How does salinity influence habitat selection and growth in juvenile American eels Anguilla rostrata?

The influence of salinity on habitat selection and growth in juvenile American eels Anguilla rostrata captured in four rivers across eastern Canada was assessed in controlled experiments in 2011 and 2012. Glass eels were first categorized according to their salinity preferences towards fresh (FW), salt (SW) or brackish water (BW) and the growth rate of each group of elvers was subsequently monitored in controlled FW and BW environments for 7 months. Most glass eels (78–89%) did not make a choice, i.e. they remained in BW. Salinity preferences were not influenced by body condition, although a possible role of pigmentation could not be ruled out. Glass eels that did make a choice displayed a similar preference for FW (60–75%) regardless of their geographic origin but glass eels from the St Lawrence Estuary displayed a significantly higher locomotor activity than those from other regions. Neither the salinity preferences showed by glass eels in the first experiment nor the rearing salinities appeared to have much influence on growth during the experiments. Elvers from Nova Scotia, however, reached a significantly higher mass than those from the St Lawrence Estuary thus supporting the hypothesis of genetically (or epigenetically) based differences for growth between A. rostrata from different origins. These results provide important ecological knowledge for the sustained exploitation and conservation of this threatened species.     

Worker brain development and colony organization in ants: Does division of labor influence neuroplasticity?

Brain compartment size allometries may adaptively reflect cognitive needs associated with behavioral development and ecology. Ants provide an informative system to study the relationship of neural architecture and development because worker tasks and sensory inputs may change with age. Additionally, tasks may be divided among morphologically and behaviorally differentiated worker groups (subcastes), reducing repertoire size through specialization and aligning brain structure with task‐specific cognitive requirements. We hypothesized that division of labor may decrease developmental neuroplasticity in workers due to the apparently limited behavioral flexibility associated with task specialization. To test this hypothesis, we compared macroscopic and cellular neuroanatomy in two ant sister clades with striking contrasts in worker morphological differentiation and colony‐level social organization: Oecophylla smaragdina , a socially complex species with large colonies and behaviorally distinct dimorphic workers, and Formica subsericea , a socially basic species with small colonies containing monomorphic workers. We quantified volumes of functionally distinct brain compartments in newly eclosed and mature workers and measured the effects of visual experience on synaptic complex (microglomeruli) organization in the mushroom bodies—regions of higher‐order sensory integration—to determine the extent of experience‐dependent neuroplasticity. We demonstrate that, contrary to our hypothesis, O. smaragdina workers have significant age‐related volume increases and synaptic reorganization in the mushroom bodies, whereas F. subsericea workers have reduced age‐related neuroplasticity. We also found no visual experience‐dependent synaptic reorganization in either species. Our findings thus suggest that changes in the mushroom body with age are associated with division of labor, and therefore social complexity, in ants. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1072–1085, 2017     

How does interferon inhibit tumour growth?

Interferon can inhibit tumour growth in experimental animals and in some patients with benign and malignant tumours. There is experimental evidence to suggest that several mechanisms may be involved: a direct effect on the tumor or an indirect effect via the host, or both. Thus, interferon may slow the rate of tumour cell multiplication and this may lead to cell death. Interferon may induce changes in the cell surface rendering tumour cells more sensitive to host defence mechanisms. Interferon may induce reversion in the phenotype of tumour cells. Interferon may stimulate specific and non-specific humoral and cellular host mechanisms. The relative importance of these different effects of interferon may vary depending on the host and the particular tumour.     

Personality in social insects: How does worker personality determine colony personality?

Social insect colonies and the workers comprising them,each exhibit consistent individual differences in behavior,also known as ‘personalities'.Because the behavior of social insect colonies emerges from the actions of their workers,individual variation among workers' personality may be important in determining the variation we observe among colonies.The reproductive unit of social insects,on which natural selection acts,is the colony,not individual workers.Therefore,it is important to understand what mechanisms govern the observed variation among colonies.Here I propose three hypotheses that address how consistent individual differences in the behavior of workers may lead to consistent individual differences in the behavior of colonies:1.Colonies differ consistently in their average of worker personality; 2.The distribution but not the average of worker personalities varies consistently among colonies; and 3.Colony personality does not emerge from its worker personality composition but from consistent external constraints.I review evidence supporting each of these hypotheses and suggest methods to further investigate them.The study of how colony personality emerges from the personalities of the workers comprising them may shed light on the mechanisms underlying consistent individual differences in the behavior of other animals.     

