Intermediate filaments: not so tough after all

The dynamic properties of cellular protein polymers such as microtubules and microfilaments depend to a large extent on the cell's capacity to modify rapidly the exchange rate between polymerized and unpolymerized pools of subunits. Until quite recently the dynamic nature of intermediate filaments was underestimated because of their biochemical stability in vitro and a paucity of studies on their characteristics in vivo. However, the recent studies described in this review show that the karyoskeletal and cytoskeletal structures that assemble from many intermediate filament proteins possess the properties expected of dynamic protein polymer networks.     

Arf-like GTPases: not so Arf-like after all

ADP-ribosylation factor (Arf) GTP-binding proteins are among the best-characterized members of the Ras superfamily of GTPases, with well-established functions in membrane-trafficking pathways. A recent watershed of genomic and structural information has identified a family of conserved related proteins: the Arf-like (Arl) GTPases. The best-characterized Arl protein, Arl2, regulates the folding of beta tubulin, and recent data suggest that Arl1 and Arf-related protein 1 (ARFRP1) are localized to the trans-Golgi network (TGN), where they function, in part, to regulate the tethering of endosome-derived transport vesicles. Other Arl proteins are localized to the cytosol, nucleus, cytoskeleton and mitochondria, which indicates that Arl proteins have diverse roles that are distinct from the known functions of traditional Arf GTPases.     

Atg9 proteins,not so different after all

Macroautophagy (hereafter autophagy) is a catabolic pathway present in all eukaryotic cells. The yeast Saccharomyces cerevisiae has been pivotal in the identification and characterization of the key autophagy-related (Atg) proteins, which play a central role in the generation of autophagosomes. The components of the core Atg/ATG machinery and their functions are highly conserved among species, although mammalian cells also have isoforms and auxiliary factors. Atg9/ATG9 is the only transmembrane protein that is part of the core Atg/ATG machinery, but it appears to have divergent localizations and molecular roles in yeast and mammals. A recent experimental analysis of the yeast endo-lysosomal system by the laboratory of Benjamin Glick, however, suggests a more simple organization of this membrane system. Although this study has not examined yeast Atg9, its findings place this protein in the same compartments as its mammalian counterpart. Here, we will discuss the implications of this conceptual change on the trafficking of yeast Atg9 and its function in autophagy.     

Colour perception in three-spined sticklebacks: sexes are not so different after all

Sexual selection theory implies a tight coupling between the evolution of male sexual display and the sensory capabilities of the female. In sexually dimorphic species it is proposed that this might lead to sex differences in a species’ perceptive abilities. However, supporting evidence for this is rare, and to date there is only one example; three-spined sticklebacks, Gasterosteus aculeatus. Here, the female’s visual system is reported to become more red-sensitive during the summer breeding season; a time when sexually mature males display a red throat and belly to potential mates. In contrast, a shift in sensitivity is not apparent in males. These results, although commonly quoted, are surprising because previous observations suggest that both sexes may benefit from the detection of the male’s red colour patch; in females the intensity of red coloration can influence the choice of mate, and in males the conspicuous red colouration can aid the detection of rival males. To investigate this paradox we repeated the original optomotor experiment using a fully controlled design. In contrast to the earlier result, we found that both males and females exhibit a shift in their sensitivity to red during the reproductive period. These new data therefore do not support the hypothesis that sex differences in perceptual abilities occur in sexually dimorphic species.     

Neurobiology of echolocation in bats

Echolocating bats (sub-order: Microchiroptera) form a highly successful group of animals, comprising approximately 700 species and an estimated 25% of living mammals. Many echolocating bats are nocturnal predators that have evolved a biological sonar system to orient and forage in three-dimensional space. Acoustic signal processing and vocal-motor control are tightly coupled, and successful echolocation depends on the coordination between auditory and motor systems. Indeed, echolocation involves adaptive changes in vocal production patterns, which, in turn, constrain the acoustic information arriving at the bat's ears and the time-scales over which neural computations take place.     

