DO SUTURE ZONES EXIST?

Remington (1968) argued that 13 suture zones exist in North America. Remington defined a suture zone as, "a band of geographic overlap between major biotic assemblages, including some pairs of species or semispecies which hybridize in the zone" (p. 322). Although initially controversial, the idea that suture zones exist has picked up momentum over the past decade, due largely to the phylogeographic work of Hewitt, Avise, and their colleagues. Nevertheless, the reality of suture zones has not yet been subjected to rigorous analysis using statistical and geographic information system (GIS) approaches. To test for the existence of Remington's suture zones, we first identified 117 terrestrial hybrid zones in Canada and the United States through a literature search for the key words "cline," "contact zone," "hybrid zone," and "hybridization" in articles published between 1970 and 2002. The 117 hybrid zones were mapped using a GIS approach and compared with a digitized version of Remington's original suture zone map. Overall, there does appear to be an association between hybrid zones and suture zones, but this association is largely attributable to clustering of hybrid zones in only two of the 13 suture zones recognized by Remington. The results suggest that evolutionary biologists should retain some skepticism toward Remington's suture zones.     

IS INBREEDING DEPRESSION LOWER IN MALADAPTED POPULATIONS? A QUANTITATIVE GENETICS MODEL

Despite abundant empirical evidence that inbreeding depression varies with both the environment and the genotypic context, theoretical predictions about such effects are still rare. Using a quantitative genetics model, we predict amounts of inbreeding depression for fitness emerging from Gaussian stabilizing selection on some phenotypic trait, on which, for simplicity, genetic effects are strictly additive. Given the strength of stabilizing selection, inbreeding depression then varies simply with the genetic variance for the trait under selection and the distance between the mean breeding value and the optimal phenotype. This allows us to relate the expected inbreeding depression to the degree of maladaptation of the population to its environment. We confront analytical predictions with simulations, in well-adapted populations at equilibrium, as well as in maladapted populations undergoing either a transient environmental shift, or gene swamping in heterogeneous habitats. We predict minimal inbreeding depression in situations of extreme maladaptation. Our model provides a new basis for interpreting experiments that measure inbreeding depression for the same set of genotypes in different environments, by demonstrating that the history of adaptation, in addition to environmental harshness per se, may account for differences in inbreeding depression.     

HOW DEPRESSED? ESTIMATES OF INBREEDING EFFECTS DURING SEED DEVELOPMENT DEPEND ON REPRODUCTIVE CONDITIONS

Inbreeding depression can reduce the performance of offspring produced by mating between relatives, with consequences for population dynamics and sexual-system evolution. In flowering plants, inbreeding depression commonly acts most intensely during seed development. This predispersal component is typically estimated by comparing seed production following exclusive self- and cross-pollination, but such estimates are unbiased only if seed production is limited by ovule availability, rather than by pollen receipt or seed-development resources. To overcome this problem, we propose experimental and statistical methods based on a model of ovule fertilization and seed development that accounts for differential fertilization by self- and cross-pollen, limited ovule viability or receptivity, differential survival of self- and cross-zygotes and limited resource availability. Simulations illustrate that the proposed methods eliminate bias in estimated predispersal inbreeding depression caused by pollen limitation and can improve estimates under resource limitation. Application of these methods to two orchid species further demonstrates their utility in identifying and estimating diverse influences on reproductive performance under typical conditions. Although our theoretical results raise questions about the reported intensity of predispersal inbreeding depression, our proposed methods guard against bias while also providing insight into plant reproduction.     

DO MELANOPHORE NERVES SHOW ANTIDROMIC RESPONSES?

1. In Fundulus heteroclitus the dispersing melanophore nerve fibers have a relatively high threshold for faradic stimulation and a low one for stimulation by cutting. When they are protected from the competing action of the concentrating fibers, they show through the responses of their melanophores well marked antidromic activities which can also be seen to a slight degree even where the concentrating fibers are active. 2. The concentrating melanophore nerve fibers in this fish have a relatively low threshold for faradic stimulation and a high one for stimulation by cutting. They also exhibit clear antidromic responses as shown by their associated melanophores.     

DO IMAGE-FORMING EYES PROMOTE EVOLUTIONARY DIVERSIFICATION?

It has been suggested that image-forming eyes promote the evolutionary diversification (measured by species richness) of the groups that possess them. Several different processes could give rise to this effect, including diversifying selection in a new adaptive zone (or zones) and a reduced rate of extinction due to enhanced competitive abilities. I tested the generality of the hypothesis that imaging eyes increase net speciation by comparing extant species numbers of 12 groups that have such eyes (as categorized by Land and Fernald 1992) with those of their cladistic sister groups that lack such organs. Even assuming the published hypotheses of phylogenetic relationships that most favor increased net speciation of visual groups, these comparisons show no significant association between imaging eyes and species richness. Increased activity, as indicated by published accounts of locomotory speed, is significantly associated with the evolution of image-forming eyes. This suggests that a large “visual adaptive zone” might be characterized by relatively high activity. However, when diversity comparisons are limited to eight cases in which the evolution of imaging eyes is associated with increased activity, there is still no significant association between such eyes and species richness. The fossil record indicates that the only visual groups that have undergone major evolutionary radiations evolved imaging eyes early in the history of metazoans (before the Silurian). The radiations of these early groups may have largely filled up niches for visual animals and thus prevented the subsequent proliferation of other groups with image-forming eyes. Alternatively, it may be that image-forming eyes have no exceptional effect on diversification or that their effects are obscured by other factors in the long run.     

