The colonization of the New World by the Palearctic species Drosophila subobscura was first detected in 1978 in South America and around 1982 in western North America. The ensuing dramatic expansion of the species, in territory as well as numbers, provides an opportunity for studying evolution in a scale rarely possible. We have used 10 restriction endonucleases to analyze the mitochondrial DNA (mtDNA) of individuals from 23 widely dispersed localities. Only two mtDNA composite morphs have been detected in the Americas. None of the two morphs has been found in Africa, and only one in the Atlantic islands; but both are widespread in Europe, which provides no clue of the precise geographic origin of the colonizers. The amount of nucleotide-substitution polymorphism detected in D. subobscura is typical for animals, but it is greater in the Old than in the New World, presumably due to the recent colonization by a limited number of colonizers. Assuming standard evolutionary rates of mtDNA base substitution, the mtDNA morphs found in D. subobscura can be traced to a single one that existed no less than one million years ago. We argue against the inference that the D. subobscura flies now living descend from only one or a few females that lived at that time. This type of inference, which we call the "Mother Eve hypothesis," has been made to conclude that the human population went through a severe constriction about 200,000 years ago, so that all living humans descend from only one or a few women who lived at that time. The Mother Eve hypothesis is fallacious.

We have examined eight enzyme polymorphisms in groups of Drosophila melanogaster flies with fast, intermediate and slow development. The allelic frequencies are similar in all three developmental classes, but the distribution of the genotypes among the classes is significantly heterogenous for the three loci on the second chromosome. When the total sample of 300 individuals is examined, significant gametic disequilibrium appears in 3 out of 13 pairs of genes located on the same chromosome and in 4 out of 15 pairs of genes located on different chromosomes. This 25% incidence of disequilibrium between pairs of genes is larger than previously observed in other natural populations (but similar to the incidence observed in laboratory populations). The greater frequency of significant gametic disequilibrium in our study is probably due to the larger number of genomes sampled.-Some models specifically predict that individuals with faster rates of development (i.e., greater fitness) should be more heterozygous (and exhibit more linkage disequilibrium) than individuals with slower development. This hypothesis is not supported by our results.

This study assesses if nudges in the form of informational videos sent via WhatsAppare effective in boosting take-up rates among vulnerable populations, specifically in the context of a regularization program for Venezuelan forced migrants in Colombia. The study randomly assigned 1,375 eligible migrants to receive one of three informational videos or be in a control group. The videos aimed at solving issues related to awareness, trust, and bottlenecks in the step-by-step registration. The main results indicate that program take-up rates for individuals who received any video, were eight percentage points lower compared to the control group. The effects are mostly driven by the treated individuals who received the links but did not watch the videos, who are older, busier, and with less internet access relative to other treated individuals. Additionally, the study evaluates the effectiveness of iterative WhatsApp surveys in collecting data from hard-to-reach populations. It finds that iterative WhatsApp surveys had low retention rates, and iterative contacts do not helped to reduce attrition.

Abstract Background Recent genomic analyses of arthropod defense mechanisms suggest conservation of key elements underlying responses to pathogens, parasites and stresses. At the center of pathogen-induced immune responses are signaling pathways triggered by the recognition of fungal, bacterial and viral signatures. These pathways result in the production of response molecules, such as antimicrobial peptides and lysozymes, which degrade or destroy invaders. Using the recently sequenced genome of the pea aphid (Acyrthosiphon pisum), we conducted the first extensive annotation of the immune and stress gene repertoire of a hemipterous insect, which is phylogenetically distantly related to previously characterized insects models. Results Strikingly, pea aphids appear to be missing genes present in insect genomes characterized to date and thought critical for recognition, signaling and killing of microbes. In line with results of gene annotation, experimental analyses designed to characterize immune response through the isolation of RNA transcripts and proteins from immune-challenged pea aphids uncovered few immune-related products. Gene expression studies, however, indicated some expression of immune and stress-related genes. Conclusions The absence of genes suspected to be essential for the insect immune response suggests that the traditional view of insect immunity may not be as broadly applicable as once thought. The limitations of the aphid immune system may be representative of a broad range of insects, or may be aphid specific. We suggest that several aspects of the aphid life style, such as their association with microbial symbionts, could facilitate survival without strong immune protection.