A POPULATION STUDY OF AN EQUATORIAL LAND SNAIL, LIMICOLARIA MARTENSIANA (ACHATINIDAE)

Near the equator in Uganda, the herbivorous land snail, Limicolaria martensiana , occurs in well-defined populations. These populations may be very large and the snails may in places occur at exceedingly high densities. The snails breed all the year round, but with two peaks that correspond with the two annual dry seasons. They enter dispause whenever the weather is very dry. The size of adult snails seems environmentally determined and it varies in different populations : the largest snails occur on soil rich in calcium. The shells of the snails are highly variable and polymorphic in colour and pattern. In particular, there is a streaked form that occurs in all populations, and four distinct pallid dilute forms. The relative frequency of the forms varies markedly in different populations. Polymorphism is greatest at high population densities and the snails are all streaked where they are rare. Polymorphism can be distinguished in Pleistocene fossil populations.     

Considerations for Group Testing: A Practical Approach for the Clinical Laboratory

Group testing, also known as pooled sample testing, was first proposed by Robert Dorfman in 1943. While sample pooling has been widely practiced in blood-banking, it is traditionally seen as anathema for clinical laboratories. However, the ongoing COVID-19 pandemic has re-ignited interest for group testing among clinical laboratories to mitigate supply shortages. We propose five criteria to assess the suitability of an analyte for pooled sample testing in general and outline a practical approach that a clinical laboratory may use to implement pooled testing for SARS-CoV-2 PCR testing. The five criteria we propose are: (1) the analyte concentrations in the diseased persons should be at least one order of magnitude (10 times) higher than in healthy persons; (2) sample dilution should not overly reduce clinical sensitivity; (3) the current prevalence must be sufficiently low for the number of samples pooled for the specific protocol; (4) there is no requirement for a fast turnaround time; and (5) there is an imperative need for resource rationing to maximise public health outcomes. The five key steps we suggest for a successful implementation are: (1) determination of when pooling takes place (pre-pre analytical, pre-analytical, analytical); (2) validation of the pooling protocol; (3) ensuring an adequate infrastructure and archival system; (4) configuration of the laboratory information system; and (5) staff training. While pool testing is not a panacea to overcome reagent shortage, it may allow broader access to testing but at the cost of reduction in sensitivity and increased turnaround time.     

ZOOPLANKTON OF LAKES MUTANDA, BUNYONYI AND MULEHE

Quantitative samples of zooplankton from three lakes in the Kigezi District of Uganda have been studied. The systematics of the zooplankton are considered, and some of the identifications given by Worthington & Ricardo (1936) in a previous study of one of these lakes are revised.
Lake Mulehe is the shallowest of the three lakes and contains the largost standing crop of zooplankton. This is in agreement with chemical data which indicato that the supply of nutrient salts in Lake Mulehe is higher than in the other two lakes.
In October 1962 the zooplankton of Lake Mutanda was characterized by the relative abundance of three species of Daphnia which were not found in the samples from the other lakes, although two of these species were present in Lake Bunyonyi in 1931. Rotifers were sparse in Lako Mutands, but here dominant by Tetramastix opoliensis. Lake Bunyonyi was richer in rotifers, but here the dominant species was Keratella tropica , whilo in Lake Mulehe the dominant rotifer was Synchaeta pectinata.
The zooplankton of Lake Mutanda in October 1962 was similar in composition to that of Lake Bunyonyi in 1931, but in 1962 the zooplankton of Lake Bunyonyi was more like that of Lake Mulehe. The possible causos of this change are discussed.     

