Subfunctionalization: How often does it occur? How long does it take?

The mechanisms responsible for the preservation of duplicate genes have been debated for more than 70 years. Recently, Lynch and Force have proposed a new explanation: subfunctionalization--after duplication the two gene copies specialize to perform complementary functions. We investigate the probability that subfunctionalization occurs, the amount of time after duplication that it takes for the outcome to be resolved, and the relationship of these quantities to the population size and mutation rates.     

How does stochasticity in colonization accelerate the speed of invasion in a cellular automaton model?

We investigate the speed of invasion waves for a single species generated by stochastic short- and/or long-distance colonizations in a time-continuous cellular automaton (CA) model on a two-dimensional homogenous landscape. By simulating the CA models, we demonstrate that stochasticity can dramatically increase the speed of invasion compared to the corresponding deterministic CA model or the corresponding one-dimensional stochastic CA model. To explain this phenomenon, we first develop a mathematical model for the invasion involving only short-distance colonization (i.e., colonization only occurs from the eight adjacent cells), and present several approximation methods for solving the model. Our analyses show that the increased wave speed in the stochastic model is due to irregularity in the shape of the wavefront. Further extension of this model to include long-distance colonization demonstrates that stochasticity influences speeds to even greater extents in this case. Using dimension analysis, we deduced a semi-empirical formula for the speed as a function of three parameters intrinsic to short- and long-distance colonization, which agrees well with simulation results. Based on these results, we discuss how important stochasticity in colonization and spatial dimensionality are in the acceleration of invasion speed.     

Learning to forage in a regenerating patchy environment: Can it fail to be optimal?

The behaviour of animals foraging along closed traplines of regenerating patches of food has been simulated using a learning rule that determines when an animal should leave the patch at which it is currently feeding to search for another one. The rule causes the animal to stay at the patch as long as it is feeding faster than it remembers doing. The foraging behaviour of one animal, and of two or more animals together, feeding in traplines containing patches of the same and of differing types has been simulated, and in all cases the foraging behaviour generated by the rule allowed the animals to exploit the food very efficiently. The learning model is also responsible for indirect social interactions among animals sharing the same trapline because the feeding of each animal reduces the availability of food for the others. This causes a population of animals to disperse themselves, on average, among patches of food according to the ideal free distribution. The relationship between the learning model and conventional optimal foraging models is examined and it is shown that it is pointless to try to account for learned behaviour in the context of optimal foraging theory.     

Aerobic dive limit: how often does it occur in nature?

Diving animals offer a unique opportunity to study the importance of physiological constraint in their everyday behaviors. An important component of the physiological capability of any diving animal is its aerobic dive limit (ADL). The ADL has only been measured in a few species. The goal of this study was to estimate the aerobic dive limit from measurements of body oxygen stores and at sea metabolism. This calculated ADL (cADL) was then compared to measurements of diving behavior of individual animals of three species of otariids, the Antarctic fur seal, Arctocephalus gazella, the Australian sea lion, Neophoca cinerea, and the New Zealand sea lion, Phocarctos hookeri. Antarctic fur seals dove well within the cADL. In contrast, many individuals of both sea lion species exceeded the cADL, some by significant amounts. Australian sea lions typically dove 1.4 times longer than the cADL, while New Zealand sea lions on average dove 1.5 times longer than the cADL. The tendency to exceed the cADL was correlated with the dive pattern of individual animals. In both Antarctic Fur Seals and Australian sea lions, deeper diving females made longer dives that approached or exceeded the cADL (P<0.01, r(2)=0.54). Australian and New Zealand sea lions with longer bottom times also exceeded the cADL to a greater degree. The two sea lions forage on the benthos while the fur seals feed shallow in the water column. It appears that benthic foraging requires these animals to reach or exceed their aerobic dive limit.     

Human TTRV30M localization within podocytes in a transgenic mouse model of transthyretin related amyloidosis: does the environment play a role?

