TY  - JOUR
A1  - Schmuck, R.
A1  - Kobelt, F.
A1  - Linsenmair, Karl Eduard
T1  - Adaptations of the reed frog Hyperbolius viridiflavus (Anura, Hyperbolidae) to its arid environment: V. Iridophores and nitrogen metabolism
N2  - Ofall amphibians living in arid habitats, reed frogs (belonging to the super species Hyperolius viridiflavus) are the most peculiar. Froglets are able to tolerate dry periods of up to 35 days or longer immediately after metamorphosis, in climatically exposed positions. They face similar problems to estivating juveniles, i.e. enduranee of long periods of high temperature and low RH with rather limited energy and water reserves. In addition, they must have had to develop meehanisms to prevent poisoning by nitrogenous wastes that rapidly accumulate during dry periods as a metabolie consequenee of maintaining a non-torpid state. During dry periods, plasma osmolarity of H. v. taeniatus froglets strongly increased, mainly through urea accumulation. Urea accumulation was also observed during metamorphic climax. During postmetamorphic growth, chromatophores develop with the density and morphology typical of the adult pigmentary pattern. The dermal iridophore layer, which is still incomplete at this time, is fully developed within 4-8 days after metamorphosis, irrespective of maintenance conditions. These iridophores mainly contain the purines guanine and hypoxanthine. The ability of these purines to reflect light provides an excellent basis for the role of iridophores in temperature regulation. In individuals experiencing dehydration stress, the initial rate of purine synthesis is doubled in eomparison to specimens continuously maintained under wet season conditions. This increase in synthesis rate leads to a rapid increase in the thiekness of the iridophore layer, thereby effectively reducing radiation absorption. Thus, the danger of overheating is diminished during periods of water shortage when evaporative cooling must be avoided. After the development of an iridophore layer of sufficient thickness for effective radiation reflectance, synthesis of iridophore pigments does not cease. Rather, this pathway is further used during the remaining dry season for solving osmotic problems eaused by accumulation of nitrogenous wastes. During prolonged water deprivation, in spite of reduced metabolic rates, purine pigments are produced at the same rate as in wet season conditions. This leads to a higher relative proportion of nitrogen end products being stored in skin pigments under dry season conditions. At the end of an experimental dry season lasting 35 days, up to 38% of the accrued nitrogen is stored in the form of osmotically inactive purines in thc skin. Thus the osmotic problems caused by evaporative water loss and urea production are greatly reduced.
KW  - Biologie
KW  - Zoologie
KW  - Frosch
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-78094
ER  - 
TY  - JOUR
A1  - Linsenmair, Karl Eduard
A1  - Schmuck, R.
T1  - Adaptations of the reed frog Hyperbolius viridiflavus to its arid environment. III. Aspects of nitrogen metabolism and osmuregulation in the reed frog, H. viridiflavus taeniatus, with special reference to the role of iridophores
N2  - Reed frogs of the superspecies Hyperolius viridiflavus occur throughout the seasonally very dry and hot African savannas. Despite their small size (300-700 mg), estivating reed frogs do not avoid stressful conditions above ground by burrowing into the soil, but endure the inhospitable climate relatively unprotected, clinging to mostly dry grass sterns. They must have emcient mechanisms to enable them to survive e.g. very high temperatures, low relative hurnidities, and high solar radiation loads. Mechanisms must also have developed to prevent poisoning by the nitrogenous wastes that inevitably result from protein and nucleotide turnover. In contrast to fossorial amphibians, estivating reed frogs do not become torpid. Reduction in metabolism is therefore rather Iimited so that nitrogenous wastes accumulate faster in these frogs than in fossorial amphibians. This severely aggravates the osmotic problems caused by dehydration. During dry periods total plasma osmolarity greatly increases, mainly due to urea accumulation. Of the total urea accumulated over 42 days of experimental water deprivation, 30% was produced during the first 7 days. In the next 7 days rise in plasma urea content was negligible. This strong initial increase of urea is seen as a byproduct of elevated amino acid catabolism following the onset of dry conditions. Tbe rise in total plasma osmolarity due to urea accumulation, however, is not totally disadvantageous, but enables fast rehydration when water is available for very short periods only. Voiding of urine and feces eeases once evaporative water loss exceeds 10% of body weight. Tberefore, during continuous water deprivation, nitrogenous end products are not excreted. After 42 days of water deprivation, bladder fluid was substantially depleted, and urea coneentration in the remaining urine (up to 447 mM) was never greater than in plasma fluid. Feces voided at the end of the dry period after water uptake contained only small amounts of nitrogenous end products. DSF (dry season frogs) seemed not to be uricotelic. Instead, up to 35% of the total nitrogenous wastes produced over 42 days of water deprivation were deposited in an osmotically inert and nontoxic form in iridophore crystals. The increase in skin purine content averaged 150 µg/mg dry weight. If urea had been the only nitrogenous waste product during an estivation period of 42 days, lethal limits of total osmolarity (about 700 mOsm) would have been reached 10-14 days earlier. Thus iridophores are not only involved in colour change and in reducing heat load by radiation remission, but are also important in osmoregulation during dry periods. The seIective advantages of deposition of guanine rather than uric acid are discussed.
