A long winter for the Red Queen: rethinking the evolution of seasonal migration

This paper advances an hypothesis that the primary adaptive driver of seasonal migration is maintenance of site fidelity to familiar breeding locations. We argue that seasonal migration is therefore principally an adaptation for geographic persistence when confronted with seasonality – analogous to hibernation, freeze tolerance, or other organismal adaptations to cyclically fluctuating environments. These ideas stand in contrast to traditional views that bird migration evolved as an adaptive dispersal strategy for exploiting new breeding areas and avoiding competitors. Our synthesis is supported by a large body of research on avian breeding biology that demonstrates the reproductive benefits of breeding‐site fidelity. Conceptualizing migration as an adaptation for persistence places new emphasis on understanding the evolutionary trade‐offs between migratory behaviour and other adaptations to fluctuating environments both within and across species. Seasonality‐induced departures from breeding areas, coupled with the reproductive benefits of maintaining breeding‐site fidelity, also provide a mechanism for explaining the evolution of migration that is agnostic to the geographic origin of migratory lineages (i.e. temperate or tropical). Thus, our framework reconciles much of the conflict in previous research on the historical biogeography of migratory species. Although migratory behaviour and geographic range change fluidly and rapidly in many populations, we argue that the loss of plasticity for migration via canalization is an overlooked aspect of the evolutionary dynamics of migration and helps explain the idiosyncratic distributions and migratory routes of long‐distance migrants. Our synthesis, which revolves around the insight that migratory organisms travel long distances simply to stay in the same place, provides a necessary evolutionary context for understanding historical biogeographic patterns in migratory lineages as well as the ecological dynamics of migratory connectivity between breeding and non‐breeding locations.     

Telomere elongation (Tel), a new mutation in Drosophila melanogaster that produces long telomeres.

In most eukaryotes telomeres are extended by telomerase. Drosophila melanogaster, however, lacks telomerase, and telomere-specific non-LTR retrotransposons, HeT-A and TART, transpose specifically to chromosome ends. A Drosophila strain, Gaiano, that has long telomeres has been identified. We extracted the major Gaiano chromosomes into an Oregon-R genetic background and examined the resulting stocks after 60 generations. In situ hybridization using HeT-A and TART sequences showed that, in stocks carrying either the X or the second chromosome from Gaiano, only the Gaiano-derived chromosomes display long telomeres. However, in stocks carrying the Gaiano third chromosome, all telomeres are substantially elongated, indicating that the Gaiano chromosome 3 carries a factor that increases HeT-A and TART addition to the telomeres. We show that this factor, termed Telomere elongation (Tel), is dominant and localizes as a single unit to 69 on the genetic map. The long telomeres tend to associate with each other in both polytene and mitotic cells. These associations depend on telomere length rather than the presence of Tel. Associations between metaphase chromosomes are resolved during anaphase, suggesting that they are mediated by either proteinaceous links or DNA hydrogen bonding, rather than covalent DNA-DNA bonds.     

Vimentin regulates peripheral nerve myelination

Myelination is a complex process that requires coordinated Schwann cell-axon interactions during development and regeneration. Positive and negative regulators of myelination have been recently described, and can belong either to Schwann cells or neurons. Vimentin is a fibrous component present in both Schwann cell and neuron cytoskeleton, the expression of which is timely and spatially regulated during development and regeneration. We now report that vimentin negatively regulates myelination, as loss of vimentin results in peripheral nerve hypermyelination, owing to increased myelin thickness in vivo, in transgenic mice and in vitro in a myelinating co-culture system. We also show that this is due to a neuron-autonomous increase in the levels of axonal neuregulin 1 (NRG1) type III. Accordingly, genetic reduction of NRG1 type III in vimentin-null mice rescues hypermyelination. Finally, we demonstrate that vimentin acts synergistically with TACE, a negative regulator of NRG1 type III activity, as shown by hypermyelination of double Vim/Tace heterozygous mice. Our results reveal a novel role for the intermediate filament vimentin in myelination, and indicate vimentin as a regulator of NRG1 type III function.     

