An analysis of allozymic characters of four species of New Zealand Amalda (Gastropoda: Olividae: Ancillinae)

Abstract

This contribution reports the results of an electrophoretic analysis of four species of the molluscan genus Amalda. The results of this analysis confirm that four taxonomically defined species are also biologically distinct, that their often considerable morphological variability is a within-species phenomenon, and that a previously undescribed form of A. depressa, which is genetically and morphologically distinct, occurs in the Bay of Islands. The genetic data were analysed cladistically and the resulting phylogenetic classification supports that based on morphology.     

Simultaneous Regulation of Cytokinetic Furrow and Nucleus Positions by Cortical Tension Contributes to Proper DNA Segregation during Late Mitosis

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What Do Pneumocystis Organisms Tell Us about the Phylogeography of Their Hosts? The Case of the Woodmouse Apodemus sylvaticus in Continental Europe and Western Mediterranean Islands

Pneumocystis fungi represent a highly diversified biological group with numerous species, which display a strong host-specificity suggesting a long co-speciation process. In the present study, the presence and genetic diversity of Pneumocystis organisms was investigated in 203 lung samples from woodmice (Apodemus sylvaticus) collected on western continental Europe and Mediterranean islands. The presence of Pneumocystis DNA was assessed by nested PCR at both large and small mitochondrial subunit (mtLSU and mtSSU) rRNA loci. Direct sequencing of nested PCR products demonstrated a very high variability among woodmouse-derived Pneumocystis organisms with a total number of 30 distinct combined mtLSU and mtSSU sequence types. However, the genetic divergence among these sequence types was very low (up to 3.87%) and the presence of several Pneumocystis species within Apodemus sylvaticus was considered unlikely. The analysis of the genetic structure of woodmouse-derived Pneumocystis revealed two distinct groups. The first one comprised Pneumocystis from woodmice collected in continental Spain, France and Balearic islands. The second one included Pneumocystis from woodmice collected in continental Italy, Corsica and Sicily. These two genetic groups were in accordance with the two lineages currently described within the host species Apodemus sylvaticus. Pneumocystis organisms are emerging as powerful tools for phylogeographic studies in mammals.     

Balancing Selection of a Frame-Shift Mutation in the MRC2 Gene Accounts for the Outbreak of the Crooked Tail Syndrome in Belgian Blue Cattle

We herein describe the positional identification of a 2-bp deletion in the open reading frame of the MRC2 receptor causing the recessive Crooked Tail Syndrome in cattle. The resulting frame-shift reveals a premature stop codon that causes nonsense-mediated decay of the mutant messenger RNA, and the virtual absence of functional Endo180 protein in affected animals. Cases exhibit skeletal anomalies thought to result from impaired extracellular matrix remodeling during ossification, and as of yet unexplained muscular symptoms. We demonstrate that carrier status is very significantly associated with desired characteristics in the general population, including enhanced muscular development, and that the resulting heterozygote advantage caused a selective sweep which explains the unexpectedly high frequency (25%) of carriers in the Belgian Blue Cattle Breed.     