How does temporal variation in habitat connectivity influence metapopulation dynamics?

Metapopulation persistence depends on connectivity between habitat patches. While emphasis has been placed on the spatial dynamics of connectivity, much less has been placed on its short‐term temporal dynamics. In many terrestrial and aquatic ecosystems, however, transient (short‐term) changes in connectivity occur as habitat patches are connected and disconnected due, for example, to climatic or hydrological variability. We evaluated the implications of transient connectivity using a network‐based metapopulation model and a series of scenarios representing temporal changes in connectivity. The transient loss of connectivity can influence metapopulation persistence, and more strongly autocorrelated temporal dynamics affect metapopulation persistence more severely. Given that many ecosystems experience short‐term and temporary loss of habitat connectivity, it is important that these dynamics are adequately represented in metapopulation models; failing to do so may yield overly optimistic‐estimates of metapopulation persistence in fragmented landscapes.     

How does light intensity influence evening dressing behavior in the cold?

Core temperature (tympanic and rectal temperatures) is lowered for several hours under diurnal bright light exposure and its evening fall is inhibited under evening bright light exposure. Melatonin may be involved in the behavior of these core temperatures. Diurnal bright light exposure for several hours may make dressing behavior and thermal sensibility in the evening cold slower and dull, compared with diurnal dim light exposure. On the contrary, evening bright light exposure for several hours may make the dressing behavior and thermal sensibility in the evening cold quicker and sharper, compared with evening dim light exposure. The underlying physiological mechanisms for these findings are that the thermoregulatory set-point would be reduced more markedly in the evening under the influence of higher elevation of melatonin under the diurnal bright light exposure, and its evening decline would be inhibited by suppression of the nocturnal rise of melatonin under evening bright light exposure.     

How does small-scale fragmentation affect litter-dwelling ants? The role of isolation

Remnant isolation following fragmentation is considered to be one of the main drivers of ecological decline in modified landscapes. Thereby, connecting remnants using ecological corridors has been increasingly suggested as being important for conservation. Our objectives were to test isolation effects on extinction, colonization and turnover rates of a litter-dwelling ant assemblage, and to evaluate effectiveness of ecological corridors to mitigate habitat fragmentation consequences. We used a mesocosm manipulative design, with three different isolation treatments: far, near and near connected by a corridor, sampled fortnightly for 60?days. Fragmentation caused an ongoing decrease in ant species richness, probably due to a negative balance between extinction and colonization. Extinction was steady with time, while colonization decreased over the same period. This outcome highlights the key role that colonization plays in the persistence of populations of litter-dwelling ants. Turnover rates increased with time in the treatment with a corridor, but remained steady in the other treatments. We conclude that corridors are important for not only immigration to remnants, but also emigration, acting as a two way traffic route. Thus, it may be an important “leakage” point for threatened species, with implications for their conservation status.     

How far does cell lineage influence cell fate specification in crustacean embryos?

In crustaceans, invariant cell lineages have been shown to occur (i) in early cleavages of several taxa and (ii) in the course of formation and differentiation of the post-naupliar germ bands in malacostracans. Work on early cleavages is still in its infancy. In contrast, the generation and proliferation of mesoteloblasts and ectoteloblasts and the subsequent proliferation and differentiation of bandlet cells have been studied in members of several subgroups of Malacostraca. Similarities and differences have been determined in order to interpret the interdependencies of the steps in the differentiation process. Some of these steps are highly conserved, as in the case of the generation of four pairs of mesoteloblasts, others are prone to phylogenetic change, as in the case of the primary ring of 19 ectoteloblasts which has been altered at least twice in evolution. A stereotyped cleavage pattern in the germ band has been shown to be independent of the origin of the precursor cells. The question whether neuroblasts in crustaceans and insects are homologous or are the result of convergent evolution is still open. However, the homology of early differentiating neurons in crustaceans and insects seems to be well established. In addition, similarities in the expression patterns of the engrailed gene are likely to be homologous and point to a close relationship between these two groups.     

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 do ants assess food volume?

