Osteohistology of a Triassic dinosaur population reveals highly variable growth trajectories typified early dinosaur ontogeny

Intraspecific variation in growth trajectories provides a fundamental source of variation upon which natural selection acts. Recent work hints that early dinosaurs possessed elevated levels of such variation compared to other archosaurs, but comprehensive data uniting body size, bone histology, and morphological variation from a stratigraphically constrained early dinosaur population are needed to test this hypothesis. The Triassic theropod Coelophysis bauri, known from a bonebed preserving a single population of coeval individuals, provides an exceptional system to assess whether highly variable growth patterns were present near the origin of Dinosauria. Twenty-four histologically sampled individuals were less than a year to at least four years old and confirm the right-skewed age distribution of the Coelophysis assemblage. Poor correlations among size, age, and morphological maturity strongly support the presence of unique, highly variable growth trajectories in early dinosaurs relative to coeval archosaurs and their living kin.

The dinosaurian femoral head experienced a morphogenetic shift from torsion to growth along the avian stem

Significant evolutionary shifts in locomotor behaviour often involve comparatively subtle anatomical transitions. For dinosaurian and avian evolution, medial overhang of the proximal femur has been central to discussions. However, there is an apparent conflict with regard to the evolutionary origin of the dinosaurian femoral head, with neontological and palaeontological data suggesting seemingly incongruent hypotheses. To reconcile this, we reconstructed the evolutionary history of morphogenesis of the proximal end of the femur from early archosaurs to crown birds. Embryological comparison of living archosaurs (crocodylians and birds) suggests the acquisition of the greater overhang of the femoral head in dinosaurs results from additional growth of the proximal end in the medial-ward direction. On the other hand, the fossil record suggests that this overhang was acquired by torsion of the proximal end, which projected in a more rostral direction ancestrally. We reconcile this apparent conflict by inferring that the medial overhang of the dinosaur femoral head was initially acquired by torsion, which was then superseded by mediad growth. Details of anatomical shifts in fossil forms support this hypothesis, and their biomechanical implications are congruent with the general consensus regarding broader morpho-functional evolution on the avian stem.

Africa's oldest dinosaurs reveal early suppression of dinosaur distribution

The vertebrate lineages that would shape Mesozoic and Cenozoic terrestrial ecosystems originated across Triassic Pangaea^1-11. By the Late Triassic (Carnian stage, ~235 million years ago), cosmopolitan 'disaster faunas' (refs. ^12-14) had given way to highly endemic assemblages^12,13 on the supercontinent. Testing the tempo and mode of the establishment of this endemism is challenging-there were few geographic barriers to dispersal across Pangaea during the Late Triassic. Instead, palaeolatitudinal climate belts, and not continental boundaries, are proposed to have controlled distribution^15-18. During this time of high endemism, dinosaurs began to disperse and thus offer an opportunity to test the timing and drivers of this biogeographic pattern. Increased sampling can test this prediction: if dinosaurs initially dispersed under palaeolatitudinal-driven endemism, then an assemblage similar to those of South America^4,19-21 and India^19,22-including the earliest dinosaurs-should be present in Carnian deposits in south-central Africa. Here we report a new Carnian assemblage from Zimbabwe that includes Africa's oldest definitive dinosaurs, including a nearly complete skeleton of the sauropodomorph Mbiresaurus raathi gen. et sp. nov. This assemblage resembles other dinosaur-bearing Carnian assemblages, suggesting that a similar vertebrate fauna ranged high-latitude austral Pangaea. The distribution of the first dinosaurs is correlated with palaeolatitude-linked climatic barriers, and dinosaurian dispersal to the rest of the supercontinent was delayed until these barriers relaxed, suggesting that climatic controls influenced the initial composition of the terrestrial faunas that persist to this day.

