PKX,the Causative Agent of Proliferative Kidney Disease (PKD) in Pacific Salmonid Fishes and Its Affinities with the Myxozoa1

Proliferative kidney disease (PKD), caused by an unclassified protozoan (PKX), is reported from Pacific salmon, Oncorhynchus tshawytscha (Walbaum) and O. kisutch (Walbaum), and steelhead trout, Salmo gairdneri Richardson, held at the Mad River Hatchery in California, USA. The cumulative mortality attributed to the disease was 95, 13, and 18% respectively. The mortalities were greatest at mean water temperatures of 12-14°C during July 1983. The ultrastructure of the PKX organism and its associated pathology during clinical disease in all three species were consistent with those of the parasite in rainbow trout (Salmo gairdneri) as described in European outbreaks. Significant mortalities did not occur after August, at which time the parasite could no longer be detected in the salmon species. The steelhead continued to exhibit parasites in the kidney interstitium and epithelium and lumens of the tubules. Myxosporidan trophozoites and developing spores were also observed in the lumens of the kidney tubules of these fish. Although a mixed infection with another parasite may have occurred, evidence suggests that the myxosporidans are later stages of PKX. They were only observed in fish exposed to water with the infective stage and were particularly prominent in recovering fish. The PKX organism is similar to UBO, an unclassified protozoan of carp suspected to be an early stage of Sphaerospora renicola Dyková & Lom. Both parasites infect the blood and kidney, divide by endogeny, and are released by disintegration of the primary mother cell. The intraluminal myxosporean forms show similarities to Sphaerospora spp. in that they are monosporous and sporoblasts are formed within pseudoplasmodia. It is possible that PKX migrates to the lumen of the kidney tubule and subsequently sporulates. If the myxosporean forms are later stages of PKX, then it would belong to the phlyum Myxozoa.     

Mating behaviour in the endangered Sonoran topminnow: speciation in action

Two species of the endangered Sonoran topminnow, Poeciliopsis occidentalis and P. sonoriensis, occur in two isolated drainage systems in southeast Arizona, U.S.A., and are allopatric throughout their range. Although these two taxa are morphologically very similar, and have been previously described as the same species or subspecies, several molecular studies have since indicated that they differ more than their morphology suggests. To determine whether the behaviours of the two species function as premating barriers to reproduction, we investigated their mating preferences and behavioural patterns in a laboratory setting. Results from no-choice mating observations showed that the mating behaviours of the two species differ. Observations conducted during multiple-choice mating trials provided evidence of assortative mating, suggesting an early stage of premating reproductive isolation.     

Correlates of substitution rate variation in mammalian protein-coding sequences

Background  

Rates of molecular evolution in different lineages can vary widely, and some of this variation might be predictable from aspects of species' biology. Investigating such predictable rate variation can help us to understand the causes of molecular evolution, and could also help to improve molecular dating methods. Here we present a comprehensive study of the life history correlates of substitution rate variation across the mammals, comparing results for mitochondrial and nuclear loci, and for synonymous and non-synonymous sites. We use phylogenetic comparative methods, refined to take into account the special nature of substitution rate data. Particular attention is paid to the widespread correlations between the components of mammalian life history, which can complicate the interpretation of results.     

A molecular approach to fertilization. II. Viability and artificial fertilization of Xenopus laevis gemetes

Conditions necessary for procuring, handling, and storing Xenopus laevis gametes have been investigated in order to develop a simple and reliable method for artificial fertilization. Temperature, sperm concentration, and ionic strength influence sperm and/or egg viability. Extension of the fertilizing capacity of sperm suspensions could be correlated with reversible repression of sperm motility. In the case of various salt solutions used for testes maceration, inhibition of sperm motility was primarily a function of the ionic strength. However, there was some specificity in the salt employed as KCl and CaCl₂ solutions gave anomalous results in comparison with those obtained with other salt solutions. The fertilizability of Xenopus laevis eggs could be extended by shedding the eggs in DeBoers solution. Using this information a simple reliable method for artificial fertilization of Xenopus laevis gametes has been described.     

Nonrandom association between Huntington disease and two loci separated by about 3 Mb on 4p16.3.

The gene for Huntington disease (HD) has been localized close to the telomere on the short arm of chromosome 4. However, refined mapping using recombinant HD chromosomes has resulted in conflicting findings and mutually exclusive candidate regions. Previously reported significant nonrandom allelic association between D4S95 and HD provided support for a more proximal location for the defective gene. In this paper, we have analyzed 17 markers, spanning approximately 6 Mb of DNA distal to locus D4S62, for nonrandom association to HD. We confirm the previous findings of nonrandom allelic association between D4S95 and HD. In addition, we provide new data showing significant nonrandom association between HD and 3 markers at D4S133 and D4S228, which are approximately 3 Mb telomeric to D4S95.     

Coat variants in cats. Gametic disequilibrium between unlinked loci

Examination of the extent and pattern of gametic disequilibrium between nine pairs of unlinked loci in four large samples of cats revealed large and consistent values. These observations appear inconsistent with either genetic drift or gene flow as causes of the disequilibrium. On the other hand, the extent of epistatic selection necessary to generate the majority of these values appears reasonable.     

Temporary tracheal occlusion in fetal sheep with lung hypoplasia does not improve postnatal lung function.

Prolonged fetal tracheal occlusion (TO) accelerates lung growth but leads to loss of alveolar epithelial type II (AE2) cells. In contrast, temporary TO leads to recovery of AE2 cells and their ability to produce surfactant. The aim of this study was to determine the effects of temporary TO in fetal sheep with lung hypoplasia on postnatal lung function, structure, and surfactant protein mRNA expression. Diaphragmatic hernia (DH) was created in 22 fetal sheep at 65 days of gestation. TO was performed between 110 days of gestation and full term (DH/TO, n = 7) and between 110 and 130 days of gestation (DH/TO+R, n = 6). Sham-operated fetuses (n = 11) served as controls. Lambs were delivered at approximately 139 days of gestation, and blood gas tensions were monitored over a 2-h resuscitation period. Temporary TO increased growth of the hypoplastic lung and restored surfactant protein mRNA expression and AE2 cell density but did not improve respiratory function above that of animals that underwent prolonged TO; DH/TO and DH/TO+R lambs were hypoxic and hypercapnic compared with Sham animals. Lung compliance remained low in DH/TO+R lambs, most likely as a consequence of the persistent increase in alveolar wall thickness in these animals.