Cytoskeleton and PCH-Induced Pigment Aggregation in Macrobrachium potiuna Erythrophores

Herein we report the effects of microtubule- and actin-like filament disrupting drugs, as well as the microtubule stabilizer taxol, on PCH-induced pigment granule aggregation within erythrophores of the freshwater crustacean Macrobrachium potiuna. Dose-response curves (DRCs) to the pigment-concentrating hormone PCH were determined under control and experimental conditions to evaluate the effects elicited by the cytoskeleton-affecting drugs. Colchicine, at temperatures 22°C and 4°C, and vinblastine significantly inhibited the aggregating response to PCH and affected the dynamics of the process, as shown by the change in the slope of the regression curve calculated from the DRCs. Lumicolchicine, a colchicine analogue with no affinity for tubulin, also inhibited pigment migration, though no change in the slope of the regression curve was observed. The inhibitory effects of lumicolchicine demonstrate that changes in sites other than cytoskeleton, such as membrane permeability, may also cause a decrease in the PCH-induced aggregating responses and that the colchicine effects may result from its action on cellular sites additional to the cytoskeleton. Taxol, a microtubule stabilizer, did not affect the DRC to PCH, and DMSO improved the PCH-evoked responses, pointing out to the maintenance of tubulin in the polymerized state as the appropriate condition for aggregation. Cytochalasin B, an actin-like filament disrupter, diminished the aggregating responses to the hormone, with no change in the slope of the regression curve, indicating that these elements take part in the process and that cytosolic calcium rise, sol/gel transformations and endoplasmic reticulum motility may well play an important role in granule migration. It is suggested that microtubules are steadily polymerized as a requirement for pigment aggregation and that the process is biphasic, the initial phase being dependent on the microtubule integrity.     

High Capacity Chemisorbents for Protein Immobilization

IMMOBILIZED proteins have been used successfully for the purification and isolation of specific natural products, particularly proteins such as antigens, antibodies, enzymes and enzyme inhibitors^1–3. They have also been used for the commercial production of biochemicals⁴ and as models for imitating enzymes bound to cellular components in vivo.     

Evolution of morphological differences with moderate genetic correlations among traits as exemplified by two flycatcher species (Ficeduia; Muscicapidae)

Theoretical work on multivariate evolution predicts that genetic correlations can act to constrain the rate at which new adaptive peaks are reached, but there is very limited empirical information available on this issue so far. To evaluate the importance of genetic correlations for evolutionary change, we studied the morphological differences between two flycatcher species (Ficeduia albicollis and F. hypoleuca) using both univariate and multivariate quantitative genetic models. Comparison of the results obtained using these different models revealed that even relatively low genetic correlations between traits will considerably increase the net selection forces needed for evolutionary changes in morphology. In particular, the divergence in wing and tail length, which are positively genetically correlated, would require a considerable amount of antagonistic selection. Because of the genetic correlations, strong selection will be needed to retain certain traits unchanged while others are changing. Based on these results, we argue that it is unlikely that small morphological differences such as between these two species could have evolved during a short (200 years) time period, i.e. the period of sympatry of these species in Sweden. These findings support the hypothesis that even relatively low genetic correlations may constrain short-term adaptive evolution in natural populations.     

Desertification in the Sahel: a reinterpretation

The impact of human management, in particular livestock grazing, on the vegetation cover of the Sahel is still debated. In a range of studies, satellite images have been used to analyze the development of the Sahelian vegetation cover over time. These studies did not reveal any significant degradation of the Sahel in the last two decades. In this paper, we examine the ecological assumptions underlying the use of satellite imagery to analyze degradation of the Sahel. Specifically, we analyze the variability of the rain‐use efficiency (RUE), which is often used as an indicator for the state of the vegetation cover. We detect a fundamental flaw in the way RUE has been handled in most remote sensing studies; they ignored the relation between annual rainfall variation and RUE. Because of the upward trend in annual rainfall that occurred during the 1980s and 1990s, this leads to a bias in the interpretation of the satellite images. In this paper, we show the importance of the variability in RUE for the analysis of remote sensing imagery of semiarid rangelands. Our analysis also shows that it is likely that there has been anthropogenic degradation of the Sahelian vegetation cover in the last two decades. This has important consequences for the debate on the impacts of grazing on semiarid rangelands. Furthermore, the occurrence of anthropogenic degradation is relevant to explain the magnitude of 20th century Sahelian droughts. The analyses also indicate that the population of the Sahel may be more vulnerable for droughts than currently assumed.     