WHAT CAN HISTORY DO FOR BIOETHICS?

This article details the relationship between history and bioethics. I argue that historians' reluctance to engage with bioethics rests on a misreading of the field as solely reducible to applied ethics, and overlooks previous enthusiasm for historical perspectives. I claim that seeing bioethics as its practitioners see it – as an interdisciplinary meeting ground – should encourage historians to collaborate in greater numbers. I conclude by outlining how bioethics might benefit from new histories of the field, and how historians can lend a fresh perspective to bioethical debates.     

Direct Observation (DO) for Drug-Resistant Tuberculosis: Do We Really DO?

Introduction

Directly-observed therapy (DOT) is recommended for drug-resistant tuberculosis (DR-TB) patients during their entire treatment duration. However, there is limited published evidence on implementation of direct observation (DO) in the field. This study aims to detail whether DO was followed with DR-TB patients in a Médecins Sans Frontières (MSF) tuberculosis program in Mumbai, India.

Methods

This was a cross-sectional, mixed-methods study. Existing qualitative data from a purposively-selected subset of 12 patients, 5 DOT-providers and 5 family members, were assessed in order to determine how DO was implemented. A questionnaire-based survey of DR-TB patients, their DOT-providers and MSF staff was completed between June and August 2014. Patients were defined as”following Strict DO” and “following DO” if a DOT-provider had seen the patient swallow his/her medications “every day” or “most of the days” respectively. If DO was not followed, reasons were also recorded. The qualitative data were analysed for theme and content and used to supplement the questionnaire-based data.

Results

A total of 70 DR-TB patients, 65 DOT-providers and 21 MSF health staff were included. Fifty-five per cent of the patients were HIV-co-infected and 41% had multidrug-resistant-TB plus additional resistance to a fluoroquinolone. Among all patients, only 14% (10/70) and 20% (14/70) self-reported “following Strict DO” and “following DO” respectively. Among DOT-providers, 46% (30/65) reported that their patients “followed DO”. MSF health staff reported none of the patients “followed DO”. Reasons for not implementing DO included the unavailability of DOT-provider, time spent, stigma and treatment adverse events. The qualitative data also revealed that “Strict DO” was rarely followed and noted the same reasons for lack of implementation.

Conclusion

This mixed-methods study has found that a majority of patients with DR-TB in Mumbai did not follow DO, and this was reported by patients and care-providers. These data likely reflect the reality of DO implementation in many high-burden settings, since this relatively small cohort was supported and closely monitored by a skilled team with access to multiple resources. The findings raise important concerns about the necessity of DO as a “pillar” of DR-TB treatment which need further validation in other settings. They also suggest that patient-centred adherence strategies might be better approaches for supporting patients on treatment.     

DO WE NEED AN EXTENDED EVOLUTIONARY SYNTHESIS?

The Modern Synthesis (MS) is the current paradigm in evolutionary biology. It was actually built by expanding on the conceptual foundations laid out by its predecessors, Darwinism and neo-Darwinism. For sometime now there has been talk of a new Extended Evolutionary Synthesis (EES), and this article begins to outline why we may need such an extension, and how it may come about. As philosopher Karl Popper has noticed, the current evolutionary theory is a theory of genes, and we still lack a theory of forms. The field began, in fact, as a theory of forms in Darwin's days, and the major goal that an EES will aim for is a unification of our theories of genes and of forms. This may be achieved through an organic grafting of novel concepts onto the foundational structure of the MS, particularly evolvability, phenotypic plasticity, epigenetic inheritance, complexity theory, and the theory of evolution in highly dimensional adaptive landscapes.     

WHAT SHALL WE DO WITH THE BLUE-GREEN COUNTERPARTS?

Lichens are troublesome organisms for taxonomists because of their special ‘ double nature ’, i.e. being composed (normally) of two partners. Only recently has it been understood properly that the same fungus can take different photosynthetic partners and develop into quite different-looking organisms, for exampleLobaria amplissimaandDendriscocaulon umhausense. The taxonomic problem is to show that two totally different-looking lichens in fact contain the same fungus. This is possible to demonstrate when mixed stands are available, but is now best done with molecular methods. Since the international code of nomenclature rules that the name of a lichen species is the name of the fungus, two different organisms with the same fungus must under the Code carry the same name, which is most impractical. To remove this unintentional complication, one must either make an exception in the Code for these cases, or establish an informal system to take care of them. The latter seems to be preferable.     