Transthyretin related amyloidosis is a nosological entity that leads to disability, diminished quality of life, all stages of chronic kidney disease and eventually death. Podocytes are polarized, highly differentiated epithelial cells important for proper nephron function. In the present study we investigated whether deposited TTRVal30Met (TTRV30M) molecules could be localized within podocytes in situ under the effect of different housing conditions (i.e. specific pathogen free [SPF] vs. non-SPF). Murine renal glomeruli from human TTRV30M (hTTRV30M) transgenic mice were examined via direct and indirect immunofluorescence techniques for the presence of hTTRV30M, murine serum amyloid P, activated caspase-3 and NPHS1. Association strength and amount of colocalization for NPHS1?ChTTRV30M, NPHS1-activated caspase-3, hTTRV30M-murine serum amyloid P were estimated. Localization of hTTRV30M in podocytes was demonstrated by immuno-electron microscopy. Renal hTTRV30M gene and NPHS1 gene expression levels were estimated. Non-SPF transgenic mice showed increased glomerular hTTRV30M deposition compared to their SPF counterparts. Furthermore increased podocytic localization of hTTRV30M was noticed in non-SPF mice. Glomerular caspase-3 activation was increased only in the non SPF housing conditions. Podocytic caspase-3 activation was increased in SPF and in non-SPF transgenic mice when compared to non transgenic controls. Environmental conditions influence glomerular deposition and podocytic localization of hTTRV30M. In this context increased caspase-3 activation occurred.     

Standardization of prey immunomarking: does a positive test always indicate predation?

A prey immunomarking procedure (PIP) in combination with generic anti-rabbit and anti-chicken immunoglobulin G (IgG) enzyme-linked immunosorbent assays (ELISAs) are used frequently to study arthropod predation. This study was conducted to: (1) further standardize the PIP as a tool for predator gut analysis research, (2) investigate the most effective means for administering IgG marks to prey items, and (3) assess the possibility of the PIP yielding false positive reactions as a consequence of a predator obtaining a mark by incidental contact with, or by a failed predation attempt on, a protein-marked prey item. The pest Lygus hesperus Knight (Hemiptera: Miridae) was tagged with either an external rabbit IgG mark, an internal chicken IgG mark, or a double (external rabbit IgG and internal chicken IgG) mark treatment. Then, the variously marked prey items were fed to chewing and piercing-sucking type predators and their gut contents were examined for the presence of IgG remains. Data revealed that all three marking treatments were highly effective at tagging targeted prey. However, ELISA results showed that the prey items should only be marked internally to maximize the likelihood of detecting prey remains while minimizing the risk of obtaining false positive errors. The merits and limitations of using the generic PIP for predator gut analysis research are discussed.     

How does life adapt to a gravitational environment? The outline of the terrestrial gastropod shell

How do several characteristics adapt to gravity while mutually influencing each other? Our study addresses this issue by focusing on the terrestrial gastropod shell. The geometric relationship between the spire index (shell height/diameter) and outline (cylindricality) is theoretically estimated. When the shell grows isometrically, a high-spired shell becomes conical in shape and a low-spired shell becomes cylindrical in shape. A physical model shows that the lowest- and highest-spired shells are the most balanced. In addition, a cone shape is the most balanced for a low-spired shell, and a column shape is the most balanced for a high-spired shell. Spire index and cylindricality measured for freshwater gastropods follow the relationship estimated by the model, whereas those for terrestrial gastropods deviate from this relationship. This translates to a high shell being more cylindrical than a flat shell, except in the case of extremely high or low shells. This suggests that the shape of the most balanced shells (lowest and highest shell heights) is constrained by coiling geometry but that relatively unbalanced shells (intermediate shell heights) do not follow a coiling geometry, as a result of adaptation to enable the snail to carry its shell more effectively.     

