Maintenance and loss of heterozygosity in a thelytokous lineage of honey bees (Apis mellifera capensis)

An asexual lineage that reproduces by automictic thelytokous parthenogenesis has a problem: rapid loss of heterozygosity resulting in effective inbreeding. Thus, the circumstances under which rare asexual lineages thrive provide insights into the trade-offs that shape the evolution of alternative reproductive strategies across taxa. A socially parasitic lineage of the Cape honey bee, Apis mellifera capensis, provides an example of a thelytokous lineage that has endured for over two decades. It has been proposed that cytological adaptations slow the loss of heterozygosity in this lineage. However, we show that heterozygosity at the complementary sex determining (csd) locus is maintained via selection against homozygous diploid males that arise from recombination. Further, because zygosity is correlated across the genome, it appears that selection against diploid males reduces loss of homozygosity at other loci. Selection against homozygotes at csd results in substantial genetic load, so that if a thelytokous lineage is to endure, unusual ecological circumstances must exist in which asexuality permits such a high degree of fecundity that the genetic load can be tolerated. Without these ecological circumstances, sex will triumph over asexuality. In A. m. capensis, these conditions are provided by the parasitic interaction with its conspecific host, Apis mellifera scutellata.     

Dynamic mutation-selection balance as an evolutionary attractor

The vast majority of mutations are deleterious and are eliminated by purifying selection. Yet in finite asexual populations, purifying selection cannot completely prevent the accumulation of deleterious mutations due to Muller's ratchet: once lost by stochastic drift, the most-fit class of genotypes is lost forever. If deleterious mutations are weakly selected, Muller's ratchet can lead to a rapid degradation of population fitness. Evidently, the long-term stability of an asexual population requires an influx of beneficial mutations that continuously compensate for the accumulation of the weakly deleterious ones. Hence any stable evolutionary state of a population in a static environment must involve a dynamic mutation-selection balance, where accumulation of deleterious mutations is on average offset by the influx of beneficial mutations. We argue that such a state can exist for any population size N and mutation rate U and calculate the fraction of beneficial mutations, ε, that maintains the balanced state. We find that a surprisingly low ε suffices to achieve stability, even in small populations in the face of high mutation rates and weak selection, maintaining a well-adapted population in spite of Muller's ratchet. This may explain the maintenance of mitochondria and other asexual genomes.     

Fatty acid and very low density lipoprotein metabolism in obese African American and Caucasian women with type 2 diabetes

Type 2 diabetes mellitus (T2DM) is associated with increased plasma triglyceride (TG) concentrations, but African Americans (AA) have lower plasma TG than Caucasians (CC). We evaluated the hypothesis that obese AA women have lower plasma TG than obese CC women do because of differences in lipid kinetics. Eleven AA and 11 CC obese women with T2DM, matched on body mass index (BMI) (AA = 37 ± 1, CC = 37 ± 1 kg/m²), age, duration of diabetes, percentage body fat, and insulin sensitivity (S_I, determined by an intravenous glucose tolerance test), were studied. Plasma TG concentration (AA = 1.14 ± 0.11, CC = 1.88 ± 0.18 mmol/l), FFA rate of appearance (R_a) into plasma (AA = 419 ± 27, CC = 503 ± 31 µmol·min⁻¹), and total VLDL-TG secretion rate (AA = 18 ± 2, CC = 29 ± 4 µmol·min⁻¹) were lower in AA than CC women (all P < 0.05). In contrast, plasma total apolipoprotein (apo)B-100 concentration (AA = 1,542 ± 179, CC = 1,620 ± 118 nmol/l) and VLDL-apoB-100 secretion rate (AA = 1.3 ± 0.1, CC = 1.3 ± 0.1 nmol·min⁻¹) were similar in both groups, so the molar ratio of VLDL-TG secretion rate to VLDL-apoB-100 secretion rate was lower in AA women than in CC women. VLDL-TG concentration was lower in AA women due to lower total VLDL-TG secretion rate. However, the VLDL-apoB-100 secretion rate was the same in both groups, demonstrating that AA women secrete smaller VLDL particles containing less TG than do CC women.     