The developing bird pelvis passes through ancestral dinosaurian conditions

Living birds (Aves) have bodies substantially modified from the ancestral reptilian condition. The avian pelvis in particular experienced major changes during the transition from early archosaurs to living birds1,2. This stepwise transformation is well documented by an excellent fossil record2-4; however, the ontogenetic alterations that underly it are less well understood. We used embryological imaging techniques to examine the morphogenesis of avian pelvic tissues in three dimensions, allowing direct comparison with the fossil record. Many ancestral dinosaurian features2 (for example, a forward-facing pubis, short ilium and pubic 'boot') are transiently present in the early morphogenesis of birds and arrive at their typical 'avian' form after transitioning through a prenatal developmental sequence that mirrors the phylogenetic sequence of character acquisition. We demonstrate quantitatively that avian pelvic ontogeny parallels the non-avian dinosaur-to-bird transition and provide evidence for phenotypic covariance within the pelvis that is conserved across Archosauria. The presence of ancestral states in avian embryos may stem from this conserved covariant relationship. In sum, our data provide evidence that the avian pelvis, whose early development has been little studied5-7, evolved through terminal addition-a mechanism8-10 whereby new apomorphic states are added to the end of a developmental sequence, resulting in expression8,11 of ancestral character states earlier in that sequence. The phenotypic integration we detected suggests a previously unrecognized mechanism for terminal addition and hints that retention of ancestral states in development is common during evolutionary transitions.

Assessing ontogenetic maturity in extinct saurian reptiles

Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life-history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least-inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260-million-year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. 'juvenile', 'mature') and provide routes for better clarity and cross-study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method-specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, 'Ontogenetic Assessment', be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well-represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well-constrained, empirically tested methods.

Hindered and compression solid settling functions - Sensor data collection, practical model identification and validation

Secondary settling tanks (SSTs) are the most hydraulically sensitive unit operations in activated sludge water resource recovery facilities (WRRF). Mathematical models for predicting activated sludge solids settling velocity include parameters that show irreducible epistemic uncertainty. Therefore, reliable and periodic calibration of the settling velocity model is key for predicting activated sludge process capacity, thus averting possible failures under wet-weather flow- and filamentous bulking conditions. The two main knowledge gaps addressed here are: (1) Do constitutive functions for hindered and compression settling exist, for which all velocity parameters can be uniquely estimated? (2) What is the optimum sensor data requirement of developing reliable settling velocity functions? Innovative settling column sensor and full-scale data were used to identify and validate amended Vesilind function for hindered settling and a new exponential function for compression settling velocity using one-dimensional and computational fluid dynamics simulations. Results indicate practical model identifiability under well-settling and filamentous bulking conditions.

Integrating gross morphology and bone histology to assess skeletal maturity in early dinosauromorphs: new insights from Dromomeron (Archosauria: Dinosauromorpha)

Understanding growth patterns is central to properly interpreting paleobiological signals in tetrapods, but assessing skeletal maturity in some extinct clades may be difficult when growth patterns are poorly constrained by a lack of ontogenetic series. To overcome this difficulty in assessing the maturity of extinct archosaurian reptiles—crocodylians, birds and their extinct relatives—many studies employ bone histology to observe indicators of the developmental stage reached by a given individual. However, the relationship between gross morphological and histological indicators of maturity has not been examined in most archosaurian groups. In this study, we examined the gross morphology of a hypothesized growth series of Dromomeron romeri femora (96.6–144.4 mm long), the first series of a non-dinosauriform dinosauromorph available for such a study. We also histologically sampled several individuals in this growth series. Previous studies reported that D. romeri lacks well-developed rugose muscle scars that appear during ontogeny in closely related dinosauromorph taxa, so integrating gross morphology and histological signal is needed to determine reliable maturity indicators for early bird-line archosaurs. We found that, although there are small, linear scars indicating muscle attachment sites across the femur, the only rugose muscle scar that appears during ontogeny is the attachment of the M. caudofemoralis longus, and only in the largest-sampled individual. This individual is also the only femur with histological indicators that asymptotic size had been reached, although smaller individuals possess some signal of decreasing growth rates (e.g., decreasing vascular density). The overall femoral bone histology of D. romeri is similar to that of other early bird-line archosaurs (e.g., woven-bone tissue, moderately to well-vascularized, longitudinal vascular canals). All these data indicate that the lack of well-developed femoral scars is autapomorphic for this species, not simply an indication of skeletal immaturity. We found no evidence of the high intraspecific variation present in early dinosaurs and other dinosauriforms, but a limited sample size of other early bird-line archosaur growth series make this tentative. The evolutionary history and phylogenetic signal of gross morphological features must be considered when assessing maturity in extinct archosaurs and their close relatives, and in some groups corroboration with bone histology or with better-known morphological characters is necessary.