Shrinking in a growing economy is not so puzzling after all

Bodenhorn, Guinnane, and Mroz (2017) argue that the diminution of heights during the Industrial Revolution and in the Antebellum U.S. is an artefact of the biased nature of the samples analyzed. We demonstrate that it would be an unfathomable coincidence if men and women all self-selected into scores of completely independent samples in such a way as to bias them in the identical direction. Instead, wWe show that BGM’s periodization is flawed and that their statistical models are misspecified, because they fail to consider the extent to which they introduce severe multicollinearity into their regressions. In addition, they fail to specify how they selected the samples they included in their analysis. In contrast, we argue that the economic transition from a predominantly agricultural to an increasingly industrial society was not a smooth process and lags in adjustment led to nutritional stresses. Height of a typical man in the U.S. decreased by 0.75 inches at a time when incomes were growing at a rate of 1.2% per annum. The developing human body of children and youth was sensitive enough to these nutritional stresses to register their effect better than monetary measures could. While nutritional status did decline during the Industrial Revolution in Europe and at the onset of modern economic in the U.S., by the second half of the 19^th century agricultural productivity caught up with the increased demand for foodstuffs and height reversals became a rarity. Thus, although markets adjusted, they did not do so instantaneously. Consequently, physical stature declined during this adjustment process although the wealthy were shielded from the increased price of nutrients. So, the divergence in average incomes and average heights at the threshold of the modern age is not so puzzling after all.     

Imaging fertilization in flowering plants, not so abominable after all

Although the discovery of double fertilization in flowering plants took place at the end of the nineteenth century little progress had been made in understanding the cellular and molecular mechanisms involved until the end of the twentieth century. After attempts to study fertilization with isolated male and female gametes, researchers turned to Arabidopsis thaliana as a model for genetic analysis and in vivo imaging. The development of confocal imaging and fluorescent proteins, coupled with new molecular insights into cell fate specification of plant gametes, allowed the development of robust markers for cells participating in double fertilization. These markers enabled the imaging of double fertilization in vivo in Arabidopsis. These studies have been coupled with the identification and molecular characterization of genes controlling fertilization in Arabidopsis. Live imaging has already provided new insights on sperm cell delivery, the equivalence of the fate of the sperm cells, gamete fusion, and re-initiation of the zygotic life. This review covers these topics and outlines many important aspects of double fertilization that remain unknown.     

The evolution of echolocation in bats

Recent molecular phylogenies have changed our perspective on the evolution of echolocation in bats. These phylogenies suggest that certain bats with sophisticated echolocation (e.g. horseshoe bats) share a common ancestry with non-echolocating bats (e.g. Old World fruit bats). One interpretation of these trees presumes that laryngeal echolocation (calls produced in the larynx) probably evolved in the ancestor of all extant bats. Echolocation might have subsequently been lost in Old World fruit bats, only to evolve secondarily (by tongue clicking) in this family. Remarkable acoustic features such as Doppler shift compensation, whispering echolocation and nasal emission of sound each show multiple convergent origins in bats. The extensive adaptive radiation in echolocation call design is shaped largely by ecology, showing how perceptual challenges imposed by the environment can often override phylogenetic constraints.     

Adaptive vocal behavior drives perception by echolocation in bats

Echolocation operates through adaptive sensorimotor systems that collectively enable the bat to localize and track sonar objects as it flies. The features of sonar signals used by a bat to probe its surroundings determine the information available to its acoustic imaging system. In turn, the bat's perception of a complex scene guides its active adjustments in the features of subsequent sonar vocalizations. Here, we propose that the bat's active vocal-motor behaviors play directly into its representation of a dynamic auditory scene.     

Embryonic evidence uncovers convergent origins of laryngeal echolocation in bats

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Object classification by echolocation in nectar feeding bats: size-independent generalization of shape

The nectar-feeding bat Glossophaga can be trained to discriminate two hollow forms, a hollow hemisphere and a paraboloid with the same diameter and depth, in total darkness. During training a saturation level of about 85-90% correct choices or more can be reached within 50-100 visits. To investigate generalization abilities, the bats were tested with pairs of the same shape but of different size. Although no reward was offered, they preferred the hollow sphere (30 mm and 50 mm diameter, but not 18 mm) over the corresponding paraboloids. Thus, the bats were able to generalize some features of the rewarded form and detect them in forms of the same shape but different size. This transposition is remarkable, since the bats could not use absolute spectral characters, but had to pay attention to size-independent features common to hollow hemispheres. Possible cues are the variation of echoes in dependence of different angles of calling direction (constant in spheres, changing with position in paraboloids) and/or the "timbre" of the echoes, i.e. their spectral pattern independent of their absolute pitch     

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.