ON THE DEVELOPMENT OF THE JUGULAR AND CEREBRAL VEINS IN FISHES

The development of the jugular and cerebral veins and adjacent lymphatic vessels in Hepsetus, Salmo, Amia, Acipenser, Neoceratodus, Scyllium and Squalus has been studied on a large embryological material. The reconstruction method has been applied. There has been much confusion in the literature on head veins. This is partly due to the rather schematic investigations of e.g. van Gelderen, and partly to the publications of de Beer and Holmgren, paying no regard to the lymphatic vessels. The currently new features on the v. capitis medialis are that in adult fishes a larger part of the vein remains than was earlier believed. It usually consists of three portions. No secondary vein takes part in the constitution of the jugular vein, as was supposed by de Beer, Holmgren and others. In actinopterygians the secondary vein is in reality represented by the anterior portion of the v. cardinalis anterior as well as of all the v. capitis lateralis, and in elasmobranchs it is only represented by the former portion. The elasmobranchian (except Squalus ) jugular vein is instead formed from the v. capitis lateralis, and in teleostomes and Squalus it is developed from two veins, viz. the anterior portion of the v. capitis medialis and all the v. capitis lateralis. The latter vein is formed from two (teleostomes) or three (elasmobranchs) loops. The v. cardinalis anterior becomes completely atrophied in Squalus , and partly atrophied in Acipenser, Amia and Neoceratodus. The development of the three main cerebral veins is described. van Gelderen's classification of the v. cerebralis media is criticized. And so also is his hypothesis for the evolution of the head veins in fishes. It is suggested that the Hepsetus type is primitive and that the Acipenser and Amia types have evolved from it or from a similar type. Neoceratodus and Squalus have rather specialised types, which seem to have evolved separately right from the base of the system.     

The evolution of mitochondrial genomes in modern frogs (Neobatrachia): nonadaptive evolution of mitochondrial genome reorganization

Background

Although mitochondrial (mt) gene order is highly conserved among vertebrates, widespread gene rearrangements occur in anurans, especially in neobatrachians. Protein coding genes in the mitogenome experience adaptive or purifying selection, yet the role that selection plays on genomic reorganization remains unclear. We sequence the mitogenomes of three species of Glandirana and hot spots of gene rearrangements of 20 frog species to investigate the diversity of mitogenomic reorganization in the Neobatrachia. By combing these data with other mitogenomes in GenBank, we evaluate if selective pressures or functional constraints act on mitogenomic reorganization in the Neobatrachia. We also look for correlations between tRNA positions and codon usage.

Results

Gene organization in Glandirana was typical of neobatrachian mitogenomes except for the presence of pseudogene trnS (AGY). Surveyed ranids largely exhibited gene arrangements typical of neobatrachian mtDNA although some gene rearrangements occurred. The correlation between codon usage and tRNA positions in neobatrachians was weak, and did not increase after identifying recurrent rearrangements as revealed by basal neobatrachians. Codon usage and tRNA positions were not significantly correlated when considering tRNA gene duplications or losses. Change in number of tRNA gene copies, which was driven by genomic reorganization, did not influence codon usage bias. Nucleotide substitution rates and d_N/d_S ratios were higher in neobatrachian mitogenomes than in archaeobatrachians, but the rates of mitogenomic reorganization and mt nucleotide diversity were not significantly correlated.

Conclusions

No evidence suggests that adaptive selection drove the reorganization of neobatrachian mitogenomes. In contrast, protein-coding genes that function in metabolism showed evidence for purifying selection, and some functional constraints appear to act on the organization of rRNA and tRNA genes. As important nonadaptive forces, genetic drift and mutation pressure may drive the fixation and evolution of mitogenomic reorganizations.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-691) contains supplementary material, which is available to authorized users.     

AN INTERPRETATION OF GULAR SIZE IN SOME ADULT COLEOPTERA

An interpretation of the gular width of some adult beetles has been attempted in terms of absolute head size and the functioning of the mounth-parts. In many groups of beetles (e.g Aphodiinae) the gular width to head width ratio remains approximately constant in species of incresing size, whereas in the Staphylininae it declines because the absolute width of the gula remains nearly constant. Thus in very large Staphylininae the gular sulci meet in the midline. It is suggested that this is due to a relative increase in the size of the mandibular adductors which is necessary to maintain the relstive biting force in larger species, this being required for the penetration of tough prey. It is postulated that this need arises because if the head width were doubled, the volume (and weight) of the head would increase about eight times, whilst the cross-sectional area of the mandibular adductors would only quadruple. A variety of species have been examined in relation to this hypothesis. It is suggested that many Carabidae do not conform because of the presence of stipital retractor muscles between the gular fidges. It also appears that because of these muscles some species have developed a mid-gular apodeme to bear the origins of the labial muscles.