Sacral anatomy of the phytosaur Smilosuchus adamanensis, with implications for pelvic girdle evolution among Archosauriformes

The sacrum - consisting of those vertebrae that articulate with the ilia - is the exclusive skeletal connection between the hindlimbs and axial skeleton in tetrapods. Therefore, the morphology of this portion of the vertebral column plays a major role in the evolution of terrestrial locomotion. Whereas most extant reptiles only possess the two plesiomorphic sacral vertebrae, additional vertebrae have been incorporated into the sacrum multiple times independently among early-diverging archosaurian (crocodylians + birds) clades. Phytosauria was a diverse, abundant, and cosmopolitan clade of archosauriforms throughout the Late Triassic, but postcrania of this clade are rarely described and few species-level taxonomic placements of phytosaurian postcranial material are available, potentially hampering knowledge of morphological disparity in the postcranial skeleton among phytosaurs. Here, we describe the sacrum of Smilosuchus adamanensis, a phytosaur recovered from the Upper Triassic Chinle Formation of Arizona. This sacrum consists of the two primordial sacral vertebrae, but has a vertebra incorporated from the trunk into the sacrum (= a dorsosacral) and is therefore the first Late Triassic phytosaur and one of the first non-archosaurian archosauromorphs to be described with more than two sacral vertebrae. Our interpretation of this element as a dorsosacral is justified by the lateral extent of the dorsosacral ribs, clear surfaces of articulation between the distal ends of the dorsosacral ribs and the first primordial sacral ribs, and the scar on the medial surface of each ilium for articulation with each dorsosacral rib. Additionally, we provide the first detailed description of the vertebral junction formed by two anteriorly projecting flanges on the first primordial sacral ribs and their corresponding facets on the centrum of the dorsosacral. Computed tomographic (CT) imaging reveals that the two primordial sacrals are not co-ossified and that the dorsosacral morphology of this specimen is not the result of obvious pathology. We place this incorporation of a trunk vertebra into the phytosaurian sacrum in a broader evolutionary context, with this shift in vertebral identity occurring at least seven times independently among Triassic archosauriforms, including at least three times in early crocodylian-line archosaurs and at least four times among bird-line archosaurs. Additionally, anteriorly projecting flanges of sacral ribs which articulate with the anterior-adjacent centrum have evolved several times in archosauriforms, and we interpret 'shared' sacral ribs (= a sacral rib that articulates with two adjacent sacral centra more or less equally) present in some archosaurian clades as a more extreme example of this morphology. In extant taxa the highly conserved Hox gene family plays a central role in the patterning of the axial skeleton, especially vertebral identity; therefore, the independent incorporation of a trunk vertebra into the sacrum across multiple archosauriform lineages may suggest a homologous underlying developmental mechanism for this evolutionary trend.

Higher relatedness mitigates mortality in a nematode with lethal male fighting

According to kin selection theory, individuals show less aggression towards their relatives. Limited dispersal promotes interactions among relatives but also increases competition among them. The evolution of cooperation in viscous populations has been subject of mainly theoretical exploration. We investigated the influence of relatedness on aggression in males of entomopathogenic nematode Steinernema longicaudum that engage in lethal fighting. In a series of in vitro experiments, we found that both competitor male group size and relatedness influence male mortality rates. Higher relatedness led to progressively lower rates of male mortality. In experimentally infected insects, wherein large numbers of males and females interact, the proportion of dead and paralysed (= terminally injured) males was higher when infection was established by infective juveniles originating from a mixture of three lines than in those infected by a single line. The results collectively show that Steinernema longicaudum males recognize their kin and consequently male mortality rates are lower in groups consisting of more related males. Furthermore, this monotonic negative relationship between aggression and relatedness suggests that kin selection benefits are still substantial even under extreme competition. Our experiments also suggest that kin recognition in entomopathogenic nematodes has a genetic basis rather than being strictly based on environmental cues. We discuss our findings within the theoretical context of the evolution of altruistic/cooperative behaviour in structured populations.