Improved biovar test for Ralstonia solanacearum

Race 3, biovar 2 strains of Ralstonia solanacearum are quarantined pathogens in Europe and Canada and Select Agent pathogens in the United States. The biovar classification of R. solanacearum strains is based on their biochemical abilities to utilize a carbohydrate panel. The standard biovar test uses bromothymol blue as a pH indicator in 15 ml culture tubes containing 3 to 5 ml of test media, and takes weeks to complete at 24 or 28 °C. We improved the biovar test by using phenol red as a pH indicator that changes color at a higher pH when a carbohydrate is utilized. We also conducted the test at 32 °C in 0.2 ml of 8-tube strips that reduced the medium needed by at least 20 fold. Using the improved test, biovars of R. solanacearum strains can be determined in 4 days when a panel of seven carbohydrates is used including glucose, trehalose, mannitol, sorbitol, dulcitol, maltose and cellobiose. To differentiate biovars 1, 2, 3 and 4, the test can be further simplified and completed in 3 days using a panel of four carbohydrates containing glucose, trehalose, maltose and dulcitol, significantly saving money, space and time.     

Folk conceptualizations of racism and antiracism in Brazil and South Africa

Abstract

Folk conceptualizations of racism can be defined as ordinary people's understandings of the sources and persistence of racism. They function as equalization strategies – by denying the legitimacy of racism – and guide beliefs regarding antiracism strategies. I explore folk explanations of racism among black professionals in Brazil and South Africa by drawing on sixty interviews with members of these groups. In Brazil, racism is understood as an historical lingering, a product of ignorance, which will disappear with time and education. In South Africa, racism is viewed as more resilient, as a part of human nature and as a consequence of the competition for resources. These explanations of racism are closely related to the antiracism narratives that are salient in these two contexts: while Brazilian respondents affirm their belief in racial mixture and moral education, South African respondents are more uncertain about the possibilities of weaker racial boundaries in their country, relying on institutional constraints as their main antiracism strategy.     

Used for ill; used for good: a century of collecting data on race in South Africa

Abstract

Data on race have been collected in South African censuses for a century. We examine the role played by the census in solidifying race as a social statistic and show that, in contrast to the majority of situations, operational and legislative factors rendered the census largely unimportant as a vehicle for doing this. Since 1994, race has been entirely self-reported and not subject to state reinterpretation. We examine the implications of this for future data collection exercises and caution against reifying race as a predictor of social outcomes in post-apartheid South Africa, and argue for its gradual phasing out.     

Successive virgin births of viable male progeny in the checkered gartersnake,Thamnophis marcianus

In recent years genotyping analysis using mini‐ and microsatellite markers has provided robust DNA‐based support for facultative parthenogenesis (FP) in several lineages of squamate reptiles (snakes and lizards) and sharks. Rather than incidental cases of reproductive error, there is growing evidence that FP is an alternative reproductive strategy and an important mode of reproduction in these phylogenetically divergent vertebrate groups. Because documentation of FP in vertebrates is in its infancy, additional instances supported by molecular genetic methods provide insights that advance our general understanding of this phenomenon. Here, in a female checkered gartersnake (Thamnophis marcianus) reared in isolation since a juvenile, we describe five successive parthenogenetic litters produced over a 7‐year period that resulted in several viable male progeny. Cross species microsatellite amplification was performed across 30 primer pairs derived from Thamnophis spp. and related natricines to the female and nine available progeny. Five loci proved heterozygous in the maternal sample with the progeny differentially homozygous at all but one locus. Combined with evidence pertaining to captive history and litter characteristics, our analysis supports a specific type of FP, terminal fusion automictic parthenogenesis, over the competing hypothesis of long‐term sperm storage. Importantly, we document that a single individual was capable of producing successive litters composed of live parthenogens. In two cases, males achieved adulthood and showed the anatomical potential to demonstrate reproductive competence (normal looking hemipenes and testes). © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 566–572.     

