, H. cruciferae, and H. goettingiana. A clade comprised of Cactodera betulae and H. hordecalis is only distantly related to the other species in the analysis.

Two-dimensional Protein Patterns in Labronema, Aporcelaimellus, and Eudorylaimus (Nematoda: Dorylaimida).

Two-dimensional polyacrylamide gel electrophoretic patterns of proteins for two isolates of Labronema from Indiana were nearly identical to the pattern for L. vulvapapillatum from Europe. The pattern for a nominal isolate of L. pacificum from Florida was very different from the patterns of nominal L. pacificum isolates from Hawaii and Fiji (which had patterns very similar to each other). Patterns for four other isolates (in Eudorylaimus and Aporcelaimellus) were different from the Labronema patterns and from each other, although some constellations of protein spots were shared among all the isolates. The study demonstrates the utility of 2-D PAGE for clarifying taxonomic problems that cannot be resolved using classical morphological data alone.

Two-Dimensional Protein Patterns in Heterodera glycines.

Two-dimensional polyacrylamide gel electrophoretic protein patterns of H. glycines from southern Indiana (Posey County) and northern Indiana (Pulaski County) were largely similar, but many differences existed. The pattern of the Posey isolate was similar to patterns from isolates collected in other areas of the United States. Unique dense protein spots in the pattern of an isolate from Hokkaido, Japan, distinguished it from patterns of six U.S. isolates.

Comparisons of Isolates of Heterodera avenae using 2-D PAGE Protein Patterns and Ribosomal DNA.

Six geographic isolates of Heterodera avenae, including two isolates each from Sweden, Australia, and the United States, were compared on the basis of 2-D PAGE protein patterns and the complete DNA sequence for the two internal transcribed ribosomal DNA spacers (rDNA ITS1 and ITS2) and the 5.8S rRNA gene. The protein pattern data and rDNA ITS sequence data both indicated that the Swedish Gotland strain of H. avenae differed markedly from the rest of the isolates. Protein patterns for the Australia isolates differed more from a Swedish strict H. avenae isolate and isolates from Oregon and Idaho, than the two U.S. isolates and the Swedish strict H. avenae isolate differed from each other. Except for the Gotland strain isolate, the rDNA ITS sequences were highly conserved among all of the H. avenae isolates, just as we earlier found them to be conserved among species of the schachtii group of Heterodera.

Sclerostylus n. gen. from Panama and Other Neotropical Species of LeptonIchoidea (Dorylaimida).

Leptonchoid species found in soil samples taken in lowland and mid-elevation seasonal forests at four locations in Panama were as follows: Sclerostylus karri n. gen., n. sp., Basirotyleptus saccatus n. sp., B. nemoralis, B. acus, B. penetrans, Doryllium neotropicum n. sp., D. minor, Tyleptus gymnochilus, Gerthus jamesi, Dorylaimoides micoletzkyi, and Tylencholaimellus macrophallus. The discoveries corroborate our earlier suggestion of a Gondwanian origin for Tyleptus and Basirotyleptus and provide data for additional biogeographical study.

Proleptonchoides southindiae n. gen., n. sp., a New Leptonchoid from South India.

Proleptonchoides southindiae n. gen., n. sp. (Dorylaimida: Leptonchidae), is described from soil around false tobacco (Lobelia excelsa) and cardamom (Elettaria cardamomurn) in South India. P. southindiae is prodelphic, has a short constricted esophageal bulb and flanged odontophore, and is phylogenetically close to Proleptonchus.