Simulated roots and host feeding enhance infection of subterranean insects by the entomopathogenic nematode Steinernema carpocapsae

Steinernema carpocapsae can be effective against root-feeding insects despite its reputation as a sedentary ambusher. In pot experiments, using twigs as surrogate roots and pine weevil larvae as targets, we tested the hypothesis that roots serve as physical routeways and conduits of feeding-associated stimuli, thus enhancing the success of S. carpocapsae applied at the surface against subterranean hosts. Insect mortality was lowest (25%) in the absence of plant material, increased to 48% when twigs linked nematodes and insects, and further increased to 69% when the insects were allowed feed on the twigs. This is the first experimental support for the root-routeway hypothesis.

Competition and intraguild predation between the braconid parasitoid Bracon hylobii and the entomopathogenic nematode Heterorhabditis downesi, natural enemies of the large pine weevil, Hylobius abietis

In biological control programmes introduced natural enemies compete with indigenous enemies for hosts and may also engage in intraguild predation when two species competing for the same prey attack and consume one another. The large pine weevil, Hylobius abietis L. (Coleoptera: Curculionidae), is an important pest of coniferous reforestation in Europe. Among its natural enemies, the parasitoid Bracon hylobii Ratz. (Hymenoptera: Braconidae) and entomopathogenic nematodes have potential as biological control agents. Both parasitoid and nematodes target the weevil larvae and, hence, there is potential for competition or intraguild predation.In this study, we examine the interaction of B. hylobii with the nematode Heterorhabditis downesi Stock, Griffin and Burnell (Nematode: Heterorhabditidae), testing the susceptibility of larvae, pupae and adults of B. hylobii to H. downesi and whether female parasitoids discriminate between nematode-infected and uninfected weevils for oviposition. In choice tests, when weevils were exposed to nematodes 1-7 days previously, no B. hylobii oviposited on nematode-infected weevil larvae. Up to 24 h, healthy weevils were twice as likely as nematode-infected ones to be used for oviposition. Bracon hylobii females did not adjust clutch size; nematode-infected hosts were either rejected or the parasitoid laid a full clutch of eggs on them.When nematodes were applied to the parasitoid feeding on weevil larvae, the nematodes parasitized the parasitoid larvae, there was a reduction in cocoon formation and fewer cocoons eclosed. Eclosion rate was not reduced when nematodes were applied to fully formed cocoons, but nearly all of the emerging adults were killed by nematodes.

Establishment, persistence, and introgression of entomopathogenic nematodes in a forest ecosystem

Entomopathogenic nematodes (EPN) are currently marketed worldwide for use in inundative biological control, where the applied natural enemy population (rather than its offspring) is expected to reduce insect numbers. Unlike classical biological control, in inundative control natural enemy establishment is not crucial in order to achieve pest suppression. Field trials in Irish forestry provided the opportunity to test predictions regarding the establishment of two exotic (Steinernema carpocapsae and Heterorhabditis megidis) and two indigenous (Steinernema feltiae and Heterorhabditis downesi) species. Nematodes were inundatively applied to pine stumps to control populations of pine weevil, Hylobius abietis, on three clearcut sites, and their persistence and spread monitored for up to five years. All species were recovered three years after application but only S. feltiae was recovered in years 4 and 5. Limited horizontal dispersal to 20 cm (but not 100 cm) was observed, but the majority of nematodes were recovered close to the area of application. Steinernema feltiae was also recovered from nearby stumps to which it had not been applied, indicating possible phoretic dispersal by weevils or other stump-associated fauna. EPN were not recovered from stumps outside the treated area, suggesting that such dispersal is quite localized. Two strains of S. feltiae (Irish and exotic) were applied. Amplified fragment length polymorphism (AFLP) analysis on 11 populations isolated from soil four years later showed that all had a much closer affinity to the applied Irish strain, suggesting persistence of this genotype and extinction of the exotic one. Some strains were clustered close together, and this is interpreted in the light of possible population genetic scenarios. The findings from the field study confirm predictions based on background knowledge of the species and demonstrate the importance of medium-term studies, as a 3-year study would have overestimated the risk of establishment of exotic species. Short-term persistence and spread of S. carpocapsae, S. feltiae, and H. downesi was also studied in pine forest mesocosms. Similar trends to field results, such as limited horizontal dispersal, even vertical distribution, and more abundant recovery of S. feltiae than of other species, point to the utility of mesocosm studies as a predictive tool.

