New Data on the Internal Anatomy of the Heterostraci (Agnatha), with General Remarks on the Phytogeny of the Craniota

Some new impressions have been observed on the visceral surface of a dorsal shield of Ctenaspis sp. from the Lower Devonian of Spitsbergen. They indicate the probable position of the ophthalmicus profundus and o. lateralis nerves, and of two branchial nerves. The impressions left by the branchial arches are also visible on the same specimen. Furthermore, a median dorsal series of circular impressions previously observed in Seretaspis zychi StensiÖ is compared to similar impressions observed in two osteostracans, and it is suggested that vertebral elements were present in the Heterostraci. Finally, the affinities of the Heterostraci are discussed and it is suggested that they may represent the sister group of the Myopterygii (Cephalaspidomorphi + Gnathostomata).     

FORM AND FUNCTION IN MARINE PHYTOPLANKTON

What is presented here is a tentative synthesis of morphological, cytological, physiological and ecological data on planktonic algae, which I hope will help in the understanding of mutual relationships. Emphasis is put on the marine phytoplankton although effort has been made to include the more significant limnological information. (1) All the algal classes, but two, are present in the marine plankton – which makes 13 classes. Many or most of them possess one or several features that are commonly viewed as animal characters, and so Bacillariophyceae (diatoms) are the more typical ‘algae’ in marine plankton. Coincidently or not, they have received much more attention than any other class. (2) Both structurally and morphodynamically, colonies of cells often appear as something else or something more than sums of cells. (3) There is a profuse variety of flagellar types and flagellar appendages, whose functional significance is open to investigation. In general, swimming velocity (ca. 1 m h^-l) exceeds sedimentation rate (ca. 0·7 m day^-1) by one order of magnitude or more. (4) Very few phytoplankters can truly be described as “naked”. Cell coverings fall into eight major categories which differ by chemical composition, structure and ontogeny. An additional, external organic coating may be widespread. Mucus and microfibrils may also be more common than previously thought. (5) The variability of chloroplast morphology and ultrastructure has not been explored for functional relationships. (6) Evidence for the presence of intracellular bacteria and viruses is rapidly increasing. (7) The suspension of algal cells in the medium depends on a number of morphological factors whose effects are often opposite. The sinking rate increases with increasing cell size and is maximum for spheroid (not spherical) shapes; colonies sink faster than the individual cells. The incidence of various shapes, appendages, mucilage and cell orientation is, essentially, intricate and/or insufficiently known. Lipidic inclusions are no longer viewed as floating devices but the ancient theory of ionic exchange has been revived. As now understood, the suspension of phytoplankton is no more a matter of floating, but rather exploring different layers and being tossed around by physical entrainment. However, questions remain the same: how do the “morphological adaptations” contribute to this, and how do different forms compare to each other? (8) As far as the absorption of nutrients is concerned, there is an advantage for phytoplankters to be small and either motile or rapidly sinking. The permeability of the various cell coverings has been ignored. The advantage of being small is confirmed by the consideration that growth rates and all the metabolic rates decrease with increasing size. However, the balance of photosynthesis against respiration for varying sizes is a complex problem. (9) After an extensive review of the literature, the existence of several “shade species” is confirmed (without ensuring that light is the responsible factor). These taxa exhibit the full range of shapes, sizes, structures and behaviour, so that the relevant morphological adaptations, if any, are at least polymorphic. (10) Although grazing certainly moulds the size spectrum and the algological spectrum of phytoplankton to a large extent, the effect of a given morphological feature can hardly be generalized, except that long appendages, mucilages, and probably colonies discourage grazers. The role of bioluminescence and trichocyst expulsion may also be considered. (11) The hope of correlating cell size with a single factor of the environment, whether temperature or something else, should be abandoned since many more factors are involved. On the other hand, multi-parametric models can justify or predict which cell size predominates under a given set of conditions (note the works of H. J. Semina and co-workers, T. R. Parsons and M. Takahashi, and E. A. Laws). (12) The ratio of surface area to volume of the cell is a meaningful physiological index. Its relative conservation among the vagaries of sizes and shapes, and its ecological regulation need further investigation. (13) Considering the profusion of data that has accumulated on the structure and functioning of planktonic algae, and realizing that sophisticated techiques are available for both kinds of studies, now is the time, it seems, for fruitful research into the relationships between form and function. Such research will certainly increase our understanding of specific variability, adaptation and diversity.     

