Sosiaalisen ympäristön vaikutus argentiinanmuurahaisen (Linepithema humile) immuunigeenien ekspressioon

Tiivistelmä. Muurahaiset ovat aitosiaalisia hyönteisiä, joiden yhdyskuntarakenne perustuu sukulaisvalintaan ja tehtävät jakavaan kastijärjestelmään. Muurahaispesä muodostaa niin kutsutun superorganismin, joka voi koostua jopa miljoonista yksilöistä. Eräitä suurimpia superorganismeja ovat argentiinanmuurahaisen (Linepithema humile) maailmalle ihmisen mukana Etelä-Amerikasta levinneet massiiviset, jopa tuhansien kilometrien laajuiset superkoloniat. Argentiinanmuurahaiset ovat monin paikoin hyvin haitallisia tuholaisia, jotka ovat uhka niin taloudellisesti kuin paikallisille endeemisille lajeillekin. Hyönteisillä ei selkärankaisista poiketen ole lainkaan adaptiivista hankinnaista immuunisysteemiä, vaan niiden immuunivaste perustuu pelkästään sisäisen ei-adaptiivisen immuniteetin aktivaatioon. Se on kuitenkin hyvin monipuolinen ja kykenee vastaamaan eri patogeenien muodostamiin uhkiin. Pääpiirteissään hyönteisten immuunijärjestelmä perustuu Toll- ja Imd-signalointireittien aktivaatioon ja niiden tuloksena aktivoituvaan spesifiseen vasteeseen. Aitososiaalisilla hyönteisillä on yksineläviä suurempi patogeenipaine ja niille on kehittynyt erilaisia sosiaalisen immuniteetin muotoja, esim. sairaiden yksilöiden poistaminen pesästä ja pesätoverien sukiminen. Tehokas sosiaalisen immuniteetti voi laskea yksilötason immuniteetin kustannuksia ja panostusta. Pro gradu -tutkimuksessani tarkastelin sosiaalisen ympäristön neljän immuunigeenin ekspressioon L. humile -kuningattarilla, riippuen siitä olivat ne olleet patogeenialtistuksen (Serratia marcescens) jälkeen eristettynä vai työläisten seurassa. Oletukseni oli, että työläisten seurassa olleilla kuningattarilla olisi alhaisempi immuunivaste. Kvantifioin geenien suhteellisen ekspressiotason kvantitatiivisella PCR:llä (qPCR) ja analysoin tuloksia kaksisuuntaisella varianssianalyysillä (ANOVA). Tulosten perusteella ei ollut nähtävissä tilastollisesti merkittävää yhteyttä sosiaalisuuden ja immuunigeenien ekspressiotason välillä. Tämä käy yksiin myös muiden viimeaikaisten tutkimusten kanssa, joiden perusteella näyttäisi siltä, että sosiaalinen immuniteetti ei korvaa yksilötason immuniteettia vaan täydentää sitä. Aihetta on syytä tutkia vielä paljon lisää suuremmilla näytemäärillä ja monipuolisemmilla analyysimenetelmillä

Electrical measurement of internal quantum efficiency and extraction efficiency of III-N light-emitting diodes

We propose a direct electrical measurement method for determining the extraction efficiency (EXE) and internal quantum efficiency(IQE) of III-Nitride light-emitting diodes(LEDs). The method is based on measuring the optical output power as a function of injection current at current densities near the external quantum efficiency (EQE) maximum and extracting IQE and EXE from the measurement data. In contrast to conventional methods, our method requires no low temperaturemeasurements or prior knowledge of the device structure. The method is far more convenient than commonly used methods because it enables measuring the EXE and IQE of different LED structures at room temperature directly in a repeatable and consistent way. This enables convenient comparison of LED structures. We apply the method to determine the IQE and EXE of one commercial LED and selected self-grown planar LED chips to compare the effects of different LED structure designs. Our results are in line with published experimental results and also give more insight to our earlier findings regarding the effects of growth parameters on the quantum efficiency. In addition, our measurement method allows estimating the Shockley-Read-Hall and radiative recombination parameters if the Auger parameter is known.Peer reviewe