Emergence and Dispersal Patterns of Two Isolates of the Entomopathogenic Nematode Steinernema feltiae

Few studies have addressed the role of the sexes in the emergence and dispersal of entomopathogenic nematodes from host insects. Individuals of two isolates of Steinernema feltiae, UK76 and SBIl, emerging from Galleria mellonella cadavers were classed as Non-Dispersed (remaining on the cadaver for up to nine days) and Dispersed (actively moving away from the cadaver). Sex ratios within both classes were examined in infective (individuals that successfully invaded bait G. mellonella) and entire (infective and noninfective individuals that matured in hanging drops of G. mellonella haemolymph) populations. Sex ratios differed significantly from 1:1 only in the SBIl Non-Dispersed entire population (female bias) and SBIl Non-Dispersed infective population (male bias). For each isolate, Dispersed individuals were significantly more infective than Non-Dispersed. However, only 11% of SBIl and 22% of UK76 Non-Dispersed individuals were found to be mature infective juveniles (IJ) compared with 78% of SBIl and 82% of UK76 Dispersed individuals (based on survival in SDS). Infective juveniles dispersing towards distant radial bait G. mellonella tended to migrate from the head region of the natal cadaver. For each isolate, a higher proportion of males than females arrived early at distant baits. SBIl males survived alone in G. mellonella cadavers for longer periods than did females, which supports the "male colonization" hypothesis.

Specificity of association between Paenibacillus spp. and the entomopathogenic nematodes, Heterorhabditis spp

Endospore-forming bacteria, Paenibacillus spp., have recently been isolated in association with insect pathogenic nematodes Heterorhabditis spp. Sporangia adhere to nematode infective juveniles (J3) and are carried with them into insects. Paenibacillus proliferates in the killed insect along with Heterorhabditis and its obligate bacterial symbiont, Photorhabdus, despite the antibiotic production of the latter. Nematode infective juveniles leave the insect cadaver with Paenibacillus sporangia attached. The specificity of the relationship between Paenibacillus and Heterorhabditis was investigated. Sporangia of nematode-associated Paenibacillus adhered to infective juveniles (but not other stages) of all Heterorhabditis species tested, and to infective juveniles of vertebrate parasitic Strongylida species, but not to a variety of other soil nematodes tested. Paenibacillus species that were not isolated from nematodes, but were phylogenetically close to the nematode-associated strains, did not adhere to Heterorhabditis, and they were also sensitive to Photorhabdus antibiotics in vitro, whereas the nematode-associated strains were not. Unusual longevity of the sporangium and resistance to Photorhabdus antibiotics may represent specific adaptations of the nematode-associated Paenibacillus strains to allow them to coexist with and be transported by Heterorhabditis. Adaptation to specific Heterorhabditis-Photorhabdus strains is evident among the three nematode-associated Paenibacillus strains (each from a different nematode strain). Paenibacillus NEM1a and NEM3 each developed best in cadavers with the nematode from which it was isolated and not at all with the nematode associate of the other strain. Differences between nematode-associated Paenibacillus strains in cross-compatibility with the various Heterorhabditis strains in cadavers could not be explained by differential sensitivity to antibiotics produced by the nematodes' Photorhabdus symbionts in vitro.

