Experimental hybridization between catfishes of the families Clariidae and Pangasiidae in Thailand

Synopsis Hybrids between the clariid speciesClarias macrocephalus andC. batrachus and the pangasiid speciesPangasius sutchi were obtained by hormone injection of brood stock and artificial fertilization. Pure parental crosses as well as all possible hybrid combinations were obtained. Fertility, hatchability, and post-yolk absorption survival was high (66–99%) in all pure parental crosses and in all crosses between the two species ofClarias. In crosses betweenClarias andPangasius fertilization was also very high (68–97%) but hatchability varied from 11 to 23% and post-yolk absorption survival from 0% inPangasius sutchi ×Clarias batrachus to about 50% inPangasius sutchi ×Clarias macrocephalus . The longest-lived hybrids ofPangasius andClarias were those ofPangasius sutchi ×Clarias macrocephalus which survived until the experiment was prematurely terminated due to contaminated food after 4 1/2 months, at which point they had grown to total lengths of 8–14cm. The hybrids comprised four morphotypes, two relativelyPangasius-like and two relativelyClarias-like, but all markedly different from the parental species.     

The phylogenetic structure of habitat shift and morphological convergence in Asian Clarias (Teleostei, Siluriformes: Clariidae)

Catfishes of the genus Clarias are an important component of the ichthyofauna in Asia and in Africa. Previous studies demonstrated a high diversity in number of species, morphology and habitat, but little was known on the evolutionary processes underlying this diversity. We analysed an original data set of molecular sequences (cytochrome b and 16S genes), habitat and geographic distributions, as well as 29 morphometric measurements taken on 454 specimens of Asian Clarias . Maximum likelihood phylogeny estimation showed an unexpected cryptic diversity due to strong morphological convergence. The patterns of intra- and interspecific phylogenetic divergence are overall explained by geographic isolation. The analysis of habitat transitions with Markovian models showed that Asian Clarias evolved from an ancestor probably living in clear waters. The most frequent transitions occurred between clear and white waters, whereas transitions towards black waters occurred only from clear waters and were rare events. The morphometric analysis suggests a complex pattern of morphological evolution with repeated convergence towards an elongated form in black waters. The phylogeographic patterns of diversification of Asian Clarias agree with previous studies on other groups and the hypothesis that changes in sea level during the Pleistocene had little influence on shaping biodiversity on the Sunda Shelf.     

The cranial base of Australopithecus afarensis: new insights from the female skull

Cranial base morphology differs among hominoids in ways that are usually attributed to some combination of an enlarged brain, retracted face and upright locomotion in humans. The human foramen magnum is anteriorly inclined and, with the occipital condyles, is forwardly located on a broad, short and flexed basicranium; the petrous elements are coronally rotated; the glenoid region is topographically complex; the nuchal lines are low; and the nuchal plane is horizontal. Australopithecus afarensis (3.7–3.0 Ma) is the earliest known species of the australopith grade in which the adult cranial base can be assessed comprehensively. This region of the adult skull was known from fragments in the 1970s, but renewed fieldwork beginning in the 1990s at the Hadar site, Ethiopia (3.4–3.0 Ma), recovered two nearly complete crania and major portions of a third, each associated with a mandible. These new specimens confirm that in small-brained, bipedal Australopithecus the foramen magnum and occipital condyles were anteriorly sited, as in humans, but without the foramen''s forward inclination. In the large male A.L. 444-2 this is associated with a short basal axis, a bilateral expansion of the base, and an inferiorly rotated, flexed occipital squama—all derived characters shared by later australopiths and humans. However, in A.L. 822-1 (a female) a more primitive morphology is present: although the foramen and condyles reside anteriorly on a short base, the nuchal lines are very high, the nuchal plane is very steep, and the base is as relatively narrow centrally. A.L. 822-1 illuminates fragmentary specimens in the 1970s Hadar collection that hint at aspects of this primitive suite, suggesting that it is a common pattern in the A. afarensis hypodigm. We explore the implications of these specimens for sexual dimorphism and evolutionary scenarios of functional integration in the hominin cranial base.     

