Predicting coral community recovery using multi‐species population dynamics models

Predicting whether, how, and to what degree communities recover from disturbance remain major challenges in ecology. To predict recovery of coral communities we applied field survey data of early recovery dynamics to a multi‐species integral projection model that captured key demographic processes driving coral population trajectories, notably density‐dependent larval recruitment. After testing model predictions against field observations, we updated the model to generate projections of future coral communities. Our results indicated that communities distributed across an island landscape followed different recovery trajectories but would reassemble to pre‐disturbed levels of coral abundance, composition, and size, thus demonstrating persistence in the provision of reef habitat and other ecosystem services. Our study indicates that coral community dynamics are predictable when accounting for the interplay between species life‐history, environmental conditions, and density‐dependence. We provide a quantitative framework for evaluating the ecological processes underlying community trajectory and characteristics important to ecosystem functioning.     

Potential feedback between coral presence and farmerfish collective behavior promotes coral recovery

Stable between‐group differences in collective behavior have been documented in a variety of social taxa. Here we evaluate the effects of such variation, often termed collective or colony‐level personality, on coral recovery in a tropical marine farmerfish system. Groups of the farmerfish Stegastes nigricans cultivate and defend gardens of palatable algae on coral reefs in the Indo‐Pacific. These gardens can promote the recruitment, growth, and survival of corals by providing a refuge from coral predation. Here we experimentally evaluate whether the collective response of farmerfish colonies is correlated across intruder feeding guilds – herbivores, corallivores and egg‐eating predators. Further, we evaluate if overall colony responsiveness or situation‐specific responsiveness (i.e. towards herbivores, corallivores, or egg‐eaters in particular) best predicts the growth of outplanted corals. Finally, we experimentally manipulated communities within S. nigricans gardens, adding either macroalgae or large colonies of coral, to assess if farmerfish behavior changes in response to the communities they occupy. Between‐group differences in collective responsiveness were repeatable across intruder guilds. Despite this consistency, responsiveness towards corallivores (porcupinefish and ornate butterflyfish) was a better predictor of outplanted coral growth than responsiveness towards herbivores or egg‐eaters. Adding large corals to farmerfish gardens increased farmerfish attacks towards intruders, pointing to possible positive feedback loops between their aggression towards intruders and the presence of corals whose growth they facilitate. These data provide evidence that among‐group behavioral variation could strongly influence the ecological properties of whole communities.     

Involvement of the MAP kinase pathways in induction of GADD45 following UV radiation

Indian hedgehog (Ihh) is highly expressed in prehypertrophic chondrocytes in vivo and has been proposed to regulate the proliferation and maturation of chondrocytes and bone collar formation in the growth plate. In high-density cultures of rabbit growth-plate chondrocytes, Ihh mRNA was also expressed at the highest level in the prehypertrophic stage. To explore endogenous factors that regulate Ihh expression in chondrocytes, we examined the effects of various growth factors on Ihh mRNA expression in this system. Retinoic acid (RA) and bone morphogenetic protein-2 enhanced Ihh mRNA expression, whereas PTH/PTH-related peptide (PTHrP) markedly suppressed Ihh expression. RA at more than 10(-8) M induced the expression of Ihh and Patched 1 (Ptc1) within 3 h, before it increased the type X collagen mRNA level at 6-24 h. Cycloheximide blocked the up-regulation of Ihh by RA, indicating the requirement of de novo protein synthesis for this stimulation. These findings suggest that RA is involved in the up-regulation of Ihh during endochondral bone formation. In contrast to RA, PTH (1-84) at 10(-7) M abolished the mRNA expression of Ihh and Ptc1 within 2-4 h, before it suppressed the expression of type X collagen at 12-24 h. The inhibition of Ihh expression by PTH (1-84) did not require de novo protein synthesis. PTH (1-34), PTHrP (1-34), and (Bu)(2)cAMP also suppressed Ihh expression. On the other hand, Ihh has been reported to induce PTHrP synthesis in the perichondrium. Consequently, the direct inhibitory action of PTH/PTHrP on Ihh appears to be a negative feedback mechanism that prevents excess PTHrP accumulation in cartilage.     

Functional design space of single-veined leaves: role of tissue hydraulic properties in constraining leaf size and shape

BACKGROUND AND AIMS: Morphological diversity of leaves is usually quantified with geometrical characters, while in many cases a simple set of biophysical parameters are involved in constraining size and shape. One of the main physiological functions of the leaf is transpiration and thus one can expect that leaf hydraulic parameters can be used to predict potential morphologies, although with the caveat that morphology in turn influences physiological parameters including light interception and boundary layer thickness and thereby heat transfer and net photosynthesis. METHODS: An iterative model was used to determine the relative sizes and shapes that are functionally possible for single-veined leaves as defined by their ability to supply the entire leaf lamina with sufficient water to prevent stomatal closure. The model variables include the hydraulic resistances associated with vein axial and radial transport, as well as with water movement through the mesophyll and the leaf surface. KEY RESULTS: The four parameters included in the model are sufficient to define a hydraulic functional design space that includes all single-veined leaf shapes found in nature, including scale-, awl- and needle-like morphologies. This exercise demonstrates that hydraulic parameters have dissimilar effects: surface resistance primarily affects leaf size, while radial and mesophyll resistances primarily affect leaf shape. CONCLUSIONS: These distinctions between hydraulic parameters, as well as the differential accessibility of different morphologies, might relate to the convergent evolutionary patterns seen in a variety of fossil lineages concerning overall morphology and anatomical detail that frequently have evolved in linear and simple multi-veined leaves.     

