The Pattern of R2 Retrotransposon Activity in Natural Populations of Drosophila simulans Reflects the Dynamic Nature of the rDNA Locus

The pattern and frequency of insertions that enable transposable elements to remain active in a population are poorly understood. The retrotransposable element R2 exclusively inserts into the 28S rRNA genes where it establishes long-term, stable relationships with its animal hosts. Previous studies with laboratory stocks of Drosophila simulans have suggested that control over R2 retrotransposition resides within the rDNA loci. In this report, we sampled 180 rDNA loci of animals collected from two natural populations of D. simulans. The two populations were found to have similar patterns of R2 activity. About half of the rDNA loci supported no or very low levels of R2 transcripts with no evidence of R2 retrotransposition. The remaining half of the rDNA loci had levels of R2 transcripts that varied in a continuous manner over almost a 100-fold range and did support new retrotransposition events. Structural analysis of the rDNA loci in 18 lines that spanned the range of R2 transcript levels in these populations revealed that R2 number and rDNA locus size varied 2-fold; however, R2 activity was not readily correlated with either of these parameters. Instead R2 activity was best correlated with the distribution of elements within the rDNA locus. Loci with no activity had larger contiguous blocks of rDNA units free of R2-insertions. These data suggest a model in which frequent recombination within the rDNA locus continually redistributes R2-inserted units resulting in changing levels of R2 activity within individual loci and persistent R2 activity within the population

Constructing the metropolitan homeland: the literatures of the white settler societies of New Zealand and Australia

This article examines the responses articulated in white settler writing from New Zealand and Australia to the location and status of these nations as postcolonial diasporas. Beginning with the early colonial sense of estrangement from and idealisation of the metropolitan homeland of Great Britain it traces a pattern of literary engagement with the European source of ethnic origin through to the present day. The article notes changing attitudes towards home and homelands due to the greater fluidity and complexity of migratory and travel paths as the binaries of home and abroad, empire and colony, metropolitan centre and provincial periphery begin to break down towards the end of the twentieth centur

Intraspecific concerted evolution of the rDNA ITS1 in anopheles farauti sensu stricto (Diptera: Culicidae) reveals recent patterns of population structure

We examined the intraindividual variation present in the first ribosomal internal transcribed spacer (ITS1) of Anopheles farauti to determine the level of divergence among populations for this important malarial vector. We isolated 187 clones from 70 individuals and found regional variation among four internal tandem repeats. The data were partitioned prior to analysis given the presence of a paralogous ITS2 sequence, called the 5'-subrepeat, inserted in the ITS1 of most clones. A high level of homogenization and population differentiation was observed for this repeat, which indicates a higher rate of turnover relative to the adjacent 'core' region. Bayesian analysis was performed using several substitutional models on both a combined and a partitioned data set. On the whole, the ITS1 phylogeny and geographic origin of the samples appear to be congruent. Some interesting exceptions indicate the spread of variant repeats between populations and the retention of ancestral polymorphism. Our data clearly demonstrate concerted evolution at the intraspecific level despite intraindividual variation and a complex internal repeat structure from a species that occupies a continuous coastal distribution. A high rate of genomic turnover in combination with a high level of sequence divergence appears to be a major factor leading to its concerted evolution within these populations

A conflict of morphological and genetic patterns in the Australian anostracan Branchinella longirostris

Branchinella longirostris is a fairy shrimp endemic to ephemeral pools on granite outcrops in southwestern Australia. The patchy nature of its habitat is thought to result in a high degree of subdivision among populations, potentially promoting speciation. We combined traditional taxonomy with a molecular phylogeny of cytochrome c oxidase I (COI) to test whether B. longirostris could be a species complex and whether the frontal appendage on the second antennae of males is a suitable character to differentiate new species. We also used nested clade analysis to assess the population structure and demographic factors explaining the geographical distributions of the mt DNA haplotypes. The results show that shapes of frontal appendages are not congruent with the mitochondrial genetic structure; however, they are positively correlated with geography. We conclude that the frontal appendage in B. longirostris is either subject to selection or a result of morphological plasticity; thus, its use in taxonomy remains uncertain. The intraspecific divergence in B. longirostris (≤7.7%) was approximately one third as large as the divergence from the outgroup (17.8–20.8%) and well within the ranges of divergence found in other crustaceans with fragmented population structure. There is some association between genetic structure and geography, resulting in the inference of restricted gene flow with isolation by distance and allopatric fragmentation as the most suitable models of the historical population processes. It is likely that the current distribution of haplotypes resulted from the dispersal of resting eggs by stochastic events (wind, birds) rather than from a fragmentation of previously continuous habitat as the estimated evolutionary age of the species (≤6.1 my) is much younger than its habitat (50–100 my). We found some evidence on the genetic level to support the hypothesis that B. longirostris could be a complex of species; however, the lack of correlation between the genetic pattern and the reproductively important frontal appendage lends a support to a view that B. longirostris is a single species with an exceptionally high intraspecific diversity