The integration of mutant loci affecting maize endosperm development in a dense genetic map using an AFLP-based procedure

In this paper, 10 mutations conditioning the appearance of defective, miniature or collapsed endosperm, but with normal sporophyte development, were considered. Homozygous mutant kernels have reduced grain weight, kernel size, density and, in some of these, higher than normal seed protein content. The mutant loci were integrated into a high-resolution genetic map in order to associate them to specific genes. We have placed 1167 AFLP markers on a consensus map using IBM2 as a backbone and reaching an average of 1 marker every 1.9 cM. We have identified AFLP markers linked to all individual mutant alleles. BSA was adopted to screen the largest possible number of primer combinations on homozygous F₃ mutant and wild type plants. The ten mutant loci are linked to the closest AFLP or SSR markers with distances ranging from 0 to 17.9 cM. The genes we have defined by the existence of mendelian mutants can now be considered good candidates for testing the association to QT loci. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and characterization of tetra-end linked oligonucleotides capable of forming monomolecular G-quadruplexes

The chemical synthesis of two new G-rich Tetra-End-Linked-oligodeoxyribonucleotides (TEL-ODNs) as well as (1)H-NMR and CD spectra of the corresponding monomolecular quadruplexes (IVa and IVb) has been reported. The new TEL-ODNs, characterized by the presence of short branches in the linker moiety, could be very useful for the achievement of monomolecular quadruplexes with predetermined strand orientation.     

The Effect of Moonlight on Scopoli's Shearwater Calonectris diomedea Colony Attendance Patterns and Nocturnal Foraging: A Test of the Foraging Efficiency Hypothesis

Moonlight is known to affect the nocturnal behaviour and activity rhythms of many organisms. For instance, predators active at night may take advantage from increased visibility afforded by the moon, while prey might regulate their activity patterns to become less detectable. Many species of pelagic seabirds attend their colony only at night, in complete darkness, avoiding approaching their nest sites under moonlight. This behaviour has been most often interpreted as an antipredator adaptation (‘predation avoidance’ hypothesis). However, it may also reflect a lower foraging efficiency during moonlit nights (‘foraging efficiency’ hypothesis). Indeed, moonlight may reduce prey availability because preferred seabird prey is known to occur at higher depths in moonlit nights. Using high‐accuracy behavioural information from data loggers, we investigated the effect of moonlight on colony attendance and at‐sea nocturnal foraging in breeding Scopoli's shearwaters Calonectris diomedea. We found that birds departing for self‐feeding trips around the full moon performed longer trips than those departing around the new moon. On nights when the moon was present only partly, nest burrow entrances took place largely in the moonless portion of the night. Moreover, contrary to predictions from the ‘foraging efficiency’ hypothesis, nocturnal foraging activity increased according to moonlight intensity, suggesting that birds increased their foraging activity when prey became more detectable. This study strengthens the idea that colony attendance behaviour is strictly controlled by moonlight in shearwaters, which is possibly related to the perception of a predation risk.     

Cytotoxin‐Associated Gene‐A – Positive Helicobacter pylori Strains Infection Increases the Risk of Recurrent Atherosclerotic Stroke

Background: CagA‐positive Helicobacter pylori infection has been found to be associated with a first‐ever atherosclerotic stroke. The aim of this study was to investigate whether these strains represent an independent risk factor for recurrent atherosclerotic stroke. Materials and Methods: We performed a longitudinal study of patients with a first‐ever large vessels stroke and resulted positive at H. pylori serology. Patients had clinical examination 1 month after the acute event, and were subsequently visited or contacted by telephone up to 3 years at 6‐month intervals. Sera obtained at the time of enrollment were frozen and analyzed for the presence of anti‐CagA antibodies at the end of the study. The primary outcome event was any fatal or nonfatal stroke after the index stroke. Results: One hundred seventy H. pylori‐positive patients were included (n = 68 CagA positive and n = 102 CagA negative). No significant difference regarding age and other stroke risk factors was detected. According to Kaplan‐Meier survival analysis, CagA‐positive patients showed a significantly higher risk for stroke recurrence than CagA‐negative ones (45.6% vs 17.6%; p < .001). Difference in the rate of recurrent stroke between the two groups persisted after Cox regression analysis taking into account possible confounding factors (hazard ratio = 3.5; 95% CI = 1.9–6.4; p < .001). Conclusions: Infection with H. pylori CagA‐positive strains increases the risk of recurrent atherosclerotic stroke. Seropositivity determination should be performed in order to identify high‐risk patients requiring a strict clinical surveillance, and the possible beneficial effect of eradication therapy should be evaluated.