The Cell Cycle in Crithidia fasciculata. Temporal Relationships between Synthesis of Deoxyribonucleic Acid in the Nucleus and in the Kinetoplast1, 2

SYNOPSIS. Autoradiographic technics with tritium-labeled thymidine have been used to determine G1, S, G2 and D for the kinetoplast and the nucleus of Crithidia fasciculata at 15, 25 and 32 C. The kinetoplast completes division before the nucleus at all 3 temperatures. The S phases of both organelles occur in approximate synchrony and are approximately equal in length but the nucleus begins and completes S before the kinetoplast at the 2 lower temperatures. This relationship is reversed at 32 C. Most of the effect of temperature on generation time is due to its effect on the length of S. The results are compared with similar studies on C. luciliae, Trypanosoma mega, other protozoa and tissue cells in culture. The role of the approximate synchrony of nuclear and kinetoplastic cycles in maintenance of the kinetoplastic condition is discussed and the hypothesis is proposed that this synchrony results from the sharing by nucleus and kinetoplast of the same mechanism for the production of the deoxyribonucleotides used in replication of their respective DNAs.     

Extracellular release of photosynthetic products by freshwater phytoplankton populations, with special reference to the algal species involved

SUMMARY. Over three successive years, depth profiles of C-fixation and excretion, chlorophyll- a concentrations, phytoplankton species composition and bacterial numbers were determined in Lake Vechten, a slightly eutrophic lake in The Netherlands. Special attention was given to the method used to measure extracellular release.
Excretion of dissolved organic ¹⁴C depended largely upon the photo-synthetic activity of the phytoplankton, ranging from 0–2.5 mg m^-1 h^-1, representing a percentage extracellular release (PER) of 0–25%.
During a period in August, however, a subsurface chlorophyll- a maximum at 5–7 m depth coincided with high excretion rates of up to 10 mg Cm^-3 h^-1 (PER = 55%). Phytoplankton analysis revealed a stratification in numbers of Mallomonas caudata with a maximum at 5–7 m depth.
The results suggest that in these water layers bacterial populations grew at the expense of the dissolved organic carbon compounds excreted by Mallomonas caudata. This means that extracellular release can temporarily function as an important nutrient source for the heterotrophie community in addition to the more or less constant dissolved organic carbon pool.     

The Papuan tortricine genus Heterochorista and the systematic position of the Sparganothini (Lepidoptera, Tortricidae)

ABSTRACT .
The previously monotypic Papuan genus Heterochorista Diakonoff, 1952 is revised and twenty-one species are recognized. Nikolaia Diakonoff, 1953 is synonymized, syn.n. with Heterochorista. The following six species are placed in new combination in Heterochorista: Nikolaia melanopsygma Diakonoff, N.inumbrata Diakonoff, N.aperta Diakonoff, Isochorista papuana Diakonoff, I.polysperma Diakonoff and Dicellitis chrysonetha Diakonoff. Thirteen new species are added to Heterochorista: acomata sp.n., rostrata sp.n., trivialis sp.n., ornata sp.n., prisca sp.n., punctulata sp.n., rufulimaculata sp.n., classeyiana sp.n., spinosa sp.n., signata sp.n., fulgens sp.n., nitida sp.n. and aura sp.n. A checklist and a key to species are provided, and adults and male and female genitalia are described and illustrated. The phylogeny of Heterochorista is outlined on the basis of a cladistic character analysis and the genus is referred to the base of the Sparganothini. The apomorphies characterizing this tribe are reviewed with regard to their phylogenetic significance and the relationship between Sparganothini, Archipini and Atterini is briefly discussed.     

Developmental Capacity of Aneuploid Xenopus Species Hybrids

Diploid as well as triploid Xenopus interspecific hybrids generate aneuploid eggs because of the presence, at meiosis, of univalent chromosomes which are presumably distributed at random. Zygotes obtained from such eggs, fertilized by either normal or UV-irradiated sperm, were analysed for their developmental capacities. All monosomics die in the course of embryogenesis, whereby optimum capacities correspond closely with those observed in monosomic mammalian embryos, especially in mice. In contrast, hyperdiploid Xenopus are relatively viable: although many die exhibiting the'haploid syndrome'or various other abnormalities, 8% of them reach metamorphosis, and 1–2% become adults. Of the latter, the karyotype was established in 13 individuals. Among them, 8–16 supernumerary chromosomes were found to be present.     

