Description de Quelques Espèces de Ciliés Hyménostomes des Genres Sathrophilus Corliss, 1960, Cyclidium O. F. Müller, 1786, Histiobalantium Stokes, 1886

RESUME. Les structures buccales de Sathrophilus vernalis Dragesco & Grolière, 1969 sont détaillées. La morphogenèse buccale de l'opisthe, semi-autonome, avec participation du scuticus et d'une cinétie postorale droite, s'accompagne d'une re-constitution de l'appareil buccal du proter. La morphologie buccale de Cyclidium sphagnetorum Šràmek-Hušek, 1949 est comparée à celles de Cyclidium citrullus Cohn, 1865 et Cyclidium glaucoma O. F. Müller, 1786. La stomatogenèse Histiobalantium majus Kahl, 1933 débute par une prolifération du scuticus vers la gauche.
SYNOPSIS. Buccal structures of Sathrophilus vernalis Dragesco & Grolière, 1969 are described. The semiautonomous buccal morphogenesis of the opisthe, involving the participation of the scuticus and the right postoral kinety, is accompanied by the reconstitution of the buccal apparatus of the proter. The buccal structure of Cyclidium sphagnetorum Šràmek-Hušek, 1949 is compared to those of Cyclidium citrullus Cohn, 1865 and Cyclidium glaucoma O. F. Müller, 1786. Stomatogenesis of Histiobalantidium majus Kahl, 1933 starts with a proliferation of the scuticus towards the left.     

Assessment of the importance of fish predation versus copepod predation on life history traits of Daphnia hyalina

Daphnia hyalina is a cladoceran present throughthe whole year except for late summer in Maranhão,a meso-eutrophic reservoir in central Portugal. Apartfrom the influence of food, both vertebrate andinvertebrate predation pressures seem to have aneffect on D. hyalina population dynamics.Enclosure experiments were designed to assess therelative importance of both types of predation. Afterthe summer crash, D. hyalina reached highernumbers in the fishless enclosures than in the lakedespite of high predation pressure upon juveniles byAcanthocyclops robustus. Fish predation upon thelargest individuals, especially large egg bearingfemales, was responsible for the lower fertility ofthe open water population when compared with theenclosure population. In the enclosures an increase intail spine length was observed. The longer tail spineprobably offered protection from copepod predation,allowing at least some of the juveniles to coexistwith their potential predator and reach the adultstage, less susceptible to copepod predation.     

Components of morphological variation in Baikalian endemial cyclopid Acanthocyclops signifer complex from different localities

Use of traditional methods for morphological studies only permits the analysis of a small part of the information embodied in morphological structures. Besides comparing populations using the mean values of characters which allows one to estimate their morphological similarity, analysis of variation among individuals within a population can be informative. Variation among individuals consists of factorial and stochastic components. The factorial component is an upper estimate of genetic heterogeneity and thus permits one to evaluate the population's adaptability. The stochastic component (estimated by fluctuating asymmetry, i.e. random deviations from perfect bilateral symmetry), being a measure of developmental stability, is an indicator of a population's fitness. Assessment of measurement error is necessary for assessment of the true value of the stochastic component and for selection of the most informative characters. Such analysis allows one to extract additional information from morphological data in comparison with methods traditionally used on copepods. This approach was applied to an analysis of morphological variation in the study of the Baikalian endemic cyclopoid Acanthocyclops signifer (Mazepova) from three different isolated localities. Characters typically used in studies of taxonomy of this group are considered here. Measurement error was rather high (more than 50% of the stochastic component), which can be explained by technical difficulties of measuring the characters. All populations differ in the mean values of the characters. This shows the taxonomic heterogeneity of this group and reveals the necessity of its taxonomic revision. Populations also differ in the level of stochastic and factorial components of the total variance. The data are interpreted from the point of view of taxonomy and the possible evolution of the group.     

In vitro studies of Coelomomyces punctatus from Anopheles quadrimaculatus and Cyclops vernalis

Attempts to grow mycelium of Coelomomyces punctatus from Anopheles quadrimaculatus larvae were made using more than 50 combinations of known vertebrate and invertebrate tissue culture media and microbiological media. Growth and/or differentiation of mycelium into sporangia were observed in several media. Significant growth of hyphal fragments and differentiation into young resting sporangia occurred in conditioned Mitsuhashi-Maramorosch insect tissue culture medium. This medium was conditioned by growth for 3 weeks in it of Varma's Anopheles stephensi tissue culture cells and was supplemented with 20% heat-inactivated fetal bovine serum and a synthetic tripeptide, glycyl-histidyl-lysine. Limited growth and elongation of lateral hyphal branches and subsequent development into resting sporangia with typical outer wall markings and pigmentation of mature forms were observed in a modified brain-heart infusion medium. Some media stimulated hyphae to develop into smooth-walled, spherical bodies of size and appearance typical of young sporangium initials but with no further maturity. In most media, no growth or development of mycelium occurred, but the fungus remained alive for 2–4 weeks. Mycelium of C. punctatus dissected from Cyclops vernalis did not grow and develop in any of the media utilized. However, in one case the mycelium differentiated into gametes shortly after dissection into modified brain-heart infusion medium.     

