Recent Advances in Our Knowledge of the Myxozoa

In the last few years two factors have helped to significantly advance our understanding of the Myxozoa. First, the phenomenal increase in fin fish aquaculture in the 1990s has lead to the increased importance of these parasites; in turn this has lead to intensified research efforts, which have increased knowledge of the development, diagnosis. and pathogenesis of myxozoans. The hallmark discovery in the 1980s that the life cycle of Myxobolus cerebralis requires development of an actinosporean stage in the oligochaete. Tubifex tubifex, led to the elucidation of the life cycles of several other myxozoans. Also, the life cycle and taxonomy of the enigmatic PKX myxozoan has been resolved: it is the alternate stage of the unusual myxozoan, Tetracapsula bryosalmonae, from bryozoans. The 18S rDNA gene of many species has been sequenced, and here we add 22 new sequences to the data set. Phylogenetic analyses using all these sequences indicate that: 1) the Myxozoa are closely related to Cnidaria (also supported by morphological data); 2) marine taxa at the genus level branch separately from genera that usually infect freshwater fishes; 3) taxa cluster more by development and tissue location than by spore morphology; 4) the tetracapsulids branched off early in myxozoan evolution, perhaps reflected by their having bryozoan, rather than annelid hosts; 5) the morphology of actinosporeans offers little information for determining their myxosporean counterparts (assuming that they exist); and 6) the marine actinosporeans from Australia appear to form a clade within the platysporinid myxosporeans. Ribosomal DNA sequences have also enabled development of diagnostic tests for myxozoans. PCR and in situ hybridisation tests based on rDNA sequences have been developed for Myxobolus cerebralis, Ceratomyxa shasta, Kudoa spp., and Tetracapsula bryosalmonae (PKX). Lectin-based and antibody tests have also been developed for certain myxozoans, such as PKX and C. shasta. We also review important diseases caused by myxozoans, which are emerging or re-emerging. Epizootics of whirling disease in wild rainbow trout (Oncorhynchus mykiss) have recently been reported throughout the Rocky Mountain states of the USA. With a dramatic increase in aquaculture of fishes using marine netpens, several marine myxozoans have been recognized or elevated in status as pathological agents. Kudoa thyrsites infections have caused severe post-harvest myoliquefaction in pen-reared Atlantic salmon (Salmo salar), and Ceratomyxa spp., Sphaerospora spp., and Myxidium leei cause disease in pen-reared sea bass (Dicentrarchus labrax) and sea bream species (family Sparidae) in Mediterranean countries.     

Challenges of metamorphosis in invertebrate hosts: maintaining parasite resistance across life‐history stages

1. Insects lack the acquired immune system of vertebrates, but there is some evidence that insect immunity can be primed against an encountered pathogen to mitigate the intensity of future infections within a life stage. 2. Many invertebrates have multiple life‐history stages separated by complete metamorphosis, but different life stages can often be infected by the same pathogens, and the potential loss of immune priming during metamorphosis could therefore have detrimental effects on the host. Evidence that invertebrate immune priming can persist through metamorphosis is still missing, and consequently it is unclear how host–parasite interactions change across different life‐history stages in the context of infection history. 3. By experimentally manipulating the infection history of the flour beetle Tribolium confusum, we show that intestinal gregarine parasite infections during the larval stage reduced parasite load in adults, demonstrating that a host‐controlled mechanism for parasite resistance can persist through complete metamorphosis in insects. 4. Infections reduced larval developmental rates and increased host mortality but only during the crucial metamorphic stage, indicating that parasites impact multiple life stages. In general, our results demonstrate that invertebrates can show surprisingly robust immune priming despite dramatic physiological changes and protect hosts across completely different life‐history stages.     

Ovoviviparity and viviparity in the Diptera

The taxonomic distribution and evolution of viviparity in Diptera is critically reviewed. The phenomenon ranges from ovoviviparity (eggs deposited at an advanced stage of embryonic development; larva emerges immediately after deposition), through viviparity (larva hatches inside female before deposition) to pupiparity (offspring deposited as pupa). Some Diptera are known to be facultatively viviparous, which is hypothesized to be a step towards the evolution of obligate viviparity. Obligate viviparity is found to comprise unilarviparity (single large larva in maternal uterus) which evolved many times independently, the rare oligolarviparity (more than one but not more than 12 larvae) and multilarviparity (large numbers of developing eggs or larvae in uterus) which is typical for the two largest clades of viviparous Diptera. Unilarviparity is either lecithotrophic (developing larva nourished by yolk of egg) or pseudo-placental (larva nourished by glandular secretions of mother). Viviparity has clearly evolved on many separate occasions in Diptera. It is recorded in 22 families, and this review identifies at least 61 independent origins of viviparity. Six families appear to have viviparity in their ground-plan. Some families have a single evolution of viviparity, others multiple evolutions. Guimaraes' model for the evolution of viviparity in Diptera is tested against phylogenetic information and the adaptive significance of viviparity is reviewed in detail. Possible correlations with life-history parameters (coprophily, parasitism, breeding in ephemeral plant parts, malacophagy and adult feeding habits – especially haematophagy) are analysed critically, as are potential advantages (shorter larval life, less investment in yolk by mother, protection of vulnerable stages, better access to breeding substrates, predation on competitors). Morphological constraints, adaptations and exaptations are reviewed, including the provision of an incubation space for the egg(s), the positioning of the egg(s) in the uterus, and maternal glands. The main morphological adaptations include greater egg size, reduction of egg respiratory filaments, thinning of chorion, modified larval respiratory system and mouthparts, and instar skipping. Female morphology and behaviour is particularly strongly modified for viviparity. The terminalia are shortened, the vagina is more muscular and tracheated, and the ovaries of unilarviparous species have a reduced number of ovarioles with alternate ovulation. Many of the final conclusions are tentative, and a plea is made for more detailed morphological and experimental study of many of the viviparous species. Viviparity in Diptera provides a fascinating example of multiple parallel evolution, and a fertile field for future research.     

