Potassium activation and K spikes in muscle fibers of the mealworm Iarva (Tenebrio molitor)

GREGARINA LUTESCENS N. SP. INFECTING THE HARLEQUIN LADYBIRD HARMONIA AXYRIDIS (COLEOPTERA: COCCINELLIDAE)

Gregarina lutescens n. sp. is described from the alimentary canal of the harlequin ladybird or multicolored Asian lady beetle, Harmonia axyridis (Coleoptera: Coccinellidae) collected from prairie fleabane, Erigeron strigosus, at Peru State College, Peru, Nemaha Co., Nebraska. Our specimens differ from all 11 known species of Gregarina infecting coccinellid beetles worldwide by differences in size and relative shape, color, and association structure. Gregarina lutescens n. sp. is smaller than 7 known species infecting coccinellid beetles but larger than the other 4 known species based on confidence interval exclusion of means. Our specimens are unique among known species of interest in their quince-yellow cytoplasm and precocious but ephemeral serial associations of up to 5 satellites. Nucleotide sequence (18S) phylogenetic analyses place the new species basal to a member of an internal clade of Gregarina that comprises gregarines parasitizing chrysomelid beetles. Phylogenetically, the analysis recovered 3 major lineages within the gregarines, representing the superfamilies Gregarinoidea, Stenophoroidea, and Stylocephaloidea and indicating the propensity of gregarines to track host lineages and environments through evolutionary time. These findings confirm the polyphyletic nature of Gregarina, which currently comprises over 300 described species, only a handful of which have documented genetic sequences suitable for phylogenetic analysis. Recollection, redescription, and molecular clarification of gregarine species infecting coccinellids would likely result in identification of a unique clade that would be an excellent system for studying the effect of intraguild host competition on parasite diversification and community structure. Ecologically, patterns of prevalence in this study indicate that G. lutescens reproduces primarily in larval hosts but depends on infections in adult beetles to overwinter, reflecting the differential vagility and frost tolerance of larval and adult host life cycle stages.

Morphology and Phylogenetic Position of Two New Gregarine Species (Apicomplexa: Eugregarinorida) Parasitizing the Lubber Grasshopper Taeniopoda centurio (Drury, 1770) (Insecta: Orthoptera: Romaleidae) in Mexico

Eugregarines are understudied apicomplexan parasites of invertebrates inhabiting marine, freshwater, and terrestrial environments. Most currently known terrestrial eugregarines have been described parasitizing the gut from less than 1% of total insect diversity, with a high likelihood that the remaining insect species are infected. Eugregarine diversity in orthopterans (grasshoppers, locusts, katydids, and crickets) is still little known. We carried out a survey of the eugregarines parasitizing the Mexican lubber grasshopper, Taeniopoda centurio, an endemic species to the northwest of Mexico. We described two new eugregarine species from the gut of the host: Amoebogregarina taeniopoda n. sp. and Quadruspinospora mexicana n. sp. Both species are morphologically dissimilar in their life-cycle stages. Our SSU rDNA phylogenetic analysis showed that both species are phylogenetically distant to each other, even though they parasitize the same host. Amoebogregarina taeniopoda n. sp. clustered within the clade Gregarinoidea, being closely related to Amoebogregarina nigra from the grasshopper Melanoplus differentialis. Quadruspinospora mexicana n. sp. clustered within the clade Actinocephaloidea and grouped with Prismatospora evansi, a parasite from dragonfly naiads. Amoebogregarina taeniopoda n. sp. and Q. mexicana n. sp. represent the first record of eugregarines found to infect a species of the family Romaleidae.