Membrane topology and sequence requirements for oil body targeting of oleosin

Oleosin protein is targeted to oil bodies via the endoplasmic reticulum (ER) and consists of a lipid-submerged hydrophobic (H) domain that is flanked by cytosolic hydrophilic domains. We investigated the relationship between oleosin ER topology and its subsequent ability to target to oil bodies. Oleosin variants were created to yield differing ER membrane topologies and tagged with a reporter enzyme. Localisation was assessed by fractionation after transient expression in embryonic cells. Membrane-straddled topologies with N-terminal sequence in the ER lumen and C-terminal sequence in the cytosol were unable to target to oil bodies efficiently. Similarly, a translocated topology with only ER membrane and lumenal sequence was unable to target to oil bodies efficiently. Both topology variants accumulated proportionately higher in ER microsomal fractions, demonstrating a block in transferring from ER to oil bodies. The residual oil body accumulation for the inverted topology was shown to be because of partial adoption of native ER membrane topology, using a reporter variant, which becomes inactivated by ER-mediated glycosylation. In addition, the importance of H domain sequence for oil body targeting was assessed using variants that maintain native ER topology. The central proline knot motif (PKM) has previously been shown to be critical for oil body targeting, but here the arms of the H domain flanking this motif were shown to be interchangeable with only a moderate reduction in oil body targeting. We conclude that oil body targeting of oleosin depends on a specific ER membrane topology but does not require a specific sequence in the H domain flanking arms.     

Ionic control of the lateral exchange of water between vascular bundles in tomato

Ions can enhance water flow through the xylem via changes in the hydraulic resistance at border pit membranes. Because flow between adjacent xylem vessels occurs primarily via bordered pit fields, it is hypothesized that xylem sap ion concentrations would affect lateral movement of water more than longitudinal flow. Using tomato as a model system, evidence is presented for ion-mediated changes in xylem hydraulic resistance and the lateral transport of water. Water flow between adjacent xylem bundles increased by approximately 50% in the presence of ions while longitudinal flow only increased by approximately 20%. However, the enhancement of lateral exchange due to ions was magnified by the presence of a pressure difference between vascular bundles. These results indicate that the degree of nutrient-sharing among sectors of a plant may depend on both nutrient concentration and the availability of water in the root zone.     

The hydraulic conductance of the angiosperm leaf lamina: a comparison of three measurement methods

A comparison was made of three methods for measuring the leaf lamina hydraulic conductance (K(lamina)) for detached mature leaves of six woody temperate angiosperm species. The high-pressure method, the evaporative flux method and the vacuum pump method involve, respectively, pushing, evaporating and pulling water out of the lamina while determining the flow rate into the petiole and the water potential drop across the leaf. Tests were made of whether the high-pressure method and vacuum pump method measurements of K(lamina) on single leaves were affected by irradiance. In Quercus rubra, the high pressure method was sensitive to irradiance; K(lamina) measured under high irradiance (>1200 micro mol m(-2) s(-1 )photosynthetically active radiation) was 4.6-8.8 times larger than under ambient laboratory lighting (approximately 6 micro mol m(-2) s(-1 )photosynthetically active radiation). By constrast, the vacuum pump method was theoretically expected to be insensitive to irradiance, and this expectation was confirmed in experiments on Hedera helix. When used in the ways recommended here, the three methods produced measurements that agreed typically within 10%. There were significant differences in species' K(lamina); values ranged from 1.24x10(-4) kg s(-1) m(-2) MPa(-1) for Acer saccharum to 2.89x10(-4) kg s(-1) m(-2) MPa(-1) for Vitis labrusca. Accurate, rapid determination of K(lamina) will allow testing of the links between K(lamina), water-use, drought tolerance, and the enormous diversity of leaf form, structure and composition.     

Tolerization as a tool for generating novel monoclonal antibodies

Standard hybridoma production involves the fusion of spleen cells from an immunized mouse with a non-secretory murine myeloma cell line. While this technology has provided numerous reagents that are highly valuable, demand is now increasing for monoclonal antibodies which can distinguish between closely related antigens. Induction of tolerance towards common antigens enables the recovery of high-specificity reagents that have previously proved elusive. This review details a number of strategies using either complex protein mixtures or purified proteins as tolerogens and subsequent immunization with a closely related immunogen.     

Understanding the Hydraulics of Porous Pipes: Tradeoffs Between Water Uptake and Root Length Utilization

The water uptake region in roots is several hundred times longer than the root diameter. The distributed nature of the uptake zone requires that the hydraulic design of roots be understood by analogy to flow through a porous pipe. Here we present results of an analytical and experimental investigation that allowed an in-depth analysis of root hydraulic properties. Measurements on nodal maize roots confirm the nonlinear distribution of water uptake predicted by the porous pipe model. The major design parameter governing the distribution of water uptake along a porous pipe is the ratio between its axial and radial hydraulic resistance. However, total flow is proportional to the pipe's overall resistance. These results suggest the existence of a tradeoff between the effective utilization of root length and the total capacity for water uptake.