How does eutrophication affect different life stages of Fucus vesiculosus in the Baltic Sea? – a conceptual model

During the last few decades the perennial seaweed Fucus vesiculosus L. has rapidly declined in large parts of the Baltic Sea. Indirect effects of eutrophication, such as increased turbidity, sedimentation, grazing and occurrence of filamentous algae, have generally been suggested as major factors causing the decline. It is only recently, however, that the effects of these factors have been experimentally tested and here we summarise these results in a new conceptual model. In many areas, it might be desirable to enhance the recovery of Fucus artificially, as the natural rate of re-establishment of this important macroalga is limited both in time and space. To be able to optimise and evaluate the potential of restoring Fucus belts in eutrophicated areas, we need to know how eutrophication affects critical steps in its life cycle, such as the attachment, germination and early growth of germlings. We suggest that more attention should be given to the survival of early post-settlement stages in Fucusas they are crucial for the maintenance and re-establishment of populations. We also stress that the two reproductive periods that the species exhibits are included in discussions concerning effects of eutrophication on Fucus, as it is likely that the outcome of reproduction will differ between the two reproductive periods. In the new conceptual model we distinguish between the effects on adult and juvenile life stages and we add the two reproductive strategies of Fucus.     

How does a hypha grow? The biophysics of pressurized growth in fungi

The mechanisms underlying the growth of fungal hyphae are rooted in the physical property of cell pressure. Internal hydrostatic pressure (turgor) is one of the major forces driving the localized expansion at the hyphal tip which causes the characteristic filamentous shape of the hypha. Calcium gradients regulate tip growth, and secretory vesicles that contribute to this process are actively transported to the growing tip by molecular motors that move along cytoskeletal structures. Turgor is controlled by an osmotic mitogen-activated protein kinase cascade that causes de novo synthesis of osmolytes and uptake of ions from the external medium. However, as discussed in this Review, turgor and pressure have additional roles in hyphal growth, such as causing the mass flow of cytoplasm from the basal mycelial network towards the expanding hyphal tips at the colony edge.     

How does variation in the environment and individual cognition explain the existence of consistent behavioral differences?

According to recent studies on animal personalities, the level of behavioral plasticity, which can be viewed as the slope of the behavioral reaction norm, varies among individuals, populations, and species. Still, it is conceptually unclear how the interaction between environmental variation and variation in animal cognition affect the evolution of behavioral plasticity and expression of animal personalities. Here, we (1) use literature to review how environmental variation and individual variation in cognition explain population and individual level expression of behavioral plasticity and (2) draw together empirically yet nontested, conceptual framework to clarify how these factors affect the evolution and expression of individually consistent behavior in nature. The framework is based on simple principles: first, information acquisition requires cognition that is inherently costly to build and maintain. Second, individual differences in animal cognition affect the differences in behavioral flexibility, i.e. the variance around the mean of the behavioral reaction norm, which defines plasticity. Third, along the lines of the evolution of cognition, we predict that environments with moderate variation favor behavioral flexibility. This occurs since in those environments costs of cognition are covered by being able to recognize and use information effectively. Similarly, nonflexible, stereotypic behaviors may be favored in environments that are either invariable or highly variable, since in those environments cognition does not give any benefits to cover the costs or cognition is not able to keep up with environmental change, respectively. If behavioral plasticity develops in response to increasing environmental variability, plasticity should dominate in environments that are moderately variable, and expression of animal personalities and behavioral syndromes may differ between environments. We give suggestions how to test our hypothesis and propose improvements to current behavioral testing protocols in the field of animal personality.     