Mus in Morocco: a Quaternary sequence of intraspecific evolution

North Africa is an intricate biogeographical region at the crossroads of immigration waves from tropical Africa and Asia. Species confined between various barriers (Atlas Mountains, arid environments such as the Sahara in the south, water masses such as the Mediterranean Sea in the north, and the Atlantic Ocean in the west) were generally forced to adapt locally to environmental changes instead of tracking their habitat by shifting their distribution area. The present study aims at providing first insight into the evolution of the genus Mus, and more specifically of the western Mediterranean species Mus spretus in this area. The study relies on the abundant Late Pleistocene and Middle Holocene fossil assemblage from the El Harhoura 2 cave (Rabat‐Témara, Morocco). This exceptional record was studied using geometric morphometrics applied to first upper and lower molars, constituting the most informative and best preserved fossil remains for such small rodents. Two main issues were addressed. (1) Geometric morphometrics was used to clarify taxonomic status and phylogenetic relationships among fossil and modern species in this area. Morphometric analysis revealed good discrimination of most modern and fossil species but failed to document intermediate forms tracing anagenetic evolution. Not mutually exclusive, the occurrence of complex processes of morphological evolution in this genus such as parallel evolution and the action of stabilizing selection may make it difficult to translate patterns of morphological evolution into phylogenetic conclusions. (2) The record was shown to document a sequence of intraspecific evolution of M. spretus. The morphology of the molars through the fossil record of El Harhoura 2 was surprisingly stable despite extensive modern variation. The limited temporal variation largely failed to correlate to palaeoenvironmental proxies. The mouse fossil record at El Harhoura 2 thus presents an intriguing case of morphological stasis despite extensive environmental changes. This long‐term stability may have been recently perturbed by anthropogenic factors including landscape changes and introduction of various competitors and predators, leading to a size reduction. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 109 , 599–621.     

Mandibles and molars of the wood mouse, Apodemus sylvaticus (L.): integrated latitudinal pattern and mosaic insular evolution

Aim The distinct nature of island populations has traditionally been attributed either to adaptation to particular insular conditions or to random genetic effects. In order to assess the relative importance of these two disparate processes, insular effects were addressed in the European wood mouse, Apodemus sylvaticus (Linnaeus, 1758). Location Wood mice from 33 localities on both mainland and various Atlantic and western Mediterranean islands were considered. This sampling covers only part of the latitudinal range of A. sylvaticus but included the two main genetic clades identified by previous studies. Islands encompass a range of geographical conditions (e.g. small islands fringing the continent through large and isolated ones). Methods The insular syndrome primarily invokes variations in body size, but ecological factors such as release from competition, niche widening and food availability should also influence other characters related to diet. In the present study, the morphology of the wood mice was quantified based on two characters involved in feeding: the size and shape of the mandibles and first upper molars. The size of the mandible is also a proxy for the body size of the animal. Patterns of morphological differentiation of both features were estimated using two‐dimensional outline analysis based on Fourier methods. Results Significant differences between mainland and island populations were observed in most cases for both the mandibles and molars. However, molars and mandibles displayed divergent patterns. Mandible shape diverged mostly on islands of intermediate remoteness and competition levels, whereas molars exhibited the greatest shape differentiation on small islands, such as Port‐Cros and Porquerolles. A mosaic pattern was also displayed for size. Body and mandible size increased on Ibiza, but molar size remained similar to mainland populations. Mosaic patterns were, however, not apparent in the mainland populations. Congruent latitudinal variations were evident for the size and shape of both mandibles and molars. Main conclusions Mosaic evolution appears to characterize insular divergence. The molar seems to be more prone to change with reduced population size on small islands, whereas the mandible could be more sensitive to peculiar environmental conditions on large and remote islands.     

HIV-1 DIS stem loop forms an obligatory bent kissing intermediate in the dimerization pathway

The HIV-1 dimerization initiation sequence (DIS) is a conserved palindrome in the apical loop of a conserved hairpin motif in the 5′-untranslated region of its RNA genome. DIS hairpin plays an important role in genome dimerization by forming a ‘kissing complex’ between two complementary hairpins. Understanding the kinetics of this interaction is key to exploiting DIS as a possible human immunodeficiency virus (HIV) drug target. Here, we present a single-molecule Förster resonance energy transfer (smFRET) study of the dimerization reaction kinetics. Our data show the real-time formation and dissociation dynamics of individual kissing complexes, as well as the formation of the mature extended duplex complex that is ultimately required for virion packaging. Interestingly, the single-molecule trajectories reveal the presence of a previously unobserved bent intermediate required for extended duplex formation. The universally conserved A272 is essential for the formation of this intermediate, which is stabilized by Mg²⁺, but not by K⁺ cations. We propose a 3D model of a possible bent intermediate and a minimal dimerization pathway consisting of three steps with two obligatory intermediates (kissing complex and bent intermediate) and driven by Mg²⁺ ions.