Brief communication: Hair density and body mass in mammals and the evolution of human hairlessness

Humans are unusual among mammals in appearing hairless. Several hypotheses propose explanations for this phenotype, but few data are available to test these hypotheses. To elucidate the evolutionary history of human “hairlessness,” a comparative approach is needed. One previous study on primate hair density concluded that great apes have systematically less dense hair than smaller primates. While there is a negative correlation between body size and hair density, it remains unclear whether great apes have less dense hair than is expected for their body size. To revisit the scaling relationship between hair density and body size in mammals, I compiled data from the literature on 23 primates and 29 nonprimate mammals and conducted Phylogenetic Generalized Least Squares regressions. Among anthropoids, there is a significant negative correlation between hair density and body mass. Chimpanzees display the largest residuals, exhibiting less dense hair than is expected for their body size. There is a negative correlation between hair density and body mass among the broader mammalian sample, although the functional significance of this scaling relationship remains to be tested. Results indicate that all primates, and chimpanzees in particular, are relatively hairless compared to other mammals. This suggests that there may have been selective pressures acting on the ancestor of humans and chimpanzees that led to an initial reduction in hair density. To further understand the evolution of human hairlessness, a systematic study of hair density and physiology in a wide range of species is necessary. Am J Phys Anthropol 152:145–150, 2013. © 2013 Wiley Periodicals, Inc.     

Towards accurate estimation of the proportion of true null hypotheses in multiple testing

BACKGROUND: Biomedical researchers are now often faced with situations where it is necessary to test a large number of hypotheses simultaneously, eg, in comparative gene expression studies using high-throughput microarray technology. To properly control false positive errors the FDR (false discovery rate) approach has become widely used in multiple testing. The accurate estimation of FDR requires the proportion of true null hypotheses being accurately estimated. To date many methods for estimating this quantity have been proposed. Typically when a new method is introduced, some simulations are carried out to show the improved accuracy of the new method. However, the simulations are often very limited to covering only a few points in the parameter space. RESULTS: Here I have carried out extensive in silico experiments to compare some commonly used methods for estimating the proportion of true null hypotheses. The coverage of these simulations is unprecedented thorough over the parameter space compared to typical simulation studies in the literature. Thus this work enables us to draw conclusions globally as to the performance of these different methods. It was found that a very simple method gives the most accurate estimation in a dominantly large area of the parameter space. Given its simplicity and its overall superior accuracy I recommend its use as the first choice for estimating the proportion of true null hypotheses in multiple testing.     

The journey of tandem running: the twists, turns and what we have learned

Tandem running, whereby one worker recruits another is utilised by many ant species. Since first being recorded, it has provided a valuable experimental tool for testing hypotheses about collective decision making, communication and even teaching. In this review I explore the journey tandem running has taken, the twists and turns in the theories surrounding it and what tandem running has taught us. This review examines the empirical research conducted on tandem running, from when it was first described, considers the theories that have arisen from that research and ultimately what has been learnt and what is still yet to be explored.     

Equivalent genetic regulatory networks in different contexts recover contrasting spatial cell patterns that resemble those in Arabidopsis root and leaf epidermis: a dynamic model

In Arabidopsis thaliana, leaf and root epidermis hairs exhibit contrasting spatial arrangements even though the genetic networks regulating their respective cell-fate determination have very similar structures and components. We integrated available experimental data for leaf and root hair patterning in dynamic network models which may be reduced to activator-inhibitor models. This integration yielded expected results for these kinds of dynamic models, including striped and dotted cell patterns which are characteristic of root and leaf epidermis, respectively. However, these formal tools have led us to novel insights on current data and to put forward precise hypotheses which can be addressed experimentally. In particular, despite subtle differences in the root and leaf networks, these have equivalent dynamical behaviors. Our simulations also suggest that only when a biasing signal positively affects an activator in the network, the system recovers striped cellular patterns similar to those of root epidermis. We also postulate that cell shape may affect pattern stability in the root. Our results thus support the idea that in this and other cases, contrasting spatial cell patterns and other evolutionary morphogenetic novelties originate from conserved genetic network modules subject to divergent contextual traits.     