How long does it take to become a proficient hunter? Implications for the evolution of extended development and long life span

Human hunting is arguably one of the most difficult activities common to foraging peoples now and in the past. Children and teenagers have usually been described as incompetent hunters in ethnographies of hunter-gatherers. This paper explores the extent to which adult-level competence is limited more by the constraints of physical capital, or body size, and brain-based capital, or skills and learning. The grandmother hypothesis requires that production is an increasing function of size alone, while the embodied capital model stipulates that production is a function of both size and delayed learning. Tests based on observational, interview, and experimental data collected among Tsimane Amerindians of the Bolivian Amazon suggest that size alone cannot explain the long delay until peak hunting productivity. Indirect encounters (e.g., smells, sounds, tracks, and scat) and shooting of stationary targets are two components of hunting ability limited primarily by physical size alone, but the more difficult components of hunting--direct encounters with important prey items and successful capture--require substantial skill. Those skills can take an additional ten to twenty years to develop after achieving adult body size.     

Reproduction in a variable environment: How does Eupelmus vuilleti, a parasitoid wasp, adjust oogenesis to host availability?

Oogenesis of the parasitoid wasp Eupelmus vuilleti is known to be dependent on host availability. However, examination of ovarian dynamics by microscopy showed that oogenesis and vitellogenesis are initiated before female eclosion and proceed 1-2 days after, independent of host presence. Oogenesis continued beyond the 2nd day only in the presence of hosts, otherwise it was replaced by egg resorption. It is thus possible to distinguish between host-independent and host-dependent periods of oogenesis. In the presence of host, each ovariole (three per ovary) contained generally three oocytes: a fully mature oocyte, a nearly mature one and an immature one. However, host deprived-females resorbed their most mature and their smallest oocytes, but kept one almost mature oocyte per ovariole. Comparison of zero, short and long host deprivation periods showed that females always had the ability to quickly lay eggs to exploit any new host. However, increased deprivation led to a reduction in the number and the viability of eggs. Enzymo-immunological measurements of ecdysteroids were made in whole females, in dissected ovaries and in newly laid eggs. Our results indicated that ecdysteroids play a major role as circulating hormones involved in the regulation of oogenesis.     

Competition and species coexistence in a metapopulation model: Can fast asymmetric migration reverse the outcome of competition in a homogeneous environment?

We investigate whether asymmetric fast migration can modify the predictions of classical competition theory and, in particular revert species dominance. We consider a model of two species competing for an implicit resource on a habitat divided into two patches. Both patches are connected through constant migration rates and in each patch local dynamics are driven by a Lotka-Volterra competition system.Local competition is asymmetric with the same superior competitor in both patches. Migration is asymmetric, species dependent and fast in comparison to local competitive interactions. The species and patches are taken to be otherwise similar: in both patches we assume the same carrying capacities for both species, and the same growth rates and pair-wise competition coefficients for each species.We show that global dynamics can be described by a classical Lotka-Volterra competition model. We found that by modifying the ratio of intraspecific migration rates for both species all possible combinations of global species relative dominance can be achieved. We find specific conditions for which the local superior competitor is globally excluded. This is to our knowledge the first study showing that fast asymmetric migration can lead to inferior competitor dominance in a homogeneous environment. We conclude that disparity of temporal scales between migration and local dynamics may have important consequences for the maintenance of biodiversity in spatially structured populations.     

How long is a piece of Strix? Methods in measuring and measuring the measurers

An experiment to quantify intra- and interobserver error in anatomical measurements found that interobserver measurements can vary by over 14% of mean specimen length; disparity in measurement increases logarithmically with the number of contributors; instructions did not reduce variation or measurement disparity; scale of the specimen influenced the precision of measurement (relative error increasing with specimen size); different methods of taking a measurement yielded different results, although they did not differ in terms of precision, and topographical complexity of the elements being considered may potentially influence error (error increasing with complexity). These results highlight concerns about introduction of noise and potential bias that should be taken into account when compiling composite datasets and meta-analyses.     

How to model the local interaction in the predator–prey system at slow diffusion in a heterogeneous environment?