On the edge of parasitoidism: a new Lower Cretaceous woodwasp forming the putative sister group of Xiphydriidae + Euhymenoptera

The fossil woodwasp Cratoenigma articulata gen. et sp.n. (Insecta: Hymenoptera) is described from the Lower Cretaceous Crato formation of Brazil. This fossil cannot be placed in any existing superfamily, but its putative phylogenetic position within Hymenoptera is discussed in detail on the basis of relevant thoracic, abdominal and wing venation characters. These characters are critically evaluated and compared with those of extant and fossil Hymenoptera. The phylogenetic position of C. articulata sp.n. is investigated relative to extant Xyelidae, Tenthredinoidea s.l., Pamphilioidea, Cephidae, Siricoidea, Xiphydriidae, Orussidae and Apocrita, and also to Mesozoic Gigasiricidae, Myrmiciidae, Daohugoidae, Sepulcidae, Anaxyelidae, Paroryssidae and Ephialtitidae. Based on the presence of a synapomorphic transscutal articulation, a plesiomorphic unconcealed mesopostnotum and autapomorphic hindwing venation (cu‐a distinctly basal to fork between M and Cu), C. articulata sp.n. most likely forms the sister group of Xiphydriidae + Euhymenoptera. This would place it well within Unicalcarida, i.e. the clade in which the transition from endophytic to parasitoid lifestyle evolved.     

Breeding season food limitation drives population decline of the Little Owl Athene noctua in Denmark

Many farmland bird species have declined markedly in Europe in recent decades because of changes in agricultural practice. The specific causes vary and are poorly known for many species. The Little Owl, which feeds extensively on large invertebrates and is strongly associated with the agricultural landscape, has declined over most of northwestern Europe, including Denmark. We investigated the likely reasons for the population decline in Denmark by identifying patterns of local extinction (scale, 5 × 5 km²) and estimating demographic parameters affecting local survival, focusing on changes over time and their relationship to habitat characteristics. The distribution of the Little Owl in Denmark contracted considerably between 1972–74 and 1993–96. The extent of contraction varied across the country, and the only habitat correlate was that local disappearance was associated with smaller amounts of agricultural land. Analyses of ring recovery data suggested a constant annual adult survival rate of 61% from 1920 to 2002, which is similar to estimates from countries with stable populations. First‐year annual survival rates were much lower than values previously reported. From the 1970s into the 21st century, the mean number of fledglings declined from around 3 to < 2 young per territory, but the decline in clutch size was considerably less. Reproductive parameters were higher closer to habitat types known to be important foraging habitats for Little Owls, and were also positively correlated with the amount of seasonally changing land cover (mostly farmland) within a 1‐km radius around nests as well as temperatures before and during the breeding season. Experimental food supplementation to breeding pairs increased the proportion of eggs that resulted in fledged young from 27 to 79%, supporting the hypothesis that the main proximate reason underlying the ongoing population decline is reduced productivity induced by energetic constraints after egg‐laying. Conservation efforts should target enhancement of food availability during the breeding season. Other farmland species dependent on large invertebrates are likely to share the problems that Little Owls face in modern agricultural landscapes.     

Phylogenetic analysis of higher taxa of Brachiopoda

Inferred phylogenetic relationships within the Brachiopoda have long been accepted as demonstrating repeated transitions from a phosphatic shell chemistry to a calcareous composition. This interpretation is reflected in the major subdivision of the phylum into the classes Inarticulata and Articulata. Cladistic analysis suggests, however, that the phosphatic-shelled and the calcareous-shelled Brachiopoda are sister groups that have had consistently separated shell chemistries from early in phylogenetic history. This separation is recognized in the class-rank divisions Lingulata and Calciata, the former of which includes the new Subclass Lingulatea, whilst the latter includes the new Subclass Craniformea together with the 'articulates' of previous classifications. □Brachiopoda, cladistic analysis, Lingulata, Lingulatea, Calciata, Craniformea.     

Colony–Substratum Relations in Scrupocellariidae (Bryozoa, Cheilostomata)

In the Bryozoa in general the colony is attached by means of the primary zooid, the ancestrula, which is permanently cemented to the substratum. The attachment is brought about, in the marine bryozoans, by the larva everting its interior sac into a basal adhesive disc secreting a thin layer of hardening mucus. In Scrupocellaria reptans no adhesive disc was found. The metamorphosing larva is fixed to the substratum by a column of loose, sticky secretion. This primary fixation is ephemeral and replaced by a secondary, permanent fixation by one pair of rootlets. Thus, the ancestrula body proper and the colony arising from it become permanently free from the substratum but anchored to it by rootlets, the primary pair and series of secondary rootlets. This unique and certainly secondarily evolved type of attachment is apparently realized in the Scrupocellariidae in general, to a more or less perfect degree. It appears as one of several possible models to meet efficiently with environmental disturbances.     

Heterochrony in Silurian phacopid trilobites as suggested by the ontogeny of Acernaspis

New material of early growth stages of the Silurian (Llandovery) trilobite Acernaspis is described. Pre-adult ontogenetic stages of this genus closely resemble adults of the post-Llandovery genus ***Ananaspis. A heterochronic descent of Ananaspis from Acernaspis is proposed. ***Ananaspis is interpreted as pae-domorphic, having arisen largely through neoteny. Neotenic changes already appear in the lineage in the last Acernaspis species, and Ananaspis then underwent continuous ncotcnic change throughout its known Silurian history. ▭ Heterochrony, neoteny, Silurian, Trilobita, Phacopidae, Acernaspis. Ananaspis.