Light and Electron Microscopy of the Spore of Myxobolus heckelii n. sp. (Myxozoa), Parasite from the Brazilian Fish Centromochlus heckelii (Teleostei, Auchenipteridae)

ABSTRACT. A myxosporean parasitizing the gill filaments of the freshwater teleost fish Centromochlus heckelii collected in the Tocantins River (Lower Amazonian Region, Brazil) is described using light and electron microscopy. This parasite produces spherical to ellipsoidal cyst-like plasmodia up to 250 μm in diameter, with a thick wall strengthened by several stratified juxtaposed crossed collagen layers, whose thickness varies according to the number of the layers. Several compressed fibroblasts are observed among the collagen fibrils. Deposits of spherical dense material are scattered at the internal periphery of the cysts. Plasmodia and different developmental stages, including immature and mature spores, filled the central region of the cysts. The spore body is ellipsoidal in valvar view and biconvex in sutural view. It is formed by two equal-sized and symmetric valves measuring 12.7 μm long (12.2–13.1) ( n =50), 6.6 μm wide (6.3–6.9) ( n =25), and 4.0 μm (3.7–4.4) ( n =20) thick. A thin layer formed by fine and anastomosed microfibrils is observed at the spore surface. Two equal, elongated pyriform polar capsules measure 2.9 μm (2.7–3.3) × 1.7 μm (1.4–2.0) ( n =25), each containing four or five oblique polar filament coils. The binucleated sporoplasm contains numerous spherical sporoplasmosomes, glycogen particles, and a large vacuole with fine granular matrix. Based on the morphological and ultrastructural differences and specificity of the host, we describe this isolate as a new myxosporidian, Myxobolus heckelii n. sp. (Myxozoa, Myxosporea).     

Extracts from the bark of Fagara heitzii (Aubr. et Pel.) (Rutaceae) tree are toxic to two weevils and the American cockroach

The bark of the Fagara heitzii tree in the west‐central African Republic of Congo (Congo–Brazzaville) is known anecdotally to provide protection for human residents against fleas and to be of use as a narcotic in fishing (similar to rotenone). We found that powder and hexane extracts from the bark of the Fagara heitzii tree contain insecticidal compounds. Dried powder (14.5 mg) on the bottom of a Petri dish is the residue at 14.494 mg per dish (LD₅₀) for 20 adult maize weevils Sitophilus zeamays after four days. The LD₅₀ of the same material to 20 adult cowpea weevils Callosobruchus maculatus was slightly higher at 16.144 mg/dish (after 48 h). These weevils cause significant economic damage to cowpea and maize in Congo–Brazzaville. Hexane extracts of the bark of Fagara heitzii were also toxic to these weevils. Symptoms of toxicity suggested the extracts were slow‐acting nerve poisons or respiratory inhibitors or both. The time needed to develop full toxicity suggested a respiratory poison. The hexane extract was also toxic to the American cockroach Periplaneta americana. The symptoms in the cockroach were similar, but cockroaches also exhibited apparent escape attempts suggesting they could detect the compounds. Signs of apparent irritation or exaggerated locomotion in all three insects also suggested irritation or nerve effects.     

Seed dispersal and population structure in Vriesea gigantea,a bromeliad from the Brazilian Atlantic Rainforest

Seed dispersal, population structure and the mating system of plant species can have great consequences on the genetic structure of populations. Vriesea gigantea is a bromeliad from southeastern Brazil which is self‐compatible and pollinator dependent for fruit set. Its populations are fertile in terms of the production of flowers, pollen, fruits and seeds. To assess the importance of seed supply for gene flow, colonization and distribution of adult individuals, the seed dispersal and population structure of V. gigantea were studied. Seeds are dispersed over short distances; most seeds land close to the mother plant. This pattern coincides with the reported aggregate distribution of bromeliad seedlings. Population structure results showed high seedling recruitment, because 51.3% developed into adults, although few juveniles reached this stage. This result is different from that for other bromeliad species from different habitat conditions. Seed dispersal and population structural patterns are consistent with previous molecular studies, revealing that V. gigantea populations are genetically structured, with low gene flow and a moderate outcrossing rate. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 317–325.     

Contrasting patterns of phenotypic variation linked to chromosomal inversions in native and colonizing populations of Drosophila subobscura

In fewer than two decades after invading the Americas, the fly Drosophila subobscura evolved latitudinal clines for chromosomal inversion frequencies and wing size that are parallel to the long‐standing ones in native Palearctic populations. By sharp contrast, wing shape clines also evolved in the New World, but the relationship with latitude was opposite to that in the Old World. Previous work has suggested that wing trait differences among individuals are partially due to the association between chromosomal inversions and particular alleles which influence the trait under consideration. Furthermore, it is well documented that a few number of effective individuals founded the New World populations, which might have modified the biometrical effect of inversions on quantitative traits. Here we evaluate the relative contribution of chromosomal inversion clines in shaping the parallel clines in wing size and contrasting clines in wing shape in native and colonizing populations of the species. Our results reveal that inversion‐size and inversion‐shape associations in native and colonizing (South America) populations are generally different, probably due to the bottleneck effect. Contingent, unpredictable evolution was suggested as an explanation for the different details involved in the otherwise parallel wing size clines between Old and New World populations of D. subobscura. We challenge this assertion and conclude that contrasting wing shape clines came out as a correlated response of inversion clines that might have been predicted considering the genetic background of colonizers.