Some ascaridoid nematodes of fishes: Heterocheilinae

Ascaridoid nematode species reported from fishes and relegated to genera listed by Sprent (1983) within the Heterocheilinae are reviewed. The following species are considered to belong in this category: Dujardinascaris malapteruri (Baylis, 1923) [= D. graberi] from Malapterurus electricus, and possibly Mormyrops engystoma, in Africa; Brevimulticaecum regoi n. sp. from Potamotrygon motoro in South America; Brevimulticaecum heterotis (Petter, Vassiliadès & Marchand, 1979) from Heterotis niloticus in Africa; Brevimulticaecum scleropagi Khalil, 1984 from Scleropages leichardti and S. jardini in Papua New Guinea and Australia. The view is expressed that these heterocheiline species are secondarily derived from related species in crocodilians. It is proposed that Gedoelstascaris Sprent, 1978 is a synonym of Brevimulticaecum Mosgovoy, in Skrjabin et al., 1952 and two new combinations are proposed: Brevimulticaecum vandenbrandeni (Baylis, 1929) and Brevimulticaecum australiensis (Baylis, 1931).     

Some ascaridoid nematodes of fishes: Paranisakis and Mawsonascaris n. g.

As a result of examination of type-material and other specimens representing species previously assigned to Paranisakis Baylis, 1923, it is proposed that this genus be reduced to one species, namely P. squatinae Baylis, 1923. The other species are distributed as follows: pastinacae Rudolphi, 1819, australis Johnston & Mawson, 1943 and laymani Mozgovoy, 1950 are assigned to a new genus Mawsonascaris. The main features differentiating Mawsonascaris from Paranisakis are: dentigerous ridges on the lips (absent in Paranisakis), digitiform extensions of the labial pulp (absent in Paranisakis), excretory pore posterior to the nerve-ring (anterior to the nerve-ring in Paranisakis) and long filiform spicules (short and stout in Paranisakis). The following new host records are reported: Rhinobatos cemiculus for P. squatinae; and Aptychotrema banksii, Rhinobatos batillum, Rhynchobatus dijddensis and Taeniura lymma for M. australis. Specimens were not available from teleosts. It is considered that the proposal of Yamaguti (1961) to raise the subgenus Ortoanisakis Mozgovoy, 1951 to full generic status be upheld provisionally, Ortoanisakis containing species from teleosts, formerly in Paranisakis, but described as having no dentigerous ridges and no gubernaculum. These include O. lophii (Yamaguti, 1935), O. halieutaeae (Yamaguti 1941), O. muraenesocis (Yamaguti, 1935), O. lophii hoplobrotulae (Yamaguti, 1941) and O. sciaenae Khan & Begum, 1971. The remaining species formerly in Paranisakis are relegated to the status of species inquirendae.     

On interrelation between genetic systematics and genomics

Review papers describing recent achievements of genomics usually do not pay attention to direct interrelation between genomics and genosystematics (DNA-systematics). Genomics on general is based in complete DNA sequencing of genomes. Initial aim of genosystematics was the same. Absence of historical perspective in review papers devoted to genomics decreases its value. In case it is done deliberately it becomes the problem of scientific ethics. It is postulated that genomics is a natural stage of genosystematics (DNA-systematics) development. Russian scientists were among the founders of these branches of biology.     

Trait divergence between endemic plants of Aegean islands and their widespread congeners

Plant Ecology - Evolutionary processes on islands, and the attributes of rare plant species restricted to islands have received increasing attention in the last decade, but most of the evidence...     

Hybrid crosses and the genetic basis of interspecific divergence in lifespan in Pristionchus nematodes