WHY DO DINOFLAGELLATES HAVE LOWER GROWTH RATES?1

Dinoflagellates have substantially lower growth rates than other taxa of similar size. These low growth rates have been suggested to reflect the lower chlorophyll a to carbon ratio (Chl a:C) in dinoflagellates, but that speculation has never been widely tested. This study tests if the variations in growth rates among taxa are related to differences in Chl a:C using published data. I collected 92 data entries from the literature representing 31 species, mostly from two divisions (Chrysophyta and Pyrrophyta), and found a significant relation (r²= 0.39) between growth and Chl a:C. Since Chl a:C is almost independent of C content, I also developed a growth model using both C and Chl a:C. Together, the two variables explain 68% of variation in algal growth. However, a further 6.4% of the variance in growth can still be attributed to phyletic differences. Low Chl a:C is only a partial explanation for the low growth rates of the dinoflagellates.     

DO PHYLOGENETIC METHODS PRODUCE TREES WITH BIASED SHAPES?

We examine whether phylogenetic methods provide biased estimates of tree shape with respect to the random branching model. We investigate the performance of five commonly used phylogenetic methods using computer simulation: (1) maximum parsimony; (2) neighbor joining; (3) UPGMA with an outgroup taxon; (4) UPGMA without an outgroup taxon; and (5) maximum likelihood. All methods provide estimates of tree shape that are, on average, more asymmetrical than the true tree, especially when rates of evolution are high. We suggest a simple explanation for the bias and propose a modified test of tree shape that corrects for it.     

EXPERIMENTALLY ENFORCED MONOGAMY: INADVERTENT SELECTION,INBREEDING, OR EVIDENCE FOR SEXUALLY ANTAGONISTIC COEVOLUTION?

There has been recent criticism of experiments that applied enforced monogamous mating to species with a long history of promiscuity. These experiments indicated that the newly introduced monogamy reversed sexually antagonistic coevolution and caused males to evolve to be less harmful to their mates and females to evolve reduced resistance to harm from males. Several authors have proposed alternative interpretations of these experimental results based on qualitative analysis. If well-founded, these criticisms would invalidate an important part of the empirical foundation for sexually antagonistic coevolution between the sexes. Although these criticisms have a reasonable basis in principle, we find that after quantitative evaluation that they are not supported.     

DO PHAGES EFFICIENTLY SHUTTLE TRANSPOSABLE ELEMENTS AMONG PROKARYOTES?

The distribution, dynamics, and evolution of insertion sequences (IS), the most frequent class of prokaryotic transposable elements, are conditioned by their ability to horizontally transfer between cells. IS horizontal transfer (HT) requires shuttling by other mobile genetic elements. It is widely assumed in the literature that these vectors are phages and plasmids. By examining the relative abundance of IS in 454 plasmid and 446 phage genomes, we found that IS are very frequent in plasmids but, surprisingly, very rare in phages. Our results indicate that IS rarity in phages reflects very strong and efficient postinsertional purifying selection, mainly caused by a higher density of deleterious insertion sites in phages compared to plasmids. As they do not tolerate IS insertions, we conclude that phages may be rather poor vectors of IS HT in prokaryotes, in sharp contrast with the conventional view.     

DO WOLBACHIA‐ASSOCIATED INCOMPATIBILITIES PROMOTE POLYANDRY?

The genetic incompatibility avoidance hypothesis as an explanation for the polyandrous mating strategies (mating with more than one male) of females of many species has received significant attention in recent years. It has received support from both empirical studies and a meta-analysis, which concludes that polyandrous females enjoy increased reproductive success through improved offspring viability relative to monandrous females. In this study we investigate whether polyandrous female Drosophila simulans improve their fitness relative to monandrous females in the face of severe Wolbachia-associated reproductive incompatibilities. We use the results of this study to develop models that test the predictions that Wolbachia should promote polyandry, and that polyandry itself may constrain the spread of Wolbachia. Uniquely, our models allow biologically relevant rates of incompatibility to coevolve with a polyandry modifier allele, which allows us to evaluate the fate of the modifier and that of Wolbachia. Our empirical results reveal that polyandrous females significantly reduce the reproductive costs of Wolbachia, owing to infected males being poor sperm competitors. The models show that this disadvantage in sperm competition can inhibit or prevent the invasion of Wolbachia. However, despite the increased reproductive success obtained by polyandrous females, the spread of a polyandry modifier allele is constrained by any costs that might be associated with polyandry and the low frequency of incompatible matings when Wolbachia has reached a stable equilibrium. Therefore, although incompatibility avoidance may be a benefit of polyandry, our findings do not support the hypothesis that genetic incompatibilities caused by Wolbachia promote the evolution of polyandry.