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Institute
- Institut für Biochemie und Biologie (220) (remove)
Sexual selection often leads to sexual dimorphism, where secondary sexual traits are more expressed in the male sex. This may be due, for example, to increased fighting or mate-guarding abilities of males expressing those traits. We investigated sexually dimorphic traits in four populations of a marine amphipod, Pontogammarus maeoticus (Gammaridea: Pontogammaridae), the most abundant amphipod species in the sublittoral zone along the southern shoreline of the Caspian Sea. Male amphipods are typically larger in body size than females, and have relatively larger posterior gnathopods and antennae. However, it remains to be studied for most other body appendages whether or not, and to what extent, they are sexually dimorphic. Using Analysis of Covariance (ANCOVA), we compared the relationships between body size and trait expression for 35 metric characters between males and females, and among the four populations examined by performing three different Discriminant Function Analyses (DFA). We detected several thus far undescribed sexual dimorphic traits such as the seventh peraeopods or the epimeral plates. We also found that the size of the propodus of the first and second gnathopods increases with increasing body size, and this allometric increase was stronger in males than in females. Finally, we found that the degree of sexual dimorphism in the expression of the width of the third epimeral plate varies across sites, suggesting that differences in ecology might affect the strength of sexual selection in different populations.
This review addresses the functional organization of the mammalian cochlea under a comparative and evolutionary perspective. A comparison of the monotreme cochlea with that of marsupial and placental mammals highlights important evolutionary steps towards a hearing organ dedicated to process higher frequencies and a larger frequency range than found in non-mammalian vertebrates. Among placental mammals, there are numerous cochlear specializations which relate to hearing range in adaptation to specific habitats that are superimposed on a common basic design. These are illustrated by examples of specialist ears which evolved excellent high frequency hearing and echolocation (bats and dolphins) and by the example of subterranean rodents with ears devoted to processing low frequencies. Furthermore, structural functional correlations important for tonotopic cochlear organization and predictions of hearing capabilities are discussed.
Target-distance computation by cortical neurons sensitive to echo delay is an essential characteristic of the auditory system of insectivorous bats. To assess if functional requirements such as detection of small insects versus larger stationary surfaces of plants are reflected in cortical properties, we compare delay-tuned neurons in a frugivorous (C. perspicillata, CP) and an insectivorous (P. parnellii, PP) bat species that belong to related families within the superfamily of Noctilionoidea. The bandwidth and shape of delay-tuning curves and the range of characteristic delays are similar in both species and hence are not related to different echolocation strategies. Most units respond at 2-6 ms echo delay with most sensitive thresholds of 20-30 dB SPL. In CP, units tuned to delays > 12 ms are slightly more abundant and are more sensitive than in PP. All delay-tuned neurons in CP reliably respond to single pure-tone stimuli, whereas such responses are only observed in 49% of delay-tuned units in PP. The cortical representation of echo delay (chronotopy) covers a larger area in CP but is less precise than described in PP. Since chronotopy is absent in certain other insectivorous bat species, it is open if these differences in topography are related to echolocation behaviour.
Lissencephaly is a severe brain developmental disease in human infants, which is usually caused by mutations in either of two genes, LIS1 and DCX. These genes encode proteins interacting with both the microtubule and the actin systems. Here, we review the implications of data on Dictyostelium LIS1 for the elucidation of LIS1 function in higher cells and emphasize the role of LIS1 and nuclear envelope proteins in nuclear positioning, which is also important for coordinated cell migration during neocortical development. Furthermore, for the first time we characterize Dictyostelium DCX, the only bona fide orthologue of human DCX outside the animal kingdom. We show that DCX functionally interacts with LIS1 and that both proteins have a cytoskeleton-independent function in chemotactic signaling during development. Dictyostelium LIS1 is also required for proper attachment of the centrosome to the nucleus and, thus, nuclear positioning, where the association of these two organelles has turned out to be crucial. It involves not only dynein and dynein-associated proteins such as LIS1 but also SUN proteins of the nuclear envelope. Analyses of Dictyostelium SUN1 mutants have underscored the importance of these proteins for the linkage of centrosomes and nuclei and for the maintenance of chromatin integrity. Taken together, we show that Dictyostelium amoebae, which provide a well-established model to study the basic aspects of chemotaxis, cell migration and development, are well suited for the investigation of the molecular and cell biological basis of developmental diseases such as lissencephaly.
We have localized TACC to the microtubule-nucleating centrosomal corona and to microtubule plus ends. Using RNAi we proved that Dictyostelium TACC promotes microtubule growth during interphase and mitosis. For the first time we show in vivo that both TACC and XMAP215 family proteins can be differentially localized to microtubule plus ends during interphase and mitosis and that TACC is mainly required for recruitment of an XMAP215-family protein to interphase microtubule plus ends but not for recruitment to centrosomes and kinetochores. Moreover, we have now a marker to study dynamics and behavior of microtubule plus ends in living Dictyostelium cells. In a combination of live cell imaging of microtubule plus ends and fluorescence recovery after photobleaching (FRAP) experiments of GFP-alpha-tubulin cells we show that Dictyostelium microtubules are dynamic only in the cell periphery, while they remain stable at the centrosome, which also appears to harbor a dynamic pool of tubulin dimers.