By comparing the behaviour of Lasius niger scouts at sucrose droplets of different volumes, we empirically identified the criterion used by each scout to assess the amount of food available as well as the rules governing its decision to lay a recruitment trail. When scouts discovered food volumes exceeding the capacity of their crop (3 or 6 μl), 90% immediately returned to the nest laying a recruitment trail. In contrast, when smaller food droplets (0.3, 0.7 or 1 μl) were offered, several scouts stayed on the foraging area, presumably exploring it for additional food. If unsuccessful, they returned to the nest without laying a trail. The droplet volume determined the percentage of trail-laying ants but had no influence on the intensity of marking when this was initiated. The key criterion that regulated the recruiting behaviour of scouts was their ability to ingest their own desired volume. This volume acted as a threshold triggering the trail-laying response of foragers. Collective regulation of foraging according to food size resulted from the interplay between the distribution of these desired volume thresholds among colony members and the food volume available. We relate some aspects of the foraging ecology of aphid-tending ants to this decision-making process. Copyright 2000 The Association for the Study of Animal Behaviour.     

How does intraspecific density regulation influence metapopulation synchrony and persistence?

Intraspecific density regulation influences the synchronization of local population dynamics through dispersal. Spatial synchrony in turn may jeopardize metapopulation persistence. Joining results from previous studies suggests that spatial synchrony is highest at moderate over-compensation and is low at compensating and at very strong over-compensating density regulation. We scrutinize this supposition of a unimodal relationship using a process-based metapopulation model with explicit local population dynamics. We extend the usually studied range of density regulation to under-compensation and analyse resulting metapopulation persistence. We find peaks of spatial synchrony not only at over-compensatory but also under-compensatory density regulation and show that effects of local density compensation on synchrony follow a bimodal rather than unimodal relationship. Persistence of metapopulations however, shows a unimodal relationship with a broad plateau of high persistence from compensatory to over-compensatory density regulation. This range of high persistence comprises both levels of low and high spatial synchrony. Thus, not synchrony alone jeopardizes metapopulation persistence, but only in interplay with high local extinction risk. The functional forms of the relations of density compensation with spatial synchrony and persistence are robust to increases in dispersal mortality, landscape dynamics, or density dependence of dispersal. However, with each of these increases the maxima of spatial synchrony and persistence shift to higher over-compensation and levels of synchrony are reduced. Overall, for over-compensation high landscape connectivity has negative effects while for under-compensation connectivity affects persistence positively. This emphasizes the importance of species life-history traits for management decisions with regard to landscape connectivity: while dispersal corridors are essential for species with under-compensatory density regulation, they may have detrimental effects for endangered species with over-compensation.     

How does the QB site influence propagate to the QA site in photosystem II?

The redox potential of the primary quinone Q(A) [E(m)(Q(A))] in photosystem II (PSII) is lowered by replacement of the native plastoquinone (PQ) with bromoxynil (BR) at the secondary quinone Q(B) binding site. Using the BR-bound PSII structure presented in the previous Fourier transform infrared and docking calculation studies, we calculated E(m)(Q(A)) considering both the protein environment in atomic detail and the protonation pattern of the titratable residues. The calculated E(m)(Q(A)) shift in response to the replacement of PQ with deprotonated BR at the Q(B) binding site [ΔE(m)(Q(A))(PQ→BR)] was -55 mV when the three regions, Q(A), the non-heme iron complex, and Q(B) (Q(B) = PQ or BR), were treated as a conjugated supramolecule (Q(A)-Fe-Q(B)). The negative charge of BR apparently contributes to the downshift in ΔE(m)(Q(A))(PQ→BR). This downshift, however, is mostly offset by the influence of the residues near Q(B). The charge delocalization over the Q(A)-Fe-Q(B) complex and the resulting H-bond strength change between Q(A) and D2-His214 are crucial factors that yield a ΔE(m)(Q(A))(PQ→BR) of -55 mV by (i) altering the electrostatic influence of the H-bond donor D2-His214 on E(m)(Q(A)) and (ii) suppressing the proton uptake events of the titratable residues that could otherwise upshift ΔE(m)(Q(A))(PQ→BR) during replacement of PQ with BR at the Q(B) site.     

How does feedback from phage infections influence the evolution of phase variation in Campylobacter?