We examine the nonlinear reaction–diffusion–advection equations to modeling of the predator–prey system under heterogeneous carrying capacity of the prey, and Holling type II functional response. When advection and diffusion fluxes are absent or small, we detect the discrepancy between the resource (carrying capacity) and species distributions. The large diffusion eliminates this effect. We propose a modification of the functional response coefficients to provide the correlation between species distribution and resource in both cases. The numerical simulation of several models both under small and moderate advection–diffusion fluxes is carried out.     

Seed Swallowing in Tamarins: Evidence of a Curative Function or Enhanced Foraging Efficiency?

Nonhuman primates represent a major component of the frugivore biomass in several rain-forest communities. Although there is considerable evidence that prosimians, monkeys, and apes serve as dispersal agents for many tropical trees, little attention has been paid to the more basic questions of why certain species of primates swallow and void seeds, and what, if any, are the advantages to an animal of having a large, hard, bolus pass through its digestive tract. We examine patterns of fruit-eating and seed-swallowing in two species of free-ranging tamarins: Saguinus mystax and Saguinus geoffroyi. Fruits commonly eaten by tamarins contain large seeds surrounded by a fibrous and adhesive pulp or arilate seed coat. They generally swallow seeds and pulp together. Intact seeds are voided over a 1- to 3-h period. Measurements of 132 seeds naturally voided by Panamanian tamarins average 11.2 mm in length and 0.3 g. The greatest number of large seeds contained in the digestive tract of a single animal at one time was 13. In the case of moustached tamarins, we collected 220 seeds. Average seed length is 11.9 mm and average seed weight is 0.3 g. At the time of capture, one animal had 26 seeds in its digestive tract. In both tamarin species, there is evidence of sex-based differences in feeding behavior. Adult female moustached and Panamanian tamarins swallowed and voided seeds of larger size than adult males did. Seed size is positively correlated with pulp weight (p <. 001), therefore females were selecting food items with higher nutritional rewards than adult males did. Given their small body size and relatively short digestive tract, why do tamarins swallow such large seeds? Although several explanations are possible, we propose that the large number and size of undigested seeds continuously passing through the tamarin gut serve a curative role in mechanically dislodging and expelling intestinal parasites—Ancanthocephala (spiny-headed worms)—from their digestive tracts.     

Nutrigenomics-based personalised nutritional advice: in search of a business model?

Nutritional advice has mainly focused on population-level recommendations. Recent developments in nutrition, communication, and marketing sciences have enabled potential deviations from this dominant business model in the direction of personalisation of nutrition advice. Such personalisation efforts can take on many forms, but these have in common that they can only be effective if they are supported by a viable business model. The present paper takes an inventory of approaches to personalised nutrition currently available in the market place as its starting point to arrive at an identification of their underlying business models. This analysis is presented as a unifying framework against which the potential of nutrigenomics-based personalised advice can be assessed. It has uncovered nine archetypical approaches to personalised nutrition advice in terms of their dominant underlying business models. Differentiating features among such business models are the type of information that is used as a basis for personalisation, the definition of the target group, the communication channels that are being adopted, and the partnerships that are built as a part of the business model. Future research should explore the consumer responses to the diversity of “archetypical” business models for personalised nutrition advice as a source of market information on which the delivery of nutrigenomics-based personalised nutrition advice may further build.     

Developmental signaling in Hydra: what does it take to build a "simple" animal?

Developmental processes in multicellular animals depend on an array of signal transduction pathways. Studies of model organisms have identified a number of such pathways and dissected them in detail. However, these model organisms are all bilaterians. Investigations of the roles of signal transduction pathways in the early-diverging metazoan Hydra have revealed that a number of the well-known developmental signaling pathways were already in place in the last common ancestor of Hydra and bilaterians. In addition to these shared pathways, it appears that developmental processes in Hydra make use of pathways involving a variety of peptides. Such pathways have not yet been identified as developmental regulators in more recently diverged animals. In this review I will summarize work to date on developmental signaling pathways in Hydra and discuss the future directions in which such work will need to proceed to realize the potential that lies in this simple animal.