Temporal Community Structure in Two Gregarines (Rotundula gammari and Heliospora longissima) Co-Infecting the Amphipod Gammarus fasciatus

This study surveyed gregarine parasites that infect the amphipod, Gammarus fasciatus , to investigate temporal dynamics in infracommunity structure. We sampled a population of hosts for 2 yr from the north branch of the Raritan River in New Jersey. These hosts were infected with 2 direct life cycle gregarine parasites, Rotundula gammari and Heliospora longissima. Infections were separated temporally, with the prevalence of R. gammari peaking within the amphipod population in the fall (prevalence = 78% year 1 and 97% year 2) and H. longissima peaking in early spring (prevalence = 41% year 1 and 52% year 2). Increases in host population density did not significantly correlate with the abundance of these 2 parasites. However, H. longissima abundance was positively correlated with host body weight while R. gammari showed no significant relationship. The mean body mass of amphipods infected with H. longissima was 20.7 ± 1. 2 mg, and with R. gammari 8.1 ± 0.2 mg, which suggests a sized-based infection pattern. Mixed species infections were infrequent with an overall prevalence of 4.6%. When both gregarine species co-infected the same host, the R. gammari but not the H. longissima infrapopulation size was significantly lower when compared to single-species infections, suggesting asymmetric interactions. We conclude that the observed temporal patterns of infection by the 2 parasites are driven by a seasonal change in host demographics and size-dependent infections. We argue that specificity for host developmental stages may have arisen as a mechanism to avoid overlap between these gregarine species.

The enigma of eugregarine epicytic folds: where gliding motility originates?

Background

In the past decades, many studies focused on the cell motility of apicomplexan invasive stages as they represent a potential target for chemotherapeutic intervention. Gregarines (Conoidasida, Gregarinasina) are a heterogeneous group that parasitize invertebrates and urochordates, and are thought to be an early branching lineage of Apicomplexa. As characteristic of apicomplexan zoites, gregarines are covered by a complicated pellicle, consisting of the plasma membrane and the closely apposed inner membrane complex, which is associated with a number of cytoskeletal elements. The cell cortex of eugregarines, the epicyte, is more complicated than that of other apicomplexans, as it forms various superficial structures.

Results

The epicyte of the eugregarines, Gregarina cuneata, G. polymorpha and G. steini, analysed in the present study is organised in longitudinal folds covering the entire cell. In mature trophozoites and gamonts, each epicytic fold exhibits similar ectoplasmic structures and is built up from the plasma membrane, inner membrane complex, 12-nm filaments, rippled dense structures and basal lamina. In addition, rib-like myonemes and an ectoplasmic network are frequently observed. Under experimental conditions, eugregarines showed varied speeds and paths of simple linear gliding. In all three species, actin and myosin were associated with the pellicle, and this actomyosin complex appeared to be restricted to the lateral parts of the epicytic folds. Treatment of living gamonts with jasplakinolide and cytochalasin D confirmed that actin actively participates in gregarine gliding. Contributions to gliding of specific subcellular components are discussed.

Conclusions

Cell motility in gregarines and other apicomplexans share features in common, i.e. a three-layered pellicle, an actomyosin complex, and the polymerisation of actin during gliding. Although the general architecture and supramolecular organisation of the pellicle is not correlated with gliding rates of eugregarines, an increase in cytoplasmic mucus concentration is correlated. Furthermore, our data suggest that gregarines utilize several mechanisms of cell motility and that this is influenced by environmental conditions.

New and emended descriptions of gregarines from flour beetles (Tribolium spp. and Palorus subdepressus: Coleoptera, Tenebrionidae)

The following new gregarine taxa are described from larvae of flour beetles (Coleoptera: Tenebrionidae): Awrygregarina billmani, n. gen., n. sp., from Tribolium brevicornis; Gregarina cloptoni, n. sp., from Tribolium freemani; Gregarina confusa, n. sp., from Tribolilum confusum; and Gregarina palori, n. sp., from Palorus subdepressus. In addition, the description of Gregarina minuta Ishii, 1914, from Tribolium castaneum, is emended. Scanning electron micrograph studies of these species' oocysts reveal differences in surface architecture. The Gregarina species have oocysts with longitudinal ridges, visible with SEM, whereas Awrygregarina billmani oocysts have fine circumferential striations; surface architecture is the main feature distinguishing the 2 gregarine genera. Although parasites from adult beetles are not included in the descriptions, adults of all host species can be infected experimentally using oocysts from the new taxa.