Chromosome study of hybrid and gynogenetic offspring of artificial crosses between members of the catfish families Clariidae and Pangasiidae

Synopsis Artificial hybridization between species of the catfish families Clariidae (Clarias macrocephalus) and Pangasiidae (Pangasius sutchi) resulted in first generation offspring comprising two intermediate morphotypes and one morphotype indistinguishable from its clariid parent. The two intermediate morphotypes apparently correspond to hybrid morphotypes 2 and 4 resulting from earlier hybridization experiments between the same parent species (Tarnchalanukit 1986). We did not obtain morphotypes 1 and 3. Chromosome spreads of the relatively pangasiid-like morphotype 2 reveal a diploid number of 57, presumably comprising one set of Clarias (n=27) and one of Pangasius (n=30) chromosomes. The relatively clariid-like morphotype 4 is a triploid with 84 chromosomes, presumably comprising two sets from Clarias (2n=54) and one from Pangasius (n=30). Finally, the morphotype indistinguishable from Clarias, is a diploid with 54 chromosomes, apparently arising from gynogenesis.     

Mesozoic Araucariaceae: Morphology and systematic relationships

The Southern Hemisphere conifer family Araucariaceae has a very restricted present day distribution, but was more widespread in the past. The genusAraucaria is represented by good fossil material in both hemispheres as early as the Jurassic, whileAgathis is only known from the Southern Hemisphere beginning in the Cretaceous. Cuticle studies of extant araucarians have enabled accurate comparisons of fossil leaves to living taxa.Araucaria SectionBunya is represented by cones of several types in the Jurassic. In addition to these remains, a suite of araucarian cones showing affinities to several sections of the genusAraucaria have been described from England, Japan and North America. Evidence that fossil araucarian cones may have produced seeds with hypogeal germination is discussed in light of recent work on germination of extant bunya seedlings and the discovery of new fossil shoots from the Jurassic Morrison Formation of Utah.     

Origin and segregation of cranial placodes in Xenopus laevis

Cranial placodes are local thickenings of the vertebrate head ectoderm that contribute to the paired sense organs (olfactory epithelium, lens, inner ear, lateral line), cranial ganglia and the adenohypophysis. Here we use tissue grafting and dye injections to generated fate maps of the dorsal cranial part of the non-neural ectoderm for Xenopus embryos between neural plate and early tailbud stages. We show that all placodes arise from a crescent-shaped area located around the anterior neural plate, the pre-placodal ectoderm. In agreement with proposed roles of Six1 and Pax genes in the specification of a panplacodal primordium and different placodal areas, respectively, we show that Six1 is expressed uniformly throughout most of the pre-placodal ectoderm, while Pax6, Pax3, Pax8 and Pax2 each are confined to specific subregions encompassing the precursors of different subsets of placodes. However, the precursors of the vagal epibranchial and posterior lateral line placodes, which arise from the posteriormost pre-placodal ectoderm, upregulate Six1 and Pax8/Pax2 only at tailbud stages. Whereas our fate map suggests that regions of origin for different placodes overlap extensively with each other and with other ectodermal fates at neural plate stages, analysis of co-labeled placodes reveals that the actual degree of overlap is much smaller. Time lapse imaging of the pre-placodal ectoderm at single cell resolution demonstrates that no directed, large-scale cell rearrangements occur, when the pre-placodal region segregates into distinct placodes at subsequent stages. Our results indicate that individuation of placodes from the pre-placodal ectoderm does not involve large-scale cell sorting in Xenopus.     

