What do mice select for in seeds?

Summary Knowledge of the basis upon which granivores select seeds is crucial to the understanding of granivory. In this study the preferences of three rodent granivores among seeds of 11 plants from the semi-arid Karoo of South Africa were estimated, and related to the physical and chemical attributes of the seeds. Seed weights and calorific, moisture, protein, polyphenol, ash, lipid and silica contents were estimated and cell contents, soluble ash and soluble carbohydrate contents were derived from these values. These attributes were determined for both the intact seeds and the portion of the seed that is ingested by the mice. The efficiency with which mice ingested the seeds (in terms of time and mass) was recorded. All three mouse species ranked the seeds similarly, and the two species for which handling efficiency was measured did not differ in this regard. Preference hierachies were highly correlated with the rate of energy intake, as predicted by optimal foraging theory. There was no correlation between rodent preferences and the gross energy content of the seeds, emphasising the importance of measuring relevant parameters. The energy yield of the seeds calculated here, in conjunction with rodent population energy requirements and dietary data, may be used to estimate potential granivore impact on the seed production of the plant community.     

Does body volume constrain reproductive output in lizards?

The numbers and sizes of eggs produced by adult females ultimately determine the viability of populations, as well as the evolutionary fitness of the females themselves. Despite an enormous amount of literature on the adaptive significance of fecundity variation within and among populations, simpler questions--such as the proximate mechanisms by which a female determines her clutch size--have attracted less attention. Our surgical manipulations show that the amount of space available to hold eggs within a female's abdomen influences her total reproductive allocation, enabling her to flexibly modify her reproductive output as she grows larger.     

What can cell cycle and ultrastructure tell us about desiccation tolerance in Leucaena leucocephala germinating seeds?

Desiccation tolerance (DT) is the ability to tolerate dehydration to levels below 0.1 g(H₂O) g^?1(dry mass) and subsequent rehydration without lethal damage. Here, it is proposed that Leucaena leucocephala, a tree species, has potential to be model tolerant species in seed research. Using flow cytometry and transmission electron microscopy, cytological changes related to loss of DT in Leucaena primary roots were followed during germination. Leucaena seeds lost their DT at the end of germination and this coincided with an increase in cellular 4C DNA content. A negative correlation between the 8C DNA content and the capacity of germinating Leucaena seeds to tolerate desiccation was also observed. Apparently, the seeds of Leucaena underwent extra cycles of endoreduplication and accumulated a high content of DNA — an event not previously linked to DT. The ultrastructural damage imposed by drying overcame Leucaena primary root cell resilience and their ability to resume normal growth. Nuclear DNA content may be used as indicator of progress of germination and loss of DT in Leucaena.     

What can myosin VI do in cells?

The recently solved structure of the myosin VI motor demonstrates that the unique insert at the end of the motor is responsible for the reversal of the normal myosin directionality. A second class-specific insert near the nucleotide-binding pocket contributes to myosin VI's unique kinetic tuning, allowing it to function either as an actin-based transporter or as an anchoring protein. Recent biochemical and biophysical studies have shown that the native molecule can form dimers upon clustering, and cell biological studies have demonstrated that it clearly does play both transport and anchoring roles in cells. These mechanistic insights allow us to speculate on how unusual aspects of myosin VI structure and function allow it to fill unique niches in cells.     

What defines successful integration into a social group for hand-reared chimpanzee infants?

Hand-rearing of captive great ape infants is sometimes necessary but can have negative behavioral consequences. Modern hand-rearing protocols, including early integration into a diverse group of conspecifics, appear to reduce the negative consequences of hand-rearing, but the process of integration is not well studied. We investigated six potential metrics of success during the introduction of two hand-reared chimpanzee infants into a troop of nine other chimpanzees at the Maryland Zoo in Baltimore. Little aggression was observed and the infants continue to be maintained in the troop at publication. As we predicted, during the introduction the hand-reared infants showed consistent levels of stress-related behaviors, participated in affiliative interactions with all available partners, and acted, received, and mutually engaged in these interactions. Solitary behaviors by these infants were similar to a mother-reared infant in the same group. Each infant also formed a relationship with a specific female that involved nest-sharing, carrying, retrieval, and intervening to reduce risk to the infant; these relationships could be classified as allomothering because they involved maternal behavior but occupied significantly less of the infants’ time than a maternal relationship. Contrary to our prediction, the hand-reared infants therefore spent significantly less time in social behavior than a mother-reared infant of the same age. In addition, the hand-reared infants continued to show strong social preferences for each other as introductions progressed and to direct a low but consistent number of nonfeeding social behaviors to humans. The successful introduction of hand-reared infants appeared to involve adding conspecific social relationships to the infants’ social repertoire, but not eliminating social interactions directed at humans.     