EFFECTS OF TEMPERATURE ON THE DEVELOPMENT OF GREGARINA CUBENSIS (APICOMPLEXA: EUGREGARINIDA) PARASITIZING BLABERUS DISCOIDALIS (BLATTARIA: BLABERIDAE)

Gregarina cubensis is an apicomplexan parasite that infects the intestinal lumen of the death's head cockroach (Blaberus discoidalis). This study evaluated the effects of 3 temperatures on the development and viability of G. cubensis. Three groups of B. discoidalis were inoculated with G. cubensis oocysts and maintained at 15, 27, and 40 C. The alimentary canal was removed from 3 cockroaches in each group every 24 hr until mature gametocysts were found in the rectum or feces, and prepared for histological examination. Gregarina cubensis establishment and development were more rapid at 15 C than at 27 C. Development of G. cubensis at 40 C did not progress beyond the intracellular stage.

TWO NEW SPECIES OF XIPHOCEPHALUS IN ELEODES TRICOSTATA AND ELEODES FUSIFORMIS (COLEOPTERA: TENEBRIONIDAE: ELEODINI) FROM THE SANDHILLS OF WESTERN NEBRASKA

Xiphocephalus triplogemmatus n. sp. and Xiphocephalus quadratogemmatus n. sp. (Apicomplexa: Eugregarinida) are described from Eleodes tricostata and Eleodes fusiformis (Coleoptera: Tenebrionidae), respectively, collected from Keith County in the sandhills of western Nebraska. Gamonts can be diagnosed with some confidence based on relative size and shape of the deutomerite, but these taxa are distinguished by differences in oocyst size, shape, and residuua number. Together with Xiphocephalus ellisi from Eleodes opacus in the same region, X. triplogemmatus and X. quadratogemmatus form a distinct Nearctic xiphocephalid group that is morphologically distinct from groups that occur in the Palearctic, Ethiopian, and Oriental regions.

NAIADOCYSTIS PHYKOTERION N. GEN., N. SP. (APICOMPLEXA: EUGREGARINIDA: HIRMOCYSTIDAE), FROM THE MEXICAN PYGMY GRASSHOPPER, PARATETTIX MEXICANUS (ORTHOPTERA: TETRIGIDAE), IN THE TEXAS BIG THICKET WITH RECOGNITION OF THREE PREVIOUSLY DESCRIBED SPECIES OF NAIADOCYSTIS

Naiadocystis phykoterion n. gen., n. sp. (Apicomplexa: Eugregarinida: Hirmocystidae), is described from the Mexican pygmy grasshopper, Paratettix mexicanus (Orthoptera: Tetrigidae), collected from sandbars along Harmon Creek, Walker County, Texas, in the western edge of the Texas Big Thicket. Naiadocystis n. gen. is distinguished by the form of the epimerite complex, a simple cordoid or toroid epimerite with an interior obconoid structure resembling a funnel that tapers to a distinct axial canal bisecting the protomerite, which is conspicuous in all stages of development, and a satellite protomerite reduced to a linearly crateriform cup or sucker that receives and enfolds posterior end of primite deutomerite. Association is precocious, caudofrontal, and biassociative. Gametocysts are spherical. Sporoducts are present but vestigial and irregular in number. Oocysts are broadly elliptoid with 4 small spherical polar knobs, 1 each at 30 degrees, 150 degrees, 210 degrees, and 330 degrees, and dehisce en masse. The species described herein are differentiated by their overall size and relative proportion of cellular structures. Naiadocystis acantholobae (Hoshide, 1952) n. comb., Naiadocystis acrydiinarum (Semans, 1939) n. comb., and Naiadocystis tetrigis (Corbel, 1968) n. comb. are recognized as members of Naiadocystis previously placed within Gregarina (Apicomplexa: Eugregarinida: Gregarinidae).