Eya1 and Six1 promote neurogenesis in the cranial placodes in a SoxB1-dependent fashion

Genes of the Eya family and of the Six1/2 subfamily are expressed throughout development of vertebrate cranial placodes and are required for their differentiation into ganglia and sense organs. How they regulate placodal neurogenesis, however, remains unclear. Through loss of function studies in Xenopus we show that Eya1 and Six1 are required for neuronal differentiation in all neurogenic placodes. The effects of overexpression of Eya1 or Six1 are dose dependent. At higher levels, Eya1 and Six1 expand the expression of SoxB1 genes (Sox2, Sox3), maintain cells in a proliferative state and block expression of neuronal determination and differentiation genes. At lower levels, Eya1 and Six1 promote neuronal differentiation, acting downstream of and/or parallel to Ngnr1. Our findings suggest that Eya1 and Six1 are required for both the regulation of placodal neuronal progenitor proliferation, through their effects on SoxB1 expression, and subsequent neuronal differentiation.     

Morphology of the olfactory system in the predatory mite Phytoseiulus Persimilis

The predatory mite Phytoseiulus persimilis locates its prey, the two-spotted spider mite, by means of herbivore-induced plant volatiles. The olfactory response to this quantitatively and qualitatively variable source of information is particularly well documented. The mites perform this task with a peripheral olfactory system that consists of just five putative olfactory sensilla that reside in a dorsal field at the tip of their first pair of legs. The receptor cells innervate a glomerular olfactory lobe just ventral of the first pedal ganglion. We have made a 3D reconstruction of the caudal half of the olfactory lobe in adult females. The glomerular organization as well as the glomerular innervation appears conserved across different individuals. The adult females have, by approximation, a 1:1 ratio of olfactory receptor cells to olfactory glomeruli.     

Morphology,ultrastructure and taxonomy of the raphidophycean algaHeterosigma akashiwo

Heterosigma akashiwo and its related algae were re-examined by light and electron microscopes using cultured materials including type cultures of bothH. akashiwo andH. inlandica as well as specimens referred to asOlisthodiscus luteus maintained in CCAP and UTEX. All the strains examined were similar to one another in appearance and ultrastructural features. They can be accommodated in a single species,H. akashiwo, which has been invalidly published. In this paper, the genus is validly desribed by providing a Latin diagnosis and designating a type species. Ultrastructural characteristics are also given for the genus.     

Morphology,biology and pesticide tolerance ofChelotogenes ornatus [Acari: Cheyletidae]

BioControl - This paper reports on the morphology, biology and pesticide tolerance ofCheletogenes ornatus (Canestrini &;amp; Fanzago), the most common predator ofPinnaspis aspidistrae (Signoret)...     

Distribution,community structure and production of fishes in the upper Speed River,Ontario: a preimpoundment study

Synopsis The upper Speed River, on which a dam was under construction, was surveyed through fourteen qualitative and six quantitative collections to determine the distribution of fishes in the river above Guelph, Ontario and in a tributary, Luteral Creek. At the quantitative localities the removal method was used to estimate density and standing crop of all species. At three of these localities age and growth of the dominant species were determined and total ecological production calculated. Two approaches to the estimation of production for the 0–1 age class were compared and found to result in differences of 33–39% in the estimates of total production, thus illustrating the extent to which methodology may affect such estimates The dominant species in the river were, Semotilus atromaculatus, Notropis cornutus, Pimephales notatus, Rhinichthys atratulus, Hypentelium nigricans, Catostomus commersoni, Ambloplites rupestris, Micropterus dolomieui and Etheostoma flabellare. Density ranged from 11126 to 74765 individuals per hectare and standing crop from 32.4 to 190.0 kg ha⁻¹. Production values at the three localities were 15, 19 and 54 kg ha⁻¹ yr⁻¹ , and are low compared with estimates for other fluvial systems. Comparison with a 1951 survey of the Speed River revealed considerable changes in the composition and distribution of fish species. The ranges of several cold-water species had contracted towards the headwaters, whereas several warm-water species had extended their ranges up the river     

Molecular analysis of the phosphoenolpyruvate-dependent l-sorbose: phosphotransferase system from Klebsiella pneumoniae and of its multidomain structure