The Native Dialectica aemula (Meyrick) and the Introduced Dialectica scalariella (Zeller) (Lepidoptera: Gracillariidae) in Australia: Characterisation of Two Closely Related Species on Boraginaceae

Two gracillariid leaf miners of the genus Dialectica Walsingham are present in Australia on plants belonging to the family Boraginaceae, one a native species here identified as Dialectica aemula (Meyrick) which was originally described from India, and the Palaearctic Dialectica scalariella (Zeller) or Echium leaf miner, deliberately introduced as a biological control agent for Echium plantagineum L. or Paterson's Curse. Differential diagnoses are given for the two species, and they are comprehensively illustrated to enable identification. In contrast to the externally indistinguishable adults, the cocoons of the two species differ significantly in shape and colour and a colour plate allows easy identification.     

Out of Africa: molecular phylogenetics and biogeography of Wolffiella (Lemnaceae)

The monophyletic genus Wolffiella (Lemnaceae) comprises 10 species divided taxonomically into three sections. Relative to other genera of Lemnaceae, Wolffiella has a restricted range, with species distributed in warm temperate to tropical areas of Africa and the Americas, with only one species occurring in both areas. Sequence data from coding (rbcL and matK) and non‐coding (trnK and rpl16 introns) regions of cpDNA were analyzed phylogenetically to resolve relationships within Wolffiella, and these results were compared to earlier allozyme and morphological studies. Allozymes, cpDNA and morphology all supported the recognition of three sections. Relationships among species were similar in most respects between the allozyme and cpDNA trees, as well as among the different plastid partitions. In Wolffiella, both non‐synonymous and synonymous substitutions were greater in matK than in rbcL, as observed in other taxa. The synonymous substitution rate in matK was similar to the substitution rate of the non‐coding regions. All partitions, including coding regions, exhibited some homoplasy. Biogeographical reconstructions from a combination of cpDNA partitions indicated that Wolffiella originated in Africa with early movement to and radiation in the Americas. The one species found in both Africa and the Americas, W. welwitschii, likely originated in the Americas and subsequently dispersed to Africa. Using the SOWH test, the cpDNA data could reject two alternative biogeographical hypotheses suggested from analyses of morphological and allozyme data. The present distribution of Wolffiella can be explained by two major dispersal events and this contrasts with the more complex species distributions in other Lemnaceae genera. Limited dispersal in Wolffiella relative to other Lemnaceae genera may be due to more recent origins of species, lower dispersibility and poorer colonizing ability. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 79 , 565–576.     

A preliminary assessment of the conservation status of Cypripedium species in the wild

The conservation of few plants produces such an emotive response as that of hardy slipper orchids of the genus Cypripedium. The genus, comprising 45 species and two varieties, is holarctic in distribution with the centre of diversity in China. Much is known about the status of some species and their populations in Europe and North America, but little information is available on the Asiatic and Mexican species. Most cypripediums are showy orchids and are well represented in herbaria, allowing an estimate of the present distribution, frequency and conservation status of the known species to be made. The authors conclude that having considered the number of herbarium specimens, nearly half of the genus may be considered threatened and in need of some legal protection if the plants are to survive in the wild. They identify a need to examine the conservation status of the taxa in in this genus more closely, and outline two important conservation tools that may help efforts to this end: the IUCN Red List Categories and Criteria for the Amendment of the Appendices of CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora).     

The importance of passerine birds as tick hosts and in the transmission of Borrelia burgdorferi,the agent of Lyme disease: a case study from Scotland

Borrelia burgdorferi sensu lato (s.l.) is the causative agent of Lyme borreliosis, the most common tick‐borne zoonosis of humans in Europe and North America. Here, we assessed the relative importance of different passerine bird species as tick hosts and their contribution to the B. burgdorferi s.l. transmission cycle in a rural residential area in Scotland. We caught 1229 birds of 22 species during the tick‐questing season. On average, 29% carried larval ticks (0.8 larvae per individual) and 5% carried nymph ticks (0.06 nymphs per individual). All attached ticks tested were Ixodes ricinus. Using a nested‐PCR, we found that 20% of nymphs tested positive to B. burgdorferi s.l. and all these were of the genospecies Borrelia garinii. We identified two new bird species carrying infected nymphs: Eurasian Siskin Carduelis spinus and European Greenfinch Carduelis chloris. Ground‐foraging species were more important than arboreal species in hosting I. ricinus nymphs and B. burgdorferi s.l. Common Blackbirds Turdus merula were the most common hosts, with Song Thrushes Turdus philomelos, Dunnocks Prunella modularis, European Greenfinches and Chaffinches Fringilla coelebs also hosting high rates of infection.