Low parasitism rates in parthenogenetic bagworm moths do not support the parasitoid hypothesis for sex

The parasite hypothesis for sex is one of the many theories that have been suggested to solve the mystery of the widespread occurrence of sex despite its high short‐term costs. It suggests that sexual lineages have an evolutionary advantage over parthenogens because they can frequently generate new genotypes that are temporarily less prone to coevolving parasites. In this study, we looked for further supporting evidence for the parasite hypothesis of sex in an attempt to understand the coexistence of sexual and parthenogenetic bagworm moths (Naryciinae). The bagworm moths and their parasitoids form one of the few natural host–parasite systems where sexual and parthenogenetic hosts are apparently not separated by ecological or geographical barriers. Furthermore, in support of the parasite hypothesis for sex, parthenogenetic presence is negatively correlated with parasitism rate. We specifically tested, by identifying the reproductive mode of the parasitized individuals, whether parasitoids preferentially attack the parthenogens in sites with both sexual and parthenogenetic forms, as predicted by the parasite hypothesis. We collected hosts from sites with different frequencies of parthenogenetic and sexual moths. A DNA barcoding approach was used to determine the reproductive mode of the parasitized hosts. Furthermore, we investigated whether differences in host and parasitoid phenology could provide an alternative explanation for the variation in parasitism rates between parthenogens and sexuals. Our results contradict the prediction of the parasite hypothesis because parthenogenetic bagworm moths were less parasitized than sexuals in sympatric sites. Our findings can be explained by differences in phenology between the parthenogenetic and sexual moths rather than genetic incompatibility between parthenogenetic hosts and parasitoids. The stable coexistence of sexual and parthenogenetic Naryciinae despite the many apparent costs of sex in this system remains a mystery. Our work adds to the list of studies were the assumptions of the parasite hypothesis for sex are not all met.     

Multilevel Control of Organelle DNA Sequence Length in Plants

We have compared the length of noncoding organelle DNA spacers in a broad sample of plant species characterized by different life history traits to test hypotheses regarding the nature of the mechanisms driving changes in their size. We first demonstrate that the spacers do not evolve at random in size but have experienced directional evolutionary trends during plant diversification. We then study the relationships between spacer lengths and other molecular features and various species attributes by taking into account population genetic processes acting within cell lineages. Comparative techniques are used to test these relationships while controlling for species phylogenetic relatedness. The results indicate that spacer length depends on mode of organelle transmission, on population genetic structure, on nucleotide content, on rates of molecular evolution, and on life history traits, in conformity with predictions based on a model of intracellular competition among replicating organelle genomes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic races associated with the genera and sections of host species in the holoparasitic plant Cytinus (Cytinaceae) in the Western Mediterranean basin

* Speciation via race formation is an important evolutionary process in parasites, producing changes that favour their development on particular host species. Here, the holoparasitic plant Cytinus, which has diverse host species in the family Cistaceae, has been used to study the occurrence of such races. * Amplified fragment length polymorphism (AFLP) analyses were performed on 174 individuals of 22 populations parasitizing 10 Cistaceae species in the Western Mediterranean basin. * Neighbour-joining, multivariate ordination analyses, and individual-based Bayesian analyses, clustered Cytinus populations into five well-characterized genetic races that, overall, agreed with the taxonomic sections of their hosts. In the AMOVA, among-races differences accounted for almost 50% of the genetic variation. The isolation-by-distance model was not supported by a Mantel test among Cytinus populations (r = 0.012; P = 0.456). All races showed low within-population genetic diversity, probably as a result of restricted pollen flow aggravated by flowering asynchrony, restricted seed dispersion, or stochastic processes. * The genetic differentiation among the five races of Cytinus is congruent with the view that these races are well-characterized lineages that have evolved independently as a result of selective pressures imposed by their hosts. This pattern, with genetically distinctive groups associated with the infrageneric sections of the host species, has not been reported previously for parasitic angiosperms.