We have cloned a 3.4 kb DNA fragment from the chromosome of Klebsiella pneumoniae that codes for a phosphoenolpyruvate-dependent l-sorbose: phosphotransferase system (PTS). The cloned fragment was sequenced and four open reading frames coding for 135 (sorF), 164 (sorB), 266 (sorA) and 274 (sorM) amino acids, respectively, were found. The corresponding proteins could be detected in a T7 overexpression system, which yielded molecular masses of about 14000 for SorF, 19000 for SorB, 25000 for SorA and 27000 for SorM. SorF and SorB have all the characteristics of soluble and intracellular proteins in accordance with their functions as EIIA^Sor and EIIB^Sor domains of the l-sorbose PTS. SorA and SorM, by contrast, are strongly hydrophobic, membrane-bound proteins with two to five putative transmembrane helices that alternate with a series of hydrophilic loops. They correspond to domains EIIC^Sor and EIID^Sor. The four proteins of the l-sorbose PTS resemble closely (27%–60%) the four subunits of a d-fructose PTS (EIIA^Lev, EIIB^Lev, EIIC^Lev, and EIID^Lev) from Bacillus subtilis and the three subunits of the d-mannose PTS (EIIA,B^Man, EIIC^Man, and EIID^Man) from Escherichia coli K-12. The three systems constitute a new PTS family, and sequence comparisons revealed highly conserved structures for the membranebound proteins. A consensus sequence for the membrane proteins was used to postulate a model for their integration into the membrane.     

Analysis of production,early growth and survival ofClarias gariepinus (Burchell),Heterobranchus longifilis (Val.) (Pisces: Clariidae) and their F1 hybrids in ponds

Clarias gariepinus andHeterobranchus longifilis were successfully hybridized to produce reciprocal F₁ progeny during a two-year study.C. gariepinus produced significantly heavier spawn thanH. longifilis during the same period. Fertilized eggs were incubated in aerated static-water in fibre-glass troughs, and hatching rates were not found to be significantly different (P<0.05) between any two of the four catfish groups produced. Eight-day old fry of each group were reared in fertilized nursery ponds, and F₁ hybrids fromH. longifilis maternal parent had the best growth and survival rates at the end of 18 days. The reciprocal cross showed intermediate growth rate between both parents. At harvest, differential growth was less pronounced among both hybrids than among the parents.     

The reproductive biology of four African catfishes (Osteichthyes: Clariidae) in Anambra River basin,Nigeria

The reproductive biology of Clarias ebriensis, C. agboyiensis, C. macromystax and C. buthupogon was investigated over a period of 32 months in Anambra River basin, Nigeria. Immature (stage I) C. ebriensis and C. agboyiensis were recruited into the fishery in October, and in September in C. macromystax and C. buthupogon. The occurrence of mature (stage III) fish all the year round indicated the potential of the Clarias species to breed at any time of the year. C. ebriensis bred from April–September while breeding occurred from May–September in the other species. The clariids matured between their first and second year of life. C. ebriensis females matured earlier than males but the reserve was the case in C. agboyiensis, C. macromystax and C. buthupogon. Ovary weight was a better indicator of egg number than either total length or body weight in all species. Communal spawning is reported for the first time in Clarias species and its significance to survival discussed.     