Campylobacter jejuni (C. jejuni) causes gastroenteritis following the consumption of contaminated poultry meat, resulting in a large health and economic burden worldwide. Phage therapy is a promising technique for eradicating C. jejuni from poultry flocks and chicken carcasses. However, C. jejuni can resist infections by some phages through stochastic, phase-variable ON/OFF switching of the phage receptors mediated by simple sequence repeats (SSR). While selection strength and exposure time influence the evolution of SSR-mediated phase variation (PV), phages offer a more complex evolutionary environment as phage replication depends on having a permissive host organism. Here, we build and explore several continuous culture bacteria-phage computational models, each analysing different phase-variable scenarios calibrated to the experimental SSR rates of C. jejuni loci and replication parameters for the F336 phage. We simulate the evolution of PV rates via the adaptive dynamics framework for varying levels of selective pressures that act on the phage-resistant state. Our results indicate that growth reducing counter-selection on a single PV locus results in the stable maintenance of the phage, while compensatory selection between bacterial states affects the evolutionary stable mutation rates (i.e. very high and very low mutation rates are evolutionarily disadvantageous), whereas, in the absence of either selective pressure the evolution of PV rates results in mutation rates below the basal values. Contrastingly, a biologically-relevant model with two phase-variable loci resulted in phage extinction and locking of the bacteria into a phage-resistant state suggesting that another counter-selective pressure is required, instance, the use of a distinct phage whose receptor is an F336-phage-resistant state. We conclude that a delicate balance between counter-selection and phage-attack can result in both the evolution of phase-variable phage receptors and persistence of PV-receptor-specific phage.     

How does spittlebug oviposition affect shoot growth and bud production in two willow species?

We measured the effects of oviposition by the spittlebug Aphrophora pectoralis on shoot growth and bud production in two willow species, Salix miyabeana and Salix sachalinensis. In autumn, adult females of A.pectoralis insert their ovipositor into the apical region of 1-year-old shoots, resulting in the death of most shoot tips within 1week. Consequently, an increase in the number of dead buds and a decrease in the number of vegetative buds on 1-year-old shoots was recorded. In the following spring, the growth of current-year shoots was greatly increased on 1-year-old shoots damaged by spittlebug oviposition. Furthermore, spittlebug oviposition increased the production rate of vegetative buds in both S.miyabeana and S.sachalinensis. However, no impact on the production rate of reproductive buds was detected in either willow. We conclude that the compensatory growth of current-year shoots and an increase in vegetative buds in the two willow species was caused by oviposition of A.pectoralis.     

How does nitrogen availability alter rhizodeposition in Lolium multiflorum Lam. during vegetative growth?

The objective of this work was to determine if the impact of nitrogen (N) on the release of organic carbon (C) into the soil by roots (rhizodeposition) correlated with the effect of this nutrient on some variables of plant growth. Lolium multiflorum Lam. was grown at two levels of N supply, either in sterile sand percolated with nutrient solution or in non-sterile soil. The axenic sand systems allowed continuous quantification of rhizodeposition and accurate analysis of root morphology whilst the soil microcosms allowed the study of ¹⁴C labelled C flows in physico-chemical and biological conditions relevant to natural soils. In the axenic sand cultures, enhanced N supply strongly increased the plant biomass, the plant N content and the shoot to root ratio. N supply altered the root morphology by increasing the root surface area and the density of apices, both being significantly positively correlated with the rate of organic C release by plant roots before sampling. This observation is consistent with the production of mucilage by root tips and with mechanisms of root exudation reported previously in the literature, i.e. the passive diffusion of roots solutes along the root with increased rate behind the root apex. We proposed a model of root net exudation, based on the number of root apices and on root soluble C that explained 60% of the variability in the rate of C release from roots at harvest. The effects of N on plant growth were less marked in soil, probably related to the relatively high supply of N from non-fertiliser soil-sources. N fertilization increased the shoot N concentration of the plants and the shoot to root ratio. Increased N supply decreased the partitioning of ¹⁴C to roots. In parallel, N fertilisation increased the root soluble ¹⁴C and the ¹⁴C recovered in the soil per unit of root biomass, suggesting a stimulation of root exudation by N supply. However, due to the high concentration of N in our unfertilised plants, this stimulation was assumed to be very weak because no significant effect of N was observed on the microbial C and on the bacterial abundance in the rhizosphere. Considering the difficulties in evaluating rhizodeposition in non sterile soil, it is suggested that the root soluble C, the root surface area and the root apex density are additional relevant variables that should be useful to measure along with the variables that are commonly determined when investigating how plant functioning impacts on the release of C by roots (i.e soil C, C of the microbial biomass, rhizosphere respiration).