Sex pheromones and trail‐following pheromone in the basal termites Zootermopsis nevadensis (Hagen) and Z. angusticollis (Hagen) (Isoptera: Termopsidae: Termopsinae)

In the context of an evolutionary study of the chemical communication in termites, sex pheromones and trail‐following pheromones were investigated in two Termopsidae, Zootermopsis nevadensis and Z. angusticollis. In these species, in which the presence of sex‐specific pheromones has been demonstrated previously, the chemical structure of the female sex pheromone has now been identified as (5E)‐2,6,10‐trimethylundeca‐5,9‐dienal and the male sex pheromone as (+)‐ or (?)‐syn‐4,6‐dimethyldodecanal. The amount of sex pheromone was estimated at 5–10 ng per individual in females and 2–5 ng in males. Because these two sympatric species do not differ in their pheromonal chemical composition, reproductive isolation is probably mediated chiefly by differences in dispersal flight chronology. The trail‐following pheromone was shown to be composed of the same compound as the male sex pheromone, that is syn‐4,6‐dimethyldodecanal. The compound syn‐4,6‐dimethyldodecanal was 10 times more active than the racemic (+/?)‐syn + (+/?)‐anti‐4,6‐dimethyldodecanal in eliciting trail‐following. The amount of syn‐4,6‐dimethyldodecanal was estimated at 0.1–0.5 ng per pseudergate. Regarding the phylogenetic aspects, the nature of the female sex pheromone of Zootermopsis is structurally akin to the trail‐following pheromone of Mastotermes darwiniensis of Mastotermitidae and Porotermes adamsoni and Stolotermes victoriensis of Termopsidae. Interestingly, the nature of the trail‐following pheromone of the Termopsinae Zootermopsis is clearly different from that of the Porotermitinae P. adamsoni and the Stolotermitinae S. victoriensis, which mirrors recent molecular data on the paraphyly of Termopsidae. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 519–530.     

Monoclonal Antibodies Identify a Subset of Dense Granules in Cryptosporidium parvum Zoites and Gamonts

ABSTRACT. Two monoclonal antibodies raised against purified oocysts and excysted sporozoites of Cryptosporidium parvum identified antigens located in the anterior half of sporozoites by indirect immunofluorescence microscopic assay. The monoclonal antibodies also reacted with Triton X-100-insoluble antigens of asexual and sexual stage parasites developing in epithelial cells in vitro and identified a 110 kilodalton antigen on immunoblots of sodium dodecyl sulfate-extracted oocysts. Immunoblotting reactivity was abolished by prior treatment of blotted antigen with periodic acid suggesting that the monoclonal antibodies recognize a carbohydrate or carbohydrate-dependent epitope(s). By immunoelectron microscopy, the antibodies reacted with a family of small, electron-dense granules located predominantly in the central region of merozoites and also with a population of cytoplasmic inclusions in macrogamonts. In addition, the monoclonal antibodies prominently labeled the parasitophorous vacuole membrane of all intracellular stages examined suggesting that the corresponding antigen(s) may be exocytosed from the granules to become associated with Triton X-100-insoluble components of the vacuolar membrane or cytoskeleton.     

Polymorphism and Ultrastructure of a Colpodean Ciliate of the Genus Platyophryides Foissner, 1987

ABSTRACT. A ciliate isolated from a pond in Brazil, transformed to a giant form when its food was shifted from a bacterial prey to a ciliate prey. This polymorphism is immediately reversible when the prey ciliates, either Tetrahymena or Colpidium , disappear from the culture medium. By its life cycle, morphology, and ultrastructure, this ciliate belongs to the Class Colpodea. it could belong to the genus Platyophryides Foissner, 1987, except that its micronucleus is not enveloped by the macronuclear membrane. The systematic position of the genus Platyophryides , the validity of the three species in this genus, and the characteristics of the Cyrtolophosidida are discussed.     

The use of artificial neural networks to predict the presence of small-bodied fish in a river

1. Discriminant factorial analysis (DFA) and artificial neural networks (ANN) were used to develop models of presence/absence for three species of small-bodied fish (minnow, Phoxinus phoxinus , gudgeon, Gobio gobio , and stone loach, Barbatula barbatula ).
2. Fish and ten environmental variables were sampled using point abundance sampling by electrofishing in the Ariège River (France) at 464 sampling points.
3. Using DFA, the percentage of correct assignments, expressed as the percentage of individuals correctly classified over the total number of examined individuals, was 62.5% for stone loach, 66.6% for gudgeon and 78% for minnow. With back-propagation of ANN, the recognition performance obtained after 500 iterations was: 82.1% for stone loach, 87.7% for gudgeon and 90.1% for minnow.
4. The better predictive performance of the artificial neural networks holds promise for other situations with non-linearly related variables.