Inverse problem for wave equation with sources and observations on disjoint sets

We consider an inverse problem for a hyperbolic partial differential equation on a compact Riemannian manifold. Assuming that $\Gamma_1$ and $\Gamma_2$ are two disjoint open subsets of the boundary of the manifold we define the restricted Dirichlet-to-Neumann operator $\Lambda_{\Gamma_1,\Gamma_2}$. This operator corresponds the boundary measurements when we have smooth sources supported on $\Gamma_1$ and the fields produced by these sources are observed on $\Gamma_2$. We show that when $\Gamma_1$ and $\Gamma_2$ are disjoint but their closures intersect at least at one point, then the restricted Dirichlet-to-Neumann operator $\Lambda_{\Gamma_1,\Gamma_2}$ determines the Riemannian manifold and the metric on it up to an isometry. In the Euclidian space, the result yields that an anisotropic wave speed inside a compact body is determined, up to a natural coordinate transformations, by measurements on the boundary of the body even when wave sources are kept away from receivers. Moreover, we show that if we have three arbitrary non-empty open subsets $\Gamma_1,\Gamma_2$, and $\Gamma_3$ of the boundary, then the restricted Dirichlet-to-Neumann operators $\Lambda_{\Gamma_j,\Gamma_k}$ for $1\leq j<k\leq 3$ determine the Riemannian manifold to an isometry. Similar result is proven also for the finite-time boundary measurements when the hyperbolic equation satisfies an exact controllability condition

The impact of thermal seasonality on terrestrial endotherm food web dynamics:a revision of the Exploitation Ecosystem Hypothesis

Abstract Many terrestrial endotherm food webs constitute three trophic level cascades. Others have two trophic level dynamics (food limited herbivores; plants adapted to tackle intense herbivory) or one trophic level dynamic (herbivorous endotherms absent, thus plants compete for the few places where they can survive and grow). According to the Exploitation Ecosystems Hypothesis (EEH), these contrasting dynamics are consequences of differences in primary productivity. The productivity thresholds for changing food web dynamics were assumed to be global constants. We challenged this assumption and found that several model parameters are sensitive to the contrast between persistently warm and seasonally cold climates. In persistently warm environments, three trophic level dynamics can be expected to prevail almost everywhere, save the most extreme deserts. We revised EEH accordingly and tested it by compiling direct evidence of three and two trophic level dynamics and by studying the global distribution of felids. In seasonally cold environments, we found evidence for three trophic level dynamics only in productive ecosystems, while evidence for two trophic level dynamics appeared in ecosystems with low primary productivity. In persistently warm environments, we found evidence for three trophic level dynamics in all types of ecosystems. The distribution of felids corroborated these results. The empirical evidence thus indicates that two trophic level dynamics, as defined by EEH, are restricted to seasonally cold biomes with low primary productivity, such as the artic–alpine tundra and the temperate steppe

Herbivore effects on ecosystem process rates in a low-productive system

Abstract Mammalian herbivores shape the structure and function of many nutrient-limited or low-productive terrestrial ecosystems through modification of plant communities and plant–soil feedbacks. In the tundra biome, mammalian herbivores may both accelerate and decelerate plant biomass growth, microbial activity and nutrient cycling, that is, ecosystem process rates. Selective foraging and associated declines of palatable species are known to be major drivers of plant–soil feedbacks. However, declines in dominant plants of low palatability often linked with high herbivore densities may also modify ecosystem process rates, yet have received little attention. We present data from an island experiment with a 10-year vole density manipulation, to test the hypothesis that herbivores accelerate process rates by decreasing the relative abundance of poorly palatable plants to palatable ones. We measured plant species abundances and community composition, nitrogen contents of green plant tissues and multiple soil and litter variables under high and low vole density. Corroborating our hypothesis, periodic high vole density increased ecosystem process rates in low-productive tundra. High vole density was associated with both increasing relative abundance of palatable forbs over unpalatable evergreen dwarf shrubs and higher plant N content both at species and at community level. Changes in plant community composition, in turn, explained variation in microbial activity in litter and soil inorganic nutrient availability. We propose a new conceptual model with two distinct vole–plant–soil feedback pathways. Voles may drive local plant–soil feedbacks that either increase or decrease ecosystem process rates, in turn promoting heterogeneity in vegetation and soils across tundra landscapes