Characterizing the genetic basis of among‐species variation in lifespan is a major goal of evolutionary gerontology research, but the very feature that defines separate species – the inability to interbreed – makes achieving this goal impractical, if not impossible, for most taxa. Pristionchus nematodes provide an intriguing system for tackling this problem, as female lifespan varies among species that can be crossed to form viable (although infertile) hybrids. By conducting reciprocal crosses among three species – two dioecious (long‐lived Pristionchus exspectatus and short‐lived Pristionchus arcanus) and one androdioecious (short‐lived Pristionchus pacificus) – we found that female lifespan was long for all hybrids, consistent with the hypothesis that the relatively short lifespans seen for P. pacificus hermaphrodites and P. arcanus females are caused by independent, recessive alleles that are masked in hybrid genomes. Cross‐direction had a small effect on survivorship for crosses involving P. exspectatus, indicating that nuclear–mitochondrial interactions may also influence Pristionchus longevity. Our findings suggest that long lifespan in P. exspectatus reflects the realization of an ancestral potential for extended longevity in the P. pacificus species complex. This work demonstrates the utility of interspecific hybrids for ageing research and provides a foundation for future work on the genetic architecture of interspecific lifespan variation.     

Biochemical systematics of some serranids from Taiwan (Pisces, Serranidae)

An electrophoretic study of genetic variation at 17 loci in ten serranids belonging to three subfamilies (Anthiinae, Epinephelinae and Serraninae) was carried out to assess their systematic relationships. A relationship dendrogram was constructed from the fenetic identities calculated b Nei's method for all pairwise cornarisons. These fishes were divided into three major welldefined groups: Anthiinae, Epinepielinae and Serraninae. Although the relationships among them appear slightly different from that deduced from morphological features; e. g., Serraninae are distant from Anthiinae and Epinephelinae biochemically, but are closer to Antiinae than to Epinephelinae morphologically. However, a tendency for an increase of the genetic distance in higher categories is obvious (Table 5).     

Biochemical and immunological characterization of genetic variants of phosphoglucose isomerase from mouse

Two electrophoretic variants of phosphoglucose isomerase (PGI) were purified from whole body extracts of DBA/2J and C57BL/6J mice by a substrate-affinity elution from an 8-(6-aminohexyl) amino-ATP-Sepharose column followed by preparative isoelectric focusing. Both PGI variants were shown to be dimers of the same molecular weight, sedimentation coefficient, and K _m for fructose-6-phosphate. The isoelectric points were found to be 8.4 and 8.7 for variants from DBA/2J and C57BL/6J mice, respectively. Differential thermal stability was observed for the two variants in 0.1 m tris-HCl buffer, pH 8.0, at 54 C; the half-lives of the purified PGI from DBA/2J and C57BL/6J mice were shown to be 3.4 and 1.8 min, respectively, under those conditions. Similar differences were observed for the enzyme variants in the crude homogenates. Antisera against PGI from DBA/2J mice were raised in rabbits. The variants from DBA/2J and C57BL/6J mice showed no significant differences in their respective inactivation curves by the antisera. Results of amino acid composition analyses and peptide mappings of the two PGI variants indicate that the genetic variation of this enzyme might result from a single charged amino acid substitution.D. J. C. is a National Institutes of Health Visiting Fellow.     

Biochemical methods and reasoning in systematics

Biochemische Methoden und Beweisführung in der Systematik Jene Systematik, welche in der Arbeit als “genetische” bezeichnet wird, kann mit einem biologischen System arbeiten, in welchem die übereinstimmung zwischen Genen und ihren phaenotypischen Auswirkungen (Nukleinsäuren, Eiweiβe) gröβer ist als bei anderen Methoden, denen phaenotypische Gestaltungen wie Metaboliten, morphologische, anatomische, Verhaltens- oder andere Merkmale zugrunde liegen. Grundsätzlich eröffnet diese geringe Differenz im Niveau der Beziehungen zwischen Genen und ihren phaenotypischen Auswirkungen die Möglichkeit, Schwierigkeiten bei der Festlegung bedeutsamer “taxonomischer Merkmale” auszuweichen, und es wird auβerdem möglich, Definitionen zu klären und den “genetkchen Abstand” zu messen. Die Biochemie der Nukleinsäuren und der Eiweiβe ermöglicht eine systematische Vorstellungswelt, welche verschieden ist von jener Systematik, die auf Anatomie und Morphologie aufgebaut ist. Es ergeben sich daher wertvolle Erweiterungen und Hilfen für Systematiker und Evolutionsforscher, welche sich urn Klassifikationen und die Erarbeitung von Stammbäumen mühen.     