Background: Soil biota effects are increasingly accepted as an important driver of the abundance and distribution of plants. While biogeographical studies on alien invasive plant species have indicated coevolution with soil biota in their native distribution range, it is unknown whether adaptation to soil biota varies among populations within the native distribution range. The question of local adaptation between plants and their soil biota has important implications for conservation of biodiversity and may justify the use of seed material from local provenances in restoration campaigns.
Methodology/Principal Findings: We studied soil biota effects in ten populations of the steppe grass Stipa capillata from two distinct regions, Europe and Asia. We tested for local adaptation at two different scales, both within (ca. 10-80 km) and between (ca. 3300 km) regions, using a reciprocal inoculation experiment in the greenhouse for nine months. Generally, negative soil biota effects were consistent. However, we did not find evidence for local adaptation: both within and between regions, growth of plants in their 'home soil' was not significantly larger relative to that in soil from other, more distant, populations.
Conclusions/Significance: Our study suggests that negative soil biota effects can prevail in different parts of a plant species' range. Absence of local adaptation points to the possibility of similar rhizosphere biota composition across populations and regions, sufficient gene flow to prevent coevolution, selection in favor of plasticity, or functional redundancy among different soil biota. From the point of view of plant - soil biota interactions, our findings indicate that the current practice of using seeds exclusively from local provenances in ecosystem restoration campaigns may not be justified.
Habitat fragmentation can lead to a decline of genetic diversity, a potential risk for the survival of natural populations. Fragmented populations can become highly differentiated due to reduced gene flow and genetic drift. A decline in number of individuals can result in lower reproductive fitness due to inbreeding effects. We investigated genetic variation within and between 11 populations of the rare and endangered plant Silene chlorantha in northeastern Germany to support conservation strategies. Genetic diversity was evaluated using AFLP techniques and the results were correlated to fitness traits. Fitness evaluation in nature and in a common garden approach was conducted. Our analysis revealed population differentiation was high and within population genetic diversity was intermediate. A clear population structure was supported by a Bayesian approach, AMOVA and neighbour-joining analysis. No correlation between genetic and geographic distance was found. Our results indicate that patterns of population differentiation were mainly caused by temporal and/or spatial isolation and genetic drift. The fitness evaluation revealed that pollinator limitation and habitat quality seem, at present, to be more important to reproductive fitness than genetic diversity by itself. Populations of S. chlorantha with low genetic diversity have the potential to increase in individual number if habitat conditions improve. This was detected in a single large population in the investigation area, which was formerly affected by bottleneck effects.
Identification of a novel heteroglycan-interacting protein, HIP 1.3, from Arabidopsis thaliana
(2011)
Plastidial degradation of transitory starch yields mainly maltose and glucose. Following the export into the cytosol, maltose acts as donor for a glucosyl transfer to cytosolic heteroglycans as mediated by a cytosolic transglucosidase (DPE2; EC 2.4.1.25) and the second glucosyl residue is liberated as glucose. The cytosolic phosphorylase (Pho2/PHS2; EC 2.4.1.1) also interacts with heteroglycans using the same intramolecular sites as DPE2. Thus, the two glucosyl transferases interconnect the cytosolic pools of glucose and glucose 1-phosphate. Due to the complex monosaccharide pattern, other heteroglycan-interacting proteins (Hips) are expected to exist.
Identification of those proteins was approached by using two types of affinity chromatography. Heteroglycans from leaves of Arabidopsis thaliana (Col-0) covalently bound to Sepharose served as ligands that were reacted with a complex mixture of buffer-soluble proteins from Arabidopsis leaves. Binding proteins were eluted by sodium chloride. For identification, SDS-PAGE, tryptic digestion and MALDI-TOF analyses were applied. A strongly interacting polypeptide (approximately 40 kDa; designated as HIP1.3) was observed as product of locus At1g09340. Arabidopsis mutants deficient in HIP1.3 were reduced in growth and contained heteroglycans displaying an altered monosaccharide pattern. Wild type plants express HIP1.3 most strongly in leaves. As revealed by immuno fluorescence, HIP1.3 is located in the cytosol of mesophyll cells but mostly associated with the cytosolic surface of the chloroplast envelope membranes. In an HIP1.3-deficient mutant the immunosignal was undetectable. Metabolic profiles from leaves of this mutant and wild type plants as well were determined by GC-MS. As compared to the wild type control, more than ten metabolites, such as ascorbic acid, fructose, fructose bisphosphate, glucose, glycine, were elevated in darkness but decreased in the light. Although the biochemical function of HIP1.3 has not yet been elucidated, it is likely to possess an important function in the central carbon metabolism of higher plants.