Microsatellites from the vairone Leuciscus souffia (Pisces: Cyprinidae) and their application to closely related species

Eleven microsatellites were isolated from the vairone Leuciscus souffia (Risso 1826), an endangered fish that inhabits river systems in and around the Alps in Europe. The level of genetic diversity was assessed in 29 individuals of the subspecies L. s. souffia, and their variability was further estimated in seven individuals of a different subspecies, L. s. muticellus. Eight of these microsatellite loci were also applied to seven closely related cyprinid species. Availability of the reported microsatellite loci will facilitate the investigation of population genetic structure of these species with applications for the development of conservation strategies and phylogeographical approaches.     

Ultrastructure of Carposporogenesis in the Red Alga Caulacanthus ustulatus (Gigartinales, Caulacanthaceae)

Carposporangium differentiation in Caulacanthus ustulatus (Turner)Ktzing proceeds through four developmental stages. The youngestcarposporangia are embedded within confluent mucilage and containa nucleus, a few small starch granules, concentric membranebodies and proplastids without a peripheral thylakoid. The intermediate-agedcarposporangia are characterized by the formation of fibrousvacuoles by a fibrous vacuole associated organelle (FVAO). Plastidsalso start to develop their internal thylakoid system. In nearlymature carposporangia, highly active, curved dictyosomes producecored vesicles, while fibrous vacuoles increase in number anddisplay a perinuclear arrangement. Abundant starch granulesare present, some of which exhibit a degenerating appearance.A carposporangium wall is formed and plastids complete theirinternal thylakoid system. Carposporangium maturation is signalledby the presence of adhesive vesicles. Fully developed and peripherallyarranged plastids, centrally located fibrous vacuoles, fewerstarch granules and a monolayered wall are the features of maturecarposporangia. Carposporogenesis, Caulacanthus ustulatus (Turner) Kützing, red algae, ultrastructure     

Host range, purification and some properties of rubus Chinese seed-borne virus

A previously undescribed virus, for which the name rubus Chinese seed-borne virus (RCSV) is proposed, was isolated from a single, symptomless plant of an unidentified Rubus species grown from seed collected in the wild in the People's Republic of China, Experimentally RCSV infected 23 out of 39 spp. in six out of eight families. The virus was seed-transmitted in Chenopodium quinoa (100%) and Nicotiana bigelowii (27%). RCSV was not transmitted by the nematodes Xiphinema diversicaudatum or X. index. The particles of RCSV were isometric, c. 30 nm in diameter with some penetrated by negative stains. In thin sections particles were found in double walled tubular structures with an outer membrane enclosing one or more tubules. In crude extracts some particles were found within single-walled tubules. Two virus-associated bands were seen in sucrose density gradients of purified preparations. The upper band was not infective and consisted of penetrated particles apparently devoid of nucleic acid. The lower, infective band was resolved into two components, of density 1.452 and 1.461 g/ml, in caesium chloride isopycnic gradients. There were two polypeptides (mol. wts c. 47 000 and 25 200 daltons) and two nucleic acid species (one of mol. wt c. 1.4 × 10⁶ daltons; the second was poorly defined by the methods used but was of higher molecular weight). RCSV was distantly related serologically (6–7 SDI) to the type isolate of strawberry latent ringspot virus (SLRV) and also reacted with antisera to serologicaly distinct grape and olive isolates of SLRV. It did not react with antisera to 10 other isometric viruses.     

