Recent speciation in the Formica rufa group ants (Hymenoptera, Formicidae): inference from mitochondrial DNA phylogeny

This study examines phylogenetic relationships among six species of the Formica rufa group ants (F. polyctena, F. rufa, F. lugubris, F. paralugubris, F. aquilonia, and F. pratensis). The phylogeny based on a 2051bp fragment of mtDNA including cyt b, tRNASer, and ND1 genes supports the division of the group into three major clusters: one with the species F. polyctena and F. rufa, one with F. aquilonia, F. lugubris, and F. paralugubris, and the third one with F. pratensis. The interspecific divergence estimates (mean 0.98 +/- 0.15% for the main phylogenetic groups) imply that radiation took place during the Pleistocene. Comparison of the divergence estimates among the F. rufa group species with divergence estimates among other closely related species of insects suggests that speciation in the group was relatively fast, and the mitochondrial lineages of F. polyctena and F. rufa have not fully separated. The haplotype tree shows also signs of transfer of mtDNA between species through hybridisation. The distribution of polygyny (multiple queens per nest) along the branches of the tree indicates that the social type characterised by highly polygynous societies and large colonial networks, has originated at least three times. The species F. aquilonia and F. paralugubris that build such large supercolonies, cluster tightly together with very little nucleotide variation, suggesting that this type of social organisation could be a factor promoting speciation in the ants.     

Exceptionally high density of NUMTs in the honeybee genome

The available genome sequences of 4 insects (the fruit fly, the African malaria mosquito, the flour beetle, and the honeybee) are used to compare the amount of mitochondrial DNA transferred to the nuclear genome (NUMTs). The data from the beetle and the bee show frequent transfer of NUMTs, whereas NUMTs in the 2 other insects are rare. The density of NUMTs in the honeybee (>1.0 bp transferred DNA per 1 kb of the nuclear sequence) is the highest in any animal studied, about ten times higher than in humans and comparable to the densities in plant genomes. The density of NUMTs in the beetle (0.056 bp/kb) is of the same order of magnitude as that in humans. The analysis of the honeybee genome indicates that NUMTs originate from all parts of the mitochondrial genome, that about two-thirds of the nuclear copies result from secondary transpositions within the nuclear genome, that the copies are significantly associated to "mariner" type transposons, and that the NUMTs consist mainly of short and fragmented copies.     

Measuring genetic relatedness in natural populations: Methodology

The estimation of relatedness within social groups, such as the colonies of a population of social insects, is an important field for evaluating hypotheses concerning the evolution and maintenance of social behaviour. The methodology of this estimation from genetic data in the absence of pedigree information has been poorly understood; we develop this methodology for b, the regression coefficient of relatedness, and discuss its applications. Both b and G (the pedigree coefficient of relatedness) are potentially asymmetric coefficients, whereas φ, r, and F_ST are necessarily symmetric. We develop an estimator for b suitable for small samples, and also one for standard deviation, and examine the properties of both using sampling simulations. The b estimator returns values slightly below E(b), and the standard deviation estimator yields conservative confidence intervals. A comparative study of b and F_ST shows that, given the same set of data, b is estimated with greater reliability than is F_ST. As is the case for F_ST, b can be used to examine population structure at various levels, and b possesses the advantage of an estimator for its standard error, which can also be used to test for heterogeneity among the loci surveyed. The actual numbers of identical genes held in common by interacting individuals, and not simply their proportions, need to be considered in using coefficients of relatedness in inclusive fitness calculations. This necessity is handled by the weighted coefficients of relatedness, G′ and b′, which have been referred to in the literature as r (as have most relatedness measures).     

Functional Subdivision of Group-ICA Results of fMRI Data Collected during Cinema Viewing

Independent component analysis (ICA) can unravel functional brain networks from functional magnetic resonance imaging (fMRI) data. The number of the estimated components affects both the spatial pattern of the identified networks and their time-course estimates. Here group-ICA was applied at four dimensionalities (10, 20, 40, and 58 components) to fMRI data collected from 15 subjects who viewed a 15-min silent film ("At land" by Maya Deren). We focused on the dorsal attention network, the default-mode network, and the sensorimotor network. The lowest dimensionalities demonstrated most prominent activity within the dorsal attention network, combined with the visual areas, and in the default-mode network; the sensorimotor network only appeared with ICA comprising at least 20 components. The results suggest that even very low-dimensional ICA can unravel the most prominent functionally-connected brain networks. However, increasing the number of components gives a more detailed picture and functionally feasible subdivision of the major networks. These results improve our understanding of the hierarchical subdivision of brain networks during viewing of a movie that provides continuous stimulation embedded in an attention-directing narrative.     

Genetic differentiation of disjunct populations of the antsFormica aquilonia andFormica lugubris in Europe

Summary The speciesFormica aquilonia andF. lugubris of the mound-building red wood ants have a disjunct boreoalpine distribution in Europe. The populations ofF. aquilonia in Finland, Switzerland and the British Isles show little genetic differentiation, whereas the populations ofF. lugubris show considerable differentiation. The Central European populations morphologically identified asF. lugubris can be genetically divided into two groups (here called types A and B). Type B is found in the Alps and the Jura mountains, and is genetically inseparable fromF. aquilonia. Type A lives sympatrically with type B in the Jura mountains and is also found in the British Isles. Sympatry of the two types in the Jura shows that these are separate species. It remains open whether type B is morphologically atypicalF. aquilonia or whether it is a separate species, perhaps with a past history of introgression betweenF. aquilonia andF. lugubris. The gene frequencies in the Finnish populations ofF. lugubris differ from those of both types A and B. Genetic differences withinF. lugubris indicate that the populations have evolved separately for a long time. The social structure ofF. lugubris colonies also shows geographic variation. The nests in Finland and the British Isles seem to be mainly monogynous and monodomous, whereas the nests in Central Europe are polygynous and form polydomous colonies.F. aquilonia has polygynous and polydomous colonies in all populations studied.     

Variation of colony types in the antFormica cinerea

Summary Formica cinerea is a rare ant species in northern Europe where it occurs in few isolated populations. Estimates of genetic relatedness among worker nestmates revealed very different colonial structures. Relatedness was g = 0.81 in one population, and g = –0.03 and = 0.01 in two others. These results indicate that some populations of the species have mainly monogynous colonies (perhaps with monandrous queens), whereas others consist of polygynous and possibly polydomous colonies. Genetic differentiation of closely located populations suggests restricted dispersal.     

The effects of deleterious mutations on linked, neutral variation in small populations.

The effects of recessive, deleterious mutations on genetic variation at linked neutral loci can be heterozygosity-decreasing because of reduced effective population sizes or heterozygosity-increasing because of associative overdominance. Here we examine the balance between these effects by simulating individual diploid genotypes in small panmictic populations. The haploid genome consists of one linkage group with 1000 loci that can have deleterious mutations and a neutral marker. Combinations of the following parameters are studied: gametic mutation rate to harmful alleles (U), population size (N), recombination rate (r), selection coefficient (s), and dominance (h). Tight linkage (r 相似文献