A Model of Filiform Hair Distribution on the Cricket Cercus

Crickets and other orthopteran insects sense air currents with a pair of abdominal appendages resembling antennae, called cerci. Each cercus in the common house cricket Acheta domesticus is covered with between 500 to 750 filiform mechanosensory hairs. The distribution of the hairs on the cerci, as well as the global patterns of their movement axes, are very stereotypical across different animals in this species, and the development of this system has been studied extensively. Although hypotheses regarding the mechanisms underlying pattern development of the hair array have been proposed in previous studies, no quantitative modeling studies have been published that test these hypotheses. We demonstrate that several aspects of the global pattern of mechanosensory hairs can be predicted with considerable accuracy using a simple model based on two independent morphogen systems. One system constrains inter-hair spacing, and the second system determines the directional movement axes of the hairs.     

Flights of fancy: possible roles of allatostatin and allatotropin in migration and reproductive success of Pseudaletia unipuncta

Many invertebrate neuropeptides have recently been identified and there is evidence that the same compound may serve different roles in different species and/or multiple functions within a given species. However, until the relevant receptors or 'knock out' animals, lacking the neuropeptide of interest, become available it will be difficult to clarify the precise inter- and intraspecific functions of these neuropeptides. In the present paper, we argue that until these tools are available a more meaningful understanding of the roles of neuropeptides could be obtained by carrying out experiments within an ecological context. Furthermore, this approach would allow us to generate hypotheses that could be rigorously tested when more sophisticated techniques are developed. We discuss these ideas using our interdisciplinary research on the reproductive biology of the true armyworm, Pseudaletia unipuncta, as a case study.     

Hairstyle as an adaptive means of displaying phenotypic quality

Although facial features that are considered beautiful have been investigated across cultures using the framework of sexual selection theory, the effects of head hair on esthetic evaluations have rarely been examined from an evolutionary perspective. In the present study the effects of six hair-styles (short, medium-length, long, disheveled, knot [hair bun], unkempt) on female facial attractiveness were examined in four dimensions (femininity, youth, health, sexiness) relative to faces without visible head hair (“basic face”). Three evolutionary hypotheses were tested (covering hypothesis, healthy mate theory, and good genes model); only the good genes model was supported by our data. According to this theory, individuals who can afford the high costs of long hair are those who have good phenotypic and genetic quality. In accordance with this hypothesis, we found that only long and medium-length hair had a significant positive effect on ratings of women’s attractiveness; the other hairstyles did not influence the evaluation of their physical beauty. Furthermore, these two hairstyles caused a much larger change in the dimension of health than in the rest of the dimensions. Finally, male raters considered the longer-haired female subjects’ health status better, especially if the subjects were less attractive women. The possible relationships between facial attractiveness and hair are discussed, and alternative explanations are presented.     

DNA sequence of the Rhizobium leguminosarum nodulation genes nodAB and C required for root hair curling

A 3.2kb fragment of DNA cloned from Rhizobium leguminosarum has been shown to contain the genes necessary for the induction of root hair curling, the first observed step in the infection of leguminous plants by R. leguminosarum. The DNA sequence of this region has been determined and three open reading frames were identified: genes corresponding to these open reading frames have been called nodA, nodB and nodC and are transcribed in that order. Mutations within the nodC gene completely blocked root hair curling. However, a subcloned fragment containing only the nodC gene did not induce normal root hair curling (although some branching was observed), indicating that the nodA and B genes may also be required for normal root hair curling. From an analysis of the predicted amino acid sequences of the nodAB and C genes it appeared unlikely that their products are secreted; therefore it is concluded that the induction of root hair curling could be due to a secreted metabolite.     