Evergreen Foliage Contributions to the Spring Growth of Taxus

Taxus media cv. Hicksii plants were grown one season under a low and high level of nitrogen fertilization. Before growth in the spring the plants were divided into two groups, one of which was defoliated and the other left intact. The growth and spring utilization of the nitrogen and carbohydrate reserves of defoliated plants were compared to the intact plants 0, 2, 4 and 6 weeks after growth started in the spring. The plants were separated into buds (all new growth), roots and stems and analyzed for changes in total nitrogen, basic and non-basic amino acids, hemicelluloses, soluble sugars, organic acids and chlorophyll. The older evergreen needles from plants grown under low nitrogen levels contain 20 % of the carbohydrate and 24% of the nitrogen used in spring growth. The needles from plants grown under high nitrogen levels contained 56% of the carbohydrate and 49% of the nitrogen used in spring growth. Removal of the old needles before spring growth removed this nitrogen and carbohydrate reserve and reduced the total plant chlorophyll content after 6 weeks of growth to 50% of that found in intact plants, with the result that defoliated plants did not show a growth response to nitrogen. Amino acids accumulated in the stems and buds of defoliated plants as carbohydrates became limiting. The defoliated plants removed 25% more available carbohydrates from the roots and stems than intact plants and their buds contained 50% less available carbohydrates. Plants without old needles showed similar growth rates under low and high nitrogen regimes and produced 33% of the dry weight of intact plants grown under high nitrogen levels and 66% of the dry weight of intact plants grown under low nitrogen levels. The old needles of taxus plants contain substantial amounts of reserve nitrogen and carbohydrate and these needles greatly influence the extent and rapidness of growth in the spring. When the needles are removed, the other tissues can supply an adequate amount of nitrogen but the carbohydrate supply becomes limiting for spring growth.     

Reduced Polyteny of Ribosomal RNA Cistrons in Giant Chromosomes of <Emphasis Type="Italic">Drosophila hydei</Emphasis><Superscript>*</Superscript>

The polytenization of rRNA cistrons in Drosophila species is studied in an attempt to follow the course of under-representation of heterochromatic compared with euchromatic chromosome regions.     

Ecological and evolutionary consequences of the trophic polymorphism in Cichlasoma citrinellum (Pisces: Cichlidae)

The neotropical cichlid fish Cichlasoma citrinellum is polymorphic in the structure of its pharyngeal jaw apparatus and external morphology. The pharyngeal jaws are either gracile and bear slender, pointed teeth (papilliform) or robust with strong, rounded teeth (molariform). Molariform morphs have a ‘benthic’, and papilliform morphs a ‘limnetic’ body form. Furthermore, this species is also polychromatic, with yellow and black morphs. The molariform morphology of the pharyngeal jaw apparatus adapts the fish for cracking and feeding on snails. Based on analysis of stomach contents, 94% of the molariform morph ate snails whereas only 19%, of the papilliform morph did so. This result suggests that the morphs occupy different ecological niches. The morphology of the pharyngeal jaw apparatus does not correlate significantly with sex, but it does with body colouration (P<0.005). Cichlasoma citrinellum mate assortatively with their own colour; therefore a mating preference for colour may lead to genetic isolation of trophic morphs. The frequency of the molariform morph differs strikingly among populations of five Nicaraguan lakes and its abundance is correlated with the abundance of snails, the fishes' principal prey item. Among populations the frequency of molariform morphs decreases in the dry season. Morphology possibly changes reversibly within particular individuals between seasons. These results suggest that phenotypic plasticity and polymorphisms may be an adaptive characteristic of cichlid fishes. Patterns of intraspecific morphological variation match patterns of interspecific morphological diversification which suggests that universal developmental mechanisms canalize the possible expressions of morphology. The ability to respond morphologically to environmental shifts, in conjunction with genetically determined trophic polymorphisms and sexual selection via mate choice, could be the basis for speciation through intermediate stages of polymorphism of the impressive adaptive radiation of cichlid fishes.     

Bacterivory by deposit-feeding mayfly larvae (Stenonema spp.)

SUMMARY.

• 1 The importance of bacteria in the diet of deposit-feeding mayflies (Stenonema spp.) from the Ogeecnee River, a sixth order low-gradient blackwater river in Georgia, U.S.A., was determined. Stenonema are abundant and productive on snags in biackwater rivers in the southeastern Coastal Plain of the U.S.A. Bacteria are abundant in the seston in this river, and are a potentially important food source.
• 2 Naturally occurring seston was fed to Stenonema larvae after bacterial DNA in the seston was labelled with methyl-[³H]thymidine. Larval respiration measurements and growth rate estimations were used to compare the amount of bacterial carbon assimilated and retained in larval tissue to the carbon requirements of the larvae.
• 3 Stenonema larvae incorporated 8.7×10⁷±1.3×10⁷ bacteria larva^?1 h^?1 This was equivalent to 93±6% of their daily growth, and 47±3% of their total daily carbon needs. Larger larvae incorporated more bacterial biomass, but mass specific incorporation was not related to size. Ingestion of bacteria while eating seston accumulated on snags appears to be an important component of the diet of Stenonema larvae in these rivers.