Genetic architecture of the cryptic species complex of Acanthocyclops vernalis (Crustacea: Copepoda). II. Crossbreeding experiments, cytogenetics, and a model of chromosomal evolution

Collectively, populations of Acanthocyclops vernalis, a species complex of freshwater copepods, are remarkably similar as to morphology and DNA content, despite variability in chromosome number. Reproductive isolation had been reported among some populations, but with each new investigation the species boundaries and factors that may influence them appeared less clear. To clarify the pattern of biological species within this group of populations, we adopted a comprehensive approach and examined patterns of reproductive isolation in populations for which morphology, chromosome number, DNA content, and 18S rDNA sequences are known. In this study we established nine isofemale lines from four sites in Wisconsin and performed 266 crosses. Crosses within and among these lines were used to relate the degree of reproductive isolation to chromosome differences and to construct a model to explain the origin and maintenance of chromosome number variability. Different gametic and somatic chromosome numbers were observed among specimens within some isofemale lines. In a few cases, gametes with different haploid numbers were produced by a single female. Matings within isofemale lines always produced at least some reproductively successful replicate crosses (produced viable, fertile offspring). Crosses between lines from the same site showed reduced success relative to within-line crosses. Crosses between populations from distant sites showed limited genetic compatibility, producing viable, fertile F1 offspring but infertile F2 adults. One cross between lines with different chromosome numbers (one with 2n = 8 and one with 2n = 10) produced fertile viable offspring, which reproduced for at least 60 generations. These hybrids had either eight or nine chromosomes in the third generation of inbreeding, and eight chromosomes after 20 generations. These hybrids also had reduced nuclear DNA contents at the third generation, a level that persisted through the 20th generation. Successful backcrosses between some hybrids and their parental lines further demonstrated the potential for genetic compatibility among forms with different chromosome numbers. We propose a model in which alterations due to Robertsonian fusions, translocations, and/or loss of chromosomal fragments generate heritable variation, only some of which leads to reproductive isolation. Hence, some of the criteria traditionally used to recognize species boundaries in animals (morphology, DNA content, chromosome number) may not apply to this species complex.     

Induction and costs of tail spine elongation in Daphnia hyalina×galeata: reduction of susceptibility to copepod predation

1. Seasonal field data showed a positive correlation between the tail spine length of Daphnia hyalina × galeata and the density of the copepod Acanthocyclops robustus . Laboratory experiments were designed to assess the mechanisms underlying the induction of tail spine elongation and to test whether this morphology reduced predation on Daphnia juveniles.
2. Both the elongated tail spine morph and control spine morph produced progeny with elongated tail spine when exposed to copepods. Instar increments, calculated from individual body length, showed that individual growth decreased in the presence of copepods. This decrease in individual growth was less pronounced in spined morphs relative to control morphs.
3. Copepods exhibited significantly higher feeding rates on control morph juveniles compared to elongated tail spine morph juveniles.
4. All Daphnia matured at instar 5 even though the control morph neonates took 24–30 more hours to mature in the presence of copepods than in the absence of copepods. Enlarged body and spine lengths of progeny coincided with reduced progeny number during the first six reproductive instars. The disadvantage of the reduced offspring number produced per female was balanced by enhanced survivorship of progeny subjected to copepod predation.     

Divergence in the calling songs between sympatric and allopatric populations of the southern wood cricket Gryllus fultoni (Orthoptera: Gryllidae)

In the eastern United States the wood cricket Gryllus fultoni (Orthoptera: Gryllidae) occurs in sympatry with G. vernalis in an area between eastern Kansas and west of the Appalachian Mountains. Calling songs were recorded from 13 sympatric and allopatric localities. Both field and laboratory recordings showed that chirp rate (CR) and pulse rate (PR) overlapped extensively between allopatric populations of G. fultoni and sympatric populations of G. vernalis; by contrast, there was little or no overlap in these variables between sympatric populations of these two species. Divergence in PR and CR between the two species was thus greater in areas of sympatry than in areas of allopatry. Our field and laboratory studies of G. fultoni calling songs thus demonstrate the pattern expected of character displacement and support the genetic assumptions of this hypothesis. Other possible explanations for the sympatric divergence such as ecological character displacement and clinal variation are discussed.     

Speciation and Phylogenetic Distances within Paxillus s. str. (Basidiomycetes, Boletales)

Abstract: This study aimed to elucidate the phylogenetic relationships within Paxillus 5. str. Collections of the Paxillus involu-tus complex from different habitats have been compared. DNA sequence data were generated from the nuclear encoded 28S gene and the ITS region. Phylogenetic analyses of the two data sets showed three clearly differentiated groups within Paxillus s. str. Collections from gardens and park areas under Betula, Cory-lus, Populus, Quercus and Tub showed to have a very close relationship to the North American species Paxillus vernalis , but are separated from P. involutus collections found in forests as well as from P. filamentosus . Possible taxonomic conclusions are discussed.     

An ecological validation of a taxonomic distinction: the ecology of Acanthocyclops vernalis and A. robustus (Crustacea: Gopepoda)

Long-standing taxonomic problems involving the vernalis complex of freshwater cyclopoid copepods of the genus Acanthocyclops have now been largely resolved, at least in Europe. Two species, A. vernalis and A. robustus , are recognizable on unambiguous morphological criteria, but each shows variation of a simular kind. Ecological data confirm this distinction. Ecological preferences are themselves reflected by the distribution patterns displayed in a restricted, but not small, area encompassing a diversity of environments. A. vernalis is eurytopic but displays a preference for acidic, calcium-poor waters, low in total ions, and is exclusively benthic. By contrast A. robustus does not colonize strongly acidic waters (min. pH 6.42) and is restricted to alkaline, or weakly acidic, nutrient-rich habitats. In some situations it becomes pelagic. While A. vernalis extends throughout the area frequented by A. robustus , the latter fails to colonize large tracts of upland country for which A. vernalis shows a definite preference and where it is common and widespread.