How can the complex epidemiology of malaria in India impact its elimination?

Malaria is a human health hazard in the tropical and subtropical zones of the globe and is poised to be eliminated by the year 2030. Despite a decrease in incidence in the past two decades, many endemic countries, including India, report cases regularly. The epidemiology of malaria in India is unique owing to several features of the Plasmodium parasites, Anopheles vectors, ecoepidemiological situations conducive to disease transmission, and susceptible humans living in rural and forested areas. Limitations in public health reach, and poor health-seeking behaviour of vulnerable populations living in hard-to-reach areas, add to the problem. We bring all of these factors together in a comprehensive framework and opine that, in spite of complexities, targeted elimination of malaria in India is achievable with planned programmatic approaches.     

What can we teach Drosophila? What can they teach us?

A number of single gene mutations dramatically reduce the ability of fruit flies to learn or to remember. Cloning of the affected genes implicated the adenylyl cyclase second-messenger system as key in learning and memory. The expression patterns of these genes, in combination with other data, indicates that brain structures called mushroom bodies are crucial for olfactory learning. However, the mushroom bodies are not dedicated solely to olfactory processing; they also mediate higher cognitive functions in the fly, such as visual context generalization. Molecular genetic manipulations, coupled with behavioral studies of the fly, will identify rudimentary neural circuits that underly multisensory learning and perhaps also the circuits that mediate more-complex brain functions, such as attention.     

What is in a model?

After reading contradictory claims of model status for some insect species, we feel a brief discussion of the topic may be useful. Here, we document a few examples where clarity on model status seems to be lacking, briefly review work on widely recognized models, and offer criteria for including any given species as a model organism.     

What do measurements of molecular biomarkers in different body fluids really tell us?

Molecular or biochemical biomarkers of joint metabolism offer promise in helping us understand joint pathology, its detection and treatment. But they have often been studied alone and in only one body fluid. Although the synovial joint is usually the focus of most arthritis pathology, it is often difficult, for a variety of reasons, to obtain synovial fluid that should best reflect changes in biomarkers related to pathology. It is therefore very important to see whether analyses of more readily obtainable sera and urine also reflect changes in synovial fluid. Catterall and colleagues, in a paper in Arthritis Research & Therapy that examines very early biomarker changes following joint injury, provide us with some insights into these important questions. As the study was very small and examined very early changes following joint injury, prior to onset of any recognisable pathology, we look forward to future larger biomarker studies of this kind in patients with clinically defined arthritic changes to which we can relate biomarker data.     

What can dry reservoir sediments in a semi-arid region in Brazil tell us about cladocera?

A study of dry sediments in a semi-arid reservoir in northeast Brazil was undertaken. Eleven quadrants were sampled along a transect in the reservoir. Sediments were collected and transferred to distilled water in the laboratory where they were subsequently filtered through a 50 m mesh filter. Ecloded cladocerans were identified. Several species hatched in the laboratory, and were compared with the cladoceran community collected before the reservoir had dried out. In previous years, only Moina minuta, Diaphanosoma spinulosumand Alonella hamulata were found in the lake, each on a different sampling date. In the laboratory, however, other species like Macrothrix sp., Leydigia ipojucae, Latonopsis australis and Ceriodaphnia cornuta f. rigaudi hatched. We observed that those quadrants, which were located in higher parts of the reservoir, and had been dry for 13 years, contained species that appeared only in these quadrants. Thus, the sediments show that independently of the species actively present in the water column, sediments store species in diapause stages: an observation that should not be overlooked, especially in biodiversity studies.     