Phased infectivity in Heterorhabditis megidis: the effects of infection density in the parental host and filial generation

Entomopathogenic nematodes can develop through two or more generations in the cadavers of killed insect hosts. Non-feeding infective juveniles from each generation emerge and may spend prolonged periods searching for a new host. The infectivity of the infective juveniles of Heterorhabditis megidis varies with time after emergence and may not reach a maximum until several weeks have passed. 'Phased infectivity' hypotheses propose that this pattern is adaptive, tending to reduce competition in new hosts. Here we provide further evidence that infectivity is phased in H. megidis. In addition, we show that the basic pattern is modified by infection density in the parental host and by filial generation. Two general patterns were observed: first, infective juveniles that developed under the least crowded conditions (F(1) infective juveniles produced in hosts infected with 16 parent nematodes) reached maximum infectivity after only 15 days, compared to 27 or 39 days for infective juveniles that developed under more crowded conditions (F(1) produced in hosts infected with 103 or 424 parent nematodes or F(2) infective juveniles). Second, infective juveniles had lower infectivity overall when produced under the most crowded conditions (F(2) versus F(1); highest versus lowest infection density). We propose that while lower overall infectivity is a necessary consequence of limited resource availability during infective juvenile development, the difference in the timing of peak infectivity reflects a shift in the fitness gains associated with being maximally infective either 'early' or 'late'. F(1) infective juveniles emerge several days before F(2) infective juveniles, and we suggest that filial generation and infection density in the parental host function as indicators of the potential risk of competition within new hosts.

Density-dependent fecundity and infective juvenile production in the entomopathogenic nematode, Heterorhabditis megidis

The entomopathogenic nematode Heterorhabditis megidis may undergo several rounds of reproduction within a single host. Infective juveniles (IJs) are formed within each generation during a process referred to as endotokia matricida, which involves the progressive consumption of the parent hermaphrodite or female by the developing IJs prior to emergence from the host cadaver. The present study examines the extent to which within-host population dynamics exhibit density-dependent variation. Particular attention is paid to the effect of infection density on the relative production of IJs and 'normal', non-infective offspring within each generation and on the emergence of the IJs from the host. Fecundity was found to be negatively density dependent across generations. However, at high infection density the first generation hermaphrodites invested relatively more in IJs at the expense of producing non-infective offspring. It is suggested that this pattern resulted from an adaptive, phenotypically plastic allocation of reproductive investment between offspring types in response to increased competition. The F1 and F2 IJs were also shown to emerge from the host in relatively discrete pulses.

Persistence of four heterorhabditis spp. isolates in soil: role of lipid reserves

Infective juveniles of four Heterorhabditis isolates (H. bacteriophora HI, H. megidis UK211 and HF85, and H. downesi M245) were stored in moist (pF 1.7) and dry (pF 3.3) loam soil at 20 degrees C for up to 141 days. Survival, assessed by the number of nematodes extracted by centrifugal flotation, declined over time, reaching fewer than 18% alive by day 141 for all but one treatment (H. bacteriophora HI in dry soil). The infectivity of nematodes in soil for Tenebrio molitor also declined over time, roughly in accordance with the decline in numbers of nematodes. Energy reserves of extracted nematodes were assessed by image analysis densitometry. There were differences among isolates both in survival and in the depletion of reserves, and there was a significant correlation between these two parameters, suggesting that the extent to which energy reserves are depleted affects survival or that a common factor influences both. However, significant nematode mortality occurred while levels of reserves remained high, and the maximum reduction in utilizable body content for any treatment was 51%, well above starvation level. Therefore, the decline in numbers of living nematodes and the reduced nematode infectivity in soil cannot directly result from starvation of the nematodes. Survival and infectivity declined more rapidly in moist than in dry soil; one isolate, H. downesi M245, was less affected by soil moisture content than the other three isolates.