Nectary structure and nectar characteristics in someBignoniaceae

The nectary structure and chemical nectar composition of 15 species belonging to 12 genera ofBignoniaceae are analyzed. All taxa bear a conspicuous nuptial nectary surrounding the ovary base. The secretory tissue is mostly supplied by phloem branches. The stomata are located in the middle and upper part of the nectary epidermis with an homogeneous distribution. The nuptial nectary is proportionally large in relation to the ovary (15–30%), disregarding the nectary volume. Most species have extranuptial nectaries in both inner and outer surfaces of the calyx. Both kinds of nectaries lack a vascular tissue that straightly supplies them. Nuptial nectar concentration (wt/wt) ranges from 19 to 68%. Sugars and amino acids are found in all species. Half of the species have hexose predominant nectars, the remaining sucrose predominant. Phenols are detected in only three species, whereas reducing acids exclusively inTecoma stans. Alkaloids and lipids were never detected. Extranuptial nectar chemical composition is analyzed in two species:Dolichandra cynanchoides andPodranea ricasoliana. Bees constitute the main flower visitors of the species studied whereas hummingbirds were seen visiting three species. A correlation analysis is performed with the data obtained. There are a few significant correlations which indicate a parallel increase of three parameters: the longer the flower length, the more voluminous the nectary and the higher stomata number, independently of the floral biotype. Phenograms are obtained using 24 floral characters including nectary and nectar data. The clusters obtained do not reflect taxonomic relationships but are useful in the understanding of animal-plant interactions when the flower biotype is considered.This paper is based on a chapter of a doctoral thesis presented at the University of Córdoba (Argentina).     

The Belohdelie frontal: new evidence of early hominid cranial morphology from the Afar of Ethiopia

Study of the Belohdelie frontal has demonstrated that this four-million-year-old specimen belongs to a very generalized hominid that may be close to the divergence point of the hominid and African ape clades. Features associated with the temporalis muscle in the Belohdelie frontal and other new hominids from Hadar (AL 333-125) and West Turkana (KNM-ER 17000) suggest that the earliest hominids shared a large anterior component of this muscle relative to the extinct and extant apes. Results of this study support the phylogenetic hypothesis put forward by many workers that A. afarensis gave rise to the “robust” Australopithecus and A. africanus clades.     

Consequences of the pollination system on genetic structure and patterns of species distribution in the Andean genus Polylepis (Rosaceae): a comparative study

As a member of the Sanguisorbinae, taxonomically complicated Polylepis Ruiz & Pav. from the South American Andes is one of the few wind-pollinated genera of Rosaceae. Here, it is suggested that problems traditionally faced in species delimitation and phylogeny reconstruction may be in part due to a combination of weak reproductive barriers and the large distances that can be covered by genetic information as a result of wind pollination. The pattern of species distribution as well as molecular data (AFLP) of Polylepis were contrasted with those of an unrelated, insect-pollinated genus of similar species number and distribution, Minthostachys (Griseb.) Spach (Lamiaceae). In the present case, extensive pollen-mediated gene flow may explain the homogenization of genetic variability over larger distances and a lower number of species restricted to individual countries in the wind-pollinated genus Polylepis, but more examples will have to be studied before arriving at final conclusions.     

Morphology and taxonomy of chain-forming species of the genus Cochlodinium (Dinophyceae)

The morphology of an unarmored chain-forming harmful dinoflagellate Cochlodinium polykrikoides and its similar species such as Cochlodinium catenatum, Cochlodinium fulvescens, and Cochlodinium convolutum was carefully observed, emphasizing the single cell stage for clarifying taxonomically important morphological features. To differentiate C. polykrikoides from C. convolutum, the shape and the position of the nucleus are useful characters. C. polykrikoides also differs from C. fulvescens in being smaller in size, possessing many rod-shaped chloroplasts and having the sulcus running just below the cingulum on the dorsal surface. Careful observation of the ichnotype of C. catenatum suggests that C. catenatum sensu Kofoid and Swezy collected from off La Jolla, CA, USA, is not identical to C. catenatum sensu Okamura and is probably a different species, in having no chloroplasts and a nucleus positioned at the center of the cell. In addition, C. polykrikoides has many morphological features in common with C. catenatum sensu Okamura except for slightly elongate cells and is probably a junior synonym of this species.     

Reconstruction and re-evaluation of the skull ofHomo antiquus (hominoidea: Homininae) from Hadar

The skull ofHomo antiquus Ferguson, 1984, represented by cranial remains of a fossilized skeleton, A.L. 288-1, from the Plio/Pleistocene of Hadar in Ethiopia, is reconstructed and the procedure described. Re-evaluation of the skull shows that it is apparently the smallest, normal, unequivocal hominid skull known; and that its cranial morphology is not Australopithecine, but Hominine.