Epidermal stem cells and skin tissue engineering in hair follicle regeneration

The reconstitution of a fully organized and functional hair follicle from dissociated cells propagated under defined tissue culture conditions is a challenge still pending in tissue engineering. The loss of hair follicles caused by injuries or pathologies such as alopecia not only affects the patients’ psychological well-being, but also endangers certain inherent functions of the skin. It is then of great interest to find different strategies aiming to regenerate or neogenerate the hair follicle under conditions proper of an adult individual. Based upon current knowledge on the epithelial and dermal cells and their interactions during the embryonic hair generation and adult hair cycling, many researchers have tried to obtain mature hair follicles using different strategies and approaches depending on the causes of hair loss. This review summarizes current advances in the different experimental strategies to regenerate or neogenerate hair follicles, with emphasis on those involving neogenesis of hair follicles in adult individuals using isolated cells and tissue engineering. Most of these experiments were performed using rodent cells, particularly from embryonic or newborn origin. However, no successful strategy to generate human hair follicles from adult cells has yet been reported. This review identifies several issues that should be considered to achieve this objective. Perhaps the most important challenge is to provide three-dimensional culture conditions mimicking the structure of living tissue. Improving culture conditions that allow the expansion of specific cells while protecting their inductive properties, as well as methods for selecting populations of epithelial stem cells, should give us the necessary tools to overcome the difficulties that constrain human hair follicle neogenesis. An analysis of patent trends shows that the number of patent applications aimed at hair follicle regeneration and neogenesis has been increasing during the last decade. This field is attractive not only to academic researchers but also to the companies that own almost half of the patents in this field.     

Confocal microscopy of hair

Confocal microscopy is an excellent method for studying the localization of fluorescent stains. Used in this way, superior 3D images can be obtained from multiple optical sections with very shallow depth of field. The main advantage of this technique is that the sample is not damaged. We have taken serial confocal sections of hair and via specific image enhancement routines have obtained high-quality 3D images enabling the visualization of cuticle scale and its pattern of distribution. This has been done on various types of hair: bleached, permed and in certain pathological conditions. This first step will allow us to characterize the hair surface in terms of its roughness, and the distribution and form of cuticular scale, parameters that have potential in the assessment of dermocosmetic efficacy.     

Assessing the potential of a "color effect" for hair analysis of 11-nor-9-carboxy-delta(9)-tetrahydrocannabinol: analysis of a large sample of hair specimens

It has been hypothesized that hair color may play a role in the concentration of various drugs of abuse in hair. Several studies have shown that melanin in hair appears to play a binding role for at least some commonly abused drugs. However, these studies have been limited by a number of factors when assessing the clinical significance of a hypothesized melanin or color effect. This study evaluates the possible effect of hair color on the concentration of 11-nor-9-carboxy-Delta(9)-tetrahydrocannabinol (c-THC) in human hair. The analysis is based on 3886 positive c-THC hair specimens drawn from a universe of approximately 80000 specimens of scalp hair harvested from the posterior vertex of the head. Analysis of variance of color categorization by c-THC concentration shows that c-THC concentration does not have a significant association with hair color (Hair Color F = 1.148, p =.332) and therefore does not have a demonstrable "color effect".     

Scanning electron microscope studies of some internal surfaces in human skin

Summary The scanning electron microscope has been used to investigate the surfaces of epidermis, hair follicles, fat cells, glands and blood vessels in sections of human skin. The appearances of structures associated with these surfaces have been described. The results demonstrate that this new instrument can become an important tool in the investigation of surface changes that might accompany the application of loads (extensive, compressive or torsional), or physiological or pathological abnormalities.We wish to thank Prof. R. M. Kenedi for his continued encouragement of this work. One of us (I.A.B.) is also grateful to the Science Research Council for the provision of a post-graduate student grant.     