Phased activity in Heterorhabditis megidis infective juveniles

The infectivity of Heterorhabditis megidis infective juveniles (IJs) increases during storage in water. We investigated whether this change can be related to other features of the IJs' behaviour. IJs were stored in water for 4 weeks at 20 degrees C, and the following parameters were assessed at intervals: infectivity for Galleria mellonella, dispersal in sand, host-finding on agar, and the percentage of IJs active in water. In addition, the behaviour of the IJs in water was described using 7 categories. Immediately after emerging from the host cadaver, IJs were highly active (99% of IJs in water were active and 65% displayed 'waving', the normal method of forward movement). Maximum responsiveness to host volatiles in an agar plate assay was recorded on day 2 (69% of IJs moved from the point of application and 44% of all IJs in the agar arena moved towards a host) and maximum dispersal in sand (5.8 cm) on day 0. These tendencies declined gradually with age, while infectivity underwent a significant increase from 11 nematodes per insect on day 0 to 38 nematodes per insect on day 9. Three phases could be distinguished in the behaviour of H. megidis IJs: an initial dispersal phase, during which infectivity was low; an infective phase, during which dispersal tendency was declining, and a third phase during which all behaviours (dispersal, infectivity and activity) were declining. Over the 4-week storage period, infectivity of H. megidis IJs was correlated (R2 = 0.83) with the percentage time IJs engaged in 'head thrusting' (a behaviour that resembles penetration). There is no evidence that the observed increase in infectivity of H. megidis strain UK211 could be accounted for by a generally greater level of motor activity, nor by an increase in responsiveness to volatile host cues, and it is suggested that it is due to an increased tendency to attempt penetration.

A role for thrombin receptor signaling in endothelial cells during embryonic development

The coagulation protease thrombin triggers fibrin formation, platelet activation, and other cellular responses at sites of tissue injury. We report a role for PAR1, a protease-activated G protein-coupled receptor for thrombin, in embryonic development. Approximately half of Par1-/- mouse embryos died at midgestation with bleeding from multiple sites. PAR1 is expressed in endothelial cells, and a PAR1 transgene driven by an endothelial-specific promoter prevented death of Par1-/- embryos. Our results suggest that the coagulation cascade and PAR1 modulate endothelial cell function in developing blood vessels and that thrombin's actions on endothelial cells-rather than on platelets, mesenchymal cells, or fibrinogen-contribute to vascular development and hemostasis in the mouse embryo.

A self-fertile species of Steinernema from Indonesia: further evidence of convergent evolution amongst entomopathogenic nematodes?

More than 20 species of the entomopathogenic nematode Steinernema have been described; to date, all reproduce exclusively by cross-fertilization of male and female individuals. Steinernema sp. strain T87 from Indonesia was found to consist largely of self-fertile hermaphrodites. Progeny were produced by morphological females both in insects (Galleria mellonella) and in hanging drops of insect haemolymph inoculated with a single infective juvenile. Sperm were present in the oviduct of unmated morphological females. Approximately 1% of infective juveniles developed into males, and males were also present in the second generation where they constituted 1-6% of the population. Under the same conditions the related species Steinernema longicaudum strain CB2B displayed typical steinernematid reproduction: cross-fertilization and a 1:1 sex ratio. It is argued that the development of hermaphroditism in Steinernema sp. T87 represents convergent evolution with Heterorhabditis, the other major genus of entomopathogenic nematode.

Occurrence and distribution of the entomopathogenic nematodes Steinernema spp. and Heterorhabditis indica in Indonesia

Soil samples from 79 sites on five islands of Indonesia were baited with insects for the recovery of entomopathogenic nematodes. Heterorhabditis and Steinernema were equally prevalent, and were recovered from 11.7% of samples representing 20.3% of sites sampled. Both genera were recovered from coastal sites only. Entomopathogenic nematodes were more prevalent on the Moluccan islands of Ambon and Seram than on Java or Bali. They were not detected on Sulawesi, where non-coastal sites only were sampled. RFLP analysis was used in the identification of nematode isolates. Heterorhabditis indica was the only heterorhabditid identified. Two RFLP types of Steinernema were identified.

Persistence of heterorhabditis infective juveniles in soil: comparison of extraction and infectivity measurements

The persistence of Heterorhabditis megidis in soil was studied over a 4-week period. On days 0, 2, 14, and 28, infective juveniles (IJ) were extracted by centrifugal flotation, Baermann funnel, and baiting of soil with Tenebrio molitor larvae, which were then dissected. Extraction efficiencies on day 0 were 82% by centrifugal flotation, 56% by Baermann funnel, and 19.8% by bait insect. The relative efficiency of the three methods changed over time. The relationship between the density of nematodes in the soil and the proportion recovered by dissection was non-linear. Up to a dose of approximately 60 IJ/insect, less than 12% became established, while at higher doses (up to 200 IJ/insect) the invasion efficiency was 23%. Mortality of bait insects increased from day 0 to day 2, but decreased to day 28. A novel method of assessing soil pathogenicity by preparing a soil density series and calculating the dose of soil or IJ that kills 50% of the bait insects gave a similar pattern. This method is recommended as a means of tracking changes in pathogenicity over time when bait insect mortality in undiluted soil is at or near 100%. Two methods of preparing a series of Heterorhabditis IJ densities in soil, either by diluting the soil itself with IJ-free soil or by adding diluted suspensions of IJ to the soil, resulted in the same bait insect mortalities.