What happens to dead birds left in a cave and its vicinity for a quarter of a century? A taphonomic experiment

Abstract

This paper describes a bird carcass-monitoring experiment carried out in a limestone cave and its immediate vicinity in southern Poland for almost a quarter of a century. Some specimens deposited outside the cave were preserved almost intact, others were only a little weathered. Soft tissues and remnants of feathers were preserved in some of the samples inside the cave. Stages of bone modifications that can occur in a cave have been distinguished and illustrated for the first time. Also, bird bones from owl pellets have been used in a carcass-monitoring experiment for the first time. Bone modifications in the form of wrinkling, bending and/or collapsing of the bone surface were recorded only on the bones of birds that decomposed inside the cave, and not on bones that had been isolated from owl pellets prior to their deposition in the cave. Therefore, it is postulated that avian – and possibly also small mammal – bones that have been defleshed, either by people or animals, have a greater chance to survive and fossilize than bones deposited as complete carcasses in a cave. This agrees with the generally accepted notion that larger assemblages of small vertebrates in caves are usually the result of predator accumulation.     

What’s in a loop?

DNAs and proteins are major classes of biomolecules that differ in many aspects. However, a considerable number of their members also share a common architectural feature that enables the assembly of multi-protein complexes and thereby permits the effective processing of signals: loop structures of substantial sizes. Here we briefly review a few representative examples and suggest a functional classification of different types of loop structures. In proteins, these loops occur in protein regions classified as intrinsically disordered. Studying such loops, their binders and their interactions with other loops should reveal much about cellular information computation and signaling network architectures. It is also expected to provide critical information for synthetic biologists and bioengineers.     

What can we teach Drosophila? What can they teach us?

A number of single gene mutations dramatically reduce the ability of fruit flies to learn or to remember. Cloning of the affected genes implicated the adenylyl cyclase second-messenger system as key in learning and memory. The expression patterns of these genes, in combination with other data, indicates that brain structures called mushroom bodies are crucial for olfactory learning. However, the mushroom bodies are not dedicated solely to olfactory processing; they also mediate higher cognitive functions in the fly, such as visual context generalization. Molecular genetic manipulations, coupled with behavioral studies of the fly, will identify rudimentary neural circuits that underly multisensory learning and perhaps also the circuits that mediate more-complex brain functions, such as attention.     

Selenoproteins—What unique properties can arise with selenocysteine in place of cysteine?

The defining entity of a selenoprotein is the inclusion of at least one selenocysteine (Sec) residue in its sequence. Sec, the 21st naturally occurring genetically encoded amino acid, differs from its significantly more common structural analog cysteine (Cys) by the identity of a single atom: Sec contains selenium instead of the sulfur found in Cys. Selenium clearly has unique chemical properties that differ from sulfur, but more striking are perhaps the similarities between the two elements. Selenium was discovered by Jöns Jacob Berzelius, a renowned Swedish scientist instrumental in establishing the institution that would become Karolinska Institutet. Written at the occasion of the bicentennial anniversary of Karolinska Institutet, this mini review focuses on the unique selenium-derived properties that may potentially arise in a protein upon the inclusion of Sec in place of Cys. With 25 human genes encoding selenoproteins and in total several thousand selenoproteins yet described in nature, it seems likely that the presence of that single selenium atom of Sec should convey some specific feature, thereby explaining the existence of selenoproteins in spite of demanding and energetically costly Sec-specific synthesis machineries. Nonetheless, most, if not all, of the currently known selenoproteins are also found as Cys-containing non-selenoprotein orthologues in other organisms, wherefore any potentially unique properties of selenoproteins are yet a matter of debate. The pK_a of free Sec (approximately 5.2) being significantly lower than that of free Cys (approximately 8.5) has often been proposed as one of the unique features of Sec. However, as discussed herein, this pK_a difference between Sec and Cys can hardly provide an evolutionary pressure for maintenance of selenoproteins. Moreover, the typically 10- to 100-fold lower enzymatic efficiencies of Sec-to-Cys mutants of selenoprotein oxidoreductases, are also weak arguments for the overall existence of selenoproteins. Here, it is however emphasized that the inherent high nucleophilicity of Sec and thereby its higher chemical reaction rate with electrophiles, as compared to Cys, seems to be a truly unique property of Sec that cannot easily be mimicked by the basicity of Cys, even within the microenvironment of a protein. The chemical rate enhancement obtained with Sec can have other consequences than those arising from a low redox potential of some Cys-dependent proteins, typically aiming at maintaining redox equilibria. Another unique aspect of Sec compared to Cys seems to be its efficient potency to support one-electron transfer reactions, which, however, has not yet been unequivocally shown as a Sec-dependent step during the natural catalysis of any known selenoprotein enzyme.