The evolution of flight and echolocation in bats: another leap in the dark

The earliest known complete bats, from the Eocene (49–53 Mya), were already capable of flapping flight and echolocation. In the absence of direct fossil evidence there have been many speculative scenarios advanced to explain the evolution of these behaviours and their distributions in extant bats. Theories assuming chiropteran monophyly have generally presumed the ancestral pre‐bat was nocturnal, arboreal and insectivorous. Following this assumption hypotheses can be divided into the echolocation first, flight first and tandem development hypotheses, all of which assume that flight evolved only once in the lineage. In contrast, the chiropteran diphyly hypothesis suggests that flight evolved twice. Evidence supporting and refuting the different hypotheses are reviewed. It is concluded that there are significant problems attached to all the current models. A novel hypothesis is advanced, which starts from the assumption that bats are monophyletic and the ancestral pre‐bat was arboreal, but diurnal and frugivorous. After the evolution of flight it is suggested that these animals were driven into the nocturnal niche by the evolution of raptorial birds, and different groups evolved either specialised nocturnal vision (megachiropterans) or echolocation (microchiropterans). A block on sensory modality transfer has retained this distribution of perceptual capabilities ever since, despite some Megachiroptera evolving rudimentary echolocation, and the dietary convergence of some Microchiroptera with the Megachiroptera. The new hypothesis overcomes many of the problems identified in previous treatments.     

Revision surgical hair restoration: repair of undesirable results

Surgical hair restoration has been performed as a treatment for male pattern hair loss for more than 40 years. Although techniques have changed dramatically over the past several years, making it possible to achieve natural-appearing results, there are still many patients with unacceptable outcomes. These patients may have had procedures performed in the past with antiquated techniques or performed recently with substandard techniques. The causes of unfavorable results can be classified into one of three categories: technical errors, poor planning, or complications. The results in these patients can be dramatically improved through a number of different reparative surgical techniques. The majority of these techniques can be performed in an office outpatient setting. More than 40 patients unsatisfied with previous surgical hair restoration have been treated with the different techniques reviewed in this article. All patients had successful outcomes with significant improvement in appearance. Despite the increased challenges when performing reparative surgery, outcomes were favorable in all patients, with small to significant improvements in appearance achieved. Some of these challenges include the limited supply of donor hairs, reduced scalp laxity, and theoretically reduced vascularity due to scarring and transected blood vessels, and patient skepticism. Furthermore, the few complications that occurred were minor and correctable, including one case each of poor hair growth associated with extensive small graft (consisting of one to four hairs) transplanting, and of scalp scarring associated with the removal and primary closure of a large number of "plug" grafts (typically grafts 3 to 4 mm in size consisting of seven or more hairs) in a single procedure.     

Algae obscura: The potential of rare species as model systems

Model organism research has provided invaluable knowledge about foundational biological principles. However, most of these studies have focused on species that are in high abundance, easy to cultivate in the lab, and represent only a small fraction of extant biodiversity. Here, we present three examples of rare algae with unusual features that we refer to as “algae obscura.” The Cyanidiophyceae (Rhodophyta), Glaucophyta, and Paulinella (rhizarian) lineages have all transitioned out of obscurity to become models for fundamental evolutionary research. Insights have been gained into the prevalence and importance of eukaryotic horizontal gene transfer, early Earth microbial community dynamics, primary plastid endosymbiosis, and the origin of Archaeplastida. By reviewing the research that has come from the exploration of these organisms, we demonstrate that underappreciated algae have the potential to help us formulate, refine, and substantiate core hypotheses and that such organisms should be considered when establishing future model systems.     

Natural enemy diversity and biological control: Making sense of the context-dependency

Numerous studies have demonstrated that diverse predator assemblages can be more effective at controlling prey populations. Yet, other studies have shown no effect of predator diversity on prey mortality, or even negative effects (for example due to intraguild predation or interference). Much research emphasis has been placed on the traits of predators that maximise functional complementarity. However, comparatively less attention has been paid to the traits of the prey or habitat that may maximise predator diversity effects, even though there must be a variety of prey niches available to be partitioned in order for niche complementarity to occur. Following this logic, we review six hypotheses for when diverse enemy assemblages should be most effective: when 1) prey communities are diverse; 2) prey have complex life cycles; 3) prey are patchily distributed in space or time; 4) studies are conducted at larger spatial and temporal scales; 5) plant structures are complex; 6) prey are abundant. Many of these hypotheses lack direct tests, particularly in agricultural systems, but we find little or no direct or indirect support for hypotheses 1, 4, 5 and 6. However, previous work does provide some support for hypotheses 2 and 3. We discuss methods to test these hypotheses directly, and suggest that natural enemy diversity may only benefit the biological control of arthropods in heterogeneous systems.     