Fatty acid composition of Heterorhabditis sp. during storage

The fatty acid composition of three North West European isolates of Heterorhabditis sp. from different geographical origins, UK211 (England), HF85 (The Netherlands) and EU17 (Estonia) was assessed directly after harvest and, for UK211 and HF85, after 5 weeks storage in water at 20 degrees C. Lipid represented 34-43% of the dry weight of fresh nematodes. Of this, neutral lipid (NL) comprised from 70% (HF85) to over 90% (UK211, EU17). The fatty acid patterns were similar between the three isolates. Oleic (C18:In-9), palmitic (C16:0), and linoleic (C18:2n-6) acid predominated with 51, 13 and 12%, respectively in the total lipid (TL) of fresh nematodes (average for the three isolates). Levels of unsaturation (U.I.) of fresh nematodes were on average 110, 112, 113 and 152 for the TL, NL, phospholipid and free fatty acid fractions, respectively. EU17 had a slightly lower U.I than the other two strains, despite its more northern origin. Changes in fatty acid composition due to storage were most significant in the NL fraction. The U.I. for the NL fraction increased during storage, suggesting a preferential use of saturated fatty acids.

Spontaneous follicular exclusion of SHP1-deficient B cells is conditional on the presence of competitor wild-type B cells

Engagement of antigen receptors on mature B lymphocytes is known to block cell entry into lymphoid follicles and promote accumulation in T cell zones, yet the molecular basis for this change in cell distribution is not understood. Previous studies have shown that follicular exclusion requires a threshold level of antigen receptor engagement combined with occupancy of follicles by B cells without equivalent receptor engagement. The possibility has been raised that follicular composition affects B cell positioning by altering the amount of available antigen and the degree of receptor occupancy. Here we show that follicular composition affects migration of mature B cells under conditions that are independent of antigen receptor occupancy. B cells deficient in the negative regulatory protein tyrosine phosphatase, SHP1, which have elevated intracellular signaling by the B cell receptor, are shown to accumulate in the T zone in the absence of their specific antigen. Follicular exclusion of SHP1-deficient B cells was found to be conditional on the presence of excess B cells that lack elevated intracellular signaling, and was not due to a failure of SHP-1-deficient cells to mature and express the follicle-homing chemokine receptor Burkitt's lymphoma receptor 1. These findings strongly suggest that signals that are negatively regulated by SHP1 promote B cell localization in T cell zones by reducing competitiveness for follicular entry, and provide further evidence that follicular composition influences the positioning of antigen-engaged B cells.

Estimation of lipid reserves in unstained living and dead nematodes by image analysis

During storage, non-feeding stages of entomopathogenic nematodes become visibly more transparent due to depletion of energy reserves. Optical density per unit area (OD per area) of infective juveniles of Steinernerna carpocapsae (All) and two Heterorhabditis isolates (UK211 and HF85) was measured with an image analysis system and compared with neutral lipid levels obtained by Oil Red O staining. Optical density (OD) measurements were compared with triglyceride levels of UK211 and HF85. Good correlations between OD per area and neutral lipids (0.90) and between OD and triglycerides (0.87) were found. Thus, OD reflects lipid levels and can be used as an indicator of lipid reserves in these nematodes. Heat-killing of nematodes had no significant effect on OD measurements, but length increased significantly. Storage in a triethanolamine in formaldehyde solution decreased the OD and OD/area by about 5% to 8%. An additional advantage of the image analysis method described is that repeated measurements can be performed on live nematodes. Key words: entomopathogenic nematode, Heterorhabditis, image analysis, neutral lipid, Oil Red O, optical density, Steinernema, triglyceride.