A simple technique for recovering larval ascaridoid nematodes from the flesh of marine fish

This paper describes and evaluates the efficiency of a simple technique for recovering larval ascaridoid nematodes (Anisakis simplex and Pseudoterranova decipiens) from the flesh of marine fish. The technique involves mechanical disintegration of the flesh in a domestic food processor, followed by visual inspection of diluted portions of the resulting homogenate under short-wave ultraviolet light. The nematodes, which remain intact, fluorescence brightly and are easily detected, particularly if the musculature has been frozen and thawed previously. The technique recovers a much higher proportion of the total number of nematodes than candling and slicing, is more rapid than pepsin-HCl digestion, and would therefore be suitable for large-scale surveys of ascaridoid nematodes in the flesh of marine fish.     

Effects of wolbachia on genetic divergence between populations: mainland-island model

Cytoplasmic incompatibility (CI) induced by intracellular bacteriais a possible mechanism for speciation. Growing empirical evidencesuggests that bacteria of the group Wolbachia may indeed actas isolating factors in recent insect speciation. Wolbachiaare cytoplasmically transmitted and can cause uni- or bidirectionalCI. We present a mainland-island model to investigate how muchimpact Wolbachia can have on genetic divergence between populations.In the first scenario we assume that the island population hasdiverged at a selected locus and ask whether genetic divergencewill be maintained after introduction of migration from themainland. In the second we explore whether divergence will originateunder migration. For simplicity, the host organisms are modeledas haploid sexuals. Simulations show that if each populationis initially infected with a different strain of Wolbachia,then higher levels of divergence occur at the locally selectedlocus than in the absence of Wolbachia. A weaker effect is seenwhen there is only unidirectional CI caused by a single strainof Wolbachia on the island. CI increases divergence becauseit reduces effective migration between mainland and island.Migrants suffer from being confronted with the wrong CI systemand this also applies to their matrilineal descendants. Moreover,there is a strong linkage disequilibrium between host genotypeand infection state, which helps to maintain Wolbachia differencesbetween the populations in the face of migration A sex biasin migration can either increase or decrease the effect of Wolbachiaon divergence. Results support the view that Wolbachia has thepotential for increasing divergence between populations andthus could enhance probabilities of speciation.     

Sheep blood polymorphism and genetic divergence between French Rambouillet and Spanish Merino: role of genetic drift

Rambouillet sheep originating from Spanish Merino have been maintained in France as a small and closed flock since their importation. After 190 years of independent evolution, the flock has markedly differentiated from its Spanish parental population. The observed differences between them were characterized by the fixation in Rambouillet of the Mb and F30 alleles, which occurred in Spanish Merino with frequencies of 0.90 and 0.80 respectively (at two distinct blood group loci M and F30) and by the absence in Rambouillet of other alleles or phenogroups (at the Tf and the A, B, C blood group loci) which were observed in Spanish Merino with frequencies ranging from 0.10 to 0.28. On the basis of their phenotypic distributions at 11 blood polymorphic loci, the two populations differed significantly from each other (total chi 2 values = 352.62, 23 df, P less than 0.001). By comparing the observed magnitude of gene frequency differences between Rambouillet and Spanish Merino with the estimate of inbreeding coefficient for Rambouillet obtained from pedigrees, it appeared that the observed genetic differences could be attributed to the evolutionary change due to random drift in the small and closed flock of Rambouillet.     

A model of immunological distances in systematics

While immunological distances among taxa have had wide use in systematics, there has been some doubt about their utility because of the observed non-metricity of such distance matrices. A model is presented here relating observed immunological distance to the actual number of antigenic site differences between taxa. This model accounts for the observed departures of these distances from the metric condition of reciprocity and triangle inequality. Based upon the model, two procedures are suggested for the transformation of immunological distances to metric distances appropriate for phylogenetic analysis. The model implies that the usual scaling adjustments applied to the immunological distance matrix are inappropriate; however, the same transformation applied instead to an initial similarity matrix will solve a scaling problem. Non-reciprocity of the distances is shown to remain a problem independent of this initial scaling problem. It is suggested that further transformation of these re-scaled distances may be obtained through an extension of the ADCLUS procedure developed in psychology. This approach suggests a general strategy for a transformation to metric distances, given a particular model of non-metricity for the data.