KW  - Biologie
KW  - Zoologie
KW  - Frosch
KW  - Hyperolius viridiflavus
KW  - Estivation
KW  - Osmoregulation
KW  - Nitrogen metabolism
KW  - lridophores
Y1  - 1988
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-78108
ER  - 
TY  - JOUR
A1  - Linsenmair, Karl Eduard
T1  - Anemomenotactic orientation in beetles and scorpions
N2  - Scorpions, living in North African semideserts are - in spite of disrupting experimental interferences - able to maintain a certain direction in their natural environment in the dark on a plane surface. Under comparable laboratory conditions, excluding the possibility of light or gravity orientation, they can orient themselves if a directed air current passes over the "arena." In most cases the scorpions do not run necessarily with or against the wind, but rather maintain constant angles to the air current for anywhere from minutes to many hours. They are running anemomenotactically (ref. 1). Under identical conditions many species of beetles also orient themselves to air currents (refs. 2 to 4). The main problems to be solved in the study of anemomenotactic orientation are: (1) Which physical qualities of the air current have an influence on the anemomenotaxis? (2) With which sense organs do beetles and scorpions perceive wind directions? (3) Which physiological mechanism is the basis of anemomenotactic orientation? (4) What is the biological significance of anemomenotaxis in beetles and scorpions? With respect to these problems, more study has been done on beetles than on scorpions. Therefore, due to lack of space, I shall discuss mainly some of the results obtained in experiments with dung beetles (Geotrupes silvaticus, G. ,Stercorarius, G. armifrons, G. niger, Scarabaeus variolosus) and tenebrionid beetles (Tenebrio molitor, Pimelia grossa, P. tenuicomis, Scaurus dubius).
KW  - Biologie
KW  - Skorpion
KW  - Käfer
Y1  - 1972
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-78118
ER  - 
TY  - JOUR
A1  - Hsieh, Yu-Lung
A1  - Linsenmair, Karl Eduard
T1  - Seasonal dynamics of arboreal spider diversity in a temperate forest
N2  - Measuring and estimating biodiversity patterns is a fundamental task of the scientist working to support conservation and informmanagement decisions.Most biodiversity studies in temperate regions were often carried out over a very short period of time (e.g., a single season) and it is often—at least tacitly—assumed that these short-termfindings are representative of long-termgeneral patterns.However, should the studied biodiversity pattern in fact contain significant temporal dynamics, perhaps leading to contradictory conclusions. Here, we studied the seasonal diversity dynamics of arboreal spider communities dwelling in 216 European beeches (Fagus sylvatica L.) to assess the spider community composition in the following seasons: two cold seasons (I:November 2005–January 2006; II: February–April) and two warm seasons (III: May–July; IV: August–October). We show that the usually measured diversity of the warmseason community (IV: 58 estimated species) alone did not deliver a reliable image of the overall diversity present in these trees, and therefore, we recommend it should not be used for sampling protocols aimed at providing a full picture of a forest’s biodiversity in the temperate zones. In particular, when the additional samplings of other seasons (I, II, III) were included, the estimated species richness nearly doubled (108). Community I possessed the lowest diversity and evenness due to the harsh winter conditions: this community was comprised of one dominant species together with several species low in abundance. Similarity was lowest (38.6%) between seasonal communities I and III, indicating a significant species turnover due to recolonization, so that community III had the highest diversity. Finally, using nonparametric estimators, we found that further sampling in late winter (February–April) is most needed to complete our inventory. Our study clearly demonstrates that seasonal dynamics of communities should be taken into account when studying biodiversity patterns of spiders, and probably forest arthropods in general.
KW  - Biologie
KW  - Araneae
KW  - canopy fogging
KW  - European beech
KW  - recolonization
KW  - species richness estimation
KW  - true diversity
Y1  - 2012
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-75158
ER  -