Suitability of the Osmotic Shock Procedure for the Analysis of Membrane Transport in Root Tips of Zea mays L.

Root tips of Zea mays L. previously subjected to osmotic shockwere studied as to uptake and efflux of glucose and uptake ofphosphate, as well as release of protein and other Lowry-positivesubstances. The osmotic shock procedure applied was similarto that frequently used in order to release periplasmic proteinsfrom bacteria. After treatment with hypertonic solutions of sorbitol (>0?3M) the uptake of phosphate and glucose is reduced and proteinis released into the medium. All osmotic treatments leadingto a significant reduction of either glucose or phosphate uptakeare accompanied by a strongly increased release of glucose andLowry-positive substances. Damage of plasma membrane barrierfunction can be directly observed by the uptake of Evans Blue(Gaff and Okong'o-Ogola, 1971) into the cells involving mainlyolder vacuolated rhizodermal cells. The occurrence and extent of the alterations of membrane semipermeabilityare strongly dependent on the duration of exposure to and theconcentration of the sorbitol solution used. The velocity ofthe osmotic transitions (from hypotonic to hypertonic and viceversa) is of minor importance. Sensibility of cells to osmotic stress increases with differentiationand vacuolation. Conditions for a selective reduction of phosphateuptake seem to occur when only meristem and near tip regionssubjected to a mild osmotic shock are used.     

中国沼蝇科二新种（双翅目：沼蝇科）

本文记述了采自中国东北沼蝇科的二个新种:Pherbellia orientalis sp.nov.属于该属的P.dorsata种团,其主要特征是翅部分为黑色,前足基跗节为鲜明的白色;Elgivamanchuricasp.nov.与该属的一个种E.divisa(Loew)相似,但可从新种光裸的前胸腹板和不同形状构造的雄性外生殖器予以区别。 新种的模式标本保存于德国波恩Alexander Koenig博物馆。     

Secondarily reduced foreleg armature in Perochaeta dikowi sp.n. (Diptera: Cyclorrhapha: Sepsidae) due to a novel mounting technique

Abstract.  The males of almost all sepsid species have strongly modified forelegs that are used to clamp the female's wingbase during mounting. Here, we describe a new species in the genus Perochaeta whose males have unmodified forelegs. We use DNA sequence data for ten genes to reconstruct the position of Perochaeta on the phylogenetic tree for Sepsidae, and reveal that the lack of foreleg armature in Perochaeta dikowi sp.n. is secondary. Through the study of the mating behaviour of the new species, we demonstrate that the loss of armature is correlated with a new mounting technique during which the males of P. dikowi do not use the foreleg to clamp the female's wingbase. Instead, the male approaches the female from behind and bends his abdomen forwards in order to establish genital contact. Our study shows how data from morphology, phylogenetics, and behavioural biology can complement each other to yield a deeper understanding of how changes in morphology and behaviour are correlated.     

Grooming and pollen manipulation in bees (Apoidea): the nature and evolution of movements involving the foreleg

Three modes of self cleaning occur in insects: nibbling by the maxillae, scraping one structure by another in one direction only, and rubbing back and forth while the respective parts are in continuous contact. This paper describes a comprehensive and comparative account of this behaviour in bees, with special reference to the cleaning of or by the forelegs. Bees, like all Hymenoptera, clean various parts of the head, including the mouthparts and the antennae, with the forelegs. Lower Hymenoptera scrape each antenna with either foreleg; in the species of Aculeata that possess the antenna cleaner (strigil) on the foreleg, only the ipsilateral leg is used. The thoracic dorsum of most bees, as in many sphecoid wasps, is scraped in a forward direction by the middle leg; Triepeolus spp., however, use the hind leg, and the Anthophorinae the foreleg. Some beetles and lacewings clean their forelegs in the mouthparts by nibbling and scraping. Most higher Hymenoptera as a rule scrape the foreleg between the ipsilateral maxilla and the labium; bees, however, clamp the foreleg between the flexed ipsilateral middle leg and then scrape it. An evolution of this behaviour is postulated via several intermediate forms derived from original stepping movements. Halictidae and Andrenidae clamp the foreleg for scraping underneath the middle tibia, whereas all other bees nearly always clamp it underneath the middle basitarsus. Very similar movements are used in various species for transferring pollen, oil, or nest materials from the foreleg to the middle leg. It is argued that the original way of pollen carrying in bees must have been by filling the crop through direct eating or by scraping pollen off the foreleg between the ipsilateral maxilla and the labium. The latter movement is widespread among bees and is homologous to the normal foreleg cleaning in the mouthparts of most other Hymenoptera. The efficiency of this behaviour is enhanced in many lower bees by a comb on the galea, which is the homologue of a similar structure widespread among aculeate wasps. In higher bees, Apidae and Anthophoridae, the galeal comb is replaced by an equifunctional stipes comb. Many bees have neither of these types of maxillary combs.     

A Weichselia-Stiehleria-Matoniaceae community within the Quedlinburg Estuary of Lower Cretaceous age

The Hauterivian community of Nathorstiana and Hausmannia and the Barremian community of Weichselia, Stiehleria, Matonidium and Phlebopteris are interpreted as river-shore communities under maritime influence. A reconstruction of Weichselia reticulata is presented, in which the pronounced dimorphism of the fronds raises problems which cannot be interpreted in terms of normal Recent xeromorphic ferns.