Genetic interactions during root hair morphogenesis in Arabidopsis

Root hairs are a major site for the uptake of water and nutrients into plants and form an increasingly important model system for studies of development of higher plants and cell biology. We have identified loss-of-function mutations in eight new genes required for hair growth in Arabidopsis: SHAVEN1 (SHV1), SHV2, and SHV3; CENTIPEDE1 (CEN1), CEN2, and CEN3; BRISTLED1 (BST1); and SUPERCENTIPEDE1 (SCN1). We combined mutations in 79 pairs of genes to determine the stages at which these and six previously known genes contribute to root hair formation. Double mutant phenotypes revealed roles for several genes that could not have been predicted from the single mutant phenotypes. For example, we show that TIP1 and RHD3 are required much earlier in hair formation than previous studies have suggested. We present a genetic model for root hair morphogenesis that defines the roles of each gene, and we suggest hypotheses about functional relationships between genes.     

Regeneration in zebrafish lateral line neuromasts: expression of the neural progenitor cell marker sox2 and proliferation-dependent and-independent mechanisms of hair cell renewal

Mechanosensory hair cells are essential for audition in vertebrates, and in many species, have the capacity for regeneration when damaged. Regeneration is robust in the fish lateral line system as new hair cells can reappear after damage induced by waterborne aminoglycoside antibiotics, platinum-based drugs, and heavy metals. Here, we characterize the loss and reappearance of lateral line hair cells induced in zebrafish larvae treated with copper sulfate using diverse molecular markers. Transgenic fish that express green fluorescent protein in different cell types in the lateral line system have allowed us to follow the regeneration of hair cells after different damage protocols. We show that conditions that damage only differentiated hair cells lead to reappearance of new hair cells within 24 h from nondividing precursors, whereas harsher conditions are followed by a longer recovery period that is accompanied by extensive cell division. In order to characterize the cell population that gives rise to new hair cells, we describe the expression of a neural stem cell marker in neuromasts. The zebrafish sox2 gene is strongly expressed in neuromast progenitor cells, including those of the migrating lateral line primordium, the accessory cells that underlie the hair cells in neuromasts, and in interneuromastic cells that give rise to new neuromasts. Moreover, we find that most of the cells that proliferate within the neuromast during regeneration express this marker. Thus, our results describe the dynamics of hair cell regeneration in zebrafish and suggest the existence of at least two mechanisms for recovery of these cells in neuromasts.     

The Semantic Structure Of Public Speaking (On Meaningful Perception)

A study of the psychological mechanisms underlying the perception of messages and of processes transforming the products of such perception (thoughts, images, percepts) into needs, motives, goals, and attitudes in the perceiver has a rich tradition of research behind it in the psychology of propaganda and mass communication. On the one hand, this has led to the accumulation of numerous interesting empirical facts and the development of corresponding theoretical hypotheses that shed light on various aspects of the perception of messages; but on the other hand, it has resulted in rigid fixation of certain a priori conceptual models of a phenomenal field that prevent any deeper probing into the vertical structure of the mechanisms of perception and has driven research to spread itself thinly in a horizontal direction. Therefore, although the new second-order problems that have been singled out concerning message perception are doubtless important and interesting, they leave unchallenged the validity and productiveness of the way the main problem itself is currently formulated. A few modifications have been attempted by contemporary investigators; but as a rule, these have been no more than particular terminological refinements and innovations. (1) A horizontal profile of the problem concerning us here has been quite fully presented in a collective work devoted especially to this topic [9].