Phylogeny of gregarines (Apicomplexa) as inferred from small-subunit rDNA and beta-tubulin

Gregarines are thought to be deep-branching apicomplexans. Accordingly, a robust inference of gregarine phylogeny is crucial to any interpretation of apicomplexan evolution, but molecular sequences from gregarines are restricted to a small number of small-subunit (SSU) rDNA sequences from derived taxa. This work examines the usefulness of SSU rDNA and beta-tubulin sequences for inferring gregarine phylogeny. SSU rRNA genes from Lecudina (Mingazzini) sp., Monocystis agilis Stein, Leidyana migrator Clopton and Gregarina polymorpha Dufour, as well as the beta-tubulin gene from Leidyana migrator, were sequenced. The results of phylogenetic analyses of alveolate taxa using both genes were consistent with an early origin of gregarines and the putative 'sister' relationship between gregarines and Cryptosporidium, but neither phylogeny was strongly supported. In addition, two SSU rDNA sequences from unidentified marine eukaryotes were found to branch among the gregarines: one was a sequence derived from the haemolymph parasite of the giant clam, Tridacna crocea, and the other was a sequence misattributed to the foraminiferan Ammonium beccarii. In all of our analyses, the SSU rDNA sequence from Colpodella sp. clustered weakly with the apicomplexans, which is consistent with ultrastructural data. Altogether, the exact position of gregarines with respect to Cryptosporidium and other apicomplexans remains to be confirmed, but the congruence of SSU rDNA and beta-tubulin trees with one another and with morphological data does suggest that further sampling of molecular data will eventually put gregarine diversity into a phylogenetic context.

The response of Gregarina niphandrodes (Apicomplexa: Eugregarinida: Septatina) to host starvation in Tenebrio molitor (Coleoptera: Tenebrionidae) adults

Numerous studies of host starvation have emphasized pathological effects of parasites on their insect host, but little attention has been focused on the effects of host starvation on the parasites. This study addressed the possibility that parasite life-cycle events could be manipulated by withholding food from the host. The system used was Gregarina niphandrodes (Apicomplexa: Eugregarinida) in Tenebrio molitor (Coleoptera: Tenebrionidae) adults. Gregarine gametocyst formation and shedding ceased after 1 day in starved beetles but continued in fed controls. There were no statistically significant differences between total lengths of associated (3 of 5 trials) or unassociated (5 of 5 trials) gregarines found between experimental and control groups, but average numbers of the 2 life cycle events were generally higher in fed hosts than in starved ones. If infected, fed control beetles continued to form gametocysts throughout the 7-day trial periods, and gametocysts could be observed in the gut. Starved experimental beetles had no gametocysts in their guts. Refeeding of starved beetles after 4 days resulted in resumption of gametocyst formation and shedding. The studies demonstrated that the gregarine life cycle could be stopped and then started at the gametocyst formation stage like an off/on switch, simply by withholding food from, then refeeding, the host.

Zinc-dependent action potentials in giant neurons of the snail, Euhadra quaestia

In giant neurons of subesophageal ganglion of the Japanese land snail, Euhadra quaestia Deshayes, permeation of Zn ions through Ca channels were investigated with a conventional current clamp method. All-or-none action potentials of long duration (90 to 120 sec) were evoked in 24 mM Zn containing salines. The overshoots were about +10 mV and the maximum rate of rises (MRRs) was about 2.9 V/sec. The amplitudes and the MRRs of the action potentials depended on external Zn ion concentrations. The action potentials were suppressed by specific Ca-channel inhibitors such as Co2+, La3+ and Verapamil, but they were resistant to Na-channel inhibitor, tetrodotoxin, even at 30 microM. It is concluded that these action potentials are generated by Zn ions permeating Ca channels in snail neuronal membrane. On the basis of Hagiwara and Takahashi's (S. Hagiwara & K. Takahashi, 1967, J. Gen. Physiol. 50:583) model of Ca channels, it is inferred that Zn ions are 5 to 10 times stronger in affinity to Ca channels than Ca ions, but 10 to 20 times less permeable.

Membrane potential as the sum of ionic and metabolic components

The resting potential of a molluscan neuron can be separated experimentally into two components: one which depends on ionic gradients and permeabilities in accordance with the Goldman equation, and a second which depends on the electrogenicity of active sodium transport.

Potassium inactivation and impedance changes during spike electrogenesis in eel electroplaques

Various degrees of pharmacological K inactivation were induced by Cs or Ba in isolated single electroplaques of the electric eel. The resulting changes in K conductance give rise to very different steady-state current-voltage characteristics. They also induce differences in ion dynamics during spike electrogenesis. The dynamic changes were studied by AC bridge methods, registering the changes in impedance in synchrony with the neurally or directly evoked spikes. While spike electrogenesis was virtually unaffected by addition of Cs or Ba, the patterns of impedance changes were very different. The various patterns are accounted for by the changes in the respective current-voltage characteristics. The data constitute new evidence for regarding the electrically excitable component of the reactive membrane as a heterogeneous electrochemical system with separate and independently reactive channels that in the electroplaques are permselective for Na and K, respectively.

Permeability of alkali metal cations in lobster muscle. A comparison of electrophysiological and osmometric analyses

Single muscle fibers from lobster walking legs are effectively impermeable to Na, but are permeable to K. They shrink in hyperosmotic NaCl; they swell in low NaCl media which are hyposmotic or which are made isosmotic with the addition of KCl. In conformity, the membrane potential is relatively insensitive to changes in external Na, while it responds according to the Nernst relation for changes in external K. When the medium is made isosmotic or hyperosmotic with RbCl the volume and membrane potential changes are of essentially the same magnitudes as those in media enriched with KCl. The time courses for attaining equilibrium are slower, indicating that Rb is less permeant than K. Substitution of CsCl for NaCl (isosmotic condition) produces no change in volume of the muscle fiber. Addition of CsCl (hyperosmotic condition) causes a shrinkage which attains a steady state, as is the case in hyperosmotic NaCl. Osmotically, therefore, Cs appears to be no more permeant than is Na. However, the membrane depolarizes slowly in Cs-enriched media and eventually comes to behave as an ideal Cs electrode. Thus, the electrode properties of the lobster muscle fiber membrane may not depend upon the diffusional relations of the membrane and ions, and the osmotic permeability of the membrane for a given cation may not correspond with the electrophysiologically deduced permeability. Comparative data on the effects of NH(4) and Li are also included and indicate several other degrees of complexity in the cell membrane.

Crayfish muscle: permeability to sodium induced by calcium depletion

Membrane of crayfish muscle fibers becomes selectively permeable to sodium when the calcium concentration of the bathing medium is reduced. Removal of calcium or its reduction below 1 or 2 millimole per liter causes large transient depolarizations up to 70 millivolts in amplitude. They resemble pro longed action potentials and occur only in the presence of sodium. The responses are abolished when tris(hydroxymethyl)aminomethane or lithium is substituted for sodium, and are blocked by tetrodotoxin even in the presence of sodium.

Behavior of delayed current under voltage clamp in the supramedullary neurons of puffer

Depolarizations applied to voltage-clamped cells bathed in the normal solution disclose an initial inward current followed by a delayed outward current. The maximum slope conductance for the peak initial current is about 30 times the leak conductance, but the maximum slope conductance for the delayed current is only about 10 times the leak conductance. During depolarizations for as long as 30 sec, the outward current does not maintain a steady level, but declines first exponentially with a time constant of about 6 msec; it then tends to increase for the next few seconds; finally, it declines slowly with a half-time of about 5 sec. Concomitant with the changes of the outward current, the membrane conductance changes, although virtually no change in electromotive force occurs. Thus, the changes in the membrane conductance represent two phases of K inactivation, one rapidly developing, the other slowly occurring, and a phase of K reactivation, which is interposed between the two inactivations. In isosmotic KCl solution after a conditioning hyperpolarization there occurs an increase in K permeability upon depolarization. When the depolarizations are maintained, the increase of K permeability undergoes changes similar to those observed in the normal medium. The significance of the K inactivation